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 3FD497E2BC for ; Tue, 22 Mar 2022 12:13:54 +0000 (UTC) Received: (from willy@localhost) by pcw.home.local (8.15.2/8.15.2/Submit) id 22MCDceW010766; Tue, 22 Mar 2022 13:13:38 +0100 Date: Tue, 22 Mar 2022 13:13:38 +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: <20220322121338.GD10306@1wt.eu> References: <20220322102115.186179-1-ammarfaizi2@gnuweeb.org> <20220322102115.186179-4-ammarfaizi2@gnuweeb.org> <8653f6784a9b4272a59a75a530663567@AcuMS.aculab.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.10.1 (2018-07-13) List-Id: 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. Willy