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 29A61C77B60 for ; Thu, 23 Mar 2023 16:35:00 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231388AbjCWQe6 (ORCPT ); Thu, 23 Mar 2023 12:34:58 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:52514 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231775AbjCWQea (ORCPT ); Thu, 23 Mar 2023 12:34:30 -0400 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id 582B538B47 for ; Thu, 23 Mar 2023 09:33:05 -0700 (PDT) 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 EF29D2F4; Thu, 23 Mar 2023 09:33:38 -0700 (PDT) Received: from FVFF77S0Q05N.cambridge.arm.com (FVFF77S0Q05N.cambridge.arm.com [10.1.31.167]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id F2E0F3F766; Thu, 23 Mar 2023 09:32:53 -0700 (PDT) Date: Thu, 23 Mar 2023 16:32:51 +0000 From: Mark Rutland To: Steven Rostedt Cc: linux-kernel@vger.kernel.org, mhiramat@kernel.org, "Jose E. Marchesi" , Nick Desaulniers Subject: Re: [PATCH] tracepoint: Fix CFI failures with tp_stub_func Message-ID: References: <20230323114012.2162285-1-mark.rutland@arm.com> <20230323085321.0f8d1b98@gandalf.local.home> <20230323122650.5a1f2db7@gandalf.local.home> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230323122650.5a1f2db7@gandalf.local.home> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Mar 23, 2023 at 12:26:50PM -0400, Steven Rostedt wrote: > On Thu, 23 Mar 2023 08:53:21 -0400 > Steven Rostedt wrote: > > > > --- a/include/linux/tracepoint.h > > > +++ b/include/linux/tracepoint.h > > > @@ -303,6 +303,7 @@ static inline struct tracepoint *tracepoint_ptr_deref(tracepoint_ptr_t *p) > > > __section("__tracepoints_strings") = #_name; \ > > > extern struct static_call_key STATIC_CALL_KEY(tp_func_##_name); \ > > > int __traceiter_##_name(void *__data, proto); \ > > > + void __tracestub_##_name(void *, proto); \ > > > struct tracepoint __tracepoint_##_name __used \ > > > __section("__tracepoints") = { \ > > > .name = __tpstrtab_##_name, \ > > > @@ -310,6 +311,7 @@ static inline struct tracepoint *tracepoint_ptr_deref(tracepoint_ptr_t *p) > > > .static_call_key = &STATIC_CALL_KEY(tp_func_##_name), \ > > > .static_call_tramp = STATIC_CALL_TRAMP_ADDR(tp_func_##_name), \ > > > .iterator = &__traceiter_##_name, \ > > > + .stub = &__tracestub_##_name, \ > > > .regfunc = _reg, \ > > > .unregfunc = _unreg, \ > > > .funcs = NULL }; \ > > > @@ -330,6 +332,9 @@ static inline struct tracepoint *tracepoint_ptr_deref(tracepoint_ptr_t *p) > > > } \ > > > return 0; \ > > > } \ > > > + void __tracestub_##_name(void *__data, proto) \ > > > + { \ > > > + } \ > > > > I purposely did not do this because this adds over a thousand stub > > functions! It adds one for *every* tracepoint (and that is a superset of > > trace events). > > And the commit that added this code: > > befe6d946551 ("tracepoint: Do not fail unregistering a probe due to memory failure") > > Has this in the change log: > > [ Note, this version does use undefined compiler behavior (assuming that > a stub function with no parameters or return, can be called by a location > that thinks it has parameters but still no return value. Static calls > do the same thing, so this trick is not without precedent. > > There's another solution that uses RCU tricks and is more complex, but > can be an alternative if this solution becomes an issue. > > Link: https://lore.kernel.org/lkml/20210127170721.58bce7cc@gandalf.local.home/ > ] FWIW, I'd be happy with that approach too -- we just happened to race with our last replies. :) Mark.