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 BD99DC0015E for ; Tue, 1 Aug 2023 15:21:04 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234928AbjHAPVE (ORCPT ); Tue, 1 Aug 2023 11:21:04 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:44578 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234942AbjHAPVA (ORCPT ); Tue, 1 Aug 2023 11:21:00 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [IPv6:2604:1380:4641:c500::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 7ED5F2107; Tue, 1 Aug 2023 08:20:41 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id D27EF615DE; Tue, 1 Aug 2023 15:20:39 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 76E81C433C7; Tue, 1 Aug 2023 15:20:38 +0000 (UTC) Date: Tue, 1 Aug 2023 11:20:36 -0400 From: Steven Rostedt To: "Masami Hiramatsu (Google)" Cc: Alexei Starovoitov , linux-trace-kernel@vger.kernel.org, LKML , Martin KaFai Lau , bpf , Sven Schnelle , Alexei Starovoitov Subject: Re: [PATCH v4 3/9] bpf/btf: Add a function to search a member of a struct/union Message-ID: <20230801112036.0d4ee60d@gandalf.local.home> In-Reply-To: <20230802000228.158f1bd605e497351611739e@kernel.org> References: <169078860386.173706.3091034523220945605.stgit@devnote2> <169078863449.173706.2322042687021909241.stgit@devnote2> <20230801085724.9bb07d2c82e5b6c6a6606848@kernel.org> <20230802000228.158f1bd605e497351611739e@kernel.org> X-Mailer: Claws Mail 3.19.1 (GTK+ 2.24.33; x86_64-pc-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-trace-kernel@vger.kernel.org On Wed, 2 Aug 2023 00:02:28 +0900 Masami Hiramatsu (Google) wrote: > > If it diverges from that it's a big issue for bpf. > > We'd have to remove all of fprobe usage. > > I could be missing something, of course. > > Yes, so that's the discussion point. At first, I will disable fprobe on BPF > if ftrace_regs is not compatible with pt_regs, but eventually it should be > handled to support arm64. I believe BPF can do it since ftrace can do. Note, for FYI let me give you a little history of where ftrace_regs came from. When I realized that all function tracing had to save all the registers that represent the arguments of a function as well as the stack pointer, I wanted to change the non FTRACE_WITH_REGS to be able to have access to those registers. This is where FTRACE_WITH_ARGS came from. My first attempt was to pass a pt_regs that was partially filled, with only the registers required for the arguments. But the x86 maintainers NACK'd that. They refused to allow a partially filled pt_regs as that could cause bugs in the future when a user may assume that the pt_regs is filled but is not. The solution was to come up with ftrace_regs, which just means it has all the registers to extract the arguments of a function and nothing more. Most implementations just have a partially filled pt_regs within it, but an API needs to be used to get to the argument values. When you say BPF uses pt_regs, is the pt_regs full or does it get passed a partially filled structure? For fast function entry, ftrace_regs is what should be used if the pt_regs is not filled. As it is only for use for function entry. It supplies all regs and stack pointer to get to all the arguments. -- Steve