[Bug sanitizer/82046] New: Bogus -fsanitize=undefined error with -O2 -Wall

[hjl.tools at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82046

            Bug ID: 82046
           Summary: Bogus -fsanitize=undefined error with -O2 -Wall
           Product: gcc
           Version: 8.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: sanitizer
          Assignee: unassigned at gcc dot gnu.org
          Reporter: hjl.tools at gmail dot com
                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, marxin at gcc dot gnu.org
  Target Milestone: ---

[hjl@gnu-6 gcc]$ cat /tmp/x.i
typedef struct sym
{
  unsigned long bb_addr[10];
  unsigned long bb_calls[10];
}
Sym;

void
annotate_with_count (Sym *b)
{
  unsigned int i;
  unsigned long last_count;
  char tmpbuf[10 * 30];
  char *p;

  p = tmpbuf;
  *p = '\0';

  for (i = 0; i < 10 && b->bb_addr[i]; i++)
    {
      last_count = b->bb_calls[i];
      if (p > tmpbuf)
        *p++ = ',';
      __builtin_sprintf (p, "%lu", last_count);
      p += __builtin_strlen (p);
    }
}
[hjl@gnu-6 gcc]$ ./xgcc -B./ -S /tmp/x.i -Wall  -O2  -fsanitize=undefined 
/tmp/x.i: In function ‘annotate_with_count’:
/tmp/x.i:24:7: warning: null destination pointer [-Wformat-overflow=]
       __builtin_sprintf (p, "%lu", last_count);
       ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
[hjl@gnu-6 gcc]$