From 743623bc5464b3d1008a97531affd4da029ca9cb Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Alex=20R=C3=B8nne=20Petersen?= <alex@alexrp.com>
Date: Tue, 25 Feb 2025 08:10:12 +0100
Subject: [PATCH] link.MachO.UnwindInfo: Handle u24 overflow for CU records
 pointing to DWARF.

Closes #23010.
---
 src/link/MachO/UnwindInfo.zig | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/src/link/MachO/UnwindInfo.zig b/src/link/MachO/UnwindInfo.zig
index cf8a49bed1..e831f50e87 100644
--- a/src/link/MachO/UnwindInfo.zig
+++ b/src/link/MachO/UnwindInfo.zig
@@ -68,7 +68,13 @@ 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 start looking for a matching CFI at the offset we specify here; it
+            // isn't actually an offset to the exact CFI for this record. A consequence of this is
+            // that if the offset doesn't fit in 24 bits, we can just leave it as zero so the
+            // unwinder starts searching at the beginning of the section.
+            if (std.math.cast(u24, fde.out_offset)) |off| {
+                rec.enc.setDwarfSectionOffset(off);
+            }
             if (fde.getLsdaAtom(macho_file)) |lsda| {
                 rec.lsda = lsda.atom_index;
                 rec.lsda_offset = fde.lsda_offset;