<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/61522>61522</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            UBsan produces incorrect report on a null-pointer-dereference
        </td>
    </tr>

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

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

    <tr>
      <th>Reporter</th>
      <td>
          shao-hua-li
      </td>
    </tr>
</table>

<pre>
    For the following code, Clang's UBsan cannot produce an incorrect report on the null-pointer-dereference. GCC'UBsan can produce the correct report.

Compiler explorer: https://godbolt.org/z/949vYEaMb

```shell
% cat a.c
struct a {
  char d
} ;
struct a b;
struct a *c;
struct a e() {
 int f[3];
  f[2]=0;
  c = 0;
  f[2]=0;
  *c = b;
  return b;
}
void main() {
    e(); 
}
%
% clang -fsanitize=undefined -O0 a.c && ./a.out
UndefinedBehaviorSanitizer:DEADLYSIGNAL
==1==ERROR: UndefinedBehaviorSanitizer: SEGV on unknown address 
...
% clang -fsanitize=undefined -O2 a.c && ./a.out
/a.c:8:3: runtime error: subtraction of unsigned offset from 0x7ffcd03c3e2c overflowed to 0x7ffcd03c3e34
SUMMARY: UndefinedBehaviorSanitizer: undefined-behavior /a.c:8:3 in 
/a.c:10:3: runtime error: subtraction of unsigned offset from 0x7ffcd03c3e2c overflowed to 0x7ffcd03c3e34
SUMMARY: UndefinedBehaviorSanitizer: undefined-behavior /a.c:10:3 in 
UndefinedBehaviorSanitizer:DEADLYSIGNAL
==1==ERROR: UndefinedBehaviorSanitizer
...
%
% gcc -fsanitize=undefined -O2 a.c && ./a.out
/a.c:11:6: runtime error: store to null pointer of type 'struct a'
%
```
</pre>
<img width="1px" height="1px" alt="" src="http://email.email.llvm.org/o/eJzUVU1v4zgM_TX0hYhhS3EcH3xw6qZYYLoDtOgCPcoyHWtXkQJJbmfm1y_80TZNZ2cWWOxhgCBOnshHPoomhffqYIhKyHaQ1ZEYQm9d6XthV_0gVlpFjW2_lnvrMPSEndXaPitzQGlbAnaFV1qYA7Dc48POC4NSGGMDnpxtB0koDCojrXMkAzo6WRfQmonLDFqvTlaZQG7VkqOOHBlJMd5cXQHLX_leyUav91wxJDUk1fx9ZY8npckhfTlp68gBr7AP4eSBV8D2wPYH2zZWh9i6A7D9N2D7Yl08PV6L2-acCTbJ_PE9ab1gLEMpAopYzoAPbpABBUK-mxFE2QuH7eKQ1wh8d2HcfISAVfIjSsC2wIozdmUCdpDtOGT1qz1OEJugOjmDJQKvMfm54Rh-sm3OQEdhcOYMgryefzxZ1eJRKPMhP8SXpIHv8MINWHZWx7FpcNV5YVRQ3wh4PZiWOmWoxdXnZCwyAtsA22AMbC9iO4TZ_eHFbke9eFLW3S8c423X11X96fH-t5vfq09LND7KTefH9d3d57uxKX5IgvfXN3-MTTqYv4x9Nija1pH3i6I4jv-1EPYDIdM_CbzaAq_4GNcNJqgjITlnp0T80AQnZFDWoO1wMNPL2qLtOk8BO2ePmHzJu062CZecmET7RK7T9plaDPbdIV_Pce8fbm-ru8efl-FVyKpZjvF9zqgMXmhJk19QzJz0m5r_u8U-tNFbPx2k_I_dlKbAq833byBYR2Mlx8mLy-Qd7yJ8PRGOM3yZPcDyy9xeBmLUlrwteCEiKtNNXrAs32TbqC9lyxO-pqTgOSvSLGXFNpVbwUk2sshlFqmSJYwnPC1YwnK-jaXMmkZ0Yt1Qkq2LFtYJHYXSsdZPx3FCR8r7gcpNmjEWadGQ9tOeYszQM06HwMaBFrly9Fk1w8HDOtHKB__GElTQVM7bZNkk_rtLSfzjSooGp8uLTaJCPzSxtEdg-zHW8lidnP2TZAC2nzL0wPaTgr8DAAD__6ZlP5k">