| author |  Pavel Verigo <paul.verigo@gmail.com> 2026-10-20 22:03:13+02:00 |
| committer |  Alex Rønne Petersen <alex@alexrp.com> 2026-10-21 00:47:14+02:00 |
| log | f356324325dc3637b93859d7b53f98f4e66009f5 |
| tree | b108392beeb8578f0075c9bad76f81ee88aabfb5 |
| parent | 427ddef0e84384c075dd01e8f1b512922c814a1c |
codegen: fix union padding
3 files changed, 29 insertions(+), 11 deletions(-)
src
- codegen.zig
codegen
test
behavior
src/codegen.zig+4-4
| ... | ... | @@ -617,6 +617,7 @@ pub fn generateSymbol( |
| 617 | 617 | else => unreachable, |
| 618 | 618 | }, |
| 619 | 619 | .un => |un| { |
| 620 | const union_begin = w.end; | |
| 620 | 621 | const layout = ty.unionGetLayout(zcu); |
| 621 | 622 | |
| 622 | 623 | if (layout.payload_size == 0) { |
| ... | ... | @@ -648,11 +649,10 @@ pub fn generateSymbol( |
| 648 | 649 | |
| 649 | 650 | if (layout.tag_size > 0 and layout.tag_align.compare(.lt, layout.payload_align)) { |
| 650 | 651 | try generateSymbol(bin_file, pt, Value.fromInterned(un.tag), w, reloc_parent); |
| 651 | ||
| 652 | if (layout.padding > 0) { | |
| 653 | try w.splatByteAll(0, layout.padding); | |
| 654 | } | |
| 655 | 652 | } |
| 653 | ||
| 654 | const padding: usize = @intCast(union_begin + layout.abi_size - w.end); | |
| 655 | if (padding > 0) try w.splatByteAll(0, padding); | |
| 656 | 656 | }, |
| 657 | 657 | .bitpack => |bitpack| try generateSymbol(bin_file, pt, .fromInterned(bitpack.backing_int_val), w, reloc_parent), |
| 658 | 658 | .memoized_call => unreachable, |
src/codegen/llvm.zig+9-7
| ... | ... | @@ -2982,13 +2982,13 @@ pub const Object = struct { |
| 2982 | 2982 | } else .normal; |
| 2983 | 2983 | |
| 2984 | 2984 | const payload_ty = ty: { |
| 2985 | if (layout.most_aligned_field_size == layout.payload_size) { | |
| 2986 | break :ty aligned_field_llvm_ty; | |
| 2987 | } | |
| 2988 | 2985 | const padding_len = if (layout.tag_size == 0) |
| 2989 | 2986 | layout.abi_size - layout.most_aligned_field_size |
| 2990 | 2987 | else |
| 2991 | 2988 | layout.payload_size - layout.most_aligned_field_size; |
| 2989 | if (padding_len == 0) { | |
| 2990 | break :ty aligned_field_llvm_ty; | |
| 2991 | } | |
| 2992 | 2992 | break :ty try o.builder.structType(.@"packed", &.{ |
| 2993 | 2993 | aligned_field_llvm_ty, |
| 2994 | 2994 | try o.builder.arrayType(padding_len, .i8), |
| ... | ... | @@ -3582,6 +3582,11 @@ pub const Object = struct { |
| 3582 | 3582 | const payload = if (un.tag != .none) p: { |
| 3583 | 3583 | const field_index = zcu.unionTagFieldIndex(union_obj, Value.fromInterned(un.tag)).?; |
| 3584 | 3584 | const field_ty = Type.fromInterned(union_obj.field_types.get(ip)[field_index]); |
| 3585 | const field_size = field_ty.abiSize(zcu); | |
| 3586 | const padding_len = if (layout.tag_size == 0) | |
| 3587 | layout.abi_size - field_size | |
| 3588 | else | |
| 3589 | layout.payload_size - field_size; | |
| 3585 | 3590 | |
| 3586 | 3591 | // Sometimes we must make an unnamed struct because LLVM does |
| 3587 | 3592 | // not support bitcasting our payload struct to the true union payload type. |
| ... | ... | @@ -3590,7 +3595,6 @@ pub const Object = struct { |
| 3590 | 3595 | need_unnamed = layout.most_aligned_field != field_index; |
| 3591 | 3596 | |
| 3592 | 3597 | if (!field_ty.hasRuntimeBits(zcu)) { |
| 3593 | const padding_len = layout.payload_size; | |
| 3594 | 3598 | break :p try o.builder.undefConst(try o.builder.arrayType(padding_len, .i8)); |
| 3595 | 3599 | } |
| 3596 | 3600 | const payload = try o.lowerValue(un.val, repr); |
| ... | ... | @@ -3598,9 +3602,7 @@ pub const Object = struct { |
| 3598 | 3602 | if (payload_ty != union_ty.structFields(&o.builder)[ |
| 3599 | 3603 | @intFromBool(layout.tag_size > 0 and layout.tag_align.compare(.gte, layout.payload_align)) |
| 3600 | 3604 | ]) need_unnamed = true; |
| 3601 | const field_size = field_ty.abiSize(zcu); | |
| 3602 | if (field_size == layout.payload_size) break :p payload; | |
| 3603 | const padding_len = layout.payload_size - field_size; | |
| 3605 | if (padding_len == 0) break :p payload; | |
| 3604 | 3606 | const padding_ty = try o.builder.arrayType(padding_len, .i8); |
| 3605 | 3607 | break :p try o.builder.structConst( |
| 3606 | 3608 | try o.builder.structType(.@"packed", &.{ payload_ty, padding_ty }), |
test/behavior/union.zig+16
| ... | ... | @@ -1162,6 +1162,22 @@ test "extern union most-aligned field is smaller" { |
| 1162 | 1162 | try expect(a != null); |
| 1163 | 1163 | } |
| 1164 | 1164 | |
| 1165 | test "union constant trailing padding" { | |
| 1166 | const S = struct { | |
| 1167 | fn doTheTest() !void { | |
| 1168 | const U = extern union { x: u32, y: [5]u8 }; | |
| 1169 | var u = [2]U{ .{ .x = 0 }, .{ .y = @splat(0xff) } }; | |
| 1170 | _ = &u; | |
| 1171 | try expect(u[0].x == 0); | |
| 1172 | try expect(u[1].y[0] == 0xff); | |
| 1173 | try expect(u[1].y[4] == 0xff); | |
| 1174 | } | |
| 1175 | }; | |
| 1176 | ||
| 1177 | try S.doTheTest(); | |
| 1178 | try comptime S.doTheTest(); | |
| 1179 | } | |
| 1180 | ||
| 1165 | 1181 | test "return an extern union from C calling convention" { |
| 1166 | 1182 | if (builtin.zig_backend == .stage2_arm) return error.SkipZigTest; // TODO |
| 1167 | 1183 | if (builtin.zig_backend == .stage2_sparc64) return error.SkipZigTest; // TODO |