From mboxrd@z Thu Jan 1 00:00:00 1970 From: Steven Rostedt Subject: Re: [tip: x86/asm] x86/asm/ftrace: Mark function_hook as function Date: Fri, 18 Oct 2019 13:37:35 -0400 Message-ID: <20191018133735.77e90e36@gandalf.local.home> References: <20191011115108.12392-22-jslaby@suse.cz> <157141622788.29376.4016565749507481510.tip-bot2@tip-bot2> <20191018124800.0a7006bb@gandalf.local.home> <20191018124956.764ac42e@gandalf.local.home> <20191018171354.GB20368@zn.tnic> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20191018171354.GB20368@zn.tnic> Sender: linux-kernel-owner@vger.kernel.org To: Borislav Petkov Cc: tip-bot2 for Jiri Slaby , linux-kernel@vger.kernel.org, linux-tip-commits@vger.kernel.org, Jiri Slaby , "H. Peter Anvin" , Ingo Molnar , Josh Poimboeuf , linux-arch@vger.kernel.org, Masami Hiramatsu , Peter Zijlstra , Thomas Gleixner , x86-ml , Ingo Molnar , Borislav Petkov List-Id: linux-arch.vger.kernel.org On Fri, 18 Oct 2019 19:13:54 +0200 Borislav Petkov wrote: > On Fri, Oct 18, 2019 at 12:49:56PM -0400, Steven Rostedt wrote: > > On Fri, 18 Oct 2019 12:48:00 -0400 > > Steven Rostedt wrote: > > > > > > Relabel function_hook to be marked really as a function. It is called > > > > from C and has the same expectations towards the stack etc. > > > > > > > And to go even further, it *does not* have the same expectations > > towards the stack. > > > > I think this patch should not be applied. > > There are a couple more markings like that now: > > $ git grep function_hook > Documentation/asm-annotations.rst:120: SYM_FUNC_START(function_hook) > Documentation/asm-annotations.rst:122: SYM_FUNC_END(function_hook) > arch/x86/kernel/ftrace_32.S:15:# define function_hook __fentry__ > arch/x86/kernel/ftrace_32.S:24:SYM_FUNC_START(function_hook) > arch/x86/kernel/ftrace_32.S:26:SYM_FUNC_END(function_hook) > arch/x86/kernel/ftrace_64.S:17:# define function_hook __fentry__ > arch/x86/kernel/ftrace_64.S:135:SYM_FUNC_START(function_hook) > arch/x86/kernel/ftrace_64.S:137:SYM_FUNC_END(function_hook) > arch/x86/kernel/ftrace_64.S:251:SYM_FUNC_START(function_hook) > arch/x86/kernel/ftrace_64.S:282:SYM_FUNC_END(function_hook) > > Frankly, I wouldn't mark this function at all as it is special and I see > a little sense to have it in stack traces but maybe Jiri has another > angle here. I'll let him comment. It just needs to be visible by modules and what not, otherwise linking will fail. > > I guess with the new nomenclature that can be SYM_CODE_* now... > > Then, this magic "function" or a global symbol with an address or > whatever that is (oh, there's #define trickery too) definitely deserves > a comment above it to explain what it is. I even have to build the .s > file to see what it turns into: The #define was because we use to support mcount or __fentry__, now we just support __fentry__, and function_hook describes it better ;-) > > .globl __fentry__ ; .p2align 4, 0x90 ; __fentry__: > retq > .type __fentry__, @function ; .size __fentry__, .-__fentry__ > > Yeah, it is called on every function entry: > > callq ffffffff81a01760 <__fentry__> > > but can we please explain with a comment above it what it is? Heh, I guess we could, which would probably be quite a long comment as it's the key behind ftrace itself. -- Steve From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail.kernel.org ([198.145.29.99]:33058 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2405459AbfJRRhj (ORCPT ); Fri, 18 Oct 2019 13:37:39 -0400 Date: Fri, 18 Oct 2019 13:37:35 -0400 From: Steven Rostedt Subject: Re: [tip: x86/asm] x86/asm/ftrace: Mark function_hook as function Message-ID: <20191018133735.77e90e36@gandalf.local.home> In-Reply-To: <20191018171354.GB20368@zn.tnic> References: <20191011115108.12392-22-jslaby@suse.cz> <157141622788.29376.4016565749507481510.tip-bot2@tip-bot2> <20191018124800.0a7006bb@gandalf.local.home> <20191018124956.764ac42e@gandalf.local.home> <20191018171354.GB20368@zn.tnic> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-arch-owner@vger.kernel.org List-ID: To: Borislav Petkov Cc: tip-bot2 for Jiri Slaby , linux-kernel@vger.kernel.org, linux-tip-commits@vger.kernel.org, Jiri Slaby , "H. Peter Anvin" , Ingo Molnar , Josh Poimboeuf , linux-arch@vger.kernel.org, Masami Hiramatsu , Peter Zijlstra , Thomas Gleixner , x86-ml , Ingo Molnar , Borislav Petkov Message-ID: <20191018173735.dpPrdX-2LluLZDbwtapealKUuUP0d9PpuffqNyO_m8c@z> On Fri, 18 Oct 2019 19:13:54 +0200 Borislav Petkov wrote: > On Fri, Oct 18, 2019 at 12:49:56PM -0400, Steven Rostedt wrote: > > On Fri, 18 Oct 2019 12:48:00 -0400 > > Steven Rostedt wrote: > > > > > > Relabel function_hook to be marked really as a function. It is called > > > > from C and has the same expectations towards the stack etc. > > > > > > > And to go even further, it *does not* have the same expectations > > towards the stack. > > > > I think this patch should not be applied. > > There are a couple more markings like that now: > > $ git grep function_hook > Documentation/asm-annotations.rst:120: SYM_FUNC_START(function_hook) > Documentation/asm-annotations.rst:122: SYM_FUNC_END(function_hook) > arch/x86/kernel/ftrace_32.S:15:# define function_hook __fentry__ > arch/x86/kernel/ftrace_32.S:24:SYM_FUNC_START(function_hook) > arch/x86/kernel/ftrace_32.S:26:SYM_FUNC_END(function_hook) > arch/x86/kernel/ftrace_64.S:17:# define function_hook __fentry__ > arch/x86/kernel/ftrace_64.S:135:SYM_FUNC_START(function_hook) > arch/x86/kernel/ftrace_64.S:137:SYM_FUNC_END(function_hook) > arch/x86/kernel/ftrace_64.S:251:SYM_FUNC_START(function_hook) > arch/x86/kernel/ftrace_64.S:282:SYM_FUNC_END(function_hook) > > Frankly, I wouldn't mark this function at all as it is special and I see > a little sense to have it in stack traces but maybe Jiri has another > angle here. I'll let him comment. It just needs to be visible by modules and what not, otherwise linking will fail. > > I guess with the new nomenclature that can be SYM_CODE_* now... > > Then, this magic "function" or a global symbol with an address or > whatever that is (oh, there's #define trickery too) definitely deserves > a comment above it to explain what it is. I even have to build the .s > file to see what it turns into: The #define was because we use to support mcount or __fentry__, now we just support __fentry__, and function_hook describes it better ;-) > > .globl __fentry__ ; .p2align 4, 0x90 ; __fentry__: > retq > .type __fentry__, @function ; .size __fentry__, .-__fentry__ > > Yeah, it is called on every function entry: > > callq ffffffff81a01760 <__fentry__> > > but can we please explain with a comment above it what it is? Heh, I guess we could, which would probably be quite a long comment as it's the key behind ftrace itself. -- Steve