From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-8.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id AFCA8CA9EC7 for ; Sat, 2 Nov 2019 12:19:08 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 845C42080F for ; Sat, 2 Nov 2019 12:19:08 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726329AbfKBMTI (ORCPT ); Sat, 2 Nov 2019 08:19:08 -0400 Received: from foss.arm.com ([217.140.110.172]:46774 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726163AbfKBMTI (ORCPT ); Sat, 2 Nov 2019 08:19:08 -0400 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 1BA8B328; Sat, 2 Nov 2019 05:19:07 -0700 (PDT) Received: from [10.162.0.144] (a075553-lin.blr.arm.com [10.162.0.144]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 785103F718; Sat, 2 Nov 2019 05:19:02 -0700 (PDT) From: Amit Daniel Kachhap Subject: Re: [PATCHv2 1/8] ftrace: add ftrace_init_nop() To: Mark Rutland , linux-arm-kernel@lists.infradead.org, Steven Rostedt Cc: linux-kernel@vger.kernel.org, catalin.marinas@arm.com, deller@gmx.de, duwe@suse.de, James.Bottomley@HansenPartnership.com, james.morse@arm.com, jeyu@kernel.org, jpoimboe@redhat.com, jthierry@redhat.com, linux-parisc@vger.kernel.org, mingo@redhat.com, peterz@infradead.org, svens@stackframe.org, takahiro.akashi@linaro.org, will@kernel.org References: <20191029165832.33606-1-mark.rutland@arm.com> <20191029165832.33606-2-mark.rutland@arm.com> Message-ID: Date: Sat, 2 Nov 2019 17:49:00 +0530 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.4.0 MIME-Version: 1.0 In-Reply-To: <20191029165832.33606-2-mark.rutland@arm.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-parisc-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-parisc@vger.kernel.org Hi Mark, On 10/29/19 10:28 PM, Mark Rutland wrote: > Architectures may need to perform special initialization of ftrace > callsites, and today they do so by special-casing ftrace_make_nop() when > the expected branch address is MCOUNT_ADDR. In some cases (e.g. for > patchable-function-entry), we don't have an mcount-like symbol and don't s/an mcount/a mcount. > want a synthetic MCOUNT_ADDR, but we may need to perform some > initialization of callsites. > > To make it possible to separate initialization from runtime > modification, and to handle cases without an mcount-like symbol, this Same as above. > patch adds an optional ftrace_init_nop() function that architectures can > implement, which does not pass a branch address. > > Where an architecture does not provide ftrace_init_nop(), we will fall > back to the existing behaviour of calling ftrace_make_nop() with > MCOUNT_ADDR. > > At the same time, ftrace_code_disable() is renamed to > ftrace_nop_initialize() to make it clearer that it is intended to > intialize a callsite into a disabled state, and is not for disabling a > callsite that has been runtime enabled. The kerneldoc description of rec > arguments is updated to cover non-mcount callsites. > > Signed-off-by: Mark Rutland > Reviewed-by: Ard Biesheuvel > Cc: Ingo Molnar > Cc: Steven Rostedt > Cc: Torsten Duwe > --- > include/linux/ftrace.h | 35 ++++++++++++++++++++++++++++++++--- > kernel/trace/ftrace.c | 6 +++--- > 2 files changed, 35 insertions(+), 6 deletions(-) > > diff --git a/include/linux/ftrace.h b/include/linux/ftrace.h > index 8a8cb3c401b2..9867d90d635e 100644 > --- a/include/linux/ftrace.h > +++ b/include/linux/ftrace.h > @@ -499,7 +499,7 @@ static inline int ftrace_disable_ftrace_graph_caller(void) { return 0; } > /** > * ftrace_make_nop - convert code into nop > * @mod: module structure if called by module load initialization > - * @rec: the mcount call site record > + * @rec: the call site record (e.g. mcount/fentry) > * @addr: the address that the call site should be calling > * > * This is a very sensitive operation and great care needs > @@ -520,9 +520,38 @@ static inline int ftrace_disable_ftrace_graph_caller(void) { return 0; } > extern int ftrace_make_nop(struct module *mod, > struct dyn_ftrace *rec, unsigned long addr); > > + > +/** > + * ftrace_init_nop - initialize a nop call site > + * @mod: module structure if called by module load initialization > + * @rec: the call site record (e.g. mcount/fentry) > + * > + * This is a very sensitive operation and great care needs > + * to be taken by the arch. The operation should carefully > + * read the location, check to see if what is read is indeed > + * what we expect it to be, and then on success of the compare, > + * it should write to the location. > + * > + * The code segment at @rec->ip should contain the contents created by > + * the compiler Nit: Will it be better to write it as "@rec->ip should store the adjusted ftrace entry address of the call site" or something like that. > + * > + * Return must be: > + * 0 on success > + * -EFAULT on error reading the location > + * -EINVAL on a failed compare of the contents > + * -EPERM on error writing to the location > + * Any other value will be considered a failure. > + */ > +#ifndef ftrace_init_nop > +static inline int ftrace_init_nop(struct module *mod, struct dyn_ftrace *rec) > +{ > + return ftrace_make_nop(mod, rec, MCOUNT_ADDR); > +} > +#endif > + Now that ftrace_init_nop is also an arch implemented function so it may be added in Documentation/trace/ftrace-design.rst along with ftrace_make_nop. In general also, adding some description about patchable-function-entry in kernel Documentation will be useful. Thanks, Amit Daniel > /** > * ftrace_make_call - convert a nop call site into a call to addr > - * @rec: the mcount call site record > + * @rec: the call site record (e.g. mcount/fentry) > * @addr: the address that the call site should call > * > * This is a very sensitive operation and great care needs > @@ -545,7 +574,7 @@ extern int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr); > #ifdef CONFIG_DYNAMIC_FTRACE_WITH_REGS > /** > * ftrace_modify_call - convert from one addr to another (no nop) > - * @rec: the mcount call site record > + * @rec: the call site record (e.g. mcount/fentry) > * @old_addr: the address expected to be currently called to > * @addr: the address to change to > * > diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c > index f296d89be757..5259d4dea675 100644 > --- a/kernel/trace/ftrace.c > +++ b/kernel/trace/ftrace.c > @@ -2494,14 +2494,14 @@ struct dyn_ftrace *ftrace_rec_iter_record(struct ftrace_rec_iter *iter) > } > > static int > -ftrace_code_disable(struct module *mod, struct dyn_ftrace *rec) > +ftrace_nop_initialize(struct module *mod, struct dyn_ftrace *rec) > { > int ret; > > if (unlikely(ftrace_disabled)) > return 0; > > - ret = ftrace_make_nop(mod, rec, MCOUNT_ADDR); > + ret = ftrace_init_nop(mod, rec); > if (ret) { > ftrace_bug_type = FTRACE_BUG_INIT; > ftrace_bug(ret, rec); > @@ -2943,7 +2943,7 @@ static int ftrace_update_code(struct module *mod, struct ftrace_page *new_pgs) > * to the NOP instructions. > */ > if (!__is_defined(CC_USING_NOP_MCOUNT) && > - !ftrace_code_disable(mod, p)) > + !ftrace_nop_initialize(mod, p)) > break; > > update_cnt++; >