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 2F129CCF9F5 for ; Wed, 6 Sep 2023 00:28:55 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S238055AbjIFA24 (ORCPT ); Tue, 5 Sep 2023 20:28:56 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:50336 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229469AbjIFA2z (ORCPT ); Tue, 5 Sep 2023 20:28:55 -0400 Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 434E21B7; Tue, 5 Sep 2023 17:28:52 -0700 (PDT) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 09624C433C7; Wed, 6 Sep 2023 00:28:47 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1693960131; bh=aZ3H8HxXEtYnYpl+2MkB0U0M6BrNOKKNBdJveQb22C0=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=ZSJODVKirg4FCXqk252o/1CZ7i7f0IFDds/anCm2fMWhIAbWnJopScVB519+xey0V yFqeMxgayVClMAdGcqi/I4RM9881S9O02430r8EA98ON2KzJ4cyKtMrohmo3AQv8OE kTo/2gO68vga5xt88u+cxCOg7pZLMbeVpxaxU9IQEpEwbhLTKkzjg3bzr7Lxk1wic8 /XBq8UeIYcIh3nceupbpVBHsMnc0+8p5fGBRQAW8bnwULGx8g8AYAJEskfPC+rrTGf 314n7UoJvn3KlrEATWo1keIqZmx7fMiiecNsoeWrAECZ66o/KcthEmVKcvmSNLAGNY QnH54swXevwLw== Date: Wed, 6 Sep 2023 09:28:45 +0900 From: Masami Hiramatsu (Google) To: Andrii Nakryiko Cc: Alexei Starovoitov , Steven Rostedt , Florent Revest , 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: [PATCH v4 5/9] ftrace: Add ftrace_partial_regs() for converting ftrace_regs to pt_regs Message-Id: <20230906092845.ce5ff494d379c73cef58cb08@kernel.org> In-Reply-To: References: <169280372795.282662.9784422934484459769.stgit@devnote2> <169280378611.282662.4078983611827223131.stgit@devnote2> <20230826105632.e3eb35fc69a65ebaf11c7741@kernel.org> 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-kernel@vger.kernel.org On Tue, 5 Sep 2023 12:50:28 -0700 Andrii Nakryiko wrote: > On Fri, Aug 25, 2023 at 6:56 PM Masami Hiramatsu wrote: > > > > On Fri, 25 Aug 2023 14:49:48 -0700 > > Andrii Nakryiko wrote: > > > > > On Wed, Aug 23, 2023 at 8:16 AM Masami Hiramatsu (Google) > > > wrote: > > > > > > > > From: Masami Hiramatsu (Google) > > > > > > > > Add ftrace_partial_regs() which converts the ftrace_regs to pt_regs. > > > > If the architecture defines its own ftrace_regs, this copies partial > > > > registers to pt_regs and returns it. If not, ftrace_regs is the same as > > > > pt_regs and ftrace_partial_regs() will return ftrace_regs::regs. > > > > > > > > Signed-off-by: Masami Hiramatsu (Google) > > > > Acked-by: Florent Revest > > > > --- > > > > Changes in v3: > > > > - Fix to use pt_regs::regs instead of x. > > > > - Return ftrace_regs::regs forcibly if HAVE_PT_REGS_COMPAT_FTRACE_REGS=y. > > > > - Fix typo. > > > > - Fix to copy correct registers to the pt_regs on arm64. > > > > Changes in v4: > > > > - Change the patch order in the series so that fprobe event can use this. > > > > --- > > > > arch/arm64/include/asm/ftrace.h | 11 +++++++++++ > > > > include/linux/ftrace.h | 17 +++++++++++++++++ > > > > 2 files changed, 28 insertions(+) > > > > > > > > diff --git a/arch/arm64/include/asm/ftrace.h b/arch/arm64/include/asm/ftrace.h > > > > index ab158196480c..5ad24f315d52 100644 > > > > --- a/arch/arm64/include/asm/ftrace.h > > > > +++ b/arch/arm64/include/asm/ftrace.h > > > > @@ -137,6 +137,17 @@ ftrace_override_function_with_return(struct ftrace_regs *fregs) > > > > fregs->pc = fregs->lr; > > > > } > > > > > > > > +static __always_inline struct pt_regs * > > > > +ftrace_partial_regs(const struct ftrace_regs *fregs, struct pt_regs *regs) > > > > +{ > > > > + memcpy(regs->regs, fregs->regs, sizeof(u64) * 9); > > > > + regs->sp = fregs->sp; > > > > + regs->pc = fregs->pc; > > > > + regs->regs[29] = fregs->fp; > > > > + regs->regs[30] = fregs->lr; > > > > > > I