<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/72639>72639</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            [asan][Darwin] Unprotected use of Apple blocks breaks build with GCC
        </td>
    </tr>

    <tr>
      <th>Labels</th>
      <td>
            new issue
      </td>
    </tr>

    <tr>
      <th>Assignees</th>
      <td>
      </td>
    </tr>

    <tr>
      <th>Reporter</th>
      <td>
          fxcoudert
      </td>
    </tr>
</table>

<pre>
    The commit at https://github.com/llvm/llvm-project/commit/020cdaff615acbdc9ef6a801075a484ef74d5070 broke build of asan on macOS with GCC. GCC does not support the Apple blocks extension (yet). Uses of blocks in other parts of the sanitisers are protected by `MISSING_BLOCKS_SUPPORT`. But the type definition is not.

Could the same thing be done here? This works for me (tested in a build of asan inside GCC):

```
diff --git a/libsanitizer/asan/asan_mac.cpp b/libsanitizer/asan/asan_mac.cpp
index 5d5146e0cde..6252fa20d5e 100644
--- a/libsanitizer/asan/asan_mac.cpp
+++ b/libsanitizer/asan/asan_mac.cpp
@@ -139,9 +139,11 @@ typedef void (*dispatch_mach_handler_function_t)(void *context,
 dispatch_mach_reason reason,
 dispatch_mach_msg_t message,
 mach_error_t error);
+#if !defined(MISSING_BLOCKS_SUPPORT)
 typedef void (^dispatch_mach_handler_t)(dispatch_mach_reason reason,
 dispatch_mach_msg_t message,
 mach_error_t error);
+#endif
 
 // A wrapper for the ObjC blocks used to support libdispatch.
 typedef struct {
```


</pre>
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