linux-kernel - Re: [PATCH] tracing/selftests: Ignore __pfx

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Date:   Wed, 8 Feb 2023 19:05:08 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Linux Trace Kernel <linux-trace-kernel@...r.kernel.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Shuah Khan <shuah@...nel.org>,
        Shuah Khan <skhan@...uxfoundation.org>
Subject: Re: [PATCH] tracing/selftests: Ignore __pfx_ symbols in kprobe test

On Tue, Feb 07, 2023 at 01:54:02PM -0500, Steven Rostedt wrote:
> On Tue, 7 Feb 2023 13:51:47 -0500
> Steven Rostedt <rostedt@...dmis.org> wrote:
> 
> > From: "Steven Rostedt (Google)" <rostedt@...dmis.org>
> > 
> > The kprobe probepoint.tc test started failing because of the added __pfx_
> > symbols that were added because of -fpatchable-function-entry=X,Y causing
> > unwinders to see them as part of the previous functions. But kprobes can
> > not be added on top of them. The selftest looks for tracefs_create_dir and
> > picks it and the previous and following functions to add at their address.
> > This caused it to include __pfx_tracefs_create_dir which is invalid to
> > attach a kprobe to and caused the test to fail.
> > 
> > Fixes: 9f2899fe36a62 ("objtool: Add option to generate prefix symbols")
> > Signed-off-by: Steven Rostedt (Google) <rostedt@...dmis.org>
> 
> This is assuming that kprobes can not be added on top of these. But another
> solution could be to have kprobes just pick the function the __pfx_ is for.
> Would that be a better solution?

Simply refusing them is simplest. I don't see a compelling reason to
make this complicated.