Bring back stack trace printing on ARM Darwin

This temporary patch fixes a segfault caused by miscompilation
by the LLD when generating stubs for initialization of thread local
storage. We effectively bypass TLS in the default panic handler
so that no segfault is generated and the stack trace is correctly
reported back to the user.

Note that, this is linked directly to a bigger issue with LLD
ziglang/zig#7527 and when resolved, we only need to remove the
`comptime` code path introduced with this patch to use the default
panic handler that relies on TLS.

Co-authored-by: Andrew Kelley <andrew@ziglang.org>

1 files changed, 18 insertions, 0 deletions

diff --git a/lib/std/debug.zig b/lib/std/debug.zig
index e4ef25724b..a434fe0e8b 100644
--- a/lib/std/debug.zig
+++ b/lib/std/debug.zig
@@ -250,6 +250,24 @@ pub fn panicExtra(trace: ?*const builtin.StackTrace, first_trace_addr: ?usize, c
         resetSegfaultHandler();
     }
 
+    if (comptime std.Target.current.isDarwin() and std.Target.current.cpu.arch == .aarch64)
+        nosuspend {
+            // As a workaround for not having threadlocal variable support in LLD for this target,
+            // we have a simpler panic implementation that does not use threadlocal variables.
+            // TODO https://github.com/ziglang/zig/issues/7527
+            const stderr = io.getStdErr().writer();
+            if (@atomicRmw(u8, &panicking, .Add, 1, .SeqCst) == 0) {
+                stderr.print("panic: " ++ format ++ "\n", args) catch os.abort();
+                if (trace) |t| {
+                    dumpStackTrace(t.*);
+                }
+                dumpCurrentStackTrace(first_trace_addr);
+            } else {
+                stderr.print("Panicked during a panic. Aborting.\n", .{}) catch os.abort();
+            }
+            os.abort();
+        };
+
     nosuspend switch (panic_stage) {
         0 => {
             panic_stage = 1;