From mboxrd@z Thu Jan 1 00:00:00 1970 From: Steven Rostedt Subject: Re: [PATCH] x86/ftrace: Get rid of function_hook Date: Mon, 21 Oct 2019 10:33:33 -0400 Message-ID: <20191021103333.066d152c@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> <20191018133735.77e90e36@gandalf.local.home> <20191018194856.GC20368@zn.tnic> <20191018163125.346e078d@gandalf.local.home> <20191019073424.GA27353@zn.tnic> <20191021141038.GC7014@zn.tnic> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20191021141038.GC7014@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 List-Id: linux-arch.vger.kernel.org On Mon, 21 Oct 2019 16:10:38 +0200 Borislav Petkov wrote: > From: Borislav Petkov > > function_hook is used as a better name than the default __fentry__ > which is the profiling counter which gcc adds before every function's > prologue. Thus, it is not called from C and cannot have the same > semantics as a pure C function - it saves/restores regs so that a C > function can be called. > > Drop the function_hook symbol and use __fentry__ directly for better > alignment with gcc's documentation. > > Switch the marking to SYM_CODE_START/_END which is reserved for > non-standard, special functions. I would break this into two patches. One that removes the function_hook name, and the other to convert to the SYM_CODE_START/END. For the removal of the function_hook patch, be sure to state some of the history for why the function_hook was created in the first place. Which would be something like this: "When ftrace first was introduced to the kernel, it used gcc's mcount profiling mechanism. The mcount mechanism would add a call to "mcount" at the start of every function but after the stack frame was set up. Later, in gcc 4.6, gcc introduced -mfentry, that would create a call to "__fentry__" instead of "mcount", before the stack frame was set up. In order to handle both cases, ftrace defined a macro "function_hook" that would be either "mcount" or "__fentry__" depending on which one was being used. The Linux kernel no longer supports the "mcount" method, thus there's no reason to keep the "function_hook" define around. Simply use "__fentry__", as there is no ambiguity to the name anymore." -- Steve > > Signed-off-by: Borislav Petkov > Cc: "H. Peter Anvin" > Cc: Ingo Molnar > Cc: Jiri Slaby > Cc: Jonathan Corbet > Cc: Josh Poimboeuf > Cc: linux-doc@vger.kernel.org > Cc: linux-kernel@vger.kernel.org > Cc: Peter Zijlstra > Cc: "Steven Rostedt (VMware)" > Cc: Thomas Gleixner > Cc: x86@kernel.org > --- > Documentation/asm-annotations.rst | 4 ++-- > arch/x86/kernel/ftrace_32.S | 8 +++----- > arch/x86/kernel/ftrace_64.S | 13 ++++++------- > 3 files changed, 11 insertions(+), 14 deletions(-) > From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail.kernel.org ([198.145.29.99]:60824 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727140AbfJUOdh (ORCPT ); Mon, 21 Oct 2019 10:33:37 -0400 Date: Mon, 21 Oct 2019 10:33:33 -0400 From: Steven Rostedt Subject: Re: [PATCH] x86/ftrace: Get rid of function_hook Message-ID: <20191021103333.066d152c@gandalf.local.home> In-Reply-To: <20191021141038.GC7014@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> <20191018133735.77e90e36@gandalf.local.home> <20191018194856.GC20368@zn.tnic> <20191018163125.346e078d@gandalf.local.home> <20191019073424.GA27353@zn.tnic> <20191021141038.GC7014@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 Message-ID: <20191021143333.W91XxDzz9aenRo7eIBkEVrDADdNAfRQ_HpQxb2nM_Uo@z> On Mon, 21 Oct 2019 16:10:38 +0200 Borislav Petkov wrote: > From: Borislav Petkov > > function_hook is used as a better name than the default __fentry__ > which is the profiling counter which gcc adds before every function's > prologue. Thus, it is not called from C and cannot have the same > semantics as a pure C function - it saves/restores regs so that a C > function can be called. > > Drop the function_hook symbol and use __fentry__ directly for better > alignment with gcc's documentation. > > Switch the marking to SYM_CODE_START/_END which is reserved for > non-standard, special functions. I would break this into two patches. One that removes the function_hook name, and the other to convert to the SYM_CODE_START/END. For the removal of the function_hook patch, be sure to state some of the history for why the function_hook was created in the first place. Which would be something like this: "When ftrace first was introduced to the kernel, it used gcc's mcount profiling mechanism. The mcount mechanism would add a call to "mcount" at the start of every function but after the stack frame was set up. Later, in gcc 4.6, gcc introduced -mfentry, that would create a call to "__fentry__" instead of "mcount", before the stack frame was set up. In order to handle both cases, ftrace defined a macro "function_hook" that would be either "mcount" or "__fentry__" depending on which one was being used. The Linux kernel no longer supports the "mcount" method, thus there's no reason to keep the "function_hook" define around. Simply use "__fentry__", as there is no ambiguity to the name anymore." -- Steve > > Signed-off-by: Borislav Petkov > Cc: "H. Peter Anvin" > Cc: Ingo Molnar > Cc: Jiri Slaby > Cc: Jonathan Corbet > Cc: Josh Poimboeuf > Cc: linux-doc@vger.kernel.org > Cc: linux-kernel@vger.kernel.org > Cc: Peter Zijlstra > Cc: "Steven Rostedt (VMware)" > Cc: Thomas Gleixner > Cc: x86@kernel.org > --- > Documentation/asm-annotations.rst | 4 ++-- > arch/x86/kernel/ftrace_32.S | 8 +++----- > arch/x86/kernel/ftrace_64.S | 13 ++++++------- > 3 files changed, 11 insertions(+), 14 deletions(-) >