From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from lindbergh.monkeyblade.net (lindbergh.monkeyblade.net [23.128.96.19]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 1CFF6748C for ; Fri, 9 Jun 2023 08:24:58 +0000 (UTC) Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id 2E3F449E6; Fri, 9 Jun 2023 01:24:37 -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 76E2DAB6; Fri, 9 Jun 2023 01:24:59 -0700 (PDT) Received: from FVFF77S0Q05N (unknown [10.57.25.215]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id A6E033F71E; Fri, 9 Jun 2023 01:24:12 -0700 (PDT) Date: Fri, 9 Jun 2023 09:24:10 +0100 From: Mark Rutland To: Andrii Nakryiko Cc: Steven Rostedt , Jiri Olsa , Masami Hiramatsu , Andrii Nakryiko , lkml , linux-trace-kernel@vger.kernel.org, bpf@vger.kernel.org, Jackie Liu Subject: Re: [PATCH RFC] ftrace: Show all functions with addresses in available_filter_functions_addrs Message-ID: References: <20230608212613.424070-1-jolsa@kernel.org> <20230608192748.435a1dbf@gandalf.local.home> Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: X-Spam-Status: No, score=-4.2 required=5.0 tests=BAYES_00,RCVD_IN_DNSWL_MED, SPF_HELO_NONE,SPF_NONE,T_SCC_BODY_TEXT_LINE autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on lindbergh.monkeyblade.net On Thu, Jun 08, 2023 at 04:55:40PM -0700, Andrii Nakryiko wrote: > On Thu, Jun 8, 2023 at 4:27 PM Steven Rostedt wrote: > > On Thu, 8 Jun 2023 15:43:03 -0700 Andrii Nakryiko wrote: > > > On Thu, Jun 8, 2023 at 2:26 PM Jiri Olsa wrote: > There are BPF tools that allow user to specify regex/glob of kernel > functions to attach to. This regex/glob is checked against > available_filter_functions to check which functions are traceable. All > good. But then also it's important to have corresponding memory > addresses for selected functions (for many reasons, e.g., to have > non-ambiguous and fast attachment by address instead of by name, or > for some post-processing based on captured IP addresses, etc). And > that means that now we need to also parse /proc/kallsyms and > cross-join it with data fetched from available_filter_functions. > > All this is unnecessary if avalable_filter_functions would just > provide function address in the first place. It's a huge > simplification. And saves memory and CPU. Do you need the address of the function entry-point or the address of the patch-site within the function? Those can differ, and the rec->ip address won't necessarily equal the address in /proc/kallsyms, so the pointer in /proc/kallsyms won't (always) match the address we could print for the ftrace site. On arm64, today we can have offsets of +0, +4, and +8, and within a single kernel image different functions can have different offsets. I suspect in future that we may have more potential offsets (e.g. due to changes for HW/SW CFI). Thanks, Mark.