Commit c5a5983150c41843f30e136471e77fd3623a7510 | zig

author	Andrew Kelley <andrew@ziglang.org> 2025-08-07 22:05:50-07:00
committer	Andrew Kelley <andrew@ziglang.org> 2025-08-07 22:26:42-07:00
log	c5a5983150c41843f30e136471e77fd3623a7510
tree	a9aa3347af08c279e1fc35049673e310584aea73
parent	94dd28b7f7bdbbebe652d3e7a791bc86591ed9c8

random patches from another branch

1 files changed, 715 insertions(+), 636 deletions(-)

src
- link
  - Dwarf.zig

src/link/Dwarf.zig+715-636

 @@ -1,4 +1,4 @@
-gpa: std.mem.Allocator,
+gpa: Allocator,
 bin_file: *link.File,
 format: DW.Format,
 endian: std.builtin.Endian,
 @@ -50,7 +50,7 @@ const ModInfo = struct {
     dirs: std.AutoArrayHashMapUnmanaged(Unit.Index, void),
     files: std.AutoArrayHashMapUnmanaged(Zcu.File.Index, void),
-    fn deinit(mod_info: *ModInfo, gpa: std.mem.Allocator) void {
+    fn deinit(mod_info: *ModInfo, gpa: Allocator) void {
         mod_info.dirs.deinit(gpa);
         mod_info.files.deinit(gpa);
         mod_info.* = undefined;
 @@ -220,13 +220,13 @@ const StringSection = struct {
         .section = Section.init,
     };
-    fn deinit(str_sec: *StringSection, gpa: std.mem.Allocator) void {
+    fn deinit(str_sec: *StringSection, gpa: Allocator) void {
         str_sec.contents.deinit(gpa);
         str_sec.map.deinit(gpa);
         str_sec.section.deinit(gpa);
     }
-    fn addString(str_sec: *StringSection, dwarf: *Dwarf, str: []const u8) UpdateError!Entry.Index {
+    fn addString(str_sec: *StringSection, dwarf: *Dwarf, str: []const u8) !Entry.Index {
         const gop = try str_sec.map.getOrPutAdapted(dwarf.gpa, str, Adapter{ .str_sec = str_sec });
         const entry: Entry.Index = @enumFromInt(gop.index);
         if (!gop.found_existing) {
 @@ -297,7 +297,7 @@ pub const Section = struct {
         .len = 0,
     };
-    fn deinit(sec: *Section, gpa: std.mem.Allocator) void {
+    fn deinit(sec: *Section, gpa: Allocator) void {
         for (sec.units.items) |*unit| unit.deinit(gpa);
         sec.units.deinit(gpa);
         sec.* = undefined;
 @@ -357,7 +357,7 @@ pub const Section = struct {
         if (sec.last == unit.toOptional()) sec.last = unit_ptr.prev;
     }
-    fn popUnit(sec: *Section, gpa: std.mem.Allocator) void {
+    fn popUnit(sec: *Section, gpa: Allocator) void {
         const unit_index: Unit.Index = @enumFromInt(sec.units.items.len - 1);
         sec.unlinkUnit(unit_index);
         var unit = sec.units.pop().?;
 @@ -518,7 +518,7 @@ const Unit = struct {
         unit.cross_section_relocs.clearRetainingCapacity();
     }
-    fn deinit(unit: *Unit, gpa: std.mem.Allocator) void {
+    fn deinit(unit: *Unit, gpa: Allocator) void {
         for (unit.entries.items) |*entry| entry.deinit(gpa);
         unit.entries.deinit(gpa);
         unit.cross_unit_relocs.deinit(gpa);
 @@ -526,7 +526,7 @@ const Unit = struct {
         unit.* = undefined;
     }
-    fn addEntry(unit: *Unit, gpa: std.mem.Allocator) std.mem.Allocator.Error!Entry.Index {
+    fn addEntry(unit: *Unit, gpa: Allocator) Allocator.Error!Entry.Index {
         if (unit.free.unwrap()) |entry| {
             const entry_ptr = unit.getEntry(entry);
             unit.free = entry_ptr.next;
 @@ -648,35 +648,33 @@ const Unit = struct {
         assert(len >= unit.trailer_len);
         if (sec == &dwarf.debug_line.section) {
             var buf: [1 + uleb128Bytes(std.math.maxInt(u32)) + 1]u8 = undefined;
-            var fbs = std.io.fixedBufferStream(&buf);
+            var bw: Writer = .fixed(&buf);
-            const writer = fbs.writer();
+            bw.writeByte(DW.LNS.extended_op) catch unreachable;
-            writer.writeByte(DW.LNS.extended_op) catch unreachable;
+            const extended_op_bytes = bw.end;
-            const extended_op_bytes = fbs.pos;
             var op_len_bytes: u5 = 1;
             while (true) switch (std.math.order(len - extended_op_bytes - op_len_bytes, @as(u32, 1) << 7 * op_len_bytes)) {
-                .lt => break uleb128(writer, len - extended_op_bytes - op_len_bytes) catch unreachable,
+                .lt => break bw.writeLeb128(len - extended_op_bytes - op_len_bytes) catch unreachable,
                 .eq => {
                     // no length will ever work, so undercount and futz with the leb encoding to make up the missing byte
                     op_len_bytes += 1;
-                    std.leb.writeUnsignedExtended(buf[fbs.pos..][0..op_len_bytes], len - extended_op_bytes - op_len_bytes);
+                    std.leb.writeUnsignedExtended((bw.writableSlice(op_len_bytes) catch unreachable), len - extended_op_bytes - op_len_bytes);
-                    fbs.pos += op_len_bytes;
                     break;
                 },
                 .gt => op_len_bytes += 1,
             };
-            assert(fbs.pos == extended_op_bytes + op_len_bytes);
+            assert(bw.end == extended_op_bytes + op_len_bytes);
-            writer.writeByte(DW.LNE.padding) catch unreachable;
+            bw.writeByte(DW.LNE.padding) catch unreachable;
-            assert(fbs.pos >= unit.trailer_len and fbs.pos <= len);
+            assert(bw.end >= unit.trailer_len and bw.end <= len);
-            return dwarf.getFile().?.pwriteAll(fbs.getWritten(), sec.off(dwarf) + start);
+            return dwarf.getFile().?.pwriteAll(bw.getWritten(), sec.off(dwarf) + start);
         }
-        var trailer = try std.ArrayList(u8).initCapacity(dwarf.gpa, len);
+        var trailer_bw: Writer = .fixed(try dwarf.gpa.alloc(u8, len));
-        defer trailer.deinit();
+        defer dwarf.gpa.free(trailer_bw.buffer);
         const fill_byte: u8 = if (sec == &dwarf.debug_abbrev.section) fill: {
             assert(uleb128Bytes(@intFromEnum(AbbrevCode.null)) == 1);
-            trailer.appendAssumeCapacity(@intFromEnum(AbbrevCode.null));
+            trailer_bw.writeByte(@intFromEnum(AbbrevCode.null)) catch unreachable;
             break :fill @intFromEnum(AbbrevCode.null);
         } else if (sec == &dwarf.debug_aranges.section) fill: {
-            trailer.appendNTimesAssumeCapacity(0, @intFromEnum(dwarf.address_size) * 2);
+            trailer_bw.splatByteAll(0, @intFromEnum(dwarf.address_size) * 2) catch unreachable;
             break :fill 0;
         } else if (sec == &dwarf.debug_frame.section) fill: {
             switch (dwarf.debug_frame.header.format) {
 @@ -684,49 +682,49 @@ const Unit = struct {
                 .debug_frame, .eh_frame => |format| {
                     const unit_len = len - dwarf.unitLengthBytes();
                     switch (dwarf.format) {
-                        .@"32" => std.mem.writeInt(u32, trailer.addManyAsArrayAssumeCapacity(4), @intCast(unit_len), dwarf.endian),
+                        .@"32" => trailer_bw.writeInt(u32, @intCast(unit_len), dwarf.endian) catch unreachable,
                         .@"64" => {
-                            std.mem.writeInt(u32, trailer.addManyAsArrayAssumeCapacity(4), std.math.maxInt(u32), dwarf.endian);
+                            trailer_bw.writeInt(u32, std.math.maxInt(u32), dwarf.endian) catch unreachable;
-                            std.mem.writeInt(u64, trailer.addManyAsArrayAssumeCapacity(8), unit_len, dwarf.endian);
+                            trailer_bw.writeInt(u64, unit_len, dwarf.endian) catch unreachable;
                         },
                     }
                     switch (format) {
                         .none => unreachable,
                         .debug_frame => {
                             switch (dwarf.format) {
-                                .@"32" => std.mem.writeInt(u32, trailer.addManyAsArrayAssumeCapacity(4), std.math.maxInt(u32), dwarf.endian),
+                                .@"32" => trailer_bw.writeInt(u32, std.math.maxInt(u32), dwarf.endian) catch unreachable,
-                                .@"64" => std.mem.writeInt(u64, trailer.addManyAsArrayAssumeCapacity(8), std.math.maxInt(u64), dwarf.endian),
+                                .@"64" => trailer_bw.writeInt(u64, std.math.maxInt(u64), dwarf.endian) catch unreachable,
                             }
-                            trailer.appendAssumeCapacity(4);
+                            trailer_bw.writeByte(4) catch unreachable;
-                            trailer.appendSliceAssumeCapacity("\x00");
+                            trailer_bw.writeAll("\x00") catch unreachable;
-                            trailer.appendAssumeCapacity(@intFromEnum(dwarf.address_size));
+                            trailer_bw.writeByte(@intFromEnum(dwarf.address_size)) catch unreachable;
-                            trailer.appendAssumeCapacity(0);
+                            trailer_bw.writeByte(0) catch unreachable;
                         },
                         .eh_frame => {
-                            std.mem.writeInt(u32, trailer.addManyAsArrayAssumeCapacity(4), 0, dwarf.endian);
+                            trailer_bw.writeInt(u32, 0, dwarf.endian) catch unreachable;
-                            trailer.appendAssumeCapacity(1);
+                            trailer_bw.writeByte(1) catch unreachable;
-                            trailer.appendSliceAssumeCapacity("\x00");
+                            trailer_bw.writeAll("\x00") catch unreachable;
                         },
                     }
-                    uleb128(trailer.fixedWriter(), 1) catch unreachable;
+                    trailer_bw.writeUleb128(1) catch unreachable;
-                    sleb128(trailer.fixedWriter(), 1) catch unreachable;
+                    trailer_bw.writeSleb128(1) catch unreachable;
-                    uleb128(trailer.fixedWriter(), 0) catch unreachable;
+                    trailer_bw.writeUleb128(0) catch unreachable;
                 },
             }
-            trailer.appendNTimesAssumeCapacity(DW.CFA.nop, unit.trailer_len - trailer.items.len);
+            trailer_bw.splatByteAll(DW.CFA.nop, unit.trailer_len - trailer_bw.end) catch unreachable;
             break :fill DW.CFA.nop;
         } else if (sec == &dwarf.debug_info.section) fill: {
             assert(uleb128Bytes(@intFromEnum(AbbrevCode.null)) == 1);
-            trailer.appendNTimesAssumeCapacity(@intFromEnum(AbbrevCode.null), 2);
+            trailer_bw.splatByteAll(@intFromEnum(AbbrevCode.null), 2) catch unreachable;
             break :fill @intFromEnum(AbbrevCode.null);
         } else if (sec == &dwarf.debug_rnglists.section) fill: {
-            trailer.appendAssumeCapacity(DW.RLE.end_of_list);
+            trailer_bw.writeByte(DW.RLE.end_of_list) catch unreachable;
             break :fill DW.RLE.end_of_list;
         } else unreachable;
-        assert(trailer.items.len == unit.trailer_len);
+        assert(trailer_bw.end == unit.trailer_len);
-        trailer.appendNTimesAssumeCapacity(fill_byte, len - unit.trailer_len);
+        trailer_bw.splatByteAll(fill_byte, len - unit.trailer_len) catch unreachable;
-        assert(trailer.items.len == len);
+        assert(trailer_bw.end == len);
-        try dwarf.getFile().?.pwriteAll(trailer.items, sec.off(dwarf) + start);
+        try dwarf.getFile().?.pwriteAll(trailer_bw.buffer, sec.off(dwarf) + start);
     }
     fn resolveRelocs(unit: *Unit, sec: *Section, dwarf: *Dwarf) RelocError!void {
 @@ -780,7 +778,7 @@ const Entry = struct {
         entry.external_relocs.clearRetainingCapacity();
     }
-    fn deinit(entry: *Entry, gpa: std.mem.Allocator) void {
+    fn deinit(entry: *Entry, gpa: Allocator) void {
         entry.cross_entry_relocs.deinit(gpa);
         entry.cross_unit_relocs.deinit(gpa);
         entry.cross_section_relocs.deinit(gpa);
 @@ -833,52 +831,52 @@ const Entry = struct {
                 1 + uleb128Bytes(std.math.maxInt(u32)) + 1,
             )
         ]u8 = undefined;
-        var fbs = std.io.fixedBufferStream(&buf);
+        var bw: Writer = .fixed(&buf);
-        const writer = fbs.writer();
         if (sec == &dwarf.debug_info.section) switch (len) {
             0 => {},
-            1 => uleb128(writer, try dwarf.refAbbrevCode(.pad_1)) catch unreachable,
+            1 => bw.writeLeb128(try dwarf.refAbbrevCode(.pad_1)) catch unreachable,
             else => {
-                uleb128(writer, try dwarf.refAbbrevCode(.pad_n)) catch unreachable;
+                bw.writeLeb128(try dwarf.refAbbrevCode(.pad_n)) catch unreachable;
-                const abbrev_code_bytes = fbs.pos;
+                const abbrev_code_bytes = bw.end;
                 var block_len_bytes: u5 = 1;
                 while (true) switch (std.math.order(len - abbrev_code_bytes - block_len_bytes, @as(u32, 1) << 7 * block_len_bytes)) {
-                    .lt => break uleb128(writer, len - abbrev_code_bytes - block_len_bytes) catch unreachable,
+                    .lt => break bw.writeLeb128(len - abbrev_code_bytes - block_len_bytes) catch unreachable,
                     .eq => {
                         // no length will ever work, so undercount and futz with the leb encoding to make up the missing byte
                         block_len_bytes += 1;
-                        std.leb.writeUnsignedExtended(buf[fbs.pos..][0..block_len_bytes], len - abbrev_code_bytes - block_len_bytes);
+                        std.leb.writeUnsignedExtended((try bw.writableSlice(block_len_bytes)), len - abbrev_code_bytes - block_len_bytes);
-                        fbs.pos += block_len_bytes;
                         break;
                     },
                     .gt => block_len_bytes += 1,
                 };
-                assert(fbs.pos == abbrev_code_bytes + block_len_bytes);
+                assert(bw.end == abbrev_code_bytes + block_len_bytes);
             },
         } else if (sec == &dwarf.debug_line.section) switch (len) {
             0 => {},
-            1 => writer.writeByte(DW.LNS.const_add_pc) catch unreachable,
+            1 => bw.writeByte(DW.LNS.const_add_pc) catch unreachable,
             else => {
-                writer.writeByte(DW.LNS.extended_op) catch unreachable;
+                bw.writeByte(DW.LNS.extended_op) catch unreachable;
-                const extended_op_bytes = fbs.pos;
+                const extended_op_bytes = bw.end;
                 var op_len_bytes: u5 = 1;
                 while (true) switch (std.math.order(len - extended_op_bytes - op_len_bytes, @as(u32, 1) << 7 * op_len_bytes)) {
-                    .lt => break uleb128(writer, len - extended_op_bytes - op_len_bytes) catch unreachable,
+                    .lt => break bw.writeLeb128(len - extended_op_bytes - op_len_bytes) catch unreachable,
                     .eq => {
                         // no length will ever work, so undercount and futz with the leb encoding to make up the missing byte
                         op_len_bytes += 1;
-                        std.leb.writeUnsignedExtended(buf[fbs.pos..][0..op_len_bytes], len - extended_op_bytes - op_len_bytes);
+                        std.leb.writeUnsignedExtended(
-                        fbs.pos += op_len_bytes;
+                            (bw.writableSlice(op_len_bytes) catch unreachable),
+                            len - extended_op_bytes - op_len_bytes,
+                        );
                         break;
                     },
                     .gt => op_len_bytes += 1,
                 };
-                assert(fbs.pos == extended_op_bytes + op_len_bytes);
+                assert(bw.end == extended_op_bytes + op_len_bytes);
-                if (len > 2) writer.writeByte(DW.LNE.padding) catch unreachable;
+                if (len > 2) bw.writeByte(DW.LNE.padding) catch unreachable;
             },
         } else assert(!sec.pad_entries_to_ideal and len == 0);
-        assert(fbs.pos <= len);
+        assert(bw.end <= len);
-        try dwarf.getFile().?.pwriteAll(fbs.getWritten(), sec.off(dwarf) + unit.off + unit.header_len + start);
+        try dwarf.getFile().?.pwriteAll(bw.getWritten(), sec.off(dwarf) + unit.off + unit.header_len + start);
     }
     fn resize(entry_ptr: *Entry, unit: *Unit, sec: *Section, dwarf: *Dwarf, len: u32) UpdateError!void {
 @@ -1133,150 +1131,149 @@ pub const Loc = union(enum) {
         };
     }
-    fn writeReg(reg: u32, op0: u8, opx: u8, writer: anytype) @TypeOf(writer).Error!void {
+    fn writeReg(bw: *Writer, reg: u32, op0: u8, opx: u8) Writer.Error!void {
         if (std.math.cast(u5, reg)) |small_reg| {
-            try writer.writeByte(op0 + small_reg);
+            try bw.writeByte(op0 + small_reg);
         } else {
-            try writer.writeByte(opx);
+            try bw.writeByte(opx);
-            try uleb128(writer, reg);
+            try bw.writeLeb128(reg);
         }
     }
-    fn write(loc: Loc, adapter: anytype) UpdateError!void {
+    fn write(loc: Loc, bw: *Writer, adapter: anytype) UpdateError!void {
-        const writer = adapter.writer();
         switch (loc) {
             .empty => {},
             .addr_reloc => |sym_index| {
-                try writer.writeByte(DW.OP.addr);
+                try bw.writeByte(DW.OP.addr);
                 try adapter.addrSym(sym_index);
             },
             .deref => |addr| {
                 try addr.write(adapter);
-                try writer.writeByte(DW.OP.deref);
+                try bw.writeByte(DW.OP.deref);
             },
             .constu => |constu| if (std.math.cast(u5, constu)) |lit| {
-                try writer.writeByte(@as(u8, DW.OP.lit0) + lit);
+                try bw.writeByte(@as(u8, DW.OP.lit0) + lit);
             } else if (std.math.cast(u8, constu)) |const1u| {
-                try writer.writeAll(&.{ DW.OP.const1u, const1u });
+                try bw.writeAll(&.{ DW.OP.const1u, const1u });
             } else if (std.math.cast(u16, constu)) |const2u| {
-                try writer.writeByte(DW.OP.const2u);
+                try bw.writeByte(DW.OP.const2u);
-                try writer.writeInt(u16, const2u, adapter.endian());
+                try bw.writeInt(u16, const2u, adapter.endian());
             } else if (std.math.cast(u21, constu)) |const3u| {
-                try writer.writeByte(DW.OP.constu);
+                try bw.writeByte(DW.OP.constu);
-                try uleb128(writer, const3u);
+                try bw.writeLeb128(const3u);
             } else if (std.math.cast(u32, constu)) |const4u| {
-                try writer.writeByte(DW.OP.const4u);
+                try bw.writeByte(DW.OP.const4u);
-                try writer.writeInt(u32, const4u, adapter.endian());
+                try bw.writeInt(u32, const4u, adapter.endian());
             } else if (std.math.cast(u49, constu)) |const7u| {
-                try writer.writeByte(DW.OP.constu);
+                try bw.writeByte(DW.OP.constu);
-                try uleb128(writer, const7u);
+                try bw.writeLeb128(const7u);
             } else {
-                try writer.writeByte(DW.OP.const8u);
+                try bw.writeByte(DW.OP.const8u);
-                try writer.writeInt(u64, constu, adapter.endian());
+                try bw.writeInt(u64, constu, adapter.endian());
