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From: "pinskia at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug analyzer/115380] New: Missing MUL_OVERFLOW support in analayzer
Date: Fri, 07 Jun 2024 02:09:57 +0000
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X-Bugzilla-Product: gcc
X-Bugzilla-Component: analyzer
X-Bugzilla-Version: 15.0
X-Bugzilla-Keywords: diagnostic
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D115380

            Bug ID: 115380
           Summary: Missing MUL_OVERFLOW support in analayzer
           Product: gcc
           Version: 15.0
            Status: UNCONFIRMED
          Keywords: diagnostic
          Severity: normal
          Priority: P3
         Component: analyzer
          Assignee: dmalcolm at gcc dot gnu.org
          Reporter: pinskia at gcc dot gnu.org
            Blocks: 109896
  Target Milestone: ---

Take (which is a modified version of g++.dg/analyzer/placement-new-size.C):
```
/* { dg-additional-options "-Wno-placement-new
-Wno-analyzer-use-of-uninitialized-value" } */

#include <new>
#include <stdlib.h>
#include <stdint.h>

void static_buffer_too_short (int t)
{
  int n =3D t*4;
  int n1 =3D (t+1);
  if (__builtin_mul_overflow(n1, 4, &n1))
    __builtin_abort();
  char buf[n];
  char *p =3D new (buf) char[n1]; /* { dg-warning "stack-based buffer overf=
low" }
*/
}

void static_buffer_too_short1 (int t)
{
  int n =3D t*4;
  int n1 =3D (t+1);
  n1 =3D n1*4;
  char buf[n];
  char *p =3D new (buf) char[n1]; /* { dg-warning "stack-based buffer overf=
low" }
*/
}

```
static_buffer_too_short should warn the same way as static_buffer_too_short1
currently does.

Note this was found while looking into the regressions developing of the pa=
tch
for PR 109896.


Referenced Bugs:

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D109896
[Bug 109896] Missed optimisation: overflow detection in multiplication
instructions for operator new=