see that orig_x0 from pt_regs is used on arm64 to get syscall's > > > first parameter. And it seems like this ftrace_regs to pt_regs > > > conversion doesn't touch orig_x0 at all. Is it maintained/preserved > > > somewhere else, or will we lose the ability to get the first syscall's > > > argument? > > > > Thanks for checking it! > > > > Does BPF uses kprobe probe to trace syscalls? Since we have raw_syscall > > trace events, no need to use kprobe to do that. (and I don't recommend to > > use kprobe to do such fixed event) > > Yeah, lots of tools and projects actually trace syscalls with kprobes. > I don't think there is anything we can do to quickly change that, so > we should avoid breaking all of them. Yes, ah, but anyway, this is the fprobe case, not kprobe. Do you use multi_kprobes for tracing syscalls? Jiri, do you know when the multi-kprobe feature is used? Is that used implicitly or explicitly? > > So getting back to my original question, is it possible to preserve orig_x0? I'm curious that the orig_x0 is stored to pt_regs of the kprobes itself because it is not a real register. There is no way to access it. You can use regs->x0 instead of that. I think the orig_x0 is stored when the syscall happened because it has another user pt_regs on the stack, right? If so, we don't need to save orig_x0 on the pt_regs for kprobes, but user can dig the stack to find the orig_x0. Here the arm64, syscall entry handler, static void el0_svc_common(struct pt_regs *regs, int scno, int sc_nr, const syscall_fn_t syscall_table[]) { unsigned long flags = read_thread_flags(); regs->orig_x0 = regs->regs[0]; regs->syscallno = scno; (BTW, it seems syscall number is saved on regs->syscallno.) It seems that if you probe the el0_svc_common() for tracing syscall, all you need is tracing $arg1 == pt_regs and $arg2 == syscall number. Thank you, > > > > > > > > > Looking at libbpf's bpf_tracing.h, other than orig_x0, I think all the > > > other registers are still preserved, so this seems to be the only > > > potential problem. > > > > Great! > > > > Thank you, > > > > > > > > > > > > + return regs; > > > > +} > > > > + > > > > int ftrace_regs_query_register_offset(const char *name); > > > > > > > > int ftrace_init_nop(struct module *mod, struct dyn_ftrace *rec); > > > > diff --git a/include/linux/ftrace.h b/include/linux/ftrace.h > > > > index c0a42d0860b8..a6ed2aa71efc 100644 > > > > --- a/include/linux/ftrace.h > > > > +++ b/include/linux/ftrace.h > > > > @@ -165,6 +165,23 @@ static __always_inline struct pt_regs *ftrace_get_regs(struct ftrace_regs *fregs > > > > return arch_ftrace_get_regs(fregs); > > > > } > > > > > > > > +#if !defined(CONFIG_HAVE_DYNAMIC_FTRACE_WITH_ARGS) || \ > > > > + defined(CONFIG_HAVE_PT_REGS_TO_FTRACE_REGS_CAST) > > > > + > > > > +static __always_inline struct pt_regs * > > > > +ftrace_partial_regs(struct ftrace_regs *fregs, struct pt_regs *regs) > > > > +{ > > > > + /* > > > > + * If CONFIG_HAVE_PT_REGS_TO_FTRACE_REGS_CAST=y, ftrace_regs memory > > > > + * layout is the same as pt_regs. So always returns that address. > > > > + * Since arch_ftrace_get_regs() will check some members and may return > > > > + * NULL, we can not use it. > > > > + */ > > > > + return &fregs->regs; > > > > +} > > > > + > > > > +#endif /* !CONFIG_HAVE_DYNAMIC_FTRACE_WITH_ARGS || CONFIG_HAVE_PT_REGS_TO_FTRACE_REGS_CAST */ > > > > + > > > > /* > > > > * When true, the ftrace_regs_{get,set}_*() functions may be used on fregs. > > > > * Note: this can be true even when ftrace_get_regs() cannot provide a pt_regs. > > > > > > > > > > > > > > -- > > Masami Hiramatsu (Google) -- Masami Hiramatsu (Google)