             },
             .consts => |consts| if (std.math.cast(i8, consts)) |const1s| {
-                try writer.writeAll(&.{ DW.OP.const1s, @bitCast(const1s) });
+                try bw.writeAll(&.{ DW.OP.const1s, @bitCast(const1s) });
             } else if (std.math.cast(i16, consts)) |const2s| {
-                try writer.writeByte(DW.OP.const2s);
+                try bw.writeByte(DW.OP.const2s);
-                try writer.writeInt(i16, const2s, adapter.endian());
+                try bw.writeInt(i16, const2s, adapter.endian());
             } else if (std.math.cast(i21, consts)) |const3s| {
-                try writer.writeByte(DW.OP.consts);
+                try bw.writeByte(DW.OP.consts);
-                try sleb128(writer, const3s);
+                try bw.writeLeb128(const3s);
             } else if (std.math.cast(i32, consts)) |const4s| {
-                try writer.writeByte(DW.OP.const4s);
+                try bw.writeByte(DW.OP.const4s);
-                try writer.writeInt(i32, const4s, adapter.endian());
+                try bw.writeInt(i32, const4s, adapter.endian());
             } else if (std.math.cast(i49, consts)) |const7s| {
-                try writer.writeByte(DW.OP.consts);
+                try bw.writeByte(DW.OP.consts);
-                try sleb128(writer, const7s);
+                try bw.writeLeb128(const7s);
             } else {
-                try writer.writeByte(DW.OP.const8s);
+                try bw.writeByte(DW.OP.const8s);
-                try writer.writeInt(i64, consts, adapter.endian());
+                try bw.writeInt(i64, consts, adapter.endian());
             },
             .plus => |plus| done: {
                 if (plus[0].getConst(u0)) |_| {
-                    try plus[1].write(adapter);
+                    try plus[1].write(bw, adapter);
                     break :done;
                 }
                 if (plus[1].getConst(u0)) |_| {
-                    try plus[0].write(adapter);
+                    try plus[0].write(bw, adapter);
                     break :done;
                 }
                 if (plus[0].getBaseReg()) |breg| {
                     if (plus[1].getConst(i65)) |offset| {
-                        try writeReg(breg, DW.OP.breg0, DW.OP.bregx, writer);
+                        try writeReg(bw, breg, DW.OP.breg0, DW.OP.bregx);
-                        try sleb128(writer, offset);
+                        try bw.writeLeb128(offset);
                         break :done;
                     }
                 }
                 if (plus[1].getBaseReg()) |breg| {
                     if (plus[0].getConst(i65)) |offset| {
-                        try writeReg(breg, DW.OP.breg0, DW.OP.bregx, writer);
+                        try writeReg(bw, breg, DW.OP.breg0, DW.OP.bregx);
-                        try sleb128(writer, offset);
+                        try bw.writeLeb128(offset);
                         break :done;
                     }
                 }
                 if (plus[0].getConst(u64)) |uconst| {
-                    try plus[1].write(adapter);
+                    try plus[1].write(bw, adapter);
-                    try writer.writeByte(DW.OP.plus_uconst);
+                    try bw.writeByte(DW.OP.plus_uconst);
-                    try uleb128(writer, uconst);
+                    try bw.writeLeb128(uconst);
                     break :done;
                 }
                 if (plus[1].getConst(u64)) |uconst| {
-                    try plus[0].write(adapter);
+                    try plus[0].write(bw, adapter);
-                    try writer.writeByte(DW.OP.plus_uconst);
+                    try bw.writeByte(DW.OP.plus_uconst);
-                    try uleb128(writer, uconst);
+                    try bw.writeLeb128(uconst);
                     break :done;
                 }
-                try plus[0].write(adapter);
+                try plus[0].write(bw, adapter);
-                try plus[1].write(adapter);
+                try plus[1].write(bw, adapter);
-                try writer.writeByte(DW.OP.plus);
+                try bw.writeByte(DW.OP.plus);
             },
-            .reg => |reg| try writeReg(reg, DW.OP.reg0, DW.OP.regx, writer),
+            .reg => |reg| try writeReg(bw, reg, DW.OP.reg0, DW.OP.regx),
             .breg => |breg| {
-                try writeReg(breg, DW.OP.breg0, DW.OP.bregx, writer);
+                try writeReg(bw, breg, DW.OP.breg0, DW.OP.bregx);
-                try sleb128(writer, 0);
+                try bw.writeSleb128(0);
             },
-            .push_object_address => try writer.writeByte(DW.OP.push_object_address),
+            .push_object_address => try bw.writeByte(DW.OP.push_object_address),
             .call => |call| {
                 for (call.args) |arg| try arg.write(adapter);
-                try writer.writeByte(DW.OP.call_ref);
+                try bw.writeByte(DW.OP.call_ref);
                 try adapter.infoEntry(call.unit, call.entry);
             },
             .form_tls_address => |addr| {
-                try addr.write(adapter);
+                try addr.write(bw, adapter);
-                try writer.writeByte(DW.OP.form_tls_address);
+                try bw.writeByte(DW.OP.form_tls_address);
             },
             .implicit_value => |value| {
-                try writer.writeByte(DW.OP.implicit_value);
+                try bw.writeByte(DW.OP.implicit_value);
-                try uleb128(writer, value.len);
+                try bw.writeLeb128(value.len);
-                try writer.writeAll(value);
+                try bw.writeAll(value);
             },
             .stack_value => |value| {
-                try value.write(adapter);
+                try value.write(bw, adapter);
-                try writer.writeByte(DW.OP.stack_value);
+                try bw.writeByte(DW.OP.stack_value);
             },
             .implicit_pointer => |implicit_pointer| {
-                try writer.writeByte(DW.OP.implicit_pointer);
+                try bw.writeByte(DW.OP.implicit_pointer);
-                try adapter.infoEntry(implicit_pointer.unit, implicit_pointer.entry);
+                try adapter.infoEntry(bw, implicit_pointer.unit, implicit_pointer.entry);
-                try sleb128(writer, implicit_pointer.offset);
+                try bw.writeLeb128(implicit_pointer.offset);
             },
             .wasm_ext => |wasm_ext| {
-                try writer.writeByte(DW.OP.WASM_location);
+                try bw.writeByte(DW.OP.WASM_location);
                 switch (wasm_ext) {
                     .local => |local| {
-                        try writer.writeByte(DW.OP.WASM_local);
+                        try bw.writeByte(DW.OP.WASM_local);
-                        try uleb128(writer, local);
+                        try bw.writeLeb128(local);
                     },
                     .global => |global| if (std.math.cast(u21, global)) |global_u21| {
-                        try writer.writeByte(DW.OP.WASM_global);
+                        try bw.writeByte(DW.OP.WASM_global);
-                        try uleb128(writer, global_u21);
+                        try bw.writeLeb128(global_u21);
                     } else {
-                        try writer.writeByte(DW.OP.WASM_global_u32);
+                        try bw.writeByte(DW.OP.WASM_global_u32);
-                        try writer.writeInt(u32, global, adapter.endian());
+                        try bw.writeInt(u32, global, adapter.endian());
                     },
                     .operand_stack => |operand_stack| {
-                        try writer.writeByte(DW.OP.WASM_operand_stack);
+                        try bw.writeByte(DW.OP.WASM_operand_stack);
-                        try uleb128(writer, operand_stack);
+                        try bw.writeLeb128(operand_stack);
                     },
                 }
             },
 @@ -1309,21 +1306,21 @@ pub const Cfa = union(enum) {
     const RegExpr = struct { reg: u32, expr: Loc };
     fn write(cfa: Cfa, wip_nav: *WipNav) UpdateError!void {
-        const writer = wip_nav.debug_frame.writer(wip_nav.dwarf.gpa);
+        const bw = &wip_nav.debug_frame.buffered_writer;
         switch (cfa) {
-            .nop => try writer.writeByte(DW.CFA.nop),
+            .nop => try bw.writeByte(DW.CFA.nop),
             .advance_loc => |loc| {
                 const delta = @divExact(loc - wip_nav.cfi.loc, wip_nav.dwarf.debug_frame.header.code_alignment_factor);
                 if (delta == 0) {} else if (std.math.cast(u6, delta)) |small_delta|
-                    try writer.writeByte(@as(u8, DW.CFA.advance_loc) + small_delta)
+                    try bw.writeByte(@as(u8, DW.CFA.advance_loc) + small_delta)
                 else if (std.math.cast(u8, delta)) |ubyte_delta|
-                    try writer.writeAll(&.{ DW.CFA.advance_loc1, ubyte_delta })
+                    try bw.writeAll(&.{ DW.CFA.advance_loc1, ubyte_delta })
                 else if (std.math.cast(u16, delta)) |uhalf_delta| {
-                    try writer.writeByte(DW.CFA.advance_loc2);
+                    try bw.writeByte(DW.CFA.advance_loc2);
-                    try writer.writeInt(u16, uhalf_delta, wip_nav.dwarf.endian);
+                    try bw.writeInt(u16, uhalf_delta, wip_nav.dwarf.endian);
                 } else if (std.math.cast(u32, delta)) |uword_delta| {
-                    try writer.writeByte(DW.CFA.advance_loc4);
+                    try bw.writeByte(DW.CFA.advance_loc4);
-                    try writer.writeInt(u32, uword_delta, wip_nav.dwarf.endian);
+                    try bw.writeInt(u32, uword_delta, wip_nav.dwarf.endian);
                 }
                 wip_nav.cfi.loc = loc;
             },
 @@ -1335,41 +1332,41 @@ pub const Cfa = union(enum) {
                 }, wip_nav.dwarf.debug_frame.header.data_alignment_factor);
                 if (std.math.cast(u63, factored_off)) |unsigned_off| {
                     if (std.math.cast(u6, reg_off.reg)) |small_reg| {
-                        try writer.writeByte(@as(u8, DW.CFA.offset) + small_reg);
+                        try bw.writeByte(@as(u8, DW.CFA.offset) + small_reg);
                     } else {
-                        try writer.writeByte(DW.CFA.offset_extended);
+                        try bw.writeByte(DW.CFA.offset_extended);
-                        try uleb128(writer, reg_off.reg);
+                        try bw.writeLeb128(reg_off.reg);
                     }
-                    try uleb128(writer, unsigned_off);
+                    try bw.writeLeb128(unsigned_off);
                 } else {
-                    try writer.writeByte(DW.CFA.offset_extended_sf);
+                    try bw.writeByte(DW.CFA.offset_extended_sf);
-                    try uleb128(writer, reg_off.reg);
+                    try bw.writeLeb128(reg_off.reg);
-                    try sleb128(writer, factored_off);
+                    try bw.writeLeb128(factored_off);
                 }
             },
             .restore => |reg| if (std.math.cast(u6, reg)) |small_reg|
-                try writer.writeByte(@as(u8, DW.CFA.restore) + small_reg)
+                try bw.writeByte(@as(u8, DW.CFA.restore) + small_reg)
             else {
-                try writer.writeByte(DW.CFA.restore_extended);
+                try bw.writeByte(DW.CFA.restore_extended);
-                try uleb128(writer, reg);
+                try bw.writeLeb128(reg);
             },
             .undefined => |reg| {
-                try writer.writeByte(DW.CFA.undefined);
+                try bw.writeByte(DW.CFA.undefined);
-                try uleb128(writer, reg);
+                try bw.writeLeb128(reg);
             },
             .same_value => |reg| {
-                try writer.writeByte(DW.CFA.same_value);
+                try bw.writeByte(DW.CFA.same_value);
-                try uleb128(writer, reg);
+                try bw.writeLeb128(reg);
             },
             .register => |regs| if (regs[0] != regs[1]) {
-                try writer.writeByte(DW.CFA.register);
+                try bw.writeByte(DW.CFA.register);
-                for (regs) |reg| try uleb128(writer, reg);
+                for (regs) |reg| try bw.writeLeb128(reg);
             } else {
-                try writer.writeByte(DW.CFA.same_value);
+                try bw.writeByte(DW.CFA.same_value);
-                try uleb128(writer, regs[0]);
+                try bw.writeLeb128(regs[0]);
             },
-            .remember_state => try writer.writeByte(DW.CFA.remember_state),
+            .remember_state => try bw.writeByte(DW.CFA.remember_state),
-            .restore_state => try writer.writeByte(DW.CFA.restore_state),
+            .restore_state => try bw.writeByte(DW.CFA.restore_state),
             .def_cfa, .def_cfa_register, .def_cfa_offset, .adjust_cfa_offset => {
                 const reg_off: RegOff = switch (cfa) {
                     else => unreachable,
 @@ -1382,51 +1379,51 @@ pub const Cfa = union(enum) {
                 const unsigned_off = std.math.cast(u63, reg_off.off);
                 if (reg_off.off == wip_nav.cfi.cfa.off) {
                     if (changed_reg) {
-                        try writer.writeByte(DW.CFA.def_cfa_register);
+                        try bw.writeByte(DW.CFA.def_cfa_register);
-                        try uleb128(writer, reg_off.reg);
+                        try bw.writeLeb128(reg_off.reg);
                     }
                 } else if (switch (wip_nav.dwarf.debug_frame.header.data_alignment_factor) {
                     0 => unreachable,
                     1 => unsigned_off != null,
                     else => |data_alignment_factor| @rem(reg_off.off, data_alignment_factor) != 0,
                 }) {
-                    try writer.writeByte(if (changed_reg) DW.CFA.def_cfa else DW.CFA.def_cfa_offset);
+                    try bw.writeByte(if (changed_reg) DW.CFA.def_cfa else DW.CFA.def_cfa_offset);
-                    if (changed_reg) try uleb128(writer, reg_off.reg);
+                    if (changed_reg) try bw.writeLeb128(reg_off.reg);
-                    try uleb128(writer, unsigned_off.?);
+                    try bw.writeLeb128(unsigned_off.?);
                 } else {
-                    try writer.writeByte(if (changed_reg) DW.CFA.def_cfa_sf else DW.CFA.def_cfa_offset_sf);
+                    try bw.writeByte(if (changed_reg) DW.CFA.def_cfa_sf else DW.CFA.def_cfa_offset_sf);
-                    if (changed_reg) try uleb128(writer, reg_off.reg);
+                    if (changed_reg) try bw.writeLeb128(reg_off.reg);
-                    try sleb128(writer, @divExact(reg_off.off, wip_nav.dwarf.debug_frame.header.data_alignment_factor));
+                    try bw.writeLeb128(@divExact(reg_off.off, wip_nav.dwarf.debug_frame.header.data_alignment_factor));
                 }
                 wip_nav.cfi.cfa = reg_off;
             },
             .def_cfa_expression => |expr| {
-                try writer.writeByte(DW.CFA.def_cfa_expression);
+                try bw.writeByte(DW.CFA.def_cfa_expression);
                 try wip_nav.frameExprLoc(expr);
             },
             .expression => |reg_expr| {
-                try writer.writeByte(DW.CFA.expression);
+                try bw.writeByte(DW.CFA.expression);
-                try uleb128(writer, reg_expr.reg);
+                try bw.writeLeb128(reg_expr.reg);
                 try wip_nav.frameExprLoc(reg_expr.expr);
             },
             .val_offset => |reg_off| {
                 const factored_off = @divExact(reg_off.off, wip_nav.dwarf.debug_frame.header.data_alignment_factor);
                 if (std.math.cast(u63, factored_off)) |unsigned_off| {
-                    try writer.writeByte(DW.CFA.val_offset);
+                    try bw.writeByte(DW.CFA.val_offset);
-                    try uleb128(writer, reg_off.reg);
+                    try bw.writeLeb128(reg_off.reg);
-                    try uleb128(writer, unsigned_off);
+                    try bw.writeLeb128(unsigned_off);
                 } else {
-                    try writer.writeByte(DW.CFA.val_offset_sf);
+                    try bw.writeByte(DW.CFA.val_offset_sf);
-                    try uleb128(writer, reg_off.reg);
+                    try bw.writeLeb128(reg_off.reg);
-                    try sleb128(writer, factored_off);
+                    try bw.writeLeb128(factored_off);
                 }
             },
             .val_expression => |reg_expr| {
-                try writer.writeByte(DW.CFA.val_expression);
+                try bw.writeByte(DW.CFA.val_expression);
-                try uleb128(writer, reg_expr.reg);
+                try bw.writeLeb128(reg_expr.reg);
                 try wip_nav.frameExprLoc(reg_expr.expr);
             },
-            .escape => |bytes| try writer.writeAll(bytes),
+            .escape => |bytes| try bw.writeAll(bytes),
         }
     }
 };
 @@ -1449,19 +1446,27 @@ pub const WipNav = struct {
         loc: u32,
         cfa: Cfa.RegOff,
     },
-    debug_frame: std.ArrayListUnmanaged(u8),
+    debug_frame: std.io.Writer.Allocating,
-    debug_info: std.ArrayListUnmanaged(u8),
+    debug_info: std.io.Writer.Allocating,
-    debug_line: std.ArrayListUnmanaged(u8),
+    debug_line: std.io.Writer.Allocating,
-    debug_loclists: std.ArrayListUnmanaged(u8),
+    debug_loclists: std.io.Writer.Allocating,
     pending_lazy: PendingLazy,
+    pub fn init(wip_nav: *WipNav) void {
+        const gpa = wip_nav.dwarf.gpa;
+        wip_nav.debug_frame.init(gpa);
+        wip_nav.debug_info.init(gpa);
+        wip_nav.debug_line.init(gpa);
+        wip_nav.debug_loclists.init(gpa);
+    }
     pub fn deinit(wip_nav: *WipNav) void {
         const gpa = wip_nav.dwarf.gpa;
         if (wip_nav.func != .none) wip_nav.blocks.deinit(gpa);
-        wip_nav.debug_frame.deinit(gpa);
+        wip_nav.debug_frame.deinit();
-        wip_nav.debug_info.deinit(gpa);
+        wip_nav.debug_info.deinit();
-        wip_nav.debug_line.deinit(gpa);
+        wip_nav.debug_line.deinit();
-        wip_nav.debug_loclists.deinit(gpa);
+        wip_nav.debug_loclists.deinit();
         wip_nav.pending_lazy.types.deinit(gpa);
         wip_nav.pending_lazy.values.deinit(gpa);
     }
 @@ -1538,7 +1543,7 @@ pub const WipNav = struct {
         delta_line: i33,
         delta_pc: u64,
     ) error{OutOfMemory}!void {
-        const dlw = wip_nav.debug_line.writer(wip_nav.dwarf.gpa);
+        const dlbw = &wip_nav.debug_line.buffered_writer;
         const header = wip_nav.dwarf.debug_line.header;
         assert(header.maximum_operations_per_instruction == 1);
 @@ -1548,8 +1553,8 @@ pub const WipNav = struct {
             delta_line - header.line_base >= header.line_range)
         remaining: {
             assert(delta_line != 0);
-            try dlw.writeByte(DW.LNS.advance_line);
+            try dlbw.writeByte(DW.LNS.advance_line);
