[Bug tree-optimization/78913] New: Probably wrong -Wformat-length= error message

[marxin at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=78913

            Bug ID: 78913
           Summary: Probably wrong -Wformat-length= error message
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: marxin at gcc dot gnu.org
                CC: msebor at gcc dot gnu.org
  Target Milestone: ---

Isolated from fcoe-utils:

$ cat /tmp/sprintf.c
struct buffer
{
  char path[512];
};

int main(int argc, char **argv)
{
  static struct buffer a;
  struct buffer out;
  __builtin_strcpy (a.path, "test");

  __builtin_snprintf (out.path, sizeof (struct buffer), "%s/_\n", a.path);
  __builtin_printf (out.path);
}

$ ./xgcc -B. /tmp/sprintf.c  -Wall -O2 && ./a.out 1
/tmp/sprintf.c: In function ‘main’:
/tmp/sprintf.c:12:61: warning: output may be truncated before the last format
character [-Wformat-length=]
   __builtin_snprintf (out.path, sizeof (struct buffer), "%s/_\n", a.path);
                                                             ^~~
/tmp/sprintf.c:12:3: note: format output between 4 and 515 bytes into a
destination of size 512
   __builtin_snprintf (out.path, sizeof (struct buffer), "%s/_\n", a.path);
   ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
test/_

I guess it's bogus as considering that strlen of path would be 512 is kind of
misleading.

Thanks,
Martin