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From: "qinzhao at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug sanitizer/102317] New: signed integer overflow sanitizer cannot
 work well with -fno-strict-overflow
Date: Mon, 13 Sep 2021 21:31:42 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D102317

            Bug ID: 102317
           Summary: signed integer overflow sanitizer cannot work well
                    with -fno-strict-overflow
           Product: gcc
           Version: 12.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: sanitizer
          Assignee: unassigned at gcc dot gnu.org
          Reporter: qinzhao at gcc dot gnu.org
                CC: dodji at gcc dot gnu.org, dvyukov at gcc dot gnu.org,
                    jakub at gcc dot gnu.org, kcc at gcc dot gnu.org, marxi=
n at gcc dot gnu.org
  Target Milestone: ---

with the latest gcc12:
$ cat wrap.c
#include <stdio.h>
#include <limits.h>

/* volatile to avoid optimization */
volatile int val;

int main(void)
{
   val =3D INT_MAX;
   val +=3D 1;
   printf("%d\n", val);
   return 0;
}
$ gcc -Wall -O2 -fsanitize=3Dsigned-integer-overflow -o wrap wrap.c
$ ./wrap
wrap.c:10:9: runtime error: signed integer overflow: 2147483647 + 1 cannot =
be
represented in type 'int'
-2147483648

Things work as expected: the overflow is detected and in this warning
mode, the result is a wrap-around.

However, the kernel builds with -fno-strict-overflow which removes
possible undefined behavior, but I still want the sanitizer to catch
this case. Currently it doesn't:

$ gcc -Wall -O2 -fsanitize=3Dsigned-integer-overflow -fno-strict-overflow -=
o wrap
wrap.c
$ ./wrap
-2147483648=