[Bug tree-optimization/80512] New: missing -Wformat-overfow on a numbered directive with width specified by "*m$"

[msebor at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80512

            Bug ID: 80512
           Summary: missing -Wformat-overfow on a numbered directive with
                    width specified by "*m$"
           Product: gcc
           Version: 7.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: msebor at gcc dot gnu.org
  Target Milestone: ---

The gimple-ssa-sprintf.c pass doesn't handle numbered directives entirely
correctly.  As a result, it fails to diagnose instances of buffer overflow such
as in the following (it has the same problem with precision):

$ cat a.c && gcc -O2 -Wall -Wextra -Wformat-overflow a.c && ./a.out
int main ()
{
  char d[10];

  int n = __builtin_sprintf (d, "%1$*1$i", 12);

  __builtin_printf ("%i: \"%s\"\n", n, d);
}
12: "          12"