From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 4D4DF4405; Sat, 11 Nov 2023 02:24:39 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="L9DUrkLZ" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 7965EC433C8; Sat, 11 Nov 2023 02:24:36 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1699669479; bh=aIdbMSq84A3+20V/l6jBNeX8gsHkBhcldmzU2v6Ubf0=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=L9DUrkLZHHyvDa1HtWTbqbTpW2YUdXB0mEO3QfEPr4+9o5+EunMDmUuAnon+jHgpS AKAuzQqzVRoUSgWMrrrcJdJcvWM5REgA76ujsqQtsZ4bMO0ADwUQkRM8YZkRMEsjGg 0kdAGA8g6hEevMAY1M7P09fWM/XxwBLzFG8ABNkcEWGZxTOZ68CLl76U0SZO2oKll6 tBYtOY4HhGEFj0lJVg6VaJMtajPSwB7/TO4DJM+LeaWQSYv6mR+6wYUPe3xfy6P7T1 7R5rBK1Wbg5IIEZmezub2+PAGq/zVkcJtAfFzbi1Z9R1SGSl1QKu+Rns6MljqupYLK cErb0ls6spKxw== Date: Sat, 11 Nov 2023 11:24:34 +0900 From: Masami Hiramatsu (Google) To: Mark Rutland 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 , Peter Zijlstra , Thomas Gleixner , Guo Ren Subject: Re: [RFC PATCH v2 01/31] tracing: Add a comment about ftrace_regs definition Message-Id: <20231111112434.2e8d76e59e6f5ed4f166ff6b@kernel.org> In-Reply-To: References: <169945345785.55307.5003201137843449313.stgit@devnote2> <169945347160.55307.1488323435914144870.stgit@devnote2> <20231109081452.fd6e091df9df1bc7c5ced38b@kernel.org> X-Mailer: Sylpheed 3.8.0beta1 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Precedence: bulk X-Mailing-List: linux-trace-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit On Fri, 10 Nov 2023 11:11:31 +0000 Mark Rutland wrote: > On Thu, Nov 09, 2023 at 08:14:52AM +0900, Masami Hiramatsu wrote: > > On Wed, 8 Nov 2023 23:24:32 +0900 > > "Masami Hiramatsu (Google)" wrote: > > > > > From: Masami Hiramatsu (Google) > > > > > > To clarify what will be expected on ftrace_regs, add a comment to the > > > architecture independent definition of the ftrace_regs. > > > > > > Signed-off-by: Masami Hiramatsu (Google) > > > --- > > > Changes in v2: > > > - newly added. > > > --- > > > include/linux/ftrace.h | 25 +++++++++++++++++++++++++ > > > 1 file changed, 25 insertions(+) > > > > > > diff --git a/include/linux/ftrace.h b/include/linux/ftrace.h > > > index e8921871ef9a..b174af91d8be 100644 > > > --- a/include/linux/ftrace.h > > > +++ b/include/linux/ftrace.h > > > @@ -118,6 +118,31 @@ extern int ftrace_enabled; > > > > > > #ifndef CONFIG_HAVE_DYNAMIC_FTRACE_WITH_ARGS > > > > > > +/** > > > + * ftrace_regs - ftrace partial/optimal register set > > > + * > > > + * ftrace_regs represents a group of registers which is used at the > > > + * function entry and exit. There are three types of registers. > > > + * > > > + * - Registers for passing the parameters to callee, including the stack > > > + * pointer. (e.g. rcx, rdx, rdi, rsi, r8, r9 and rsp on x86_64) > > > + * - Registers for passing the return values to caller. > > > + * (e.g. rax and rdx on x86_64) > > > + * - Registers for hooking the function return including the frame pointer > > > + * (the frame pointer is architecture/config dependent) > > > + * (e.g. rbp and rsp for x86_64) > > > > Oops, I found the program counter/instruction pointer must be saved too. > > This is used for live patching. One question is that if the IP is modified > > at the return handler, what should we do? Return to the specified address? > > I'm a bit confused here; currently we use fgraph_ret_regs for function returns, > are we going to replace that with ftrace_regs? Yes. It is limited and does not have APIs compatibility. > > I think it makes sense for the PC/IP to be the address the return handler will > eventually return to (and hence allowing it to be overridden), but that does > mean we'll need to go recover the return address *before* we invoke any return > handlers. The actual return address has been recovered from shadow stack at first, and callback the handlers. See __ftrace_return_to_handler() and ftrace_pop_return_trace(). So it is easy to set it to the ftrace_regs :) Thank you! > > Thanks, > Mark. -- Masami Hiramatsu (Google)