<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/95635>95635</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            __builtin_object_size incorrect size when passed to function
        </td>
    </tr>

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

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

    <tr>
      <th>Reporter</th>
      <td>
          kevans91
      </td>
    </tr>
</table>

<pre>
    Consider the following example:

```
#include <stdio.h> 
 
static void 
check_size(void *ptr) 
{ 
 
    printf("%p, %zu\n", ptr, __builtin_object_size(ptr, 1)); 
} 
 
int 
main(int argc, char *argv[]) 
{ 
    struct { 
        unsigned char padding_l; 
        unsigned char buf[41]; 
        unsigned char padding_r; 
    } __stack; 
 
 check_size(&__stack.buf); 
 printf("%p, %zu\n", &__stack.buf, __builtin_object_size(&__stack.buf, 1)); 
 return (0); 
} 
```

When compiled with -O1 or higher, I observe the following:
```
0x806c11d6, 42
0x806c11d6, 41
```

That is, the `__builtin_object_size()` invocation in `check_size` returns a result as if it had been invoked as `__builtin_object_size(ptr, 0);` rather than `__builtin_object_size(ptr, 1);`.  This makes `_FORTIFY_SOURCE` a little more lenient than it should be in some weird corner cases.
</pre>
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