The callee is not setting up the stack frame correctly. mode_t is a
short, but it must be word aligned on the stack. One can observe this
fact by reviewing what GCC actually generates by this code:
int foo(char *path, int flags, short mode, int word) {
return 0;
}
int main(void) {
return foo("hello", 123, 755, 0xdeadbeef);
}
The above generates the following. Please note the word alignment of
the short value:
On Nov 19, 2008, at 11:25 AM, R.Matthew Emerson wrote:
I work on a Common Lisp compiler.
We have a way to call C library functions from the lisp. We process
the C headers with a custom ffigen and use the resulting data to
know the C types, number of arguments, and so forth.
When we call open(2) on 32-bit x86, though, something odd seems to
be happening.
From the libc sources (Libc-498/sys/open.c), we see
/*
* open stub: The legacy interface never automatically associated a
controlling
* tty, so we always pass O_NOCTTY.
*/
int
open(const char *path, int flags, mode_t mode)
{
return(__open_nocancel(path, flags | O_NOCTTY, mode));
}
The problem here is that if we call this with only two args, this
code will trash a word in the caller's frame (see [1] and [2] marked
above).
Like I mentioned, we see the
int open(const char *, int, ...)
prototype in fcntl.h, and don't know anything about the
__DARWIN_ALIAS_C(open) stuff, which is why we end up calling the
"legacy" interface.
Do I need some remedial i386 ABI instruction? Or is something else
wrong?
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