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Dwarf.Unwind: handle macOS deviation from standard

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Apparently the `__eh_frame` in Mach-O binaries doesn't include the
terminator entry, but in all other respects it acts like `.eh_frame`
rather than `.debug_frame`. I have no idea.
This commit is contained in:
mlugg 2025-09-26 12:00:41 +01:00
parent 156cd8f678
commit 8950831d3c
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GPG Key ID: 3F5B7DCCBF4AF02E
3 changed files with 12 additions and 6 deletions
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14
lib/std/debug/Dwarf/Unwind.zig
View File

@ -475,10 +475,15 @@ pub fn prepare(
addr_size_bytes: u8,
endian: Endian,
need_lookup: bool,
/// The `__eh_frame` section in Mach-O binaries deviates from the standard `.eh_frame` section
/// in one way which this function needs to be aware of.
is_macho: bool,
) !void {
if (unwind.cie_list.len > 0 and (!need_lookup or unwind.lookup != null)) return;
unwind.cie_list.clearRetainingCapacity();
if (is_macho) assert(unwind.lookup == null or unwind.lookup.? != .eh_frame_hdr);
const section = unwind.frame_section;
var r: Reader = .fixed(section.bytes);
@ -519,10 +524,11 @@ pub fn prepare(
.terminator => break true,
}
} else false;
switch (section.id) {
.eh_frame => if (!saw_terminator) return bad(), // `.eh_frame` indicates the end of the CIE/FDE list with a sentinel entry
.debug_frame => if (saw_terminator) return bad(), // `.debug_frame` uses the section bounds and does not specify a sentinel entry
}
const expect_terminator = switch (section.id) {
.eh_frame => !is_macho, // `.eh_frame` indicates the end of the CIE/FDE list with a sentinel entry, though macOS omits this
.debug_frame => false, // `.debug_frame` uses the section bounds and does not specify a sentinel entry
};
if (saw_terminator != expect_terminator) return bad();
std.mem.sortUnstable(SortedFdeEntry, fde_list.items, {}, struct {
fn lessThan(ctx: void, a: SortedFdeEntry, b: SortedFdeEntry) bool {

2
lib/std/debug/SelfInfo/DarwinModule.zig
View File

@ -59,7 +59,7 @@ fn loadUnwindInfo(module: *const DarwinModule, gpa: Allocator, out: *DebugInfo)
var dwarf: Dwarf.Unwind = .initSection(.eh_frame, @intFromPtr(eh_frame.ptr) - vmaddr_slide, eh_frame);
errdefer dwarf.deinit(gpa);
// We don't need lookups, so this call is just for scanning CIEs.
dwarf.prepare(gpa, @sizeOf(usize), native_endian, false) catch |err| switch (err) {
dwarf.prepare(gpa, @sizeOf(usize), native_endian, false, true) catch |err| switch (err) {
error.ReadFailed => unreachable, // it's all fixed buffers
error.InvalidDebugInfo,
error.MissingDebugInfo,

2
lib/std/debug/SelfInfo/ElfModule.zig
View File

@ -228,7 +228,7 @@ pub fn getSymbolAtAddress(module: *const ElfModule, gpa: Allocator, di: *DebugIn
};
}
fn prepareUnwindLookup(unwind: *Dwarf.Unwind, gpa: Allocator) Error!void {
unwind.prepare(gpa, @sizeOf(usize), native_endian, true) catch |err| switch (err) {
unwind.prepare(gpa, @sizeOf(usize), native_endian, true, false) catch |err| switch (err) {
error.ReadFailed => unreachable, // it's all fixed buffers
error.InvalidDebugInfo,
error.MissingDebugInfo,