Messages in this thread | | | Date | Tue, 22 Mar 2022 14:41:00 +0100 | From | Willy Tarreau <> | Subject | Re: [RFC PATCH v2 3/8] tools/nolibc: i386: Implement syscall with 6 arguments |
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On Tue, Mar 22, 2022 at 01:39:41PM +0000, David Laight wrote: > From: Ammar Faizi > > Sent: 22 March 2022 13:37 > > > > On 3/22/22 8:34 PM, Willy Tarreau wrote: > > >> I turned out GCC refuses to use "rm" if we compile without -fomit-frame-pointer > > >> (e.g. without optimization / -O0). So I will still use "m" here. > > > > > > OK that's fine. then you can probably simplify it like this: > > > > > > long _arg6 = (long)(arg6); /* Might be in memory */ \ > > > \ > > > asm volatile ( \ > > > "pushl %%ebp\n\t" \ > > > "movl %[_arg6], %%ebp\n\t" \ > > > "int $0x80\n\t" \ > > > "popl %%ebp\n\t" \ > > > : "=a"(_ret) \ > > > : "r"(_num), "r"(_arg1), "r"(_arg2), "r"(_arg3), \ > > > "r"(_arg4),"r"(_arg5), [_arg6]"m"(_arg6) \ > > > : "memory", "cc" \ > > > ); \ > > > > > > See ? no more push, no more addl, direct load from memory. > > > > Uggh... I crafted the same code like you suggested before, but then > > I realized it's buggy, it's buggy because %[_arg6] may live in N(%esp). > > > > When you pushl %ebp, the %esp changes, N(%esp) no longer points to the > > 6-th argument. > > Yep - that is why I wrote the 'push arg6'.
Got it and you're right indeed, sorry for the noise :-)
Willy
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