Commit c23a5ccd19f08d485820a1d5deea04a6e10fe7bb | zig

author	Alex Rønne Petersen <alex@alexrp.com> 2025-10-07 09:28:43+02:00
committer	Alex Rønne Petersen <alex@alexrp.com> 2025-10-07 09:28:43+02:00
log	c23a5ccd19f08d485820a1d5deea04a6e10fe7bb
tree	a474edb89937dc46cb5639b3ed8619409f831369
parent	6893e7feeed8b528d0a03d3491f4254bbcf5c7ce
signature	Signed by SSH key SHA256:7B/LJ7bpR1eX8aCXSr4mtd5M45VMPKcx9zY8e95b5QM

std.debug.Dwarf.SelfUnwinder: skip caching rules for unsupported registers

For unwinding purposes, we don't care about unsupported registers. Yet because
we added these rules to the cache entry, we'd later try to evaluate them and
thus fail the unwind attempt for no good reason. They'd also take up cache rule
slots that would be better spent on actually relevant registers.

Note that any attempt to read unsupported registers during unwinding will still
fail the unwind attempt as expected.

1 files changed, 16 insertions(+), 8 deletions(-)

lib
- std
  - debug
    Dwarf
    SelfUnwinder.zig

lib/std/debug/Dwarf/SelfUnwinder.zig+16-8

...	...	@@ -15,14 +15,14 @@ cfi_vm: Dwarf.Unwind.VirtualMachine,
15	15	expr_vm: Dwarf.expression.StackMachine(.{ .call_frame_context = true }),
16	16
17	17	pub const CacheEntry = struct {
18		const max_regs = 32;
	18	const max_rules = 32;
19	19
20	20	pc: usize,
21	21	cie: *const Dwarf.Unwind.CommonInformationEntry,
22	22	cfa_rule: Dwarf.Unwind.VirtualMachine.CfaRule,
23	23	num_rules: u8,
24		rules_regs: [max_regs]u16,
25		rules: [max_regs]Dwarf.Unwind.VirtualMachine.RegisterRule,
	24	rules_regs: [max_rules]u16,
	25	rules: [max_rules]Dwarf.Unwind.VirtualMachine.RegisterRule,
26	26
27	27	pub fn find(entries: []const CacheEntry, pc: usize) ?*const CacheEntry {
28	28	assert(pc != 0);
...	...	@@ -108,22 +108,30 @@ pub fn computeRules(
108	108
109	109	unwinder.cfi_vm.reset();
110	110	const row = try unwinder.cfi_vm.runTo(gpa, pc_vaddr, cie, &fde, @sizeOf(usize), native_endian);
111		const cols = unwinder.cfi_vm.rowColumns(&row);
112
113		if (cols.len > CacheEntry.max_regs) return error.UnsupportedDebugInfo;
114	111
115	112	var entry: CacheEntry = .{
116	113	.pc = unwinder.pc,
117	114	.cie = cie,
118	115	.cfa_rule = row.cfa,
119		.num_rules = @intCast(cols.len),
	116	.num_rules = undefined,
120	117	.rules_regs = undefined,
121	118	.rules = undefined,
122	119	};
123		for (cols, 0..) \|col, i\| {
	120	var i: usize = 0;
	121	for (unwinder.cfi_vm.rowColumns(&row)) \|col\| {
	122	if (i == CacheEntry.max_rules) return error.UnsupportedDebugInfo;
	123
	124	_ = unwinder.cpu_state.dwarfRegisterBytes(col.register) catch \|err\| switch (err) {
	125	// Reading an unsupported register during unwinding will result in an error, so there is
	126	// no point wasting a rule slot in the cache entry for it.
	127	error.UnsupportedRegister => continue,
	128	error.InvalidRegister => return error.InvalidDebugInfo,
	129	};
124	130	entry.rules_regs[i] = col.register;
125	131	entry.rules[i] = col.rule;
	132	i += 1;
126	133	}
	134	entry.num_rules = @intCast(i);
127	135	return entry;
128	136	}
129	137