Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755445AbbFLX2a (ORCPT ); Fri, 12 Jun 2015 19:28:30 -0400 Received: from mail-la0-f52.google.com ([209.85.215.52]:32801 "EHLO mail-la0-f52.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752101AbbFLX22 (ORCPT ); Fri, 12 Jun 2015 19:28:28 -0400 MIME-Version: 1.0 In-Reply-To: <20150610062110.GA1165@gmail.com> References: <1433876051-26604-1-git-send-email-dvlasenk@redhat.com> <1433876051-26604-3-git-send-email-dvlasenk@redhat.com> <20150610062110.GA1165@gmail.com> From: Andy Lutomirski Date: Fri, 12 Jun 2015 16:28:06 -0700 Message-ID: Subject: Re: [PATCH 3/5] x86/asm/entry/32: Shorten __audit_syscall_entry args preparation To: Ingo Molnar Cc: Frederic Weisbecker , Denys Vlasenko , Kees Cook , Borislav Petkov , "linux-kernel@vger.kernel.org" , Alexei Starovoitov , Oleg Nesterov , Will Drewry , Steven Rostedt , X86 ML , "H. Peter Anvin" , Linus Torvalds Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2340 Lines: 50 On Jun 9, 2015 11:21 PM, "Ingo Molnar" wrote: > > > * Denys Vlasenko wrote: > > > We use three MOVs to swap edx and ecx. We can use one XCHG instead. > > > > Expand the comments. It's difficult to keep track which arg# every register > > corresponds to, so spell it out. > > > + /* > > + * At this point, registers hold syscall args in 32-bit ABI: > > + * eax is syscall#, args are in ebx,ecx,edx,esi,edi,ebp. > > + * Shuffle them to match what __audit_syscall_entry() wants. > > + */ > > + movl %esi, %r8d /* arg5 (r8): 4th syscall arg */ > > + xchg %ecx, %edx /* arg4 (rcx): 3rd syscall arg (edx) */ > > + /* arg3 (rdx): 2nd syscall arg (ecx) */ > > + movl %ebx, %esi /* arg2 (rsi): 1st syscall arg */ > > + movl %eax, %edi /* arg1 (rdi): syscall number */ > > call __audit_syscall_entry > > So while we are at it I improved this a bit more, to: > > /* > * At this point, registers hold syscall args in 32-bit syscall ABI: > * eax is syscall#, args are in ebx,ecx,edx,esi,edi,ebp. > * > * We want to pass them to __audit_syscall_entry(), which is a 64-bit > * C function with 5 parameters, so shuffle them to match what > * __audit_syscall_entry() expects: rdi,rsi,rdx,rcx,r8. > */ > movl %esi, %r8d /* arg5 (r8 ) <= 4th syscall arg (esi) */ > xchg %ecx, %edx /* arg4 (rcx) <= 3rd syscall arg (edx) */ > /* arg3 (rdx) <= 2nd syscall arg (ecx) */ > movl %ebx, %esi /* arg2 (rsi) <= 1st syscall arg (ebx) */ > movl %eax, %edi /* arg1 (rdi) <= syscall number (eax) */ > call __audit_syscall_entry > > Btw., syscall auditing is not auditing syscall arguments #5 and #6? Indeed. That's the least of its problems. Don't ever read that code or you might accidentally git rm it. --Andy -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/