GCC function call optimization error

[Bryan Mills <bmills at andrew dot cmu dot edu>]

I am using GCC 3.2.1 for an Operating Systems course at CMU;
We're using a lot of inline assembly, and I discovered some flagrantly 
incorrect GCC output in argument passing for functions.
Specifically, writing arguments before function calls is apparently not 
flagged to rely on the value of %esp.

Please see the attached almost-minimal test-case for an example.


Bryan Mills
void foo(int bar)
{
}

int main()
{
    int returnCode;
    
    foo(-1); /* not broken */
    asm volatile("pushl $0" : : : "esp"); /* put a 0 on the stack */
    foo(-1); /* broken -- should not overwrite value just placed on stack */
    asm volatile("popl %0" : "=r" (returnCode) : : "esp"); /* should be 0, actually 1 */
    
    exit(returnCode);
}