-            try sleb128(dlw, delta_line);
+            try dlbw.writeLeb128(delta_line);
             break :remaining 0;
         } else delta_line);
 @@ -1557,68 +1562,68 @@ pub const WipNav = struct {
             header.maximum_operations_per_instruction + delta_op;
         const max_op_advance: u9 = (std.math.maxInt(u8) - header.opcode_base) / header.line_range;
         const remaining_op_advance: u8 = @intCast(if (op_advance >= 2 * max_op_advance) remaining: {
-            try dlw.writeByte(DW.LNS.advance_pc);
+            try dlbw.writeByte(DW.LNS.advance_pc);
-            try uleb128(dlw, op_advance);
+            try dlbw.writeLeb128(op_advance);
             break :remaining 0;
         } else if (op_advance >= max_op_advance) remaining: {
-            try dlw.writeByte(DW.LNS.const_add_pc);
+            try dlbw.writeByte(DW.LNS.const_add_pc);
             break :remaining op_advance - max_op_advance;
         } else op_advance);
-        if (remaining_delta_line == 0 and remaining_op_advance == 0)
+        try dlbw.writeByte(
-            try dlw.writeByte(DW.LNS.copy)
+            if (remaining_delta_line == 0 and remaining_op_advance == 0)
-        else
+                DW.LNS.copy
-            try dlw.writeByte(@intCast((remaining_delta_line - header.line_base) +
+            else
-                (header.line_range * remaining_op_advance) + header.opcode_base));
+                @intCast((remaining_delta_line - header.line_base) +
+                    (header.line_range * remaining_op_advance) + header.opcode_base),
+        );
     }
-    pub fn setColumn(wip_nav: *WipNav, column: u32) error{OutOfMemory}!void {
+    pub fn setColumn(wip_nav: *WipNav, column: u32) Allocator.Error!void {
-        const dlw = wip_nav.debug_line.writer(wip_nav.dwarf.gpa);
+        const dlbw = &wip_nav.debug_line.buffered_writer;
-        try dlw.writeByte(DW.LNS.set_column);
+        try dlbw.writeByte(DW.LNS.set_column);
-        try uleb128(dlw, column + 1);
+        try dlbw.writeLeb128(column + 1);
     }
-    pub fn negateStmt(wip_nav: *WipNav) error{OutOfMemory}!void {
+    pub fn negateStmt(wip_nav: *WipNav) Allocator.Error!void {
-        const dlw = wip_nav.debug_line.writer(wip_nav.dwarf.gpa);
+        return wip_nav.debug_line.buffered_writer.writeByte(DW.LNS.negate_stmt);
-        try dlw.writeByte(DW.LNS.negate_stmt);
     }
-    pub fn setPrologueEnd(wip_nav: *WipNav) error{OutOfMemory}!void {
+    pub fn setPrologueEnd(wip_nav: *WipNav) Allocator.Error!void {
-        const dlw = wip_nav.debug_line.writer(wip_nav.dwarf.gpa);
+        return wip_nav.debug_line.buffered_writer.writeByte(DW.LNS.set_prologue_end);
-        try dlw.writeByte(DW.LNS.set_prologue_end);
     }
-    pub fn setEpilogueBegin(wip_nav: *WipNav) error{OutOfMemory}!void {
+    pub fn setEpilogueBegin(wip_nav: *WipNav) Allocator.Error!void {
-        const dlw = wip_nav.debug_line.writer(wip_nav.dwarf.gpa);
+        return wip_nav.debug_line.buffered_writer.writeByte(DW.LNS.set_epilogue_begin);
-        try dlw.writeByte(DW.LNS.set_epilogue_begin);
     }
     pub fn enterBlock(wip_nav: *WipNav, code_off: u64) UpdateError!void {
         const dwarf = wip_nav.dwarf;
-        const diw = wip_nav.debug_info.writer(dwarf.gpa);
+        const dibw = &wip_nav.debug_info.buffered_writer;
         const block = try wip_nav.blocks.addOne(dwarf.gpa);
-        block.abbrev_code = @intCast(wip_nav.debug_info.items.len);
+        block.abbrev_code = @intCast(dibw.count);
         try wip_nav.abbrevCode(.block);
         block.low_pc_off = code_off;
         try wip_nav.infoAddrSym(wip_nav.func_sym_index, code_off);
-        block.high_pc = @intCast(wip_nav.debug_info.items.len);
+        block.high_pc = @intCast(dibw.count);
-        try diw.writeInt(u32, 0, dwarf.endian);
+        try dibw.writeInt(u32, 0, dwarf.endian);
         wip_nav.any_children = false;
     }
     pub fn leaveBlock(wip_nav: *WipNav, code_off: u64) UpdateError!void {
         const block_bytes = comptime uleb128Bytes(@intFromEnum(AbbrevCode.block));
         const block = wip_nav.blocks.pop().?;
+        const dib = wip_nav.debug_info.getWritten();
         if (wip_nav.any_children)
-            try uleb128(wip_nav.debug_info.writer(wip_nav.dwarf.gpa), @intFromEnum(AbbrevCode.null))
+            try wip_nav.debug_info.buffered_writer.writeLeb128(@intFromEnum(AbbrevCode.null))
         else
             std.leb.writeUnsignedFixed(
                 block_bytes,
-                wip_nav.debug_info.items[block.abbrev_code..][0..block_bytes],
+                dib[block.abbrev_code..][0..block_bytes],
                 try wip_nav.dwarf.refAbbrevCode(.empty_block),
             );
-        std.mem.writeInt(u32, wip_nav.debug_info.items[block.high_pc..][0..4], @intCast(code_off - block.low_pc_off), wip_nav.dwarf.endian);
+        std.mem.writeInt(u32, dib[block.high_pc..][0..4], @intCast(code_off - block.low_pc_off), wip_nav.dwarf.endian);
         wip_nav.any_children = true;
     }
 @@ -1631,18 +1636,18 @@ pub const WipNav = struct {
     ) UpdateError!void {
         const dwarf = wip_nav.dwarf;
         const zcu = wip_nav.pt.zcu;
-        const diw = wip_nav.debug_info.writer(dwarf.gpa);
+        const dibw = &wip_nav.debug_info.buffered_writer;
         const block = try wip_nav.blocks.addOne(dwarf.gpa);
-        block.abbrev_code = @intCast(wip_nav.debug_info.items.len);
+        block.abbrev_code = @intCast(dibw.count);
         try wip_nav.abbrevCode(.inlined_func);
         try wip_nav.refNav(zcu.funcInfo(func).owner_nav);
-        try uleb128(diw, zcu.navSrcLine(zcu.funcInfo(wip_nav.func).owner_nav) + line + 1);
+        try dibw.writeLeb128(zcu.navSrcLine(zcu.funcInfo(wip_nav.func).owner_nav) + line + 1);
-        try uleb128(diw, column + 1);
+        try dibw.writeLeb128(column + 1);
         block.low_pc_off = code_off;
         try wip_nav.infoAddrSym(wip_nav.func_sym_index, code_off);
-        block.high_pc = @intCast(wip_nav.debug_info.items.len);
+        block.high_pc = @intCast(dibw.count);
-        try diw.writeInt(u32, 0, dwarf.endian);
+        try dibw.writeInt(u32, 0, dwarf.endian);
         try wip_nav.setInlineFunc(func);
         wip_nav.any_children = false;
     }
 @@ -1650,15 +1655,16 @@ pub const WipNav = struct {
     pub fn leaveInlineFunc(wip_nav: *WipNav, func: InternPool.Index, code_off: u64) UpdateError!void {
         const inlined_func_bytes = comptime uleb128Bytes(@intFromEnum(AbbrevCode.inlined_func));
         const block = wip_nav.blocks.pop().?;
+        const dib = wip_nav.debug_info.getWritten();
         if (wip_nav.any_children)
-            try uleb128(wip_nav.debug_info.writer(wip_nav.dwarf.gpa), @intFromEnum(AbbrevCode.null))
+            try wip_nav.debug_info.buffered_writer.writeLeb128(@intFromEnum(AbbrevCode.null))
         else
             std.leb.writeUnsignedFixed(
                 inlined_func_bytes,
-                wip_nav.debug_info.items[block.abbrev_code..][0..inlined_func_bytes],
+                dib[block.abbrev_code..][0..inlined_func_bytes],
                 try wip_nav.dwarf.refAbbrevCode(.empty_inlined_func),
             );
-        std.mem.writeInt(u32, wip_nav.debug_info.items[block.high_pc..][0..4], @intCast(code_off - block.low_pc_off), wip_nav.dwarf.endian);
+        std.mem.writeInt(u32, dib[block.high_pc..][0..4], @intCast(code_off - block.low_pc_off), wip_nav.dwarf.endian);
         try wip_nav.setInlineFunc(func);
         wip_nav.any_children = true;
     }
 @@ -1672,22 +1678,22 @@ pub const WipNav = struct {
         const new_file = zcu.navFileScopeIndex(new_func_info.owner_nav);
         const new_unit = try dwarf.getUnit(zcu.fileByIndex(new_file).mod.?);
-        const dlw = wip_nav.debug_line.writer(dwarf.gpa);
+        const dlbw = &wip_nav.debug_line.buffered_writer;
         if (dwarf.incremental()) {
             const new_nav_gop = try dwarf.navs.getOrPut(dwarf.gpa, new_func_info.owner_nav);
             errdefer _ = if (!new_nav_gop.found_existing) dwarf.navs.pop();
             if (!new_nav_gop.found_existing) new_nav_gop.value_ptr.* = try dwarf.addCommonEntry(new_unit);
-            try dlw.writeByte(DW.LNS.extended_op);
+            try dlbw.writeByte(DW.LNS.extended_op);
-            try uleb128(dlw, 1 + dwarf.sectionOffsetBytes());
+            try dlbw.writeLeb128(1 + dwarf.sectionOffsetBytes());
-            try dlw.writeByte(DW.LNE.ZIG_set_decl);
+            try dlbw.writeByte(DW.LNE.ZIG_set_decl);
             try dwarf.debug_line.section.getUnit(wip_nav.unit).getEntry(wip_nav.entry).cross_section_relocs.append(dwarf.gpa, .{
-                .source_off = @intCast(wip_nav.debug_line.items.len),
+                .source_off = @intCast(dlbw.count),
                 .target_sec = .debug_info,
                 .target_unit = new_unit,
                 .target_entry = new_nav_gop.value_ptr.toOptional(),
             });
-            try dlw.writeByteNTimes(0, dwarf.sectionOffsetBytes());
+            try dlbw.splatByteAll(0, dwarf.sectionOffsetBytes());
             return;
         }
 @@ -1698,42 +1704,49 @@ pub const WipNav = struct {
             try mod_info.dirs.put(dwarf.gpa, new_unit, {});
             const file_gop = try mod_info.files.getOrPut(dwarf.gpa, new_file);
-            try dlw.writeByte(DW.LNS.set_file);
+            try dlbw.writeByte(DW.LNS.set_file);
-            try uleb128(dlw, file_gop.index);
+            try dlbw.writeLeb128(file_gop.index);
         }
         const old_src_line: i33 = zcu.navSrcLine(old_func_info.owner_nav);
         const new_src_line: i33 = zcu.navSrcLine(new_func_info.owner_nav);
         if (new_src_line != old_src_line) {
-            try dlw.writeByte(DW.LNS.advance_line);
+            try dlbw.writeByte(DW.LNS.advance_line);
-            try sleb128(dlw, new_src_line - old_src_line);
+            try dlbw.writeLeb128(new_src_line - old_src_line);
         }
         wip_nav.func = func;
     }
-    fn externalReloc(wip_nav: *WipNav, sec: *Section, reloc: ExternalReloc) std.mem.Allocator.Error!void {
+    fn externalReloc(wip_nav: *WipNav, sec: *Section, reloc: ExternalReloc) Allocator.Error!void {
         try sec.getUnit(wip_nav.unit).getEntry(wip_nav.entry).external_relocs.append(wip_nav.dwarf.gpa, reloc);
     }
-    pub fn infoExternalReloc(wip_nav: *WipNav, reloc: ExternalReloc) std.mem.Allocator.Error!void {
+    pub fn infoExternalReloc(wip_nav: *WipNav, reloc: ExternalReloc) Allocator.Error!void {
         try wip_nav.externalReloc(&wip_nav.dwarf.debug_info.section, reloc);
     }
-    fn frameExternalReloc(wip_nav: *WipNav, reloc: ExternalReloc) std.mem.Allocator.Error!void {
+    fn frameExternalReloc(wip_nav: *WipNav, reloc: ExternalReloc) Allocator.Error!void {
         try wip_nav.externalReloc(&wip_nav.dwarf.debug_frame.section, reloc);
     }
     fn abbrevCode(wip_nav: *WipNav, abbrev_code: AbbrevCode) UpdateError!void {
-        try uleb128(wip_nav.debug_info.writer(wip_nav.dwarf.gpa), try wip_nav.dwarf.refAbbrevCode(abbrev_code));
+        try wip_nav.debug_info.buffered_writer.writeLeb128(try wip_nav.dwarf.refAbbrevCode(abbrev_code));
     }
-    fn sectionOffset(wip_nav: *WipNav, comptime sec: Section.Index, target_sec: Section.Index, target_unit: Unit.Index, target_entry: Entry.Index, target_off: u32) UpdateError!void {
+    fn sectionOffset(
+        wip_nav: *WipNav,
+        comptime sec: Section.Index,
+        target_sec: Section.Index,
+        target_unit: Unit.Index,
+        target_entry: Entry.Index,
+        target_off: u32,
+    ) UpdateError!void {
         const dwarf = wip_nav.dwarf;
         const gpa = dwarf.gpa;
         const entry_ptr = @field(dwarf, @tagName(sec)).section.getUnit(wip_nav.unit).getEntry(wip_nav.entry);
-        const bytes = &@field(wip_nav, @tagName(sec));
+        const bw = &@field(wip_nav, @tagName(sec)).buffered_writer;
-        const source_off: u32 = @intCast(bytes.items.len);
+        const source_off: u32 = @intCast(bw.count);
         if (target_sec != sec) {
             try entry_ptr.cross_section_relocs.append(gpa, .{
                 .source_off = source_off,
 @@ -1756,7 +1769,7 @@ pub const WipNav = struct {
                 .target_off = target_off,
             });
         }
-        try bytes.appendNTimes(gpa, 0, dwarf.sectionOffsetBytes());
+        try bw.splatByteAll(0, dwarf.sectionOffsetBytes());
     }
     fn infoSectionOffset(wip_nav: *WipNav, target_sec: Section.Index, target_unit: Unit.Index, target_entry: Entry.Index, target_off: u32) UpdateError!void {
 @@ -1768,93 +1781,93 @@ pub const WipNav = struct {
     }
     const ExprLocCounter = struct {
-        const Stream = std.io.CountingWriter(std.io.NullWriter);
-        stream: Stream,
         section_offset_bytes: u32,
         address_size: AddressSize,
         fn init(dwarf: *Dwarf) ExprLocCounter {
             return .{
-                .stream = std.io.countingWriter(std.io.null_writer),
                 .section_offset_bytes = dwarf.sectionOffsetBytes(),
                 .address_size = dwarf.address_size,
             };
         }
-        fn writer(counter: *ExprLocCounter) Stream.Writer {
-            return counter.stream.writer();
-        }
         fn endian(_: ExprLocCounter) std.builtin.Endian {
             return @import("builtin").cpu.arch.endian();
         }
-        fn addrSym(counter: *ExprLocCounter, _: u32) error{}!void {
+        fn addrSym(counter: ExprLocCounter, bw: *Writer, _: u32) error{}!void {
-            counter.stream.bytes_written += @intFromEnum(counter.address_size);
+            bw.count += @intFromEnum(counter.address_size);
         }
-        fn infoEntry(counter: *ExprLocCounter, _: Unit.Index, _: Entry.Index) error{}!void {
+        fn infoEntry(counter: ExprLocCounter, bw: *Writer, _: Unit.Index, _: Entry.Index) error{}!void {
-            counter.stream.bytes_written += counter.section_offset_bytes;
+            bw.count += counter.section_offset_bytes;
         }
     };
     fn infoExprLoc(wip_nav: *WipNav, loc: Loc) UpdateError!void {
-        var counter: ExprLocCounter = .init(wip_nav.dwarf);
+        const bw = &wip_nav.debug_info.buffered_writer;
-        try loc.write(&counter);
+        const counter: ExprLocCounter = .init(wip_nav.dwarf);
+        const start = bw.count;
+        try loc.write(bw, counter);
+        const len = bw.count - start;
+        bw.count = start;
+        wip_nav.debug_info.shrinkRetainingCapacity(start);
         const adapter: struct {
             wip_nav: *WipNav,
-            fn writer(ctx: @This()) std.ArrayListUnmanaged(u8).Writer {
-                return ctx.wip_nav.debug_info.writer(ctx.wip_nav.dwarf.gpa);
-            }
             fn endian(ctx: @This()) std.builtin.Endian {
                 return ctx.wip_nav.dwarf.endian;
             }
-            fn addrSym(ctx: @This(), sym_index: u32) UpdateError!void {
+            fn addrSym(ctx: @This(), _: *Writer, sym_index: u32) UpdateError!void {
                 try ctx.wip_nav.infoAddrSym(sym_index, 0);
             }
-            fn infoEntry(ctx: @This(), unit: Unit.Index, entry: Entry.Index) UpdateError!void {
+            fn infoEntry(ctx: @This(), _: *Writer, unit: Unit.Index, entry: Entry.Index) UpdateError!void {
                 try ctx.wip_nav.infoSectionOffset(.debug_info, unit, entry, 0);
             }
         } = .{ .wip_nav = wip_nav };
-        try uleb128(adapter.writer(), counter.stream.bytes_written);
+        try bw.writeLeb128(len);
-        try loc.write(adapter);
+        try loc.write(bw, adapter);
     }
     fn infoAddrSym(wip_nav: *WipNav, sym_index: u32, sym_off: u64) UpdateError!void {
+        const dibw = &wip_nav.debug_info.buffered_writer;
         try wip_nav.infoExternalReloc(.{
-            .source_off = @intCast(wip_nav.debug_info.items.len),
+            .source_off = @intCast(dibw.count),
             .target_sym = sym_index,
             .target_off = sym_off,
         });
-        try wip_nav.debug_info.appendNTimes(wip_nav.dwarf.gpa, 0, @intFromEnum(wip_nav.dwarf.address_size));
+        try dibw.splatByteAll(0, @intFromEnum(wip_nav.dwarf.address_size));
     }
     fn frameExprLoc(wip_nav: *WipNav, loc: Loc) UpdateError!void {
-        var counter: ExprLocCounter = .init(wip_nav.dwarf);
+        const bw = &wip_nav.debug_frame.buffered_writer;
-        try loc.write(&counter);
+        const counter: ExprLocCounter = .init(wip_nav.dwarf);
+        const start = bw.count;
+        try loc.write(bw, counter);
+        const len = bw.count - start;
+        bw.count = start;
+        wip_nav.debug_frame.shrinkRetainingCapacity(start);
         const adapter: struct {
             wip_nav: *WipNav,
-            fn writer(ctx: @This()) std.ArrayListUnmanaged(u8).Writer {
-                return ctx.wip_nav.debug_frame.writer(ctx.wip_nav.dwarf.gpa);
-            }
             fn endian(ctx: @This()) std.builtin.Endian {
                 return ctx.wip_nav.dwarf.endian;
             }
-            fn addrSym(ctx: @This(), sym_index: u32) UpdateError!void {
+            fn addrSym(ctx: @This(), _: *Writer, sym_index: u32) UpdateError!void {
                 try ctx.wip_nav.frameAddrSym(sym_index, 0);
             }
-            fn infoEntry(ctx: @This(), unit: Unit.Index, entry: Entry.Index) UpdateError!void {
+            fn infoEntry(ctx: @This(), _: *Writer, unit: Unit.Index, entry: Entry.Index) UpdateError!void {
                 try ctx.wip_nav.sectionOffset(.debug_frame, .debug_info, unit, entry, 0);
             }
         } = .{ .wip_nav = wip_nav };
-        try uleb128(adapter.writer(), counter.stream.bytes_written);
+        try bw.writeLeb128(len);
-        try loc.write(adapter);
+        try loc.write(bw, adapter);
     }
     fn frameAddrSym(wip_nav: *WipNav, sym_index: u32, sym_off: u64) UpdateError!void {
+        const dfbw = &wip_nav.debug_frame.buffered_writer;
         try wip_nav.frameExternalReloc(.{
-            .source_off = @intCast(wip_nav.debug_frame.items.len),
+            .source_off = @intCast(dfbw.count),
             .target_sym = sym_index,
             .target_off = sym_off,
         });
-        try wip_nav.debug_frame.appendNTimes(wip_nav.dwarf.gpa, 0, @intFromEnum(wip_nav.dwarf.address_size));
+        try dfbw.splatByteAll(0, @intFromEnum(wip_nav.dwarf.address_size));
     }
     fn getNavEntry(wip_nav: *WipNav, nav_index: InternPool.Nav.Index) UpdateError!struct { Unit.Index, Entry.Index } {
 @@ -1922,38 +1935,41 @@ pub const WipNav = struct {
         try wip_nav.infoSectionOffset(.debug_info, unit, entry, 0);
     }
-    fn refForward(wip_nav: *WipNav) std.mem.Allocator.Error!u32 {
+    fn refForward(wip_nav: *WipNav) Allocator.Error!u32 {
         const dwarf = wip_nav.dwarf;
+        const dibw = &wip_nav.debug_info.buffered_writer;
         const cross_entry_relocs = &dwarf.debug_info.section.getUnit(wip_nav.unit).getEntry(wip_nav.entry).cross_entry_relocs;
         const reloc_index: u32 = @intCast(cross_entry_relocs.items.len);
