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Message-ID: <3b8984ecfbcd4c93aeb468d01728cd74@AcuMS.aculab.com>
Date: Tue, 22 Mar 2022 13:39:41 +0000
From: David Laight <David.Laight@...LAB.COM>
To: 'Ammar Faizi' <ammarfaizi2@...weeb.org>, Willy Tarreau <w@....eu>
CC: "Paul E. McKenney" <paulmck@...nel.org>,
Alviro Iskandar Setiawan <alviro.iskandar@...weeb.org>,
Nugraha <richiisei@...il.com>,
"Linux Kernel Mailing List" <linux-kernel@...r.kernel.org>,
GNU/Weeb Mailing List <gwml@...r.gnuweeb.org>,
"x86@...nel.org" <x86@...nel.org>,
"llvm@...ts.linux.dev" <llvm@...ts.linux.dev>
Subject: RE: [RFC PATCH v2 3/8] tools/nolibc: i386: Implement syscall with 6
arguments
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'.
David
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