From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on gnuweeb.org X-Spam-Level: X-Spam-Status: No, score=-0.0 required=5.0 tests=SPF_HELO_PASS,SPF_PASS autolearn=ham autolearn_force=no version=3.4.6 Received: from 1wt.eu (wtarreau.pck.nerim.net [62.212.114.60]) by gnuweeb.org (Postfix) with ESMTP id 3BE697E2DF for ; Tue, 22 Mar 2022 13:34:29 +0000 (UTC) Received: (from willy@localhost) by pcw.home.local (8.15.2/8.15.2/Submit) id 22MDYDRu011026; Tue, 22 Mar 2022 14:34:13 +0100 Date: Tue, 22 Mar 2022 14:34:13 +0100 From: Willy Tarreau To: Ammar Faizi Cc: David Laight , "Paul E. McKenney" , Alviro Iskandar Setiawan , Nugraha , Linux Kernel Mailing List , GNU/Weeb Mailing List , "x86@kernel.org" , "llvm@lists.linux.dev" Subject: Re: [RFC PATCH v2 3/8] tools/nolibc: i386: Implement syscall with 6 arguments Message-ID: <20220322133413.GG10306@1wt.eu> References: <20220322102115.186179-1-ammarfaizi2@gnuweeb.org> <20220322102115.186179-4-ammarfaizi2@gnuweeb.org> <8653f6784a9b4272a59a75a530663567@AcuMS.aculab.com> <20220322121338.GD10306@1wt.eu> <81569a1c-a6d3-ceb2-a1f1-f229a024d684@gnuweeb.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <81569a1c-a6d3-ceb2-a1f1-f229a024d684@gnuweeb.org> User-Agent: Mutt/1.10.1 (2018-07-13) List-Id: On Tue, Mar 22, 2022 at 08:26:37PM +0700, Ammar Faizi wrote: > On 3/22/22 7:13 PM, Willy Tarreau wrote: > > On Tue, Mar 22, 2022 at 07:02:53PM +0700, Ammar Faizi wrote: > > > I propose the > > > following macro (this is not so much different with other my_syscall macro), > > > expect the 6th argument can be in reg or mem. > > > > > > The "rm" constraint here gives the opportunity for the compiler to use %ebp > > > instead of memory if -fomit-frame-pointer is turned on. > > > > > > #define my_syscall6(num, arg1, arg2, arg3, arg4, arg5, arg6) \ > > > ({ \ > > > long _ret; \ > > > register long _num asm("eax") = (num); \ > > > register long _arg1 asm("ebx") = (long)(arg1); \ > > > register long _arg2 asm("ecx") = (long)(arg2); \ > > > register long _arg3 asm("edx") = (long)(arg3); \ > > > register long _arg4 asm("esi") = (long)(arg4); \ > > > register long _arg5 asm("edi") = (long)(arg5); \ > > > long _arg6 = (long)(arg6); /* Might be in memory */ \ > > > \ > > > asm volatile ( \ > > > "pushl %[_arg6]\n\t" \ > > > "pushl %%ebp\n\t" \ > > > "movl 4(%%esp), %%ebp\n\t" \ > > > "int $0x80\n\t" \ > > > "popl %%ebp\n\t" \ > > > "addl $4,%%esp\n\t" \ > > > : "=a"(_ret) \ > > > : "r"(_num), "r"(_arg1), "r"(_arg2), "r"(_arg3), \ > > > "r"(_arg4),"r"(_arg5), [_arg6]"rm"(_arg6) \ > > > : "memory", "cc" \ > > > ); \ > > > _ret; \ > > > }) > > > > > > What do you think? > > > > Hmmm indeed that comes back to the existing constructs and is certainly > > more in line with the rest of the code (plus it will not be affected by > > -O0). > > > > I seem to remember a register allocation issue which kept me away from > > implementing it this way on i386 back then, but given that my focus was > > not as much on i386 as it was on other platforms, it's likely that I have > > not insisted too much and not tried this one which looks like the way to > > go to me. > > 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. Willy