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Message-ID: <20230710233400.5aaf024e@gandalf.local.home>
Date: Mon, 10 Jul 2023 23:34:00 -0400
From: Steven Rostedt <rostedt@...dmis.org>
To: "Masami Hiramatsu (Google)" <mhiramat@...nel.org>
Cc: Dan Carpenter <dan.carpenter@...aro.org>,
linux-trace-kernel@...r.kernel.org,
LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v4 4/4] tracing/probes: Fix to record 0-length data_loc
in fetch_store_string*() if fails
On Tue, 11 Jul 2023 11:11:51 +0900
"Masami Hiramatsu (Google)" <mhiramat@...nel.org> wrote:
> --- a/kernel/trace/trace_probe_tmpl.h
> +++ b/kernel/trace/trace_probe_tmpl.h
> @@ -267,9 +267,7 @@ store_trace_args(void *data, struct trace_probe *tp, void *rec,
> if (unlikely(arg->dynamic))
> *dl = make_data_loc(maxlen, dyndata - base);
> ret = process_fetch_insn(arg->code, rec, dl, base);
> - if (unlikely(ret < 0 && arg->dynamic)) {
> - *dl = make_data_loc(0, dyndata - base);
> - } else {
> + if (unlikely(ret > 0 && arg->dynamic)) {
To match the current code, that should be:
if (likely(ret >= 0 || !arg->dynamic)) {
But I'm guessing that the original code was buggy, as the else block should
only have been processed if arg->dynamic was set? That is, it should have been:
if (arg->dynamic) {
if (unlikely(ret < 0)) {
*dl = make_data_loc(0, dyndata - base);
} else {
dyndata += ret;
maxlen -= ret;
}
}
I guess you only want to update if arg->dynamic is true (even though that
wasn't the case before :-/) But in any case, I think you want likely() and
not unlikely().
if (arg->dynamic && likely(ret > 0)) {
That is, if we only want to updated this if the arg is dynamic.
And I don't think that the arg->dynamic() should have likely/unlikely
around it, as that's determined by user space, and the kernel should not be
adding assumptions about what user space wants.
-- Steve
> dyndata += ret;
> maxlen -= ret;
> }
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