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));
}
and the code for this (on Mac OS X 10.5.5) is
0x90925a44 <open>: push %ebp
0x90925a45 <open+1>: mov %esp,%ebp
0x90925a47 <open+3>: mov 0xc(%ebp),%eax
0x90925a4a <open+6>: movzwl 0x10(%ebp),%edx ; [1]
0x90925a4e <open+10>: or $0x20000,%eax
0x90925a53 <open+15>: mov %edx,0x10(%ebp) ; [2]
0x90925a56 <open+18>: mov %eax,0xc(%ebp)
0x90925a59 <open+21>: leave
0x90925a5a <open+22>: jmp 0x908a0e88 <open$NOCANCEL$UNIX2003>
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?
