From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753099AbdCOVOW (ORCPT ); Wed, 15 Mar 2017 17:14:22 -0400 Received: from mx1.redhat.com ([209.132.183.28]:59882 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751277AbdCOVOT (ORCPT ); Wed, 15 Mar 2017 17:14:19 -0400 DMARC-Filter: OpenDMARC Filter v1.3.2 mx1.redhat.com 0E74BC04B31B Authentication-Results: ext-mx07.extmail.prod.ext.phx2.redhat.com; dmarc=none (p=none dis=none) header.from=redhat.com Authentication-Results: ext-mx07.extmail.prod.ext.phx2.redhat.com; spf=pass smtp.mailfrom=jpoimboe@redhat.com DKIM-Filter: OpenDKIM Filter v2.11.0 mx1.redhat.com 0E74BC04B31B Date: Wed, 15 Mar 2017 16:13:43 -0500 From: Josh Poimboeuf To: Steven Rostedt Cc: linux-kernel@vger.kernel.org, Ingo Molnar , Andrew Morton , Thomas Gleixner , Peter Zijlstra , Masami Hiramatsu , "H. Peter Anvin" , Andy Lutomirski , Linus Torvalds Subject: Re: [RFC][PATCH 4/5] ftrace/x86_32: Clean up ftrace_regs_caller Message-ID: <20170315211343.q62tvl7rd6ourdlv@treble> References: <20170315195527.703131481@goodmis.org> <20170315200255.564342348@goodmis.org> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20170315200255.564342348@goodmis.org> User-Agent: Mutt/1.6.0.1 (2016-04-01) X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.31]); Wed, 15 Mar 2017 21:13:46 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Mar 15, 2017 at 03:55:31PM -0400, Steven Rostedt wrote: > From: "Steven Rostedt (VMware)" > > When ftrace_regs_caller was created, it was designed to preserve flags as > much as possible as it needed to act just like a breakpoint triggered on the > same location. But the design is over complicated as it treated all > operations as modifying flags. But push, mov and lea do not modify flags. > This means the code can become more simplified by allowing flags to be > stored further down. > > Making ftrace_regs_caller simpler will also be useful in implementing fentry > logic. > > Signed-off-by: Steven Rostedt (VMware) > --- > arch/x86/kernel/ftrace_32.S | 45 +++++++++++++++++++++++++-------------------- > 1 file changed, 25 insertions(+), 20 deletions(-) > > diff --git a/arch/x86/kernel/ftrace_32.S b/arch/x86/kernel/ftrace_32.S > index 73d61a62649d..8ca33d9806ac 100644 > --- a/arch/x86/kernel/ftrace_32.S > +++ b/arch/x86/kernel/ftrace_32.S > @@ -55,23 +55,30 @@ WEAK(ftrace_stub) > END(ftrace_caller) > > ENTRY(ftrace_regs_caller) > - pushf /* push flags before compare (in cs location) */ > - > /* > * i386 does not save SS and ESP when coming from kernel. > * Instead, to get sp, ®s->sp is used (see ptrace.h). > * Unfortunately, that means eflags must be at the same location > * as the current return ip is. We move the return ip into the > - * ip location, and move flags into the return ip location. > - */ > - pushl 4(%esp) /* save return ip into ip slot */ > + * regs->ip location, and move flags into the return ip location. > + */ > + pushl $__KERNEL_CS > + pushl 4(%esp) /* Save the return ip */ > + > + /* temporarily save flags in the orig_ax location */ > + pushf > > - pushl $0 /* Load 0 into orig_ax */ > pushl %gs > pushl %fs > pushl %es > pushl %ds > pushl %eax > + > + /* move flags into the location of where the return ip was */ > + movl 5*4(%esp), %eax > + movl $0, (%esp) /* Load 0 into orig_ax */ This writes a 0 into regs->ax instead of regs->orig_ax. -- Josh