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 C68D2C41513 for ; Wed, 9 Aug 2023 14:10:22 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232428AbjHIOKW (ORCPT ); Wed, 9 Aug 2023 10:10:22 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:50564 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229978AbjHIOKV (ORCPT ); Wed, 9 Aug 2023 10:10:21 -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 4CFF21FD7; Wed, 9 Aug 2023 07:10:18 -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 CB58663226; Wed, 9 Aug 2023 14:10:17 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id BF941C433C8; Wed, 9 Aug 2023 14:10:13 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1691590217; bh=2eEmHOtaW98wEIaTzp1lW7UBm7j4xm9z1dP/0aIC++8=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=R9HffduBuPOErEDethBZPLCgOiIDoL5ALMjPA5YwJbsIEtlphtvcF5EQ1XxOQz+T5 bge7lkcC+E9rS8ioMfGLf1kgPPAAF/qrhkbin4oikq+BCiwUYAUbdFBoijg20wyKBG EpaP3M9ZFVIjouUYix6gT0jQWzoMGJK/hY6vl4CE91QmIzkD9selukv1VTxuwaPUvD ObOWf5lLnlBwExfhxAicq1Ufi+pPDzA3eme/iNZobG+vZJmLKGnRBWttFWaaJOIZQc r4zW1yZnWwvEOSXW14L73xPPx+9Abe5gLLExjGgTryXBg1bsXCjCh3YmGUM0bt1JlS a5GhL+hIz1AsA== Date: Wed, 9 Aug 2023 23:10:11 +0900 From: Masami Hiramatsu (Google) To: Florent Revest Cc: Alexei Starovoitov , Steven Rostedt , linux-trace-kernel@vger.kernel.org, LKML , Martin KaFai Lau , bpf , Sven Schnelle , Alexei Starovoitov , Jiri Olsa , Arnaldo Carvalho de Melo , Daniel Borkmann , Alan Maguire , Mark Rutland , Peter Zijlstra , Thomas Gleixner Subject: Re: [RFC PATCH v2 1/6] fprobe: Use fprobe_regs in fprobe entry handler Message-Id: <20230809231011.b125bd68887a5659db59905e@kernel.org> In-Reply-To: References: <169139090386.324433.6412259486776991296.stgit@devnote2> <169139091575.324433.13168120610633669432.stgit@devnote2> X-Mailer: Sylpheed 3.7.0 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-trace-kernel@vger.kernel.org Hi Florent, On Wed, 9 Aug 2023 12:28:38 +0200 Florent Revest wrote: > On Mon, Aug 7, 2023 at 8:48 AM Masami Hiramatsu (Google) > wrote: > > > > From: Masami Hiramatsu (Google) > > > > This allows fprobes to be available with CONFIG_DYNAMIC_FTRACE_WITH_ARGS > > instead of CONFIG_DYNAMIC_FTRACE_WITH_REGS, then we can enable fprobe > > on arm64. > > This patch lets fprobe code build on configs WITH_ARGS and !WITH_REGS > but fprobe wouldn't run on these builds because fprobe still registers > to ftrace with FTRACE_OPS_FL_SAVE_REGS, which would fail on > !WITH_REGS. Shouldn't we also let the fprobe_init callers decide > whether they want REGS or not ? Ah, I think you meant FPROBE_EVENTS? Yes I forgot to add the dependency on it. But fprobe itself can work because fprobe just pass the ftrace_regs to the handlers. (Note that exit callback may not work until next patch) > > > static int > > kprobe_multi_link_handler(struct fprobe *fp, unsigned long fentry_ip, > > - unsigned long ret_ip, struct pt_regs *regs, > > + unsigned long ret_ip, struct ftrace_regs *fregs, > > void *data) > > { > > struct bpf_kprobe_multi_link *link; > > + struct pt_regs *regs = ftrace_get_regs(fregs); > > + > > + if (!regs) > > + return 0; > > (with the above comment addressed) this means that BPF multi_kprobe > would successfully attach on builds WITH_ARGS but the programs would > never actually run because here regs would be 0. This is a confusing > failure mode for the user. I think that if multi_kprobe won't work > (because we don't have a pt_regs conversion path yet), the user should > be notified at attachment time that they won't be getting any events. Yes, so I changed it will not be compiled in that case. @@ -2460,7 +2460,7 @@ static int __init bpf_event_init(void) fs_initcall(bpf_event_init); #endif /* CONFIG_MODULES */ -#ifdef CONFIG_FPROBE +#ifdef CONFIG_DYNAMIC_FTRACE_WITH_REGS struct bpf_kprobe_multi_link { struct bpf_link link; struct fprobe fp; > That's why I think kprobe_multi should inform fprobe_init that it > wants FTRACE_OPS_FL_SAVE_REGS and fail if that's not possible (no > trampoline for it for example) Yeah, that's another possibility, but in the previous thread we discussed and agreed to introduce the ftrace_partial_regs() which will copy the partial registers from ftrace_regs to pt_regs. Thank you, -- Masami Hiramatsu (Google)