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link.MachO.UnwindInfo: Handle u24 overflow for CU records pointing to DWARF. #23011

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Merged
merged 2 commits into from
Feb 25, 2025
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link.MachO.UnwindInfo: Handle u24 overflow for CU records pointing to DWARF. #23011

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link.MachO.UnwindInfo: Handle u24 overflow for CU records pointing to…
alexrp Feb 25, 2025
466ce48
link.MachO.UnwindInfo: reproduce lld's comment
andrewrk Feb 25, 2025
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13 changes: 12 additions & 1 deletion src/link/MachO/UnwindInfo.zig
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Original file line number Diff line number Diff line change
Expand Up @@ -68,7 +68,18 @@ pub fn generate(info: *UnwindInfo, macho_file: *MachO) !void {
for (info.records.items) |ref| {
const rec = ref.getUnwindRecord(macho_file);
if (rec.getFde(macho_file)) |fde| {
rec.enc.setDwarfSectionOffset(@intCast(fde.out_offset));
// The unwinder will look for the DWARF entry starting at the hint,
// assuming the hint points to a valid CFI record start. If it
// fails to find the record, it proceeds in a linear search through
// the contiguous CFI records from the hint until the end of the
// section. Ideally, in the case where the offset is too large to
// be encoded, we would instead encode the largest possible offset
// to a valid CFI record, but since we don't keep track of that,
// just encode zero -- the start of the section is always the start
// of a CFI record.
const hint = std.math.cast(u24, fde.out_offset) orelse 0;
rec.enc.setDwarfSectionOffset(hint);
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Great find! Is there a test case demonstrating the issue in action I wonder?

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I don't think we have an easy test case, but the following PRs hit it at various points: #21498, #22605, #22488

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Thanks!


if (fde.getLsdaAtom(macho_file)) |lsda| {
rec.lsda = lsda.atom_index;
rec.lsda_offset = fde.lsda_offset;
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