The following works on i386, sparc32 and sparc64, but produces a compiler warning on x86-64, then prints garbage and crashses when run:

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

void func3(va_list *ap) {
        int test = va_arg(*ap,int);
        fprintf(stderr,"%d\n",test);
}

void func2(va_list ap) {
        func3(&ap);
}

void func1(int start, ...) {
        va_list ap;

        va_start(ap,start);

        func2(ap);

        va_end(ap);
}

int main() {
        fprintf(stderr,"This should print 1:\n");
        func1(2,1);
        return 0;
}
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test.c: In function `func2':
test.c:10: warning: passing arg 1 of `func3' from incompatible pointer type
---------------------------
This should print 1:
-7609280
Segmentation fault