[Bug #21150] macOS: Temporary workaround at unwinding coroutine

On arm64 macOS, libunwind (both of system library and homebrew
llvm-18) seems not to handle our coroutine switching code.

Author: nobu

addr2line.c

@@ -296,9 +296,11 @@ fill_filename(int file, uint8_t format, uint16_t version, const char *include_di
         for (i = 1; i <= file; i++) {
             filename = p;
             if (!*p) {
+#ifndef __APPLE__
                 /* Need to output binary file name? */
                 kprintf("Unexpected file number %d in %s at %tx\n",
                         file, binary_filename, filenames - obj->mapped);
+#endif
                 return;
             }
             while (*p) p++;

thread_pthread_mn.c

@@ -429,7 +429,12 @@ native_thread_check_and_create_shared(rb_vm_t *vm)
     }
 }
 
-static COROUTINE
+#ifdef __APPLE__
+# define co_start ruby_coroutine_start
+#else
+static
+#endif
+COROUTINE
 co_start(struct coroutine_context *from, struct coroutine_context *self)
 {
 #ifdef RUBY_ASAN_ENABLED

vm_dump.c

@@ -510,6 +510,15 @@ rb_vmdebug_thread_dump_state(FILE *errout, VALUE self)
 #  include <libunwind.h>
 #  include <sys/mman.h>
 #  undef backtrace
+
+static bool
+is_coroutine_start(unw_word_t ip)
+{
+    struct coroutine_context;
+    extern void ruby_coroutine_start(struct coroutine_context *, struct coroutine_context *);
+    return ((void *)(ip) == (void *)ruby_coroutine_start);
+}
+
 int
 backtrace(void **trace, int size)
 {
@@ -617,6 +626,9 @@ backtrace(void **trace, int size)
         // I wish I could use "ptrauth_strip()" but I get an error:
         // "this target does not support pointer authentication"
         trace[n++] = (void *)(ip & 0x7fffffffffffull);
+
+        // Apple's libunwind can't handle our coroutine switching code
+        if (is_coroutine_start(ip)) break;
     }
     return n;
 #  endif