MIPS: va_arg is unable to correct extract an empty zero-length array

[Nick Clifton <nickc at redhat dot com>]

Hi Eric, Hi Richard,

  A customer has reported the following bug with the MIPS target.  Since
  it is for a GNU extension to the C language (zero-length arrays) that
  is being used in a non-intended fashion (the zero-length array is in a
  structure with no other fields) I doubt if you will want to
  investigate the problem too much, but I thought that it was worth
  reporting anyway:

    % mips64vr-elf-gcc -mgp32 -O2 -Tddb.ld -march=vr5500 bug.c
    % mips64vr-elf-run a.out
    assertion "arg4 == va4" failed: file "bug.c", line 40, function: foo

  As an aside if the type3 structure in bug.c is given another,
  non-zero-length field, then the test passes.

Cheers
  Nick

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

typedef int * type1;

typedef struct 
{
  union u1 { double f1; long int f2; } f3[0];
} type3;

typedef int type4;

static type1 arg1 = 0;
static double arg2 = 1.0;
static type3 arg3 = {{}};
static type4 arg4 = 0x12345678;

void
foo (double parm,
     ...)
{
  va_list  ap;
  type1    va1;
  double   va2;
  type3    va3;
  type4    va4;

  va_start (ap, parm);

  va1 = va_arg (ap, type1);
  assert (arg1 == va1);

  va2 = va_arg (ap, double);
  assert (arg2 == va2);

  va3 = va_arg (ap, type3);

  va4 = va_arg (ap, type4);
  assert (arg4 == va4);

  va_end (ap);
}

int
main (void)
{
  foo (1.0, arg1, arg2, arg3, arg4);
  return 0;
}