         try cross_entry_relocs.append(dwarf.gpa, .{
-            .source_off = @intCast(wip_nav.debug_info.items.len),
+            .source_off = @intCast(dibw.count),
             .target_entry = undefined,
             .target_off = undefined,
         });
-        try wip_nav.debug_info.appendNTimes(dwarf.gpa, 0, dwarf.sectionOffsetBytes());
+        try dibw.splatByteAll(0, dwarf.sectionOffsetBytes());
         return reloc_index;
     }
     fn finishForward(wip_nav: *WipNav, reloc_index: u32) void {
         const reloc = &wip_nav.dwarf.debug_info.section.getUnit(wip_nav.unit).getEntry(wip_nav.entry).cross_entry_relocs.items[reloc_index];
         reloc.target_entry = wip_nav.entry.toOptional();
-        reloc.target_off = @intCast(wip_nav.debug_info.items.len);
+        reloc.target_off = @intCast(wip_nav.debug_info.buffered_writer.count);
     }
     fn blockValue(wip_nav: *WipNav, src_loc: Zcu.LazySrcLoc, val: Value) UpdateError!void {
         const ty = val.typeOf(wip_nav.pt.zcu);
-        const diw = wip_nav.debug_info.writer(wip_nav.dwarf.gpa);
+        const dibw = &wip_nav.debug_info.buffered_writer;
         const bytes = if (ty.hasRuntimeBits(wip_nav.pt.zcu)) ty.abiSize(wip_nav.pt.zcu) else 0;
-        try uleb128(diw, bytes);
+        try dibw.writeLeb128(bytes);
         if (bytes == 0) return;
-        const old_len = wip_nav.debug_info.items.len;
+        var dial = wip_nav.debug_info.toArrayList();
+        defer _ = wip_nav.debug_info.fromArrayList(wip_nav.dwarf.gpa, &dial);
+        const old_len = dial.items.len;
         try codegen.generateSymbol(
             wip_nav.dwarf.bin_file,
             wip_nav.pt,
             src_loc,
             val,
-            &wip_nav.debug_info,
+            &dial,
             .{ .debug_output = .{ .dwarf = wip_nav } },
         );
         if (old_len + bytes != wip_nav.debug_info.items.len) {
 @@ -1975,7 +1991,7 @@ pub const WipNav = struct {
         big_int: std.math.big.int.Const,
     ) UpdateError!void {
         const zcu = wip_nav.pt.zcu;
-        const diw = wip_nav.debug_info.writer(wip_nav.dwarf.gpa);
+        const dibw = &wip_nav.debug_info.buffered_writer;
         const signedness = switch (ty.toIntern()) {
             .comptime_int_type, .comptime_float_type => .signed,
             else => ty.intInfo(zcu).signedness,
 @@ -1986,7 +2002,7 @@ pub const WipNav = struct {
                 .signed => abbrev_code.sdata,
                 .unsigned => abbrev_code.udata,
             });
-            try wip_nav.debug_info.ensureUnusedCapacity(wip_nav.dwarf.gpa, std.math.divCeil(usize, bits, 7) catch unreachable);
+            _ = try dibw.writableSliceGreedy(std.math.divCeil(usize, bits, 7) catch unreachable);
             var bit: usize = 0;
             var carry: u1 = 1;
             while (bit < bits) {
 @@ -2003,16 +2019,17 @@ pub const WipNav = struct {
                     break :twos_comp_part twos_comp_part;
                 };
                 bit += 7;
-                wip_nav.debug_info.appendAssumeCapacity(@as(u8, if (bit < bits) 0x80 else 0x00) | twos_comp_part);
+                dibw.writeByte(@as(u8, if (bit < bits) 0x80 else 0x00) | twos_comp_part) catch unreachable;
             }
         } else {
             try wip_nav.abbrevCode(abbrev_code.block);
             const bytes = @max(ty.abiSize(zcu), std.math.divCeil(usize, bits, 8) catch unreachable);
-            try uleb128(diw, bytes);
+            try dibw.writeLeb128(bytes);
             big_int.writeTwosComplement(
-                try wip_nav.debug_info.addManyAsSlice(wip_nav.dwarf.gpa, @intCast(bytes)),
+                try dibw.writableSliceGreedy(@intCast(bytes)),
                 wip_nav.dwarf.endian,
             );
+            dibw.advance(@intCast(bytes));
         }
     }
 @@ -2045,7 +2062,7 @@ pub const WipNav = struct {
         const zcu = wip_nav.pt.zcu;
         const ip = &zcu.intern_pool;
         const dwarf = wip_nav.dwarf;
-        const diw = wip_nav.debug_info.writer(dwarf.gpa);
+        const dibw = &wip_nav.debug_info.buffered_writer;
         const orig_entry = wip_nav.entry;
         defer wip_nav.entry = orig_entry;
 @@ -2096,15 +2113,15 @@ pub const WipNav = struct {
         try wip_nav.abbrevCode(if (is_generic_decl) abbrev_code.generic_decl else abbrev_code.decl);
         try wip_nav.refType((if (is_generic_decl) null else parent_type) orelse
             .fromInterned(zcu.fileRootType(file)));
-        assert(wip_nav.debug_info.items.len == DebugInfo.declEntryLineOff(dwarf));
+        assert(dibw.count == DebugInfo.declEntryLineOff(dwarf));
-        try diw.writeInt(u32, decl.src_line + 1, dwarf.endian);
+        try dibw.writeInt(u32, decl.src_line + 1, dwarf.endian);
-        try uleb128(diw, decl.src_column + 1);
+        try dibw.writeLeb128(decl.src_column + 1);
-        try diw.writeByte(if (decl.is_pub) DW.ACCESS.public else DW.ACCESS.private);
+        try dibw.writeByte(if (decl.is_pub) DW.ACCESS.public else DW.ACCESS.private);
         try wip_nav.strp(nav.name.toSlice(ip));
         if (!is_generic_decl) return;
         const generic_decl_entry = wip_nav.entry;
-        try dwarf.debug_info.section.replaceEntry(wip_nav.unit, generic_decl_entry, dwarf, wip_nav.debug_info.items);
+        try dwarf.debug_info.section.replaceEntry(wip_nav.unit, generic_decl_entry, dwarf, wip_nav.debug_info.getWritten());
         wip_nav.debug_info.clearRetainingCapacity();
         wip_nav.entry = orig_entry;
         try wip_nav.abbrevCode(abbrev_code.decl_instance);
 @@ -2408,12 +2425,63 @@ pub fn initWipNav(
     nav_index: InternPool.Nav.Index,
     sym_index: u32,
 ) error{ OutOfMemory, CodegenFail }!?WipNav {
-    return initWipNavInner(dwarf, pt, nav_index, sym_index) catch |err| switch (err) {
+    return dwarf.initWipNavInner(pt, nav_index, sym_index) catch |err| switch (err) {
+        error.OutOfMemory => return error.OutOfMemory,
+        else => |e| return pt.zcu.codegenFail(nav_index, "failed to init dwarf nav: {s}", .{@errorName(e)}),
+    };
+}
+pub fn finishWipNavFunc(
+    dwarf: *Dwarf,
+    pt: Zcu.PerThread,
+    nav_index: InternPool.Nav.Index,
+    code_size: u64,
+    wip_nav: *WipNav,
+) error{ OutOfMemory, CodegenFail }!void {
+    return dwarf.finishWipNavFuncInner(pt, nav_index, code_size, wip_nav) catch |err| switch (err) {
+        error.OutOfMemory => return error.OutOfMemory,
+        else => |e| return pt.zcu.codegenFail(nav_index, "failed to finish dwarf func nav: {s}", .{@errorName(e)}),
+    };
+}
+pub fn finishWipNav(
+    dwarf: *Dwarf,
+    pt: Zcu.PerThread,
+    nav_index: InternPool.Nav.Index,
+    wip_nav: *WipNav,
+) error{ OutOfMemory, CodegenFail }!void {
+    return dwarf.finishWipNavInner(pt, nav_index, wip_nav) catch |err| switch (err) {
+        error.OutOfMemory => return error.OutOfMemory,
+        else => |e| return pt.zcu.codegenFail(nav_index, "failed to finish dwarf nav: {s}", .{@errorName(e)}),
+    };
+}
+pub fn updateComptimeNav(
+    dwarf: *Dwarf,
+    pt: Zcu.PerThread,
+    nav_index: InternPool.Nav.Index,
+) error{ OutOfMemory, CodegenFail }!void {
+    return dwarf.updateComptimeNavInner(pt, nav_index) catch |err| switch (err) {
+        error.OutOfMemory => return error.OutOfMemory,
+        else => |e| return pt.zcu.codegenFail(nav_index, "failed to update dwarf comptime nav: {s}", .{@errorName(e)}),
+    };
+}
+pub fn updateContainerType(
+    dwarf: *Dwarf,
+    pt: Zcu.PerThread,
+    type_index: InternPool.Index,
+) error{ OutOfMemory, CodegenFail }!void {
+    return dwarf.updateContainerType(pt, type_index) catch |err| switch (err) {
         error.OutOfMemory => return error.OutOfMemory,
-        else => |e| return pt.zcu.codegenFail(nav_index, "failed to init dwarf: {s}", .{@errorName(e)}),
+        else => |e| return pt.zcu.codegenFailType(type_index, "failed to update dwarf comptime nav: {s}", .{@errorName(e)}),
     };
 }
+pub fn flushModule(dwarf: *Dwarf, pt: Zcu.PerThread) FlushError!void {
+    return dwarf.flushModuleInner(pt);
+}
 fn initWipNavInner(
     dwarf: *Dwarf,
     pt: Zcu.PerThread,
 @@ -2468,17 +2536,17 @@ fn initWipNavInner(
         .func_high_pc = undefined,
         .blocks = undefined,
         .cfi = undefined,
-        .debug_frame = .empty,
+        .debug_frame = undefined,
-        .debug_info = .empty,
+        .debug_info = undefined,
-        .debug_line = .empty,
+        .debug_line = undefined,
-        .debug_loclists = .empty,
+        .debug_loclists = undefined,
         .pending_lazy = .empty,
     };
     errdefer wip_nav.deinit();
     switch (nav_key) {
         else => {
-            const diw = wip_nav.debug_info.writer(dwarf.gpa);
+            const dibw = &wip_nav.debug_info.buffered_writer;
             try wip_nav.declCommon(.{
                 .decl = .decl_var,
                 .generic_decl = .generic_decl_var,
 @@ -2499,9 +2567,9 @@ fn initWipNavInner(
                 .@"const" => {
                     const const_ty_reloc_index = try wip_nav.refForward();
                     try wip_nav.infoExprLoc(loc);
-                    try uleb128(diw, nav.status.fully_resolved.alignment.toByteUnits() orelse
+                    try dibw.writeLeb128(nav.status.fully_resolved.alignment.toByteUnits() orelse
                         ty.abiAlignment(zcu).toByteUnits().?);
-                    try diw.writeByte(@intFromBool(decl.linkage != .normal));
+                    try dibw.writeByte(@intFromBool(decl.linkage != .normal));
                     wip_nav.finishForward(const_ty_reloc_index);
                     try wip_nav.abbrevCode(.is_const);
                     try wip_nav.refType(ty);
 @@ -2509,9 +2577,9 @@ fn initWipNavInner(
                 .@"var" => {
                     try wip_nav.refType(ty);
                     try wip_nav.infoExprLoc(loc);
-                    try uleb128(diw, nav.status.fully_resolved.alignment.toByteUnits() orelse
+                    try dibw.writeLeb128(dibw, nav.status.fully_resolved.alignment.toByteUnits() orelse
                         ty.abiAlignment(zcu).toByteUnits().?);
-                    try diw.writeByte(@intFromBool(decl.linkage != .normal));
+                    try dibw.writeByte(@intFromBool(decl.linkage != .normal));
                 },
             }
         },
 @@ -2536,39 +2604,39 @@ fn initWipNavInner(
                 .none => {},
                 .debug_frame, .eh_frame => |format| {
                     const entry = dwarf.debug_frame.section.getUnit(wip_nav.unit).getEntry(wip_nav.entry);
-                    const dfw = wip_nav.debug_frame.writer(dwarf.gpa);
+                    const dfbw = &wip_nav.debug_frame.buffered_writer;
                     switch (dwarf.format) {
-                        .@"32" => try dfw.writeInt(u32, undefined, dwarf.endian),
+                        .@"32" => try dfbw.writeInt(u32, undefined, dwarf.endian),
                         .@"64" => {
-                            try dfw.writeInt(u32, std.math.maxInt(u32), dwarf.endian);
+                            try dfbw.writeInt(u32, std.math.maxInt(u32), dwarf.endian);
-                            try dfw.writeInt(u64, undefined, dwarf.endian);
+                            try dfbw.writeInt(u64, undefined, dwarf.endian);
                         },
                     }
                     switch (format) {
                         .none => unreachable,
                         .debug_frame => {
                             try entry.cross_entry_relocs.append(dwarf.gpa, .{
-                                .source_off = @intCast(wip_nav.debug_frame.items.len),
+                                .source_off = @intCast(dfbw.count),
                             });
-                            try dfw.writeByteNTimes(0, dwarf.sectionOffsetBytes());
+                            try dfbw.splatByteAll(0, dwarf.sectionOffsetBytes());
                             try wip_nav.frameAddrSym(sym_index, 0);
-                            try dfw.writeByteNTimes(undefined, @intFromEnum(dwarf.address_size));
+                            try dfbw.splatByteAll(undefined, @intFromEnum(dwarf.address_size));
                         },
                         .eh_frame => {
-                            try dfw.writeInt(u32, undefined, dwarf.endian);
+                            try dfbw.writeInt(u32, undefined, dwarf.endian);
                             try wip_nav.frameExternalReloc(.{
-                                .source_off = @intCast(wip_nav.debug_frame.items.len),
+                                .source_off = @intCast(dfbw.count),
                                 .target_sym = sym_index,
                             });
-                            try dfw.writeInt(u32, 0, dwarf.endian);
+                            try dfbw.writeInt(u32, 0, dwarf.endian);
-                            try dfw.writeInt(u32, undefined, dwarf.endian);
+                            try dfbw.writeInt(u32, undefined, dwarf.endian);
-                            try uleb128(dfw, 0);
+                            try dfbw.writeUleb128(0);
                         },
                     }
                 },
             }
-            const diw = wip_nav.debug_info.writer(dwarf.gpa);
+            const dibw = &wip_nav.debug_info.buffered_writer;
             try wip_nav.declCommon(.{
                 .decl = .decl_func,
                 .generic_decl = .generic_decl_func,
 @@ -2578,47 +2646,47 @@ fn initWipNavInner(
             try wip_nav.refType(.fromInterned(func_type.return_type));
             try wip_nav.infoAddrSym(sym_index, 0);
             wip_nav.func_high_pc = @intCast(wip_nav.debug_info.items.len);
-            try diw.writeInt(u32, 0, dwarf.endian);
+            try dibw.writeInt(u32, 0, dwarf.endian);
             const target = &mod.resolved_target.result;
-            try uleb128(diw, switch (nav.status.fully_resolved.alignment) {
+            try dibw.writeLeb128(switch (nav.status.fully_resolved.alignment) {
                 .none => target_info.defaultFunctionAlignment(target),
                 else => |a| a.maxStrict(target_info.minFunctionAlignment(target)),
             }.toByteUnits().?);
-            try diw.writeByte(@intFromBool(decl.linkage != .normal));
+            try dibw.writeByte(@intFromBool(decl.linkage != .normal));
-            try diw.writeByte(@intFromBool(func_type.return_type == .noreturn_type));
+            try dibw.writeByte(@intFromBool(func_type.return_type == .noreturn_type));
-            const dlw = wip_nav.debug_line.writer(dwarf.gpa);
+            const dlbw = &wip_nav.debug_line.buffered_writer;
-            try dlw.writeByte(DW.LNS.extended_op);
+            try dlbw.writeByte(DW.LNS.extended_op);
             if (dwarf.incremental()) {
-                try uleb128(dlw, 1 + dwarf.sectionOffsetBytes());
+                try dlbw.writeLeb128(1 + dwarf.sectionOffsetBytes());
-                try dlw.writeByte(DW.LNE.ZIG_set_decl);
+                try dlbw.writeByte(DW.LNE.ZIG_set_decl);
                 try dwarf.debug_line.section.getUnit(wip_nav.unit).getEntry(wip_nav.entry).cross_section_relocs.append(dwarf.gpa, .{
-                    .source_off = @intCast(wip_nav.debug_line.items.len),
+                    .source_off = @intCast(dlbw.count),
                     .target_sec = .debug_info,
                     .target_unit = wip_nav.unit,
                     .target_entry = wip_nav.entry.toOptional(),
                 });
-                try dlw.writeByteNTimes(0, dwarf.sectionOffsetBytes());
+                try dlbw.splatByteAll(0, dwarf.sectionOffsetBytes());
-                try dlw.writeByte(DW.LNS.set_column);
+                try dlbw.writeByte(DW.LNS.set_column);
-                try uleb128(dlw, func.lbrace_column + 1);
+                try dlbw.writeLeb128(func.lbrace_column + 1);
                 try wip_nav.advancePCAndLine(func.lbrace_line, 0);
             } else {
-                try uleb128(dlw, 1 + @intFromEnum(dwarf.address_size));
+                try dlbw.writeLeb128(1 + @intFromEnum(dwarf.address_size));
-                try dlw.writeByte(DW.LNE.set_address);
+                try dlbw.writeByte(DW.LNE.set_address);
                 try dwarf.debug_line.section.getUnit(wip_nav.unit).getEntry(wip_nav.entry).external_relocs.append(dwarf.gpa, .{
-                    .source_off = @intCast(wip_nav.debug_line.items.len),
+                    .source_off = @intCast(dlbw.count),
                     .target_sym = sym_index,
                 });
-                try dlw.writeByteNTimes(0, @intFromEnum(dwarf.address_size));
+                try dlbw.splatByteAll(0, @intFromEnum(dwarf.address_size));
                 const file_gop = try dwarf.getModInfo(unit).files.getOrPut(dwarf.gpa, inst_info.file);
-                try dlw.writeByte(DW.LNS.set_file);
+                try dlbw.writeByte(DW.LNS.set_file);
-                try uleb128(dlw, file_gop.index);
+                try dlbw.writeLeb128(file_gop.index);
-                try dlw.writeByte(DW.LNS.set_column);
+                try dlbw.writeByte(DW.LNS.set_column);
-                try uleb128(dlw, func.lbrace_column + 1);
+                try dlbw.writeLeb128(func.lbrace_column + 1);
                 try wip_nav.advancePCAndLine(@intCast(decl.src_line + func.lbrace_line), 0);
             }
 @@ -2627,7 +2695,7 @@ fn initWipNavInner(
     return wip_nav;
 }
-pub fn finishWipNavFunc(
+fn finishWipNavFuncInner(
     dwarf: *Dwarf,
     pt: Zcu.PerThread,
     nav_index: InternPool.Nav.Index,
 @@ -2656,12 +2724,9 @@ pub fn finishWipNavFunc(
     switch (dwarf.debug_frame.header.format) {
         .none => {},
         .debug_frame, .eh_frame => |format| {
-            try wip_nav.debug_frame.appendNTimes(
+            const dfbw = &wip_nav.debug_frame.buffered_writer;
-                dwarf.gpa,
+            try dfbw.splatByteAll(DW.CFA.nop, @intCast(dwarf.debug_frame.section.alignment.forward(dfbw.count) - dfbw.count));
-                DW.CFA.nop,
+            const contents = wip_nav.debug_frame.getWritten();
-                @intCast(dwarf.debug_frame.section.alignment.forward(wip_nav.debug_frame.items.len) - wip_nav.debug_frame.items.len),
-            );
-            const contents = wip_nav.debug_frame.items;
             try dwarf.debug_frame.section.resizeEntry(wip_nav.unit, wip_nav.entry, dwarf, @intCast(contents.len));
             const unit = dwarf.debug_frame.section.getUnit(wip_nav.unit);
             const entry = unit.getEntry(wip_nav.entry);
 @@ -2688,14 +2753,14 @@ pub fn finishWipNavFunc(
         },
     }
     {
-        std.mem.writeInt(u32, wip_nav.debug_info.items[wip_nav.func_high_pc..][0..4], @intCast(code_size), dwarf.endian);
+        std.mem.writeInt(u32, wip_nav.debug_info.getWritten()[wip_nav.func_high_pc..][0..4], @intCast(code_size), dwarf.endian);
         if (wip_nav.any_children) {
-            const diw = wip_nav.debug_info.writer(dwarf.gpa);
+            const dibw = &wip_nav.debug_info.buffered_writer;
-            try uleb128(diw, @intFromEnum(AbbrevCode.null));
