stdarg x86_64 problems...

[John Colvin]

When I compile the following code with -m32 and -m64 i get a 
totally different result, the documentation suggests that they 
should be the same...

import core.stdc.stdarg, std.stdio;
void main() {
        foo(0,5,4,3);
}

void foo(int dummy, ...) {
        va_list ap;
                
        for(int i; i<10; ++i) {
                version(X86_64) {
                        va_start(ap, __va_argsave);
                }
                else version(X86) {
                        va_start(ap, dummy);
                }       
                else
                        static assert(false, "Unsupported platform");
                
                int tmp;
                va_arg!(int)(ap,tmp);
                writeln(ap," ", tmp);
        }
}

when compiled with -m32 I get:

FF960278 5
FF960278 5
FF960278 5
FF960278 5
FF960278 5

and with -m64 I get:

7FFFCDF941D0 5
7FFFCDF941D0 4
7FFFCDF941D0 3
7FFFCDF941D0 38
7FFFCDF941D0 -839302560

(the end stuff is garbage, different every time)

I'm uncertain, even after looking over the stdarg src, why this 
would happen. The correct output is all 5s obviously.