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From: "crrodriguez at opensuse dot org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug middle-end/111775] New: -Wstrict-flex-arrays missing
 diagnostics with unions
Date: Wed, 11 Oct 2023 19:39:34 +0000
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X-Bugzilla-Product: gcc
X-Bugzilla-Component: middle-end
X-Bugzilla-Version: 14.0
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X-Bugzilla-Priority: P3
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D111775

            Bug ID: 111775
           Summary: -Wstrict-flex-arrays missing diagnostics with unions
           Product: gcc
           Version: 14.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: middle-end
          Assignee: unassigned at gcc dot gnu.org
          Reporter: crrodriguez at opensuse dot org
  Target Milestone: ---

following code is not diagnosed

#include <stddef.h>
#include <stdlib.h>
#include <stdio.h>

struct foo {
        int dum;
union {
/* or  [1] */
        char a[0];
        wchar_t b[0];
      } fn;
};


int main(void)
{
        struct foo *f =3D malloc(sizeof(*f));
       /* or really any use of the union does not matter */
        printf("%p", f->fn.b);
        free(f);
        return 0;

}

compile options

-Wall -fstrict-flex-arrays -Werror=3Dstrict-flex-arrays -O2

This test is a silly mockup of real widespread code, which goes undiagnosed
until test suites run and/or is built with ubsan.=