<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/90501>90501</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            [-Wunsafe-buffer-usage] unsafe_buffer_usage pragmas are not preserved in precompiled headers (PCH)
        </td>
    </tr>

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

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

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

<pre>
    a.h:
```
#ifndef A_H
#define A_H

int a(int *s) {
#pragma clang unsafe_buffer_usage begin
 return s[1];
#pragma clang unsafe_buffer_usage end
}

#endif
```

main.cc:
```
#include "a.h"

int main() {
  int s[] = {1, 2, 3};
  return a(s);
}
```

build.sh:
#!/bin/sh
set +x

CXX=/usr/bin/clang++

echo WITHOUT PCH
$CXX -I. -Werror=unsafe-buffer-usage -c main.cc -o main || exit

echo WITH PCH
$CXX -I. -Werror=unsafe-buffer-usage -x c++-header -c a.h -o a.gch || exit
$CXX -I. -Werror=unsafe-buffer-usage -include a -c main.cc -o main || exit
```
Result:
```
$ ./build.sh
WITHOUT PCH
WITH PCH
In file included from main.cc:1:
/Users/danakj/s/repro/a.h:6:10: error: unsafe buffer access [-Werror,-Wunsafe-buffer-usage]
  return s[1];
         ^
1 error generated.
```

Here's a commit that added [support for (de)serializing `#pragma pack`](https://github.com/SNSystems/llvm-debuginfo-analyzer/commit/963695562cbe907b50d360c2d115b76ba09f4953), though it will look different for pragmas that are not annotating a record.

`#pragma clang diagnostic push/ignore/pop` are preserved in the PCH, and here's part of the mechanism for doing so: https://github.com/llvm/llvm-project/blob/d566a5cd22b4a653f10698f90c691a1452dad5ce/clang/lib/Serialization/ASTWriter.cpp#L1092

Note that replacing the `clang unsafe_buffer_usage` pragmas with `clang diagnostic` pragmas does resolve the compilation error through the PCH, confirming that the latter are serialized but the former are not.

</pre>
<img width="1px" height="1px" alt="" src="http://email.email.llvm.org/o/eJycll2vmzgTxz-NczMKAoMhXOQiLw9qpUfd1Z5W59xVxh7ALdjINn379CsDyclp06rdCJHEL-OZ3_xngDunWo24J-xI2HnDJ98Zu5dc848fNrWRX_c86kh6IPGZxAeSx-u1_KWparTEBg7vX12HJDZK483QfFfaAyd0F74JPThCSyDF8bprtLwdOIie6xYm7XiD7-upadC-nxxvEWpslV6Wg0U_WQ2OsGNC2Jmkf2AHtVwXF-dbBwlNUUvV3I90vg9c6UiIX-HQop8kAqE0cKP0ewTBBKG7F9EDhBm3pABIeg5TCaEnoOGWBkfT69o19sAyQHyO_RrOPdfrSfUycjeppCmhCaFVHRyqXLcMOwzpOX653Xt6eiLpmdBqcva6YQZM6DFcN2tRdAYeX7999de7t_D36aqK7PT0BNvXEWwf0VpjSXpekrNdkrNdkrMVsEKGrZl_AilOpDgBflH-7kH_5ZQvIBbXtx1yiTacy6MunMmjVnR3Dv1t2xcJ8N8L5mWy_kE39f7nAssgChm4JHMe_YH2SyqvNTSqR1j9ktBYM8CzlJMbSVTvHFpHaLU0gKALQiuLozWEVksnyMOemKQHWDEc1jKDhQNwIdA5IOx4IUVP28c7rELlvhT1DwUNlw9h_1tGkuVYaFGj5R5l9AvVv0KLhBYOOAgzDMqD77gHLgMHwo5uGkdjPTTGAqE7iYSWDq3ivfqmdAvB3LWljFx8DAPsTOiu8350gRytCK1a5bupjoQZCK0e3jx8dR6HgK7vPw1bifXUKt2YLde8__oNQxUt_hBalXmal4zlVNRYxkXNYpnmsaAySVhd5DWPyyYrWRpqnZ7Ad2ZqO1AePqu-h96YjyBVgIp6CWRx162hWgRtPHCtjec-BMXBojD2Cu6K77vmKRVvtXFeCRgn1xFaqVabALQazUjyeDY-WnRoP6EEpcF3OAuPnoBrCd0F_8itB9PM8wOKjmvlhtlZaYJLzgQZ_YJp4HjBOVrzAUVAV_emDmJlec6ZkJTWGc9Z2iRxXu6aMhZ5mfAkY1RyyQQ-d62qV2Hjw5pq7pUJPe3w8PbRKo82EuNIaPr_JC5fdPA3xuPC1eLYcxF8DzGRPP7pAyeAuqTks_Ld8-JnwLdrpEEHFp3pP-FsXJhhVP3s46p939lZBDe4hdGNssPiEPfzVM-9D_VoES6iRgn1tMw2xg7rrDZ-FcNG7lNZpiXf4D4pkixL6K5INt2elVnOWYGiKRvOM5mU6a7JRNns8jSJGduoPY1pFme0TIqsYEnU0JLmO0xLIQUrkoJkMQ5c9VFIYmRsu1HOTbgvYxYnm57X2Lv5NYRSjZ9hngwPUHbe2P2c-HpqHcniXjnvnq145fv5_eVnPebuW8CF9qU-Xsh4DAUSoGPQcHhAuNAeZtTlZrL9_o-lOocTOsIc7r8BAAD__xQ_29Y">