From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932839AbbFGIdo (ORCPT ); Sun, 7 Jun 2015 04:33:44 -0400 Received: from terminus.zytor.com ([198.137.202.10]:53064 "EHLO terminus.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932814AbbFGIdc (ORCPT ); Sun, 7 Jun 2015 04:33:32 -0400 Date: Sun, 7 Jun 2015 01:32:32 -0700 From: tip-bot for Denys Vlasenko Message-ID: Cc: brgerst@gmail.com, wad@chromium.org, mingo@kernel.org, luto@amacapital.net, dvlasenk@redhat.com, akpm@linux-foundation.org, bp@alien8.de, hpa@zytor.com, oleg@redhat.com, ast@plumgrid.com, rostedt@goodmis.org, torvalds@linux-foundation.org, keescook@chromium.org, tglx@linutronix.de, peterz@infradead.org, fweisbec@gmail.com, linux-kernel@vger.kernel.org Reply-To: ast@plumgrid.com, oleg@redhat.com, rostedt@goodmis.org, bp@alien8.de, hpa@zytor.com, brgerst@gmail.com, wad@chromium.org, mingo@kernel.org, akpm@linux-foundation.org, dvlasenk@redhat.com, luto@amacapital.net, linux-kernel@vger.kernel.org, fweisbec@gmail.com, tglx@linutronix.de, peterz@infradead.org, keescook@chromium.org, torvalds@linux-foundation.org In-Reply-To: <1433339930-20880-1-git-send-email-dvlasenk@redhat.com> References: <1433339930-20880-1-git-send-email-dvlasenk@redhat.com> To: linux-tip-commits@vger.kernel.org Subject: [tip:x86/asm] x86/asm/entry/32: Explain the stub32_clone logic Git-Commit-ID: 5cdc683b7d8b3341a3d18e0c5498bc1e4f3fb990 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: 5cdc683b7d8b3341a3d18e0c5498bc1e4f3fb990 Gitweb: http://git.kernel.org/tip/5cdc683b7d8b3341a3d18e0c5498bc1e4f3fb990 Author: Denys Vlasenko AuthorDate: Wed, 3 Jun 2015 15:58:49 +0200 Committer: Ingo Molnar CommitDate: Fri, 5 Jun 2015 13:41:27 +0200 x86/asm/entry/32: Explain the stub32_clone logic The reason for copying of %r8 to %rcx is quite non-obvious. Add a comment which explains why it is done. 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: 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/1433339930-20880-1-git-send-email-dvlasenk@redhat.com Signed-off-by: Ingo Molnar --- arch/x86/entry/ia32entry.S | 8 ++++++++ 1 file changed, 8 insertions(+) diff --git a/arch/x86/entry/ia32entry.S b/arch/x86/entry/ia32entry.S index 4bb9f7b..d0c7b28 100644 --- a/arch/x86/entry/ia32entry.S +++ b/arch/x86/entry/ia32entry.S @@ -528,6 +528,14 @@ GLOBAL(\label) ALIGN 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: + */ mov %r8, %rcx jmp ia32_ptregs_common