site_archiver@lists.apple.com Delivered-To: darwin-dev@lists.apple.com On Nov 19, 2008, at 3:23 PM, Dave Zarzycki wrote: [...] So if we do something like pushl <precious stuff> pushl $O_RDONLY pushl <address of path> call _open On Nov 19, 2008, at 11:25 AM, R.Matthew Emerson wrote: I work on a Common Lisp compiler.
From the libc sources (Libc-498/sys/open.c), we see 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> Like I mentioned, we see the int open(const char *, int, ...)
Do not post admin requests to the list. They will be ignored. Darwin-dev mailing list (Darwin-dev@lists.apple.com) Help/Unsubscribe/Update your Subscription: http://lists.apple.com/mailman/options/darwin-dev/site_archiver%40lists.appl... 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: But in this case, there is no mode argument for the caller to properly align. I'm sorry if I'm being thick, but if I call the open stub in libc with only two arguments, e.g. like with open(path, O_RDONLY), isn't the libc stub trashing the word where a mode argument would be if I'd called it with 3 arguments? then, the <precious stuff> word on stack below the O_RDONLY word is going to get its high half zeroed. 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. /* * 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). 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? This email sent to site_archiver@lists.apple.com