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Fix SIGSEGV handler for AArch64 Darwin targets

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* ucontext_t ptr is 8-byte aligned instead of 16-byte aligned which @alignCast() expects
* Retrieve pc address from ucontext_t since unwind_state is null
* Work around __mcontext_data being written incorrectly by the kernel
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Cezary Kupaj 2025-05-14 05:38:38 +02:00 • committed by GitHub
parent 5b606d435d
commit 518105471e
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1 changed files with 27 additions and 3 deletions
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30
lib/std/debug.zig
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@ -441,7 +441,13 @@ pub fn dumpStackTraceFromBase(context: *ThreadContext) void {
var it = StackIterator.initWithContext(null, debug_info, context) catch return;
defer it.deinit();
printSourceAtAddress(debug_info, stderr, it.unwind_state.?.dwarf_context.pc, tty_config) catch return;
// DWARF unwinding on aarch64-macos is not complete so we need to get pc address from mcontext
const pc_addr = if (builtin.target.os.tag.isDarwin() and native_arch == .aarch64)
context.mcontext.ss.pc
else
it.unwind_state.?.dwarf_context.pc;
printSourceAtAddress(debug_info, stderr, pc_addr, tty_config) catch return;
while (it.next()) |return_address| {
printLastUnwindError(&it, debug_info, stderr, tty_config);
@ -1483,8 +1489,26 @@ fn dumpSegfaultInfoPosix(sig: i32, code: i32, addr: usize, ctx_ptr: ?*anyopaque)
.aarch64,
.aarch64_be,
=> {
const ctx: *posix.ucontext_t = @ptrCast(@alignCast(ctx_ptr));
dumpStackTraceFromBase(ctx);
// Some kernels don't align `ctx_ptr` properly. Handle this defensively.
const ctx: *align(1) posix.ucontext_t = @ptrCast(ctx_ptr);
var new_ctx: posix.ucontext_t = ctx.*;
if (builtin.os.tag.isDarwin() and builtin.cpu.arch == .aarch64) {
// The kernel incorrectly writes the contents of `__mcontext_data` right after `mcontext`,
// rather than after the 8 bytes of padding that are supposed to sit between the two. Copy the
// contents to the right place so that the `mcontext` pointer will be correct after the
// `relocateContext` call below.
new_ctx.__mcontext_data = @as(*align(1) extern struct {
onstack: c_int,
sigmask: std.c.sigset_t,
stack: std.c.stack_t,
link: ?*std.c.ucontext_t,
mcsize: u64,
mcontext: *std.c.mcontext_t,
__mcontext_data: std.c.mcontext_t align(@sizeOf(usize)), // Disable padding after `mcontext`.
}, @ptrCast(ctx)).__mcontext_data;
}
relocateContext(&new_ctx);
dumpStackTraceFromBase(&new_ctx);
},
else => {},
}