+            try dibw.writeLeb128(@intFromEnum(AbbrevCode.null));
         } else {
-            const abbrev_code_buf = wip_nav.debug_info.items[0..AbbrevCode.decl_bytes];
+            const abbrev_code_buf = wip_nav.debug_info.getWritten()[0..AbbrevCode.decl_bytes];
-            var abbrev_code_fbs = std.io.fixedBufferStream(abbrev_code_buf);
+            var abbrev_code_br: std.io.Reader = .fixed(abbrev_code_buf);
-            const abbrev_code: AbbrevCode = @enumFromInt(std.leb.readUleb128(@typeInfo(AbbrevCode).@"enum".tag_type, abbrev_code_fbs.reader()) catch unreachable);
+            const abbrev_code: AbbrevCode = @enumFromInt(abbrev_code_br.takeLeb128(@typeInfo(AbbrevCode).@"enum".tag_type) catch unreachable);
             std.leb.writeUnsignedFixed(
                 AbbrevCode.decl_bytes,
                 abbrev_code_buf,
 @@ -2727,10 +2792,10 @@ pub fn finishWipNavFunc(
         );
     }
-    try dwarf.finishWipNav(pt, nav_index, wip_nav);
+    try dwarf.finishWipNavInner(pt, nav_index, wip_nav);
 }
-pub fn finishWipNav(
+fn finishWipNavInner(
     dwarf: *Dwarf,
     pt: Zcu.PerThread,
     nav_index: InternPool.Nav.Index,
 @@ -2741,26 +2806,20 @@ pub fn finishWipNav(
     const nav = ip.getNav(nav_index);
     log.debug("finishWipNav({f})", .{nav.fqn.fmt(ip)});
-    try dwarf.debug_info.section.replaceEntry(wip_nav.unit, wip_nav.entry, dwarf, wip_nav.debug_info.items);
+    try dwarf.debug_info.section.replaceEntry(wip_nav.unit, wip_nav.entry, dwarf, wip_nav.debug_info.getWritten());
-    if (wip_nav.debug_line.items.len > 0) {
+    const debug_line = wip_nav.debug_line.getWritten();
-        const dlw = wip_nav.debug_line.writer(dwarf.gpa);
+    if (debug_line.len > 0) {
-        try dlw.writeByte(DW.LNS.extended_op);
+        const dlbw = &wip_nav.debug_line.buffered_writer;
-        try uleb128(dlw, 1);
+        try dlbw.writeByte(DW.LNS.extended_op);
-        try dlw.writeByte(DW.LNE.end_sequence);
+        try dlbw.writeUleb128(1);
-        try dwarf.debug_line.section.replaceEntry(wip_nav.unit, wip_nav.entry, dwarf, wip_nav.debug_line.items);
+        try dlbw.writeByte(DW.LNE.end_sequence);
+        try dwarf.debug_line.section.replaceEntry(wip_nav.unit, wip_nav.entry, dwarf, wip_nav.debug_line.getWritten());
     }
-    try dwarf.debug_loclists.section.replaceEntry(wip_nav.unit, wip_nav.entry, dwarf, wip_nav.debug_loclists.items);
+    try dwarf.debug_loclists.section.replaceEntry(wip_nav.unit, wip_nav.entry, dwarf, wip_nav.debug_loclists.getWritten());
     try wip_nav.updateLazy(zcu.navSrcLoc(nav_index));
 }
-pub fn updateComptimeNav(dwarf: *Dwarf, pt: Zcu.PerThread, nav_index: InternPool.Nav.Index) error{ OutOfMemory, CodegenFail }!void {
-    return updateComptimeNavInner(dwarf, pt, nav_index) catch |err| switch (err) {
-        error.OutOfMemory => return error.OutOfMemory,
-        else => |e| return pt.zcu.codegenFail(nav_index, "failed to update dwarf: {s}", .{@errorName(e)}),
-    };
-}
 fn updateComptimeNavInner(dwarf: *Dwarf, pt: Zcu.PerThread, nav_index: InternPool.Nav.Index) !void {
     const zcu = pt.zcu;
     const ip = &zcu.intern_pool;
 @@ -2799,12 +2858,13 @@ fn updateComptimeNavInner(dwarf: *Dwarf, pt: Zcu.PerThread, nav_index: InternPoo
         .func_high_pc = undefined,
         .blocks = undefined,
         .cfi = undefined,
-        .debug_frame = .empty,
+        .debug_frame = undefined,
-        .debug_info = .empty,
+        .debug_info = undefined,
-        .debug_line = .empty,
+        .debug_line = undefined,
-        .debug_loclists = .empty,
+        .debug_loclists = undefined,
         .pending_lazy = .empty,
     };
+    wip_nav.init();
     defer wip_nav.deinit();
     const nav_gop = try dwarf.navs.getOrPut(dwarf.gpa, nav_index);
 @@ -2848,7 +2908,7 @@ fn updateComptimeNavInner(dwarf: *Dwarf, pt: Zcu.PerThread, nav_index: InternPoo
             }
             wip_nav.entry = nav_gop.value_ptr.*;
-            const diw = wip_nav.debug_info.writer(dwarf.gpa);
+            const dibw = &wip_nav.debug_info.buffered_writer;
             switch (loaded_struct.layout) {
                 .auto, .@"extern" => {
 @@ -2861,9 +2921,9 @@ fn updateComptimeNavInner(dwarf: *Dwarf, pt: Zcu.PerThread, nav_index: InternPoo
                         .generic_decl = .generic_decl_const,
                         .decl_instance = .decl_instance_struct,
                     }, &nav, inst_info.file, &decl);
-                    if (loaded_struct.field_types.len == 0) try diw.writeByte(@intFromBool(false)) else {
+                    if (loaded_struct.field_types.len == 0) try dibw.writeByte(@intFromBool(false)) else {
-                        try uleb128(diw, nav_val.toType().abiSize(zcu));
+                        try dibw.writeLeb128(nav_val.toType().abiSize(zcu));
-                        try uleb128(diw, nav_val.toType().abiAlignment(zcu).toByteUnits().?);
+                        try dibw.writeLeb128(nav_val.toType().abiAlignment(zcu).toByteUnits().?);
                         for (0..loaded_struct.field_types.len) |field_index| {
                             const is_comptime = loaded_struct.fieldIsComptime(ip, field_index);
                             const field_init = loaded_struct.fieldInit(ip, field_index);
 @@ -2899,8 +2959,8 @@ fn updateComptimeNavInner(dwarf: *Dwarf, pt: Zcu.PerThread, nav_index: InternPoo
                             }
                             try wip_nav.refType(field_type);
                             if (!is_comptime) {
-                                try uleb128(diw, loaded_struct.offsets.get(ip)[field_index]);
+                                try dibw.writeLeb128(loaded_struct.offsets.get(ip)[field_index]);
-                                try uleb128(diw, loaded_struct.fieldAlign(ip, field_index).toByteUnits() orelse
+                                try dibw.writeLeb128(loaded_struct.fieldAlign(ip, field_index).toByteUnits() orelse
                                     field_type.abiAlignment(zcu).toByteUnits().?);
                             }
                             if (has_comptime_state)
 @@ -2908,7 +2968,7 @@ fn updateComptimeNavInner(dwarf: *Dwarf, pt: Zcu.PerThread, nav_index: InternPoo
                             else if (has_runtime_bits)
                                 try wip_nav.blockValue(nav_src_loc, .fromInterned(field_init));
                         }
-                        try uleb128(diw, @intFromEnum(AbbrevCode.null));
+                        try dibw.writeLeb128(@intFromEnum(AbbrevCode.null));
                     }
                 },
                 .@"packed" => {
 @@ -2924,10 +2984,10 @@ fn updateComptimeNavInner(dwarf: *Dwarf, pt: Zcu.PerThread, nav_index: InternPoo
                         try wip_nav.strp(loaded_struct.fieldName(ip, field_index).unwrap().?.toSlice(ip));
                         const field_type: Type = .fromInterned(loaded_struct.field_types.get(ip)[field_index]);
                         try wip_nav.refType(field_type);
-                        try uleb128(diw, field_bit_offset);
+                        try dibw.writeLeb128(field_bit_offset);
                         field_bit_offset += @intCast(field_type.bitSize(zcu));
                     }
-                    try uleb128(diw, @intFromEnum(AbbrevCode.null));
+                    try dibw.writeLeb128(@intFromEnum(AbbrevCode.null));
                 },
             }
             break :tag .done;
 @@ -2950,7 +3010,7 @@ fn updateComptimeNavInner(dwarf: *Dwarf, pt: Zcu.PerThread, nav_index: InternPoo
                 type_gop.value_ptr.* = nav_gop.value_ptr.*;
             }
             wip_nav.entry = nav_gop.value_ptr.*;
-            const diw = wip_nav.debug_info.writer(dwarf.gpa);
+            const dibw = &wip_nav.debug_info.buffered_writer;
             try wip_nav.declCommon(if (loaded_enum.names.len > 0) .{
                 .decl = .decl_enum,
                 .generic_decl = .generic_decl_const,
 @@ -2969,7 +3029,7 @@ fn updateComptimeNavInner(dwarf: *Dwarf, pt: Zcu.PerThread, nav_index: InternPoo
                 }, field_index);
                 try wip_nav.strp(loaded_enum.names.get(ip)[field_index].toSlice(ip));
             }
-            if (loaded_enum.names.len > 0) try uleb128(diw, @intFromEnum(AbbrevCode.null));
+            if (loaded_enum.names.len > 0) try dibw.writeLeb128(@intFromEnum(AbbrevCode.null));
             break :tag .done;
         },
         .union_type => tag: {
 @@ -2989,15 +3049,15 @@ fn updateComptimeNavInner(dwarf: *Dwarf, pt: Zcu.PerThread, nav_index: InternPoo
                 type_gop.value_ptr.* = nav_gop.value_ptr.*;
             }
             wip_nav.entry = nav_gop.value_ptr.*;
-            const diw = wip_nav.debug_info.writer(dwarf.gpa);
+            const dibw = &wip_nav.debug_info.buffered_writer;
             try wip_nav.declCommon(.{
                 .decl = .decl_union,
                 .generic_decl = .generic_decl_const,
                 .decl_instance = .decl_instance_union,
             }, &nav, inst_info.file, &decl);
             const union_layout = Type.getUnionLayout(loaded_union, zcu);
-            try uleb128(diw, union_layout.abi_size);
+            try dibw.writeLeb128(union_layout.abi_size);
-            try uleb128(diw, union_layout.abi_align.toByteUnits().?);
+            try dibw.writeLeb128(union_layout.abi_align.toByteUnits().?);
             const loaded_tag = loaded_union.loadTagType(ip);
             if (loaded_union.hasTag(ip)) {
                 try wip_nav.abbrevCode(.tagged_union);
 @@ -3005,13 +3065,13 @@ fn updateComptimeNavInner(dwarf: *Dwarf, pt: Zcu.PerThread, nav_index: InternPoo
                     .debug_info,
                     wip_nav.unit,
                     wip_nav.entry,
-                    @intCast(wip_nav.debug_info.items.len + dwarf.sectionOffsetBytes()),
+                    @intCast(dibw.count + dwarf.sectionOffsetBytes()),
                 );
                 {
                     try wip_nav.abbrevCode(.generated_field);
                     try wip_nav.strp("tag");
                     try wip_nav.refType(.fromInterned(loaded_union.enum_tag_ty));
-                    try uleb128(diw, union_layout.tagOffset());
+                    try dibw.writeLeb128(union_layout.tagOffset());
                     for (0..loaded_union.field_types.len) |field_index| {
                         try wip_nav.enumConstValue(loaded_tag, .{
 @@ -3024,23 +3084,23 @@ fn updateComptimeNavInner(dwarf: *Dwarf, pt: Zcu.PerThread, nav_index: InternPoo
                             try wip_nav.strp(loaded_tag.names.get(ip)[field_index].toSlice(ip));
                             const field_type: Type = .fromInterned(loaded_union.field_types.get(ip)[field_index]);
                             try wip_nav.refType(field_type);
-                            try uleb128(diw, union_layout.payloadOffset());
+                            try dibw.writeLeb128(union_layout.payloadOffset());
-                            try uleb128(diw, loaded_union.fieldAlign(ip, field_index).toByteUnits() orelse
+                            try dibw.writeLeb128(loaded_union.fieldAlign(ip, field_index).toByteUnits() orelse
                                 if (field_type.isNoReturn(zcu)) 1 else field_type.abiAlignment(zcu).toByteUnits().?);
                         }
-                        try uleb128(diw, @intFromEnum(AbbrevCode.null));
+                        try dibw.writeLeb128(@intFromEnum(AbbrevCode.null));
                     }
                 }
-                try uleb128(diw, @intFromEnum(AbbrevCode.null));
+                try dibw.writeLeb128(@intFromEnum(AbbrevCode.null));
             } else for (0..loaded_union.field_types.len) |field_index| {
                 try wip_nav.abbrevCode(.untagged_union_field);
                 try wip_nav.strp(loaded_tag.names.get(ip)[field_index].toSlice(ip));
                 const field_type: Type = .fromInterned(loaded_union.field_types.get(ip)[field_index]);
                 try wip_nav.refType(field_type);
-                try uleb128(diw, loaded_union.fieldAlign(ip, field_index).toByteUnits() orelse
+                try dibw.writeLeb128(loaded_union.fieldAlign(ip, field_index).toByteUnits() orelse
                     field_type.abiAlignment(zcu).toByteUnits().?);
             }
-            try uleb128(diw, @intFromEnum(AbbrevCode.null));
+            try dibw.writeLeb128(@intFromEnum(AbbrevCode.null));
             break :tag .done;
         },
         .opaque_type => tag: {
 @@ -3060,13 +3120,13 @@ fn updateComptimeNavInner(dwarf: *Dwarf, pt: Zcu.PerThread, nav_index: InternPoo
                 type_gop.value_ptr.* = nav_gop.value_ptr.*;
             }
             wip_nav.entry = nav_gop.value_ptr.*;
-            const diw = wip_nav.debug_info.writer(dwarf.gpa);
+            const dibw = &wip_nav.debug_info.buffered_writer;
             try wip_nav.declCommon(.{
                 .decl = .decl_namespace_struct,
                 .generic_decl = .generic_decl_const,
                 .decl_instance = .decl_instance_namespace_struct,
             }, &nav, inst_info.file, &decl);
-            try diw.writeByte(@intFromBool(true));
+            try dibw.writeByte(@intFromBool(true));
             break :tag .done;
         },
         .undef,
 @@ -3104,7 +3164,7 @@ fn updateComptimeNavInner(dwarf: *Dwarf, pt: Zcu.PerThread, nav_index: InternPoo
             const is_nullary = !func_type.is_var_args and for (0..func_type.param_types.len) |param_index| {
                 if (!func_type.paramIsComptime(std.math.cast(u5, param_index) orelse break false)) break false;
             } else true;
-            const diw = wip_nav.debug_info.writer(dwarf.gpa);
+            const dibw = &wip_nav.debug_info.buffered_writer;
             try wip_nav.declCommon(if (is_nullary) .{
                 .decl = .decl_nullary_func_generic,
                 .generic_decl = .generic_decl_func,
 @@ -3123,7 +3183,7 @@ fn updateComptimeNavInner(dwarf: *Dwarf, pt: Zcu.PerThread, nav_index: InternPoo
                     try wip_nav.refType(.fromInterned(func_type.param_types.get(ip)[param_index]));
                 }
                 if (func_type.is_var_args) try wip_nav.abbrevCode(.is_var_args);
-                try uleb128(diw, @intFromEnum(AbbrevCode.null));
+                try dibw.writeLeb128(@intFromEnum(AbbrevCode.null));
             }
             break :tag .done;
         },
 @@ -3148,7 +3208,7 @@ fn updateComptimeNavInner(dwarf: *Dwarf, pt: Zcu.PerThread, nav_index: InternPoo
             try wip_nav.refType(nav_val.toType());
         },
         .decl_var => {
-            const diw = wip_nav.debug_info.writer(dwarf.gpa);
+            const dibw = &wip_nav.debug_info.buffered_writer;
             try wip_nav.declCommon(.{
                 .decl = .decl_var,
                 .generic_decl = .generic_decl_var,
 @@ -3158,12 +3218,12 @@ fn updateComptimeNavInner(dwarf: *Dwarf, pt: Zcu.PerThread, nav_index: InternPoo
             const nav_ty = nav_val.typeOf(zcu);
             try wip_nav.refType(nav_ty);
             try wip_nav.blockValue(nav_src_loc, nav_val);
-            try uleb128(diw, nav.status.fully_resolved.alignment.toByteUnits() orelse
+            try dibw.writeLeb128(nav.status.fully_resolved.alignment.toByteUnits() orelse
                 nav_ty.abiAlignment(zcu).toByteUnits().?);
-            try diw.writeByte(@intFromBool(decl.linkage != .normal));
+            try dibw.writeByte(@intFromBool(decl.linkage != .normal));
         },
         .decl_const => {
-            const diw = wip_nav.debug_info.writer(dwarf.gpa);
+            const dibw = &wip_nav.debug_info.buffered_writer;
             const nav_ty = nav_val.typeOf(zcu);
             const has_runtime_bits = nav_ty.hasRuntimeBits(zcu);
             const has_comptime_state = nav_ty.comptimeOnly(zcu) and try nav_ty.onePossibleValue(pt) == null;
 @@ -3186,9 +3246,9 @@ fn updateComptimeNavInner(dwarf: *Dwarf, pt: Zcu.PerThread, nav_index: InternPoo
             }, &nav, inst_info.file, &decl);
             try wip_nav.strp(nav.fqn.toSlice(ip));
             const nav_ty_reloc_index = try wip_nav.refForward();
-            try uleb128(diw, nav.status.fully_resolved.alignment.toByteUnits() orelse
+            try dibw.writeLeb128(nav.status.fully_resolved.alignment.toByteUnits() orelse
                 nav_ty.abiAlignment(zcu).toByteUnits().?);
-            try diw.writeByte(@intFromBool(decl.linkage != .normal));
+            try dibw.writeByte(@intFromBool(decl.linkage != .normal));
             if (has_runtime_bits) try wip_nav.blockValue(nav_src_loc, nav_val);
             if (has_comptime_state) try wip_nav.refValue(nav_val);
             wip_nav.finishForward(nav_ty_reloc_index);
 @@ -3204,7 +3264,7 @@ fn updateComptimeNavInner(dwarf: *Dwarf, pt: Zcu.PerThread, nav_index: InternPoo
             try wip_nav.refNav(owner_nav);
         },
     }
-    try dwarf.debug_info.section.replaceEntry(wip_nav.unit, wip_nav.entry, dwarf, wip_nav.debug_info.items);
+    try dwarf.debug_info.section.replaceEntry(wip_nav.unit, wip_nav.entry, dwarf, wip_nav.debug_info.getWritten());
     try wip_nav.updateLazy(nav_src_loc);
 }
 @@ -3235,18 +3295,19 @@ fn updateLazyType(
         .func_high_pc = undefined,
         .blocks = undefined,
         .cfi = undefined,
-        .debug_frame = .empty,
+        .debug_frame = undefined,
-        .debug_info = .empty,
+        .debug_info = undefined,
-        .debug_line = .empty,
+        .debug_line = undefined,
-        .debug_loclists = .empty,
+        .debug_loclists = undefined,
         .pending_lazy = pending_lazy.*,
     };
+    wip_nav.init();
     defer {
         pending_lazy.* = wip_nav.pending_lazy;
         wip_nav.pending_lazy = .empty;
         wip_nav.deinit();
     }
-    const diw = wip_nav.debug_info.writer(dwarf.gpa);
+    const dibw = &wip_nav.debug_info.buffered_writer;
     const name = switch (type_index) {
         .generic_poison_type => "",
         else => try std.fmt.allocPrint(dwarf.gpa, "{f}", .{ty.fmt(pt)}),
 @@ -3261,12 +3322,12 @@ fn updateLazyType(
         .int_type => |int_type| {
             try wip_nav.abbrevCode(.numeric_type);
             try wip_nav.strp(name);
-            try diw.writeByte(switch (int_type.signedness) {
+            try dibw.writeByte(switch (int_type.signedness) {
                 inline .signed, .unsigned => |signedness| @field(DW.ATE, @tagName(signedness)),
             });
-            try uleb128(diw, int_type.bits);
+            try dibw.writeLeb128(int_type.bits);
-            try uleb128(diw, ty.abiSize(zcu));
+            try dibw.writeLeb128(ty.abiSize(zcu));
-            try uleb128(diw, ty.abiAlignment(zcu).toByteUnits().?);
+            try dibw.writeLeb128(ty.abiAlignment(zcu).toByteUnits().?);
         },
         .ptr_type => |ptr_type| switch (ptr_type.flags.size) {
             .one, .many, .c => {
 @@ -3274,14 +3335,14 @@ fn updateLazyType(
                 try wip_nav.abbrevCode(if (ptr_type.sentinel == .none) .ptr_type else .ptr_sentinel_type);
