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 C762A15853B; Mon, 3 Mar 2025 06:36:11 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1740983771; cv=none; b=L+8/4X5Lua77SF/9kmJLUbbwKsgzOsk1os8VIgDwWpEBmnKSiGWfTJ/a0YiOOqL3i+Z8xHFXdbSwNw+V+CpPkINEBVh5VVqhxgfT5WNJ+sZeJeR0NfkR+itBgik3TBhc4Z0aienNQR8yF9XqemLOOFPIpuzEA/xyYnZqIP40hms= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1740983771; c=relaxed/simple; bh=HqvhAMtCZRjUm1Q7HW15Lf7hRzeADdKMZCORIoQCpHc=; h=Date:From:To:Cc:Subject:Message-Id:In-Reply-To:References: Mime-Version:Content-Type; b=YtrFJWFq8EwmEXMbmTy6UOOIEtsIXC2FJ1KdlXax4kM2DhdTPcj5dEcn8i8+MX7rwYIzt1rRpzL0abZPfS0EW/P53TfLbd3oLjTkHpc2X0jWNNRCTh8fMPa0aOqG2vC9++GOhGreJZxB6vewfQ1t7iMlXmI/5xnhMYPlq3RRZs0= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=PDg5OUbF; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="PDg5OUbF" Received: by smtp.kernel.org (Postfix) with ESMTPSA id E43E7C4CED6; Mon, 3 Mar 2025 06:36:09 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1740983771; bh=HqvhAMtCZRjUm1Q7HW15Lf7hRzeADdKMZCORIoQCpHc=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=PDg5OUbFhLhIGRt0iZtKwAJGKJARFmkHwRTABE4PQcFkz5oGSu5M52IvQNaRtAmN9 9D8ML9Arf8xYZcttdA+TcgpUSiwWEBA71Es+MUw0TRzeTcHaFJaj8N8yoqqkzoxK9T E27WJt4Av62moJ5tKzK5osfeQeiXVeH0HR4dGHBPPTGz3waD4Aa0vfcKi0Adh9QV1n Fm34uaEje9EpzyCQIkwUpH0P3//aJNP6ih0Wa2bZKfcqFmUyZ5M5PF08PHTWT7pZGg QEAGzW6j361Kp81iqkXpLccnQjn4Zu/r08c4QhurVA1/9/YLEMYr4N1T6AN+l1v9lC +fwUB6WtfhtaA== Date: Mon, 3 Mar 2025 15:36:07 +0900 From: Masami Hiramatsu (Google) To: Steven Rostedt Cc: Mathieu Desnoyers , linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org Subject: Re: [PATCH] tracing: probe-events: Add comments about entry data storing code Message-Id: <20250303153607.da48fad3e90a28bc8c7f50e6@kernel.org> In-Reply-To: <20250228174712.44e03694@gandalf.local.home> References: <174061715004.501424.333819546601401102.stgit@devnote2> <20250228174712.44e03694@gandalf.local.home> 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, 28 Feb 2025 17:47:12 -0500 Steven Rostedt wrote: > On Thu, 27 Feb 2025 09:45:50 +0900 > "Masami Hiramatsu (Google)" wrote: > > > From: Masami Hiramatsu (Google) > > > > Add comments about entry data storing code to __store_entry_arg() and > > traceprobe_get_entry_data_size(). These are a bit complicated because of > > building the entry data storing code and scanning it. > > > > This just add comments, no behavior change. > > > > Reported-by: Steven Rostedt > > Closes: https://lore.kernel.org/all/20250226102223.586d7119@gandalf.local.home/ > > Signed-off-by: Masami Hiramatsu (Google) > > --- > > kernel/trace/trace_probe.c | 28 ++++++++++++++++++++++++++++ > > 1 file changed, 28 insertions(+) > > > > diff --git a/kernel/trace/trace_probe.c b/kernel/trace/trace_probe.c > > index 8f58ee1e8858..2eeecb6c95ee 100644 > > --- a/kernel/trace/trace_probe.c > > +++ b/kernel/trace/trace_probe.c > > @@ -770,6 +770,10 @@ static int check_prepare_btf_string_fetch(char *typename, > > > > #ifdef CONFIG_HAVE_FUNCTION_ARG_ACCESS_API > > > > +/* > > + * Add the entry code to store the 'argnum'th parameter and return the offset > > + * in the entry data buffer where the data will be stored. > > + */ > > static int __store_entry_arg(struct trace_probe *tp, int argnum) > > { > > struct probe_entry_arg *earg = tp->entry_arg; > > @@ -793,6 +797,20 @@ static int __store_entry_arg(struct trace_probe *tp, int argnum) > > tp->entry_arg = earg; > > } > > > > + /* > > + * The entry code array is repeating the pair of > > + * [FETCH_OP_ARG(argnum)][FETCH_OP_ST_EDATA(offset of entry data buffer)] > > + * and the rest of entries are filled with [FETCH_OP_END]. > > + * > > + * To reduce the redundant function parameter fetching, we scan the entry > > + * code array to find the FETCH_OP_ARG which already fetches the 'argnum' > > + * parameter. If it doesn't match, update 'offset' to find the last > > + * offset. > > + * If we find the FETCH_OP_END without matching FETCH_OP_ARG entry, we > > + * will save the entry with FETCH_OP_ARG and FETCH_OP_ST_EDATA, and > > + * return data offset so that caller can find the data offset in the entry > > + * data buffer. > > + */ > > So I'm still not 100% sure what is happening here, but at least these > comments can help me figure it out if I spend some time gawking at the code > a bit more ;-) I think the code is a bit complicated too. I will rewrite it a bit. > > Reviewed-by: Steven Rostedt (Google) Thanks you! > > -- Steve > > > > offset = 0; > > for (i = 0; i < earg->size - 1; i++) { > > switch (earg->code[i].op) { > > @@ -826,6 +844,16 @@ int traceprobe_get_entry_data_size(struct trace_probe *tp) > > if (!earg) > > return 0; > > > > + /* > > + * earg->code[] array has an operation sequence which is run in > > + * the entry handler. > > + * The sequence stopped by FETCH_OP_END and each data stored in > > + * the entry data buffer by FETCH_OP_ST_EDATA. The FETCH_OP_ST_EDATA > > + * stores the data at the data buffer + its offset, and all data are > > + * "unsigned long" size. The offset must be increased when a data is > > + * stored. Thus we need to find the last FETCH_OP_ST_EDATA in the > > + * code array. > > + */ > > for (i = 0; i < earg->size; i++) { > > switch (earg->code[i].op) { > > case FETCH_OP_END: > -- Masami Hiramatsu (Google)