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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 0CD25C636D4 for ; Thu, 2 Feb 2023 15:54:49 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232580AbjBBPyr (ORCPT ); Thu, 2 Feb 2023 10:54:47 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:56278 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231695AbjBBPyo (ORCPT ); Thu, 2 Feb 2023 10:54:44 -0500 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id 110D0677A2; Thu, 2 Feb 2023 07:54:38 -0800 (PST) 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 F3FAFC14; Thu, 2 Feb 2023 07:55:19 -0800 (PST) Received: from FVFF77S0Q05N.cambridge.arm.com (FVFF77S0Q05N.cambridge.arm.com [10.1.27.141]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id DD3763F64C; Thu, 2 Feb 2023 07:54:35 -0800 (PST) Date: Thu, 2 Feb 2023 15:54:33 +0000 From: Mark Rutland To: Florent Revest Cc: linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org, bpf@vger.kernel.org, catalin.marinas@arm.com, will@kernel.org, rostedt@goodmis.org, mhiramat@kernel.org, ast@kernel.org, daniel@iogearbox.net, andrii@kernel.org, kpsingh@kernel.org, jolsa@kernel.org, xukuohai@huaweicloud.com Subject: Re: [PATCH 5/8] ftrace: Make DIRECT_CALLS work WITH_ARGS and !WITH_REGS Message-ID: References: <20230201163420.1579014-1-revest@chromium.org> <20230201163420.1579014-6-revest@chromium.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230201163420.1579014-6-revest@chromium.org> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Feb 01, 2023 at 05:34:17PM +0100, Florent Revest wrote: > Direct called trampolines can be called in two ways: > - either from the ftrace callsite. In this case, they do not access any > struct ftrace_regs nor pt_regs > - Or, if a ftrace ops is also attached, from the end of a ftrace > trampoline. In this case, the call_direct_funcs ops is in charge of > setting the direct call trampoline's address in a struct ftrace_regs > > Since "ftrace: pass fregs to arch_ftrace_set_direct_caller()", the later > case no longer requires a full pt_regs. Minor nit, but could we please have the commit ID, e.g. | Since commit: | | 9705bc70960459ae ("ftrace: pass fregs to arch_ftrace_set_direct_caller()") | | The latter case no longer requires a full pt_regs. > It only needs a struct > ftrace_regs so DIRECT_CALLS can work with both WITH_ARGS or WITH_REGS. > With architectures like arm64 already abandoning WITH_REGS in favor of > WITH_ARGS, it's important to have DIRECT_CALLS work WITH_ARGS only. > > Signed-off-by: Florent Revest > --- > kernel/trace/Kconfig | 2 +- > kernel/trace/ftrace.c | 2 +- > 2 files changed, 2 insertions(+), 2 deletions(-) > > diff --git a/kernel/trace/Kconfig b/kernel/trace/Kconfig > index 5df427a2321d..4496a7c69810 100644 > --- a/kernel/trace/Kconfig > +++ b/kernel/trace/Kconfig > @@ -257,7 +257,7 @@ config DYNAMIC_FTRACE_WITH_REGS > > config DYNAMIC_FTRACE_WITH_DIRECT_CALLS > def_bool y > - depends on DYNAMIC_FTRACE_WITH_REGS > + depends on DYNAMIC_FTRACE_WITH_REGS || DYNAMIC_FTRACE_WITH_ARGS > depends on HAVE_DYNAMIC_FTRACE_WITH_DIRECT_CALLS > > config DYNAMIC_FTRACE_WITH_CALL_OPS > diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c > index b0426de11c45..73b6f6489ba1 100644 > --- a/kernel/trace/ftrace.c > +++ b/kernel/trace/ftrace.c > @@ -5282,7 +5282,7 @@ static LIST_HEAD(ftrace_direct_funcs); > > static int register_ftrace_function_nolock(struct ftrace_ops *ops); > > -#define MULTI_FLAGS (FTRACE_OPS_FL_DIRECT | FTRACE_OPS_FL_SAVE_REGS) > +#define MULTI_FLAGS (FTRACE_OPS_FL_DIRECT) Unfortunately, I think this is broken for architectures where: * DYNAMIC_FTRACE_WITH_DIRECT_CALLS=y * DYNAMIC_FTRACE_WITH_REGS=y * DYNAMIC_FTRACE_WITH_ARGS=n ... since those might pass a NULL ftrace_regs around, and so when using the list ops arch_ftrace_set_direct_caller() might blow up accessing an element of ftrace_regs. It looks like 32-bit x86 is the only case with that combination, and its ftrace_caller implementation passes a NULL regs, so I reckon that'll blow up. However, it looks like there aren't any FTRACE_DIRECT samples wired up for 32-bit x86, so I'm not aware of a test case we can use. We could make the FTRACE_OPS_FL_SAVE_REGS flag conditional, or we could implement DYNAMIC_FTRACE_WITH_ARGS for 32-bit x86 and have DYNAMIC_FTRACE_WITH_DIRECT_CALLS depend solely on that. Thanks, Mark.