                 try wip_nav.strp(name);
                 if (ptr_type.sentinel != .none) try wip_nav.blockValue(src_loc, .fromInterned(ptr_type.sentinel));
-                try uleb128(diw, ptr_type.flags.alignment.toByteUnits() orelse
+                try dibw.writeLeb128(ptr_type.flags.alignment.toByteUnits() orelse
                     ptr_child_type.abiAlignment(zcu).toByteUnits().?);
-                try diw.writeByte(@intFromEnum(ptr_type.flags.address_space));
+                try dibw.writeByte(@intFromEnum(ptr_type.flags.address_space));
                 if (ptr_type.flags.is_const or ptr_type.flags.is_volatile) try wip_nav.infoSectionOffset(
                     .debug_info,
                     wip_nav.unit,
                     wip_nav.entry,
-                    @intCast(wip_nav.debug_info.items.len + dwarf.sectionOffsetBytes()),
+                    @intCast(dibw.count + dwarf.sectionOffsetBytes()),
                 ) else try wip_nav.refType(ptr_child_type);
                 if (ptr_type.flags.is_const) {
                     try wip_nav.abbrevCode(.is_const);
 @@ -3289,7 +3350,7 @@ fn updateLazyType(
                         .debug_info,
                         wip_nav.unit,
                         wip_nav.entry,
-                        @intCast(wip_nav.debug_info.items.len + dwarf.sectionOffsetBytes()),
+                        @intCast(dibw.count + dwarf.sectionOffsetBytes()),
                     ) else try wip_nav.refType(ptr_child_type);
                 }
                 if (ptr_type.flags.is_volatile) {
 @@ -3300,19 +3361,19 @@ fn updateLazyType(
             .slice => {
                 try wip_nav.abbrevCode(.generated_struct_type);
                 try wip_nav.strp(name);
-                try uleb128(diw, ty.abiSize(zcu));
+                try dibw.writeLeb128(ty.abiSize(zcu));
-                try uleb128(diw, ty.abiAlignment(zcu).toByteUnits().?);
+                try dibw.writeLeb128(ty.abiAlignment(zcu).toByteUnits().?);
                 try wip_nav.abbrevCode(.generated_field);
                 try wip_nav.strp("ptr");
                 const ptr_field_type = ty.slicePtrFieldType(zcu);
                 try wip_nav.refType(ptr_field_type);
-                try uleb128(diw, 0);
+                try dibw.writeUleb128(0);
                 try wip_nav.abbrevCode(.generated_field);
                 try wip_nav.strp("len");
                 const len_field_type: Type = .usize;
                 try wip_nav.refType(len_field_type);
-                try uleb128(diw, len_field_type.abiAlignment(zcu).forward(ptr_field_type.abiSize(zcu)));
+                try dibw.writeLeb128(len_field_type.abiAlignment(zcu).forward(ptr_field_type.abiSize(zcu)));
-                try uleb128(diw, @intFromEnum(AbbrevCode.null));
+                try dibw.writeLeb128(@intFromEnum(AbbrevCode.null));
             },
         },
         .array_type => |array_type| {
 @@ -3323,8 +3384,8 @@ fn updateLazyType(
             try wip_nav.refType(array_child_type);
             try wip_nav.abbrevCode(.array_index);
             try wip_nav.refType(.usize);
-            try uleb128(diw, array_type.len);
+            try dibw.writeLeb128(array_type.len);
-            try uleb128(diw, @intFromEnum(AbbrevCode.null));
+            try dibw.writeLeb128(@intFromEnum(AbbrevCode.null));
         },
         .vector_type => |vector_type| {
             try wip_nav.abbrevCode(.vector_type);
 @@ -3332,22 +3393,22 @@ fn updateLazyType(
             try wip_nav.refType(.fromInterned(vector_type.child));
             try wip_nav.abbrevCode(.array_index);
             try wip_nav.refType(.usize);
-            try uleb128(diw, vector_type.len);
+            try dibw.writeLeb128(vector_type.len);
-            try uleb128(diw, @intFromEnum(AbbrevCode.null));
+            try dibw.writeLeb128(@intFromEnum(AbbrevCode.null));
         },
         .opt_type => |opt_child_type_index| {
             const opt_child_type: Type = .fromInterned(opt_child_type_index);
             const opt_repr = optRepr(opt_child_type, zcu);
             try wip_nav.abbrevCode(.generated_union_type);
             try wip_nav.strp(name);
-            try uleb128(diw, ty.abiSize(zcu));
+            try dibw.writeLeb128(ty.abiSize(zcu));
-            try uleb128(diw, ty.abiAlignment(zcu).toByteUnits().?);
+            try dibw.writeLeb128(ty.abiAlignment(zcu).toByteUnits().?);
             switch (opt_repr) {
                 .opv_null => {
                     try wip_nav.abbrevCode(.generated_field);
                     try wip_nav.strp("null");
                     try wip_nav.refType(.null);
-                    try uleb128(diw, 0);
+                    try dibw.writeUleb128(0);
                 },
                 .unpacked, .error_set, .pointer => {
                     try wip_nav.abbrevCode(.tagged_union);
 @@ -3355,7 +3416,7 @@ fn updateLazyType(
                         .debug_info,
                         wip_nav.unit,
                         wip_nav.entry,
-                        @intCast(wip_nav.debug_info.items.len + dwarf.sectionOffsetBytes()),
+                        @intCast(dibw.count + dwarf.sectionOffsetBytes()),
                     );
                     {
                         try wip_nav.abbrevCode(.generated_field);
 @@ -3364,7 +3425,7 @@ fn updateLazyType(
                             .opv_null => unreachable,
                             .unpacked => {
                                 try wip_nav.refType(.bool);
-                                try uleb128(diw, if (opt_child_type.hasRuntimeBits(zcu))
+                                try dibw.writeLeb128(if (opt_child_type.hasRuntimeBits(zcu))
                                     opt_child_type.abiSize(zcu)
                                 else
                                     0);
 @@ -3374,37 +3435,37 @@ fn updateLazyType(
                                     .signedness = .unsigned,
                                     .bits = zcu.errorSetBits(),
                                 } })));
-                                try uleb128(diw, 0);
+                                try dibw.writeUleb128(0);
                             },
                             .pointer => {
                                 try wip_nav.refType(.usize);
-                                try uleb128(diw, 0);
+                                try dibw.writeUleb128(0);
                             },
                         }
                         try wip_nav.abbrevCode(.unsigned_tagged_union_field);
-                        try uleb128(diw, 0);
+                        try dibw.writeUleb128(0);
                         {
                             try wip_nav.abbrevCode(.generated_field);
                             try wip_nav.strp("null");
                             try wip_nav.refType(.null);
-                            try uleb128(diw, 0);
+                            try dibw.writeUleb128(0);
                         }
-                        try uleb128(diw, @intFromEnum(AbbrevCode.null));
+                        try dibw.writeLeb128(@intFromEnum(AbbrevCode.null));
                         try wip_nav.abbrevCode(.tagged_union_default_field);
                         {
                             try wip_nav.abbrevCode(.generated_field);
                             try wip_nav.strp("?");
                             try wip_nav.refType(opt_child_type);
-                            try uleb128(diw, 0);
+                            try dibw.writeUleb128(0);
                         }
-                        try uleb128(diw, @intFromEnum(AbbrevCode.null));
+                        try dibw.writeLeb128(@intFromEnum(AbbrevCode.null));
                     }
-                    try uleb128(diw, @intFromEnum(AbbrevCode.null));
+                    try dibw.writeLeb128(@intFromEnum(AbbrevCode.null));
                 },
             }
-            try uleb128(diw, @intFromEnum(AbbrevCode.null));
+            try dibw.writeLeb128(@intFromEnum(AbbrevCode.null));
         },
         .anyframe_type => unreachable,
         .error_union_type => |error_union_type| {
 @@ -3423,11 +3484,11 @@ fn updateLazyType(
             if (error_union_type.error_set_type != .generic_poison_type and
                 error_union_type.payload_type != .generic_poison_type)
             {
-                try uleb128(diw, ty.abiSize(zcu));
+                try dibw.writeLeb128(ty.abiSize(zcu));
-                try uleb128(diw, ty.abiAlignment(zcu).toByteUnits().?);
+                try dibw.writeLeb128(ty.abiAlignment(zcu).toByteUnits().?);
             } else {
-                try uleb128(diw, 0);
+                try dibw.writeUleb128(0);
-                try uleb128(diw, 1);
+                try dibw.writeUleb128(1);
             }
             {
                 try wip_nav.abbrevCode(.tagged_union);
 @@ -3435,7 +3496,7 @@ fn updateLazyType(
                     .debug_info,
                     wip_nav.unit,
                     wip_nav.entry,
-                    @intCast(wip_nav.debug_info.items.len + dwarf.sectionOffsetBytes()),
+                    @intCast(dibw.count + dwarf.sectionOffsetBytes()),
                 );
                 {
                     try wip_nav.abbrevCode(.generated_field);
 @@ -3444,30 +3505,30 @@ fn updateLazyType(
                         .signedness = .unsigned,
                         .bits = zcu.errorSetBits(),
                     } })));
-                    try uleb128(diw, error_union_error_set_offset);
+                    try dibw.writeLeb128(error_union_error_set_offset);
                     try wip_nav.abbrevCode(.unsigned_tagged_union_field);
-                    try uleb128(diw, 0);
+                    try dibw.writeUleb128(0);
                     {
                         try wip_nav.abbrevCode(.generated_field);
                         try wip_nav.strp("value");
                         try wip_nav.refType(error_union_payload_type);
-                        try uleb128(diw, error_union_payload_offset);
+                        try dibw.writeLeb128(error_union_payload_offset);
                     }
-                    try uleb128(diw, @intFromEnum(AbbrevCode.null));
+                    try dibw.writeLeb128(@intFromEnum(AbbrevCode.null));
                     try wip_nav.abbrevCode(.tagged_union_default_field);
                     {
                         try wip_nav.abbrevCode(.generated_field);
                         try wip_nav.strp("error");
                         try wip_nav.refType(error_union_error_set_type);
-                        try uleb128(diw, error_union_error_set_offset);
+                        try dibw.writeLeb128(error_union_error_set_offset);
                     }
-                    try uleb128(diw, @intFromEnum(AbbrevCode.null));
+                    try dibw.writeLeb128(@intFromEnum(AbbrevCode.null));
                 }
-                try uleb128(diw, @intFromEnum(AbbrevCode.null));
+                try dibw.writeLeb128(@intFromEnum(AbbrevCode.null));
             }
-            try uleb128(diw, @intFromEnum(AbbrevCode.null));
+            try dibw.writeLeb128(@intFromEnum(AbbrevCode.null));
         },
         .simple_type => |simple_type| switch (simple_type) {
             .f16,
 @@ -3491,7 +3552,7 @@ fn updateLazyType(
             => {
                 try wip_nav.abbrevCode(.numeric_type);
                 try wip_nav.strp(name);
-                try diw.writeByte(if (type_index == .bool_type)
+                try dibw.writeByte(if (type_index == .bool_type)
                     DW.ATE.boolean
                 else if (ty.isRuntimeFloat())
                     DW.ATE.float
 @@ -3501,9 +3562,9 @@ fn updateLazyType(
                     DW.ATE.unsigned
                 else
                     unreachable);
-                try uleb128(diw, ty.bitSize(zcu));
+                try dibw.writeLeb128(ty.bitSize(zcu));
-                try uleb128(diw, ty.abiSize(zcu));
+                try dibw.writeLeb128(ty.abiSize(zcu));
-                try uleb128(diw, ty.abiAlignment(zcu).toByteUnits().?);
+                try dibw.writeLeb128(ty.abiAlignment(zcu).toByteUnits().?);
             },
             .anyopaque,
             .void,
 @@ -3529,12 +3590,12 @@ fn updateLazyType(
         .tuple_type => |tuple_type| if (tuple_type.types.len == 0) {
             try wip_nav.abbrevCode(.generated_empty_struct_type);
             try wip_nav.strp(name);
-            try diw.writeByte(@intFromBool(false));
+            try dibw.writeByte(@intFromBool(false));
         } else {
             try wip_nav.abbrevCode(.generated_struct_type);
             try wip_nav.strp(name);
-            try uleb128(diw, ty.abiSize(zcu));
+            try dibw.writeLeb128(ty.abiSize(zcu));
-            try uleb128(diw, ty.abiAlignment(zcu).toByteUnits().?);
+            try dibw.writeLeb128(ty.abiAlignment(zcu).toByteUnits().?);
             var field_byte_offset: u64 = 0;
             for (0..tuple_type.types.len) |field_index| {
                 const comptime_value = tuple_type.values.get(ip)[field_index];
 @@ -3563,8 +3624,8 @@ fn updateLazyType(
                 if (comptime_value == .none) {
                     const field_align = field_type.abiAlignment(zcu);
                     field_byte_offset = field_align.forward(field_byte_offset);
-                    try uleb128(diw, field_byte_offset);
+                    try dibw.writeLeb128(field_byte_offset);
-                    try uleb128(diw, field_type.abiAlignment(zcu).toByteUnits().?);
+                    try dibw.writeLeb128(field_type.abiAlignment(zcu).toByteUnits().?);
                     field_byte_offset += field_type.abiSize(zcu);
                 }
                 if (has_comptime_state)
 @@ -3572,7 +3633,7 @@ fn updateLazyType(
                 else if (has_runtime_bits)
                     try wip_nav.blockValue(src_loc, .fromInterned(comptime_value));
             }
-            try uleb128(diw, @intFromEnum(AbbrevCode.null));
+            try dibw.writeLeb128(@intFromEnum(AbbrevCode.null));
         },
         .enum_type => {
             const loaded_enum = ip.loadEnumType(type_index);
 @@ -3587,7 +3648,7 @@ fn updateLazyType(
                 }, field_index);
                 try wip_nav.strp(loaded_enum.names.get(ip)[field_index].toSlice(ip));
             }
-            if (loaded_enum.names.len > 0) try uleb128(diw, @intFromEnum(AbbrevCode.null));
+            if (loaded_enum.names.len > 0) try dibw.writeLeb128(@intFromEnum(AbbrevCode.null));
         },
         .func_type => |func_type| {
             const is_nullary = func_type.param_types.len == 0 and !func_type.is_var_args;
 @@ -3655,7 +3716,7 @@ fn updateLazyType(
                     else => .nocall,
                 };
             };
-            try diw.writeByte(@intFromEnum(cc));
+            try dibw.writeByte(@intFromEnum(cc));
             try wip_nav.refType(.fromInterned(func_type.return_type));
             if (!is_nullary) {
                 for (0..func_type.param_types.len) |param_index| {
 @@ -3663,7 +3724,7 @@ fn updateLazyType(
                     try wip_nav.refType(.fromInterned(func_type.param_types.get(ip)[param_index]));
                 }
                 if (func_type.is_var_args) try wip_nav.abbrevCode(.is_var_args);
-                try uleb128(diw, @intFromEnum(AbbrevCode.null));
+                try dibw.writeLeb128(@intFromEnum(AbbrevCode.null));
             }
         },
         .error_set_type => |error_set_type| {
 @@ -3676,10 +3737,10 @@ fn updateLazyType(
             for (0..error_set_type.names.len) |field_index| {
                 const field_name = error_set_type.names.get(ip)[field_index];
                 try wip_nav.abbrevCode(.unsigned_enum_field);
-                try uleb128(diw, ip.getErrorValueIfExists(field_name).?);
+                try dibw.writeLeb128(ip.getErrorValueIfExists(field_name).?);
                 try wip_nav.strp(field_name.toSlice(ip));
             }
-            if (error_set_type.names.len > 0) try uleb128(diw, @intFromEnum(AbbrevCode.null));
+            if (error_set_type.names.len > 0) try dibw.writeLeb128(@intFromEnum(AbbrevCode.null));
         },
         .inferred_error_set_type => |func| {
             try wip_nav.abbrevCode(.inferred_error_set_type);
 @@ -3711,7 +3772,7 @@ fn updateLazyType(
         .memoized_call,
         => unreachable,
     }
-    try dwarf.debug_info.section.replaceEntry(wip_nav.unit, wip_nav.entry, dwarf, wip_nav.debug_info.items);
+    try dwarf.debug_info.section.replaceEntry(wip_nav.unit, wip_nav.entry, dwarf, wip_nav.debug_info.getWritten());
 }
 fn updateLazyValue(
 @@ -3739,18 +3800,19 @@ fn updateLazyValue(
         .func_high_pc = undefined,
         .blocks = undefined,
         .cfi = undefined,
-        .debug_frame = .empty,
+        .debug_frame = undefined,
-        .debug_info = .empty,
+        .debug_info = undefined,
-        .debug_line = .empty,
+        .debug_line = undefined,
-        .debug_loclists = .empty,
+        .debug_loclists = undefined,
         .pending_lazy = pending_lazy.*,
     };
+    wip_nav.init();
     defer {
         pending_lazy.* = wip_nav.pending_lazy;
         wip_nav.pending_lazy = .empty;
         wip_nav.deinit();
     }
-    const diw = wip_nav.debug_info.writer(dwarf.gpa);
+    const dibw = &wip_nav.debug_info.buffered_writer;
     var big_int_space: Value.BigIntSpace = undefined;
     switch (ip.indexToKey(value_index)) {
         .int_type,
 @@ -3788,7 +3850,7 @@ fn updateLazyValue(
         .err => |err| {
             try wip_nav.abbrevCode(.udata_comptime_value);
             try wip_nav.refType(.fromInterned(err.ty));
-            try uleb128(diw, try pt.getErrorValue(err.name));
+            try dibw.writeLeb128(try pt.getErrorValue(err.name));
         },
         .error_union => |error_union| {
             try wip_nav.abbrevCode(.aggregate_comptime_value);
 @@ -3800,8 +3862,8 @@ fn updateLazyValue(
             {
                 try wip_nav.abbrevCode(.comptime_value_field_runtime_bits);
                 try wip_nav.strp("is_error");
-                try uleb128(diw, err_abi_size);
+                try dibw.writeLeb128(err_abi_size);
-                dwarf.writeInt(try wip_nav.debug_info.addManyAsSlice(dwarf.gpa, err_abi_size), err_value);
+                try dwarf.writeIntTo(dibw, err_abi_size, err_value);
             }
             payload_field: switch (error_union.val) {
                 .err_name => {},
 @@ -3825,8 +3887,8 @@ fn updateLazyValue(
             {
                 try wip_nav.abbrevCode(.comptime_value_field_runtime_bits);
                 try wip_nav.strp("error");
-                try uleb128(diw, err_abi_size);
+                try dibw.writeLeb128(err_abi_size);
-                dwarf.writeInt(try wip_nav.debug_info.addManyAsSlice(dwarf.gpa, err_abi_size), err_value);
+                try dwarf.writeIntTo(dibw, err_abi_size, err_value);
