[Bug target/50818] va_list is filled incorrectly in functions with ms_abi attribute on amd64

["steven.shi at intel dot com" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=50818

Steven Shi <steven.shi at intel dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |steven.shi at intel dot com

--- Comment #5 from Steven Shi <steven.shi at intel dot com> ---
Hi Bizjak,
Your Executable testcase cannot really work with -mabi=ms on the command line.
If add a printf() in the while loop to output the sum value as below example,
the testcase will fail again with Segmentation fault even building with with
-mabi=ms.

$ gcc -O2 -mabi=ms pr50818.c
$ ./a.out
Segmentation fault (core dumped)


#include <stdio.h>

int
__attribute__((ms_abi))
foo (int n, ...)
{
  __builtin_va_list ap;
  int sum = 0;

  __builtin_va_start (ap, n);

  while (n--) {
    sum += __builtin_va_arg (ap, int);
    printf("sum = %d\n", sum);
  }
  __builtin_va_end (ap);

  return sum;
}

int main ()
{
  int res = foo (10, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10);

  if (res != 55)
    __builtin_abort ();

  return 0;
}