[Bug target/24306] New: va_arg gets confused when skipping over certain zero-sized types

["bje at gcc dot gnu dot org" <gcc-bugzilla at gcc dot gnu dot org>]

va_arg seems to mess up the va_list when variadic variables have size 0, but
when have large alignment requirements.  When the alignment is small, this
seems to work by chance.

$ gcc foo.c -o foo && ./foo
3 0

#include <stdarg.h>
#include <stdio.h>

typedef int __attribute__ ((vector_size (16))) foo_t;

struct s
{
  foo_t f[0];
} s1;

void
check (int x, ...)
{
  int y;
  va_list ap;

  va_start (ap, x);
  va_arg (ap, struct s);
  y = va_arg (ap, int);

  /* Expect output: 3 7  */
  printf ("%d %d\n", x, y);
}

int main()
{
  check (3, s1, 7);
  return 0;
}


-- 
           Summary: va_arg gets confused when skipping over certain zero-
                    sized types
           Product: gcc
           Version: 4.1.0
            Status: UNCONFIRMED
          Keywords: wrong-code
          Severity: major
          Priority: P2
         Component: target
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: bje at gcc dot gnu dot org
GCC target triplet: i686-pc-linux-gnu


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=24306