From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932857AbbFGIeR (ORCPT ); Sun, 7 Jun 2015 04:34:17 -0400 Received: from terminus.zytor.com ([198.137.202.10]:53085 "EHLO terminus.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751682AbbFGIdy (ORCPT ); Sun, 7 Jun 2015 04:33:54 -0400 Date: Sun, 7 Jun 2015 01:32:49 -0700 From: tip-bot for Denys Vlasenko Message-ID: Cc: linux-kernel@vger.kernel.org, rostedt@goodmis.org, wad@chromium.org, akpm@linux-foundation.org, tglx@linutronix.de, brgerst@gmail.com, josh@joshtriplett.org, hpa@zytor.com, torvalds@linux-foundation.org, dvlasenk@redhat.com, luto@amacapital.net, keescook@chromium.org, mingo@kernel.org, fweisbec@gmail.com, peterz@infradead.org, ast@plumgrid.com, bp@alien8.de, oleg@redhat.com Reply-To: keescook@chromium.org, luto@amacapital.net, hpa@zytor.com, josh@joshtriplett.org, dvlasenk@redhat.com, torvalds@linux-foundation.org, bp@alien8.de, oleg@redhat.com, mingo@kernel.org, ast@plumgrid.com, fweisbec@gmail.com, peterz@infradead.org, akpm@linux-foundation.org, wad@chromium.org, rostedt@goodmis.org, linux-kernel@vger.kernel.org, brgerst@gmail.com, tglx@linutronix.de In-Reply-To: <1433339930-20880-2-git-send-email-dvlasenk@redhat.com> References: <1433339930-20880-2-git-send-email-dvlasenk@redhat.com> To: linux-tip-commits@vger.kernel.org Subject: [tip:x86/asm] x86/asm/entry/32: Remove unnecessary optimization in stub32_clone Git-Commit-ID: 7a5a9824c18f93415944c997dc6bb8eecfddd2e7 X-Mailer: tip-git-log-daemon Robot-ID: Robot-Unsubscribe: Contact to get blacklisted from these emails MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Content-Type: text/plain; charset=UTF-8 Content-Disposition: inline Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Commit-ID: 7a5a9824c18f93415944c997dc6bb8eecfddd2e7 Gitweb: http://git.kernel.org/tip/7a5a9824c18f93415944c997dc6bb8eecfddd2e7 Author: Denys Vlasenko AuthorDate: Wed, 3 Jun 2015 15:58:50 +0200 Committer: Ingo Molnar CommitDate: Fri, 5 Jun 2015 13:41:28 +0200 x86/asm/entry/32: Remove unnecessary optimization in stub32_clone Really swap arguments #4 and #5 in stub32_clone instead of "optimizing" it into a move. Yes, tls_val is currently unused. Yes, on some CPUs XCHG is a little bit more expensive than MOV. But a cycle or two on an expensive syscall like clone() is way below noise floor, and this optimization is simply not worth the obfuscation of logic. [ There's also ongoing work on the clone() ABI by Josh Triplett that will depend on this change later on. ] Signed-off-by: Denys Vlasenko Cc: Alexei Starovoitov Cc: Andrew Morton Cc: Andy Lutomirski Cc: Borislav Petkov Cc: Brian Gerst Cc: Frederic Weisbecker Cc: H. Peter Anvin Cc: Josh Triplett Cc: Kees Cook Cc: Linus Torvalds Cc: Oleg Nesterov Cc: Peter Zijlstra Cc: Steven Rostedt Cc: Thomas Gleixner Cc: Will Drewry Link: http://lkml.kernel.org/r/1433339930-20880-2-git-send-email-dvlasenk@redhat.com Signed-off-by: Ingo Molnar --- arch/x86/entry/ia32entry.S | 13 ++++++------- 1 file changed, 6 insertions(+), 7 deletions(-) diff --git a/arch/x86/entry/ia32entry.S b/arch/x86/entry/ia32entry.S index d0c7b28..9558dac 100644 --- a/arch/x86/entry/ia32entry.S +++ b/arch/x86/entry/ia32entry.S @@ -529,14 +529,13 @@ GLOBAL(\label) GLOBAL(stub32_clone) leaq sys_clone(%rip), %rax /* - * 32-bit clone API is clone(..., int tls_val, int *child_tidptr). - * 64-bit clone API is clone(..., int *child_tidptr, int tls_val). - * Native 64-bit kernel's sys_clone() implements the latter. - * We need to swap args here. But since tls_val is in fact ignored - * by sys_clone(), we can get away with an assignment - * (arg4 = arg5) instead of a full swap: + * The 32-bit clone ABI is: clone(..., int tls_val, int *child_tidptr). + * The 64-bit clone ABI is: clone(..., int *child_tidptr, int tls_val). + * + * The native 64-bit kernel's sys_clone() implements the latter, + * so we need to swap arguments here before calling it: */ - mov %r8, %rcx + xchg %r8, %rcx jmp ia32_ptregs_common ALIGN