             }
             switch (error_union.val) {
                 .err_name => {},
 @@ -3836,7 +3898,7 @@ fn updateLazyValue(
                 },
             }
             try wip_nav.refType(.fromInterned(error_union.ty));
-            try uleb128(diw, @intFromEnum(AbbrevCode.null));
+            try dibw.writeLeb128(@intFromEnum(AbbrevCode.null));
         },
         .enum_literal => |enum_literal| {
             try wip_nav.abbrevCode(.string_comptime_value);
 @@ -3857,24 +3919,24 @@ fn updateLazyValue(
             switch (float.storage) {
                 .f16 => |f16_val| {
                     try wip_nav.abbrevCode(.data2_comptime_value);
-                    try diw.writeInt(u16, @bitCast(f16_val), dwarf.endian);
+                    try dibw.writeInt(u16, @bitCast(f16_val), dwarf.endian);
                 },
                 .f32 => |f32_val| {
                     try wip_nav.abbrevCode(.data4_comptime_value);
-                    try diw.writeInt(u32, @bitCast(f32_val), dwarf.endian);
+                    try dibw.writeInt(u32, @bitCast(f32_val), dwarf.endian);
                 },
                 .f64 => |f64_val| {
                     try wip_nav.abbrevCode(.data8_comptime_value);
-                    try diw.writeInt(u64, @bitCast(f64_val), dwarf.endian);
+                    try dibw.writeInt(u64, @bitCast(f64_val), dwarf.endian);
                 },
                 .f80 => |f80_val| {
                     try wip_nav.abbrevCode(.block_comptime_value);
-                    try uleb128(diw, @divExact(80, 8));
+                    try dibw.writeUleb128(@divExact(80, 8));
-                    try diw.writeInt(u80, @bitCast(f80_val), dwarf.endian);
+                    try dibw.writeInt(u80, @bitCast(f80_val), dwarf.endian);
                 },
                 .f128 => |f128_val| {
                     try wip_nav.abbrevCode(.data16_comptime_value);
-                    try diw.writeInt(u128, @bitCast(f128_val), dwarf.endian);
+                    try dibw.writeInt(u128, @bitCast(f128_val), dwarf.endian);
                 },
             }
             try wip_nav.refType(.fromInterned(float.ty));
 @@ -3891,14 +3953,14 @@ fn updateLazyValue(
                             const uav_ty: Type = .fromInterned(ip.typeOf(uav.val));
                             if (try uav_ty.onePossibleValue(pt)) |_| {
                                 try wip_nav.abbrevCode(.udata_comptime_value);
-                                try uleb128(diw, ip.indexToKey(uav.orig_ty).ptr_type.flags.alignment.toByteUnits() orelse
+                                try dibw.writeLeb128(ip.indexToKey(uav.orig_ty).ptr_type.flags.alignment.toByteUnits() orelse
                                     uav_ty.abiAlignment(zcu).toByteUnits().?);
                                 break :location;
                             } else break try wip_nav.getValueEntry(.fromInterned(uav.val));
                         },
                         .int => {
                             try wip_nav.abbrevCode(.udata_comptime_value);
-                            try uleb128(diw, byte_offset);
+                            try dibw.writeLeb128(byte_offset);
                             break :location;
                         },
                         .eu_payload => |eu_ptr| {
 @@ -3937,7 +3999,7 @@ fn updateLazyValue(
                 try wip_nav.strp("len");
                 try wip_nav.blockValue(src_loc, .fromInterned(slice.len));
             }
-            try uleb128(diw, @intFromEnum(AbbrevCode.null));
+            try dibw.writeLeb128(@intFromEnum(AbbrevCode.null));
         },
         .opt => |opt| {
             const opt_child_type: Type = .fromInterned(ip.indexToKey(opt.ty).opt_type);
 @@ -3947,7 +4009,7 @@ fn updateLazyValue(
                 try wip_nav.abbrevCode(.comptime_value_field_runtime_bits);
                 try wip_nav.strp("has_value");
                 switch (optRepr(opt_child_type, zcu)) {
-                    .opv_null => try uleb128(diw, 0),
+                    .opv_null => try dibw.writeUleb128(0),
                     .unpacked => try wip_nav.blockValue(src_loc, .makeBool(opt.val != .none)),
                     .error_set => try wip_nav.blockValue(src_loc, .fromInterned(value_index)),
                     .pointer => if (opt_child_type.comptimeOnly(zcu)) {
 @@ -3957,8 +4019,8 @@ fn updateLazyValue(
                             .none => 0,
                             else => opt_child_type.ptrAlignment(zcu).toByteUnits().?,
                         });
-                        try uleb128(diw, bytes.len);
+                        try dibw.writeLeb128(bytes.len);
-                        try diw.writeAll(bytes);
+                        try dibw.writeAll(bytes);
                     } else try wip_nav.blockValue(src_loc, .fromInterned(value_index)),
                 }
             }
 @@ -3977,7 +4039,7 @@ fn updateLazyValue(
                 else
                     try wip_nav.blockValue(src_loc, .fromInterned(opt.val));
             }
-            try uleb128(diw, @intFromEnum(AbbrevCode.null));
+            try dibw.writeLeb128(@intFromEnum(AbbrevCode.null));
         },
         .aggregate => |aggregate| {
             try wip_nav.abbrevCode(.aggregate_comptime_value);
 @@ -4062,7 +4124,7 @@ fn updateLazyValue(
                 },
                 else => unreachable,
             }
-            try uleb128(diw, @intFromEnum(AbbrevCode.null));
+            try dibw.writeLeb128(@intFromEnum(AbbrevCode.null));
         },
         .un => |un| {
             try wip_nav.abbrevCode(.aggregate_comptime_value);
 @@ -4087,11 +4149,11 @@ fn updateLazyValue(
                 else
                     try wip_nav.blockValue(src_loc, .fromInterned(un.val));
             }
-            try uleb128(diw, @intFromEnum(AbbrevCode.null));
+            try dibw.writeLeb128(@intFromEnum(AbbrevCode.null));
         },
         .memoized_call => unreachable, // not a value
     }
-    try dwarf.debug_info.section.replaceEntry(wip_nav.unit, wip_nav.entry, dwarf, wip_nav.debug_info.items);
+    try dwarf.debug_info.section.replaceEntry(wip_nav.unit, wip_nav.entry, dwarf, wip_nav.debug_info.getWritten());
 }
 fn optRepr(opt_child_type: Type, zcu: *const Zcu) enum {
 @@ -4111,7 +4173,7 @@ fn optRepr(opt_child_type: Type, zcu: *const Zcu) enum {
     };
 }
-pub fn updateContainerType(dwarf: *Dwarf, pt: Zcu.PerThread, type_index: InternPool.Index) UpdateError!void {
+fn updateContainerTypeInner(dwarf: *Dwarf, pt: Zcu.PerThread, type_index: InternPool.Index) UpdateError!void {
     const zcu = pt.zcu;
     const ip = &zcu.intern_pool;
     const ty: Type = .fromInterned(type_index);
 @@ -4438,25 +4500,26 @@ fn refAbbrevCode(dwarf: *Dwarf, abbrev_code: AbbrevCode) UpdateError!@typeInfo(A
     assert(abbrev_code != .null);
     const entry: Entry.Index = @enumFromInt(@intFromEnum(abbrev_code));
     if (dwarf.debug_abbrev.section.getUnit(DebugAbbrev.unit).getEntry(entry).len > 0) return @intFromEnum(abbrev_code);
-    var debug_abbrev: std.ArrayList(u8) = .init(dwarf.gpa);
+    var daaw: std.io.Writer.Allocating = .init(dwarf.gpa);
-    defer debug_abbrev.deinit();
+    defer daaw.deinit();
-    const daw = debug_abbrev.writer();
+    const dabw = &daaw.interface;
     const abbrev = AbbrevCode.abbrevs.get(abbrev_code);
-    try uleb128(daw, @intFromEnum(abbrev_code));
+    try dabw.writeLeb128(@intFromEnum(abbrev_code));
-    try uleb128(daw, @intFromEnum(abbrev.tag));
+    try dabw.writeLeb128(@intFromEnum(abbrev.tag));
-    try daw.writeByte(if (abbrev.children) DW.CHILDREN.yes else DW.CHILDREN.no);
+    try dabw.writeByte(if (abbrev.children) DW.CHILDREN.yes else DW.CHILDREN.no);
-    for (abbrev.attrs) |*attr| inline for (attr) |info| try uleb128(daw, @intFromEnum(info));
+    for (abbrev.attrs) |*attr| inline for (attr) |info| try dabw.writeLeb128(@intFromEnum(info));
-    for (0..2) |_| try uleb128(daw, 0);
+    for (0..2) |_| try dabw.writeUleb128(0);
-    try dwarf.debug_abbrev.section.replaceEntry(DebugAbbrev.unit, entry, dwarf, debug_abbrev.items);
+    try dwarf.debug_abbrev.section.replaceEntry(DebugAbbrev.unit, entry, dwarf, daaw.getWritten());
     return @intFromEnum(abbrev_code);
 }
 pub fn flush(dwarf: *Dwarf, pt: Zcu.PerThread) FlushError!void {
+    const gpa = dwarf.gpa;
     const zcu = pt.zcu;
     const ip = &zcu.intern_pool;
     {
-        const type_gop = try dwarf.types.getOrPut(dwarf.gpa, .anyerror_type);
+        const type_gop = try dwarf.types.getOrPut(gpa, .anyerror_type);
         if (!type_gop.found_existing) type_gop.value_ptr.* = try dwarf.addCommonEntry(.main);
         var wip_nav: WipNav = .{
             .dwarf = dwarf,
 @@ -4469,14 +4532,15 @@ pub fn flush(dwarf: *Dwarf, pt: Zcu.PerThread) FlushError!void {
             .func_high_pc = undefined,
             .blocks = undefined,
             .cfi = undefined,
-            .debug_frame = .empty,
+            .debug_frame = undefined,
-            .debug_info = .empty,
+            .debug_info = undefined,
-            .debug_line = .empty,
+            .debug_line = undefined,
-            .debug_loclists = .empty,
+            .debug_loclists = undefined,
             .pending_lazy = .empty,
         };
+        wip_nav.init();
         defer wip_nav.deinit();
-        const diw = wip_nav.debug_info.writer(dwarf.gpa);
+        const dibw = &wip_nav.debug_info.buffered_writer;
         const global_error_set_names = ip.global_error_set.getNamesFromMainThread();
         try wip_nav.abbrevCode(if (global_error_set_names.len == 0) .generated_empty_enum_type else .generated_enum_type);
         try wip_nav.strp("anyerror");
 @@ -4486,50 +4550,52 @@ pub fn flush(dwarf: *Dwarf, pt: Zcu.PerThread) FlushError!void {
         } })));
         for (global_error_set_names, 1..) |name, value| {
             try wip_nav.abbrevCode(.unsigned_enum_field);
-            try uleb128(diw, value);
+            try dibw.writeLeb128(value);
             try wip_nav.strp(name.toSlice(ip));
         }
-        if (global_error_set_names.len > 0) try uleb128(diw, @intFromEnum(AbbrevCode.null));
+        if (global_error_set_names.len > 0) try dibw.writeLeb128(@intFromEnum(AbbrevCode.null));
-        try dwarf.debug_info.section.replaceEntry(wip_nav.unit, wip_nav.entry, dwarf, wip_nav.debug_info.items);
+        try dwarf.debug_info.section.replaceEntry(wip_nav.unit, wip_nav.entry, dwarf, dibw.getWritten());
         try wip_nav.updateLazy(.unneeded);
     }
     for (dwarf.mods.keys(), dwarf.mods.values()) |mod, *mod_info| {
-        const root_dir_path = try mod.root.toAbsolute(zcu.comp.dirs, dwarf.gpa);
+        const root_dir_path = try mod.root.toAbsolute(zcu.comp.dirs, gpa);
-        defer dwarf.gpa.free(root_dir_path);
+        defer gpa.free(root_dir_path);
         mod_info.root_dir_path = try dwarf.debug_line_str.addString(dwarf, root_dir_path);
     }
-    var header: std.ArrayList(u8) = .init(dwarf.gpa);
+    var header: std.ArrayListUnmanaged(u8) = .empty;
-    defer header.deinit();
+    defer header.deinit(gpa);
+    var header_bw: Writer = undefined;
     if (dwarf.debug_aranges.section.dirty) {
         for (dwarf.debug_aranges.section.units.items, 0..) |*unit_ptr, unit_index| {
             const unit: Unit.Index = @enumFromInt(unit_index);
             unit_ptr.clear();
-            try unit_ptr.cross_section_relocs.ensureTotalCapacity(dwarf.gpa, 1);
+            try unit_ptr.cross_section_relocs.ensureTotalCapacity(gpa, 1);
-            header.clearRetainingCapacity();
+            try header.resize(gpa, unit_ptr.header_len);
-            try header.ensureTotalCapacity(unit_ptr.header_len);
+            header_bw = .fixed(header.items);
             const unit_len = (if (unit_ptr.next.unwrap()) |next_unit|
                 dwarf.debug_aranges.section.getUnit(next_unit).off
             else
                 dwarf.debug_aranges.section.len) - unit_ptr.off - dwarf.unitLengthBytes();
             switch (dwarf.format) {
-                .@"32" => std.mem.writeInt(u32, header.addManyAsArrayAssumeCapacity(4), @intCast(unit_len), dwarf.endian),
+                .@"32" => header_bw.writeInt(u32, @intCast(unit_len), dwarf.endian) catch unreachable,
                 .@"64" => {
-                    std.mem.writeInt(u32, header.addManyAsArrayAssumeCapacity(4), std.math.maxInt(u32), dwarf.endian);
+                    header_bw.writeInt(u32, std.math.maxInt(u32), dwarf.endian) catch unreachable;
-                    std.mem.writeInt(u64, header.addManyAsArrayAssumeCapacity(8), unit_len, dwarf.endian);
+                    header_bw.writeInt(u64, unit_len, dwarf.endian) catch unreachable;
                 },
             }
-            std.mem.writeInt(u16, header.addManyAsArrayAssumeCapacity(2), 2, dwarf.endian);
+            header_bw.writeInt(u16, 2, dwarf.endian) catch unreachable;
             unit_ptr.cross_section_relocs.appendAssumeCapacity(.{
-                .source_off = @intCast(header.items.len),
+                .source_off = @intCast(header_bw.end),
                 .target_sec = .debug_info,
                 .target_unit = unit,
             });
-            header.appendNTimesAssumeCapacity(0, dwarf.sectionOffsetBytes());
+            header_bw.splatByteAll(0, dwarf.sectionOffsetBytes()) catch unreachable;
-            header.appendSliceAssumeCapacity(&.{ @intFromEnum(dwarf.address_size), 0 });
+            header_bw.writeAll(&.{ @intFromEnum(dwarf.address_size), 0 }) catch unreachable;
-            header.appendNTimesAssumeCapacity(0, unit_ptr.header_len - header.items.len);
+            header_bw.splatByteAll(0, unit_ptr.header_len - header_bw.end) catch unreachable;
-            try unit_ptr.replaceHeader(&dwarf.debug_aranges.section, dwarf, header.items);
+            assert(header_bw.end == header_bw.buffer.len);
+            try unit_ptr.replaceHeader(&dwarf.debug_aranges.section, dwarf, header_bw.buffer);
             try unit_ptr.writeTrailer(&dwarf.debug_aranges.section, dwarf);
         }
         dwarf.debug_aranges.section.dirty = false;
 @@ -4544,31 +4610,33 @@ pub fn flush(dwarf: *Dwarf, pt: Zcu.PerThread) FlushError!void {
                     dev.check(.x86_64_backend);
                     const Register = @import("../arch/x86_64/bits.zig").Register;
                     for (dwarf.debug_frame.section.units.items) |*unit| {
-                        header.clearRetainingCapacity();
+                        try header.resize(gpa, unit.header_len);
-                        try header.ensureTotalCapacity(unit.header_len);
+                        header_bw = .fixed(header.items);
                         const unit_len = unit.header_len - dwarf.unitLengthBytes();
                         switch (dwarf.format) {
-                            .@"32" => std.mem.writeInt(u32, header.addManyAsArrayAssumeCapacity(4), @intCast(unit_len), dwarf.endian),
+                            .@"32" => header_bw.writeInt(u32, @intCast(unit_len), dwarf.endian) catch unreachable,
                             .@"64" => {
-                                std.mem.writeInt(u32, header.addManyAsArrayAssumeCapacity(4), std.math.maxInt(u32), dwarf.endian);
+                                header_bw.writeInt(u32, std.math.maxInt(u32), dwarf.endian) catch unreachable;
-                                std.mem.writeInt(u64, header.addManyAsArrayAssumeCapacity(8), unit_len, dwarf.endian);
+                                header_bw.writeInt(u64, unit_len, dwarf.endian) catch unreachable;
                             },
                         }
-                        header.appendNTimesAssumeCapacity(0, 4);
+                        header_bw.splatByteAll(0, 4) catch unreachable;
-                        header.appendAssumeCapacity(1);
+                        header_bw.writeByte(1) catch unreachable;
-                        header.appendSliceAssumeCapacity("zR\x00");
+                        header_bw.writeAll("zR\x00") catch unreachable;
-                        uleb128(header.fixedWriter(), dwarf.debug_frame.header.code_alignment_factor) catch unreachable;
+                        header_bw.writeLeb128(dwarf.debug_frame.header.code_alignment_factor) catch unreachable;
-                        sleb128(header.fixedWriter(), dwarf.debug_frame.header.data_alignment_factor) catch unreachable;
+                        header_bw.writeLeb128(dwarf.debug_frame.header.data_alignment_factor) catch unreachable;
-                        uleb128(header.fixedWriter(), dwarf.debug_frame.header.return_address_register) catch unreachable;
+                        header_bw.writeLeb128(dwarf.debug_frame.header.return_address_register) catch unreachable;
-                        uleb128(header.fixedWriter(), 1) catch unreachable;
+                        header_bw.writeUleb128(1) catch unreachable;
-                        header.appendAssumeCapacity(DW.EH.PE.pcrel | DW.EH.PE.sdata4);
+                        header_bw.writeByte(DW.EH.PE.pcrel | DW.EH.PE.sdata4) catch unreachable;
-                        header.appendAssumeCapacity(DW.CFA.def_cfa_sf);
+                        header_bw.writeByte(DW.CFA.def_cfa_sf) catch unreachable;
-                        uleb128(header.fixedWriter(), Register.rsp.dwarfNum()) catch unreachable;
+                        header_bw.writeUleb128(1) catch unreachable;
-                        sleb128(header.fixedWriter(), -1) catch unreachable;
+                        header_bw.writeLeb128(Register.rsp.dwarfNum()) catch unreachable;
-                        header.appendAssumeCapacity(@as(u8, DW.CFA.offset) + Register.rip.dwarfNum());
+                        header_bw.writeSleb128(-1) catch unreachable;
-                        uleb128(header.fixedWriter(), 1) catch unreachable;
+                        header_bw.writeByte(@as(u8, DW.CFA.offset) + Register.rip.dwarfNum()) catch unreachable;
-                        header.appendNTimesAssumeCapacity(DW.CFA.nop, unit.header_len - header.items.len);
+                        header_bw.writeUleb128(1) catch unreachable;
-                        try unit.replaceHeader(&dwarf.debug_frame.section, dwarf, header.items);
+                        header_bw.splatByteAll(DW.CFA.nop, unit.header_len - header_bw.end) catch unreachable;
+                        assert(header_bw.end == header_bw.buffer.len);
+                        try unit.replaceHeader(&dwarf.debug_frame.section, dwarf, header_bw.buffer);
                         try unit.writeTrailer(&dwarf.debug_frame.section, dwarf);
                     }
                 },
 @@ -4581,83 +4649,84 @@ pub fn flush(dwarf: *Dwarf, pt: Zcu.PerThread) FlushError!void {
         for (dwarf.mods.keys(), dwarf.mods.values(), dwarf.debug_info.section.units.items, 0..) |mod, mod_info, *unit_ptr, unit_index| {
             const unit: Unit.Index = @enumFromInt(unit_index);
             unit_ptr.clear();
-            try unit_ptr.cross_unit_relocs.ensureTotalCapacity(dwarf.gpa, 1);
+            try unit_ptr.cross_unit_relocs.ensureTotalCapacity(gpa, 1);
