va_arg bug of emscripten

va-args-bug.c

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

typedef struct type_a {
  union {
    double f;
    void *p;
    int i;
    short sym;
  } value;
} type_a;

enum mrb_vtype {
  MRB_TT_FALSE = 0,   /*   0 */
  MRB_TT_CLASS = 9    /*   9 */
};

typedef struct type_b {
  enum mrb_vtype tt:8;
} type_b;

void print_type_a(int argc, ...);
void print_type_b(int argc, ...);

int main(int argc, char *argv[])
{
  type_a a;
  type_b b;
  a.value.p = (void*) 0x12345678;
  b.tt = MRB_TT_CLASS;

  printf("The original address of a is: %p\n", a.value.p);
  printf("The original type of b is: %d\n", b.tt);

  print_type_a(1, a);
  print_type_b(1, b);

  return 0;
}

void print_type_a(int argc, ...) {
  va_list ap;
  type_a a;

  va_start(ap, argc);
  a = va_arg(ap, type_a);
  va_end(ap);

  printf("The current address of a is: %p\n", a.value.p);
}

void print_type_b(int argc, ...) {
  va_list ap;
  type_b b;

  va_start(ap, argc);
  b = va_arg(ap, type_b);
  va_end(ap);

  printf("The current type of b is: %d\n", b.tt);
}