-            try unit_ptr.cross_section_relocs.ensureTotalCapacity(dwarf.gpa, 7);
+            try unit_ptr.cross_section_relocs.ensureTotalCapacity(gpa, 7);
-            header.clearRetainingCapacity();
+            try header.resize(gpa, unit_ptr.header_len);
-            try header.ensureTotalCapacity(unit_ptr.header_len);
+            header_bw = .fixed(header.items);
             const unit_len = (if (unit_ptr.next.unwrap()) |next_unit|
                 dwarf.debug_info.section.getUnit(next_unit).off
             else
                 dwarf.debug_info.section.len) - unit_ptr.off - dwarf.unitLengthBytes();
             switch (dwarf.format) {
-                .@"32" => std.mem.writeInt(u32, header.addManyAsArrayAssumeCapacity(4), @intCast(unit_len), dwarf.endian),
+                .@"32" => header_bw.writeInt(u32, @intCast(unit_len), dwarf.endian) catch unreachable,
                 .@"64" => {
-                    std.mem.writeInt(u32, header.addManyAsArrayAssumeCapacity(4), std.math.maxInt(u32), dwarf.endian);
+                    header_bw.writeInt(u32, std.math.maxInt(u32), dwarf.endian) catch unreachable;
-                    std.mem.writeInt(u64, header.addManyAsArrayAssumeCapacity(8), unit_len, dwarf.endian);
+                    header_bw.writeInt(u64, unit_len, dwarf.endian) catch unreachable;
                 },
             }
-            std.mem.writeInt(u16, header.addManyAsArrayAssumeCapacity(2), 5, dwarf.endian);
+            header_bw.writeInt(u16, 5, dwarf.endian) catch unreachable;
-            header.appendSliceAssumeCapacity(&.{ DW.UT.compile, @intFromEnum(dwarf.address_size) });
+            header_bw.writeAll(&.{ DW.UT.compile, @intFromEnum(dwarf.address_size) }) catch unreachable;
             unit_ptr.cross_section_relocs.appendAssumeCapacity(.{
-                .source_off = @intCast(header.items.len),
+                .source_off = @intCast(header_bw.end),
                 .target_sec = .debug_abbrev,
                 .target_unit = DebugAbbrev.unit,
             });
-            header.appendNTimesAssumeCapacity(0, dwarf.sectionOffsetBytes());
+            header_bw.splatByteAll(0, dwarf.sectionOffsetBytes()) catch unreachable;
-            const compile_unit_off: u32 = @intCast(header.items.len);
+            const compile_unit_off: u32 = @intCast(header_bw.end);
-            uleb128(header.fixedWriter(), try dwarf.refAbbrevCode(.compile_unit)) catch unreachable;
+            header_bw.writeLeb128(try dwarf.refAbbrevCode(.compile_unit)) catch unreachable;
-            header.appendAssumeCapacity(DW.LANG.Zig);
+            header_bw.writeByte(DW.LANG.Zig) catch unreachable;
             unit_ptr.cross_section_relocs.appendAssumeCapacity(.{
-                .source_off = @intCast(header.items.len),
+                .source_off = @intCast(header_bw.end),
                 .target_sec = .debug_line_str,
                 .target_unit = StringSection.unit,
                 .target_entry = (try dwarf.debug_line_str.addString(dwarf, "zig " ++ @import("build_options").version)).toOptional(),
             });
-            header.appendNTimesAssumeCapacity(0, dwarf.sectionOffsetBytes());
+            header_bw.splatByteAll(0, dwarf.sectionOffsetBytes()) catch unreachable;
             unit_ptr.cross_section_relocs.appendAssumeCapacity(.{
-                .source_off = @intCast(header.items.len),
+                .source_off = @intCast(header_bw.end),
                 .target_sec = .debug_line_str,
                 .target_unit = StringSection.unit,
                 .target_entry = mod_info.root_dir_path.toOptional(),
             });
-            header.appendNTimesAssumeCapacity(0, dwarf.sectionOffsetBytes());
+            header_bw.splatByteAll(0, dwarf.sectionOffsetBytes()) catch unreachable;
             unit_ptr.cross_section_relocs.appendAssumeCapacity(.{
-                .source_off = @intCast(header.items.len),
+                .source_off = @intCast(header_bw.end),
                 .target_sec = .debug_line_str,
                 .target_unit = StringSection.unit,
                 .target_entry = (try dwarf.debug_line_str.addString(dwarf, mod.root_src_path)).toOptional(),
             });
-            header.appendNTimesAssumeCapacity(0, dwarf.sectionOffsetBytes());
+            header_bw.splatByteAll(0, dwarf.sectionOffsetBytes()) catch unreachable;
             unit_ptr.cross_unit_relocs.appendAssumeCapacity(.{
-                .source_off = @intCast(header.items.len),
+                .source_off = @intCast(header_bw.end),
                 .target_unit = .main,
                 .target_off = compile_unit_off,
             });
-            header.appendNTimesAssumeCapacity(0, dwarf.sectionOffsetBytes());
+            header_bw.splatByteAll(0, dwarf.sectionOffsetBytes()) catch unreachable;
             unit_ptr.cross_section_relocs.appendAssumeCapacity(.{
-                .source_off = @intCast(header.items.len),
+                .source_off = @intCast(header_bw.end),
                 .target_sec = .debug_line,
                 .target_unit = unit,
             });
-            header.appendNTimesAssumeCapacity(0, dwarf.sectionOffsetBytes());
+            header_bw.splatByteAll(0, dwarf.sectionOffsetBytes()) catch unreachable;
             unit_ptr.cross_section_relocs.appendAssumeCapacity(.{
-                .source_off = @intCast(header.items.len),
+                .source_off = @intCast(header_bw.end),
                 .target_sec = .debug_rnglists,
                 .target_unit = unit,
                 .target_off = DebugRngLists.baseOffset(dwarf),
             });
-            header.appendNTimesAssumeCapacity(0, dwarf.sectionOffsetBytes());
+            header_bw.splatByteAll(0, dwarf.sectionOffsetBytes()) catch unreachable;
-            uleb128(header.fixedWriter(), 0) catch unreachable;
+            header_bw.writeUleb128(0) catch unreachable;
-            uleb128(header.fixedWriter(), try dwarf.refAbbrevCode(.module)) catch unreachable;
+            header_bw.writeLeb128(try dwarf.refAbbrevCode(.module)) catch unreachable;
             unit_ptr.cross_section_relocs.appendAssumeCapacity(.{
-                .source_off = @intCast(header.items.len),
+                .source_off = @intCast(header_bw.end),
                 .target_sec = .debug_str,
                 .target_unit = StringSection.unit,
                 .target_entry = (try dwarf.debug_str.addString(dwarf, mod.fully_qualified_name)).toOptional(),
             });
-            header.appendNTimesAssumeCapacity(0, dwarf.sectionOffsetBytes());
+            header_bw.splatByteAll(0, dwarf.sectionOffsetBytes()) catch unreachable;
-            uleb128(header.fixedWriter(), 0) catch unreachable;
+            header_bw.writeUleb128(0) catch unreachable;
-            try unit_ptr.replaceHeader(&dwarf.debug_info.section, dwarf, header.items);
+            assert(header_bw.end == header_bw.buffer.len);
+            try unit_ptr.replaceHeader(&dwarf.debug_info.section, dwarf, header_bw.buffer);
             try unit_ptr.writeTrailer(&dwarf.debug_info.section, dwarf);
         }
         dwarf.debug_info.section.dirty = false;
 @@ -4681,33 +4750,37 @@ pub fn flush(dwarf: *Dwarf, pt: Zcu.PerThread) FlushError!void {
         );
         for (dwarf.mods.values(), dwarf.debug_line.section.units.items) |mod_info, *unit| {
             unit.clear();
-            try unit.cross_section_relocs.ensureTotalCapacity(dwarf.gpa, mod_info.dirs.count() + 2 * (mod_info.files.count()));
+            try unit.cross_section_relocs.ensureTotalCapacity(gpa, mod_info.dirs.count() + 2 * (mod_info.files.count()));
-            header.clearRetainingCapacity();
+            try header.resize(gpa, unit.header_len);
-            try header.ensureTotalCapacity(unit.header_len);
+            header_bw = .fixed(header.items);
             const unit_len = (if (unit.next.unwrap()) |next_unit|
                 dwarf.debug_line.section.getUnit(next_unit).off
             else
                 dwarf.debug_line.section.len) - unit.off - dwarf.unitLengthBytes();
             switch (dwarf.format) {
-                .@"32" => std.mem.writeInt(u32, header.addManyAsArrayAssumeCapacity(4), @intCast(unit_len), dwarf.endian),
+                .@"32" => header_bw.writeInt(u32, @intCast(unit_len), dwarf.endian) catch unreachable,
                 .@"64" => {
-                    std.mem.writeInt(u32, header.addManyAsArrayAssumeCapacity(4), std.math.maxInt(u32), dwarf.endian);
+                    header_bw.writeInt(u32, std.math.maxInt(u32), dwarf.endian) catch unreachable;
-                    std.mem.writeInt(u64, header.addManyAsArrayAssumeCapacity(8), unit_len, dwarf.endian);
+                    header_bw.writeInt(u64, unit_len, dwarf.endian) catch unreachable;
                 },
             }
-            std.mem.writeInt(u16, header.addManyAsArrayAssumeCapacity(2), 5, dwarf.endian);
+            header_bw.writeInt(u16, 5, dwarf.endian) catch unreachable;
-            header.appendSliceAssumeCapacity(&.{ @intFromEnum(dwarf.address_size), 0 });
+            header_bw.writeAll(&.{ @intFromEnum(dwarf.address_size), 0 }) catch unreachable;
-            dwarf.writeInt(header.addManyAsSliceAssumeCapacity(dwarf.sectionOffsetBytes()), unit.header_len - header.items.len);
+            dwarf.writeIntTo(
+                &header_bw,
+                dwarf.sectionOffsetBytes(),
+                unit.header_len - header_bw.end,
+            ) catch unreachable;
             const StandardOpcode = DeclValEnum(DW.LNS);
-            header.appendSliceAssumeCapacity(&[_]u8{
+            header_bw.writeAll(&.{
                 dwarf.debug_line.header.minimum_instruction_length,
                 dwarf.debug_line.header.maximum_operations_per_instruction,
                 @intFromBool(dwarf.debug_line.header.default_is_stmt),
                 @bitCast(dwarf.debug_line.header.line_base),
                 dwarf.debug_line.header.line_range,
                 dwarf.debug_line.header.opcode_base,
-            });
+            }) catch unreachable;
-            header.appendSliceAssumeCapacity(std.enums.EnumArray(StandardOpcode, u8).init(.{
+            header_bw.writeAll(std.enums.EnumArray(StandardOpcode, u8).init(.{
                 .extended_op = undefined,
                 .copy = 0,
                 .advance_pc = 1,
 @@ -4721,44 +4794,45 @@ pub fn flush(dwarf: *Dwarf, pt: Zcu.PerThread) FlushError!void {
                 .set_prologue_end = 0,
                 .set_epilogue_begin = 0,
                 .set_isa = 1,
-            }).values[1..dwarf.debug_line.header.opcode_base]);
+            }).values[1..dwarf.debug_line.header.opcode_base]) catch unreachable;
-            header.appendAssumeCapacity(1);
+            header_bw.writeByte(1) catch unreachable;
-            uleb128(header.fixedWriter(), DW.LNCT.path) catch unreachable;
+            header_bw.writeLeb128(@as(u14, DW.LNCT.path)) catch unreachable;
-            uleb128(header.fixedWriter(), DW.FORM.line_strp) catch unreachable;
+            header_bw.writeLeb128(@as(u13, DW.FORM.line_strp)) catch unreachable;
-            uleb128(header.fixedWriter(), mod_info.dirs.count()) catch unreachable;
+            header_bw.writeLeb128(mod_info.dirs.count()) catch unreachable;
             for (mod_info.dirs.keys()) |dir_unit| {
                 unit.cross_section_relocs.appendAssumeCapacity(.{
-                    .source_off = @intCast(header.items.len),
+                    .source_off = @intCast(header_bw.end),
                     .target_sec = .debug_line_str,
                     .target_unit = StringSection.unit,
                     .target_entry = dwarf.getModInfo(dir_unit).root_dir_path.toOptional(),
                 });
-                header.appendNTimesAssumeCapacity(0, dwarf.sectionOffsetBytes());
+                header_bw.splatByteAll(0, dwarf.sectionOffsetBytes()) catch unreachable;
             }
             const dir_index_info = DebugLine.dirIndexInfo(@intCast(mod_info.dirs.count()));
-            header.appendAssumeCapacity(3);
+            header_bw.writeByte(3) catch unreachable;
-            uleb128(header.fixedWriter(), DW.LNCT.path) catch unreachable;
+            header_bw.writeLeb128(@as(u14, DW.LNCT.path)) catch unreachable;
-            uleb128(header.fixedWriter(), DW.FORM.line_strp) catch unreachable;
+            header_bw.writeLeb128(@as(u13, DW.FORM.line_strp)) catch unreachable;
-            uleb128(header.fixedWriter(), DW.LNCT.directory_index) catch unreachable;
+            header_bw.writeLeb128(@as(u14, DW.LNCT.directory_index)) catch unreachable;
-            uleb128(header.fixedWriter(), @intFromEnum(dir_index_info.form)) catch unreachable;
+            header_bw.writeLeb128(@intFromEnum(dir_index_info.form)) catch unreachable;
-            uleb128(header.fixedWriter(), DW.LNCT.LLVM_source) catch unreachable;
+            header_bw.writeLeb128(@as(u14, DW.LNCT.LLVM_source)) catch unreachable;
-            uleb128(header.fixedWriter(), DW.FORM.line_strp) catch unreachable;
+            header_bw.writeLeb128(@as(u13, DW.FORM.line_strp)) catch unreachable;
-            uleb128(header.fixedWriter(), mod_info.files.count()) catch unreachable;
+            header_bw.writeLeb128(mod_info.files.count()) catch unreachable;
             for (mod_info.files.keys()) |file_index| {
                 const file = zcu.fileByIndex(file_index);
                 unit.cross_section_relocs.appendAssumeCapacity(.{
-                    .source_off = @intCast(header.items.len),
+                    .source_off = @intCast(header_bw.end),
                     .target_sec = .debug_line_str,
                     .target_unit = StringSection.unit,
                     .target_entry = (try dwarf.debug_line_str.addString(dwarf, file.sub_file_path)).toOptional(),
                 });
                 header.appendNTimesAssumeCapacity(0, dwarf.sectionOffsetBytes());
-                dwarf.writeInt(
+                dwarf.writeIntTo(
-                    header.addManyAsSliceAssumeCapacity(dir_index_info.bytes),
+                    &header_bw,
+                    dir_index_info.bytes,
                     mod_info.dirs.getIndex(dwarf.getUnitIfExists(file.mod.?).?) orelse 0,
                 );
                 unit.cross_section_relocs.appendAssumeCapacity(.{
-                    .source_off = @intCast(header.items.len),
+                    .source_off = @intCast(header_bw.end),
                     .target_sec = .debug_line_str,
                     .target_unit = StringSection.unit,
                     .target_entry = (try dwarf.debug_line_str.addString(
 @@ -4766,9 +4840,10 @@ pub fn flush(dwarf: *Dwarf, pt: Zcu.PerThread) FlushError!void {
                         if (file.is_builtin) file.source.? else "",
                     )).toOptional(),
                 });
-                header.appendNTimesAssumeCapacity(0, dwarf.sectionOffsetBytes());
+                header_bw.splatByteAll(0, dwarf.sectionOffsetBytes()) catch unreachable;
             }
-            try unit.replaceHeader(&dwarf.debug_line.section, dwarf, header.items);
+            assert(header_bw.end == header_bw.buffer.len);
+            try unit.replaceHeader(&dwarf.debug_line.section, dwarf, header_bw.buffer);
             try unit.writeTrailer(&dwarf.debug_line.section, dwarf);
         }
         dwarf.debug_line.section.dirty = false;
 @@ -4784,24 +4859,25 @@ pub fn flush(dwarf: *Dwarf, pt: Zcu.PerThread) FlushError!void {
     }
     if (dwarf.debug_rnglists.section.dirty) {
         for (dwarf.debug_rnglists.section.units.items) |*unit| {
-            header.clearRetainingCapacity();
+            try header.resize(gpa, unit.header_len);
-            try header.ensureTotalCapacity(unit.header_len);
+            header_bw = .fixed(header.items);
             const unit_len = (if (unit.next.unwrap()) |next_unit|
                 dwarf.debug_rnglists.section.getUnit(next_unit).off
             else
                 dwarf.debug_rnglists.section.len) - unit.off - dwarf.unitLengthBytes();
             switch (dwarf.format) {
-                .@"32" => std.mem.writeInt(u32, header.addManyAsArrayAssumeCapacity(4), @intCast(unit_len), dwarf.endian),
+                .@"32" => header_bw.writeInt(u32, @intCast(unit_len), dwarf.endian) catch unreachable,
                 .@"64" => {
-                    std.mem.writeInt(u32, header.addManyAsArrayAssumeCapacity(4), std.math.maxInt(u32), dwarf.endian);
+                    header_bw.writeInt(u32, std.math.maxInt(u32), dwarf.endian) catch unreachable;
-                    std.mem.writeInt(u64, header.addManyAsArrayAssumeCapacity(8), unit_len, dwarf.endian);
+                    header_bw.writeInt(u64, unit_len, dwarf.endian) catch unreachable;
                 },
             }
-            std.mem.writeInt(u16, header.addManyAsArrayAssumeCapacity(2), 5, dwarf.endian);
+            header_bw.writeInt(u16, 5, dwarf.endian) catch unreachable;
-            header.appendSliceAssumeCapacity(&.{ @intFromEnum(dwarf.address_size), 0 });
+            header_bw.writeAll(&.{ @intFromEnum(dwarf.address_size), 0 }) catch unreachable;
-            std.mem.writeInt(u32, header.addManyAsArrayAssumeCapacity(4), 1, dwarf.endian);
+            header_bw.writeInt(u32, 1, dwarf.endian) catch unreachable;
-            dwarf.writeInt(header.addManyAsSliceAssumeCapacity(dwarf.sectionOffsetBytes()), dwarf.sectionOffsetBytes() * 1);
+            dwarf.writeIntTo(&header_bw, dwarf.sectionOffsetBytes(), dwarf.sectionOffsetBytes() * 1) catch unreachable;
-            try unit.replaceHeader(&dwarf.debug_rnglists.section, dwarf, header.items);
+            assert(header_bw.end == header_bw.buffer.len);
+            try unit.replaceHeader(&dwarf.debug_rnglists.section, dwarf, header_bw.buffer);
             try unit.writeTrailer(&dwarf.debug_rnglists.section, dwarf);
         }
         dwarf.debug_rnglists.section.dirty = false;
 @@ -6000,6 +6076,10 @@ fn writeInt(dwarf: *Dwarf, buf: []u8, int: u64) void {
     }
 }
+fn writeIntTo(dwarf: *Dwarf, bw: *Writer, len: usize, int: u64) !void {
+    dwarf.writeInt(try bw.writableSlice(len), int);
+}
 fn resolveReloc(dwarf: *Dwarf, source: u64, target: u64, size: u32) RelocError!void {
     var buf: [8]u8 = undefined;
     dwarf.writeInt(buf[0..size], target);
 @@ -6026,7 +6106,6 @@ fn uleb128Bytes(value: anytype) u32 {
     d.writer.writeUleb128(value) catch unreachable;
     return @intCast(d.count + d.writer.end);
 }
 fn sleb128Bytes(value: anytype) u32 {
     var trash_buffer: [64]u8 = undefined;
     var d: std.Io.Writer.Discarding = .init(&trash_buffer);
 @@ -6053,7 +6132,7 @@ const codegen = @import("../codegen.zig");
 const dev = @import("../dev.zig");
 const link = @import("../link.zig");
 const log = std.log.scoped(.dwarf);
-const sleb128 = std.leb.writeIleb128;
 const std = @import("std");
 const target_info = @import("../target.zig");
-const uleb128 = std.leb.writeUleb128;
+const Allocator = std.mem.Allocator;
+const Writer = std.io.Writer;