linux-kernel - Re: [PATCH] selftests/ftrace: Select an existing function in kprobe

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Date:   Mon, 8 Jul 2019 16:10:29 -0300
From:   Thadeu Lima de Souza Cascardo <cascardo@...onical.com>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Shuah Khan <shuahkhan@...il.com>,
        Ingo Molnar <mingo@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH] selftests/ftrace: Select an existing function in
 kprobe_eventname test

On Fri, Mar 22, 2019 at 03:09:23PM -0400, Steven Rostedt wrote:
> From: Steven Rostedt (VMware) <rostedt@...dmis.org>
> 
> Running the ftrace selftests on the latest kernel caused the
> kprobe_eventname test to fail. It was due to the test that searches for
> a function with at "dot" in the name and adding a probe to that.
> Unfortunately, for this test, it picked:
> 
>  optimize_nops.isra.2.cold.4
> 
> Which happens to be marked as "__init", which means it no longer exists
> in the kernel! (kallsyms keeps those function names around for tracing
> purposes)
> 
> As only functions that still exist are in the
> available_filter_functions file, as they are removed when the functions
> are freed at boot or module exit, have the test search for a function
> with ".isra." in the name as well as being in the
> available_filter_functions (if the file exists).
> 

This fixes a similar problem for me.

Tested-by: Thadeu Lima de Souza Cascardo <cascardo@...onical.com>

> Signed-off-by: Steven Rostedt (VMware) <rostedt@...dmis.org>
> ---
> diff --git a/tools/testing/selftests/ftrace/test.d/kprobe/kprobe_eventname.tc b/tools/testing/selftests/ftrace/test.d/kprobe/kprobe_eventname.tc
> index 3fb70e01b1fe..3ff236719b6e 100644
> --- a/tools/testing/selftests/ftrace/test.d/kprobe/kprobe_eventname.tc
> +++ b/tools/testing/selftests/ftrace/test.d/kprobe/kprobe_eventname.tc
> @@ -24,7 +24,21 @@ test -d events/kprobes2/event2 || exit_failure
>  
>  :;: "Add an event on dot function without name" ;:
>  
> -FUNC=`grep -m 10 " [tT] .*\.isra\..*$" /proc/kallsyms | tail -n 1 | cut -f 3 -d " "`
> +find_dot_func() {
> +	if [ ! -f available_filter_functions ]; then
> +		grep -m 10 " [tT] .*\.isra\..*$" /proc/kallsyms | tail -n 1 | cut -f 3 -d " "
> +		return;
> +	fi
> +
> +	grep " [tT] .*\.isra\..*" /proc/kallsyms | cut -f 3 -d " " | while read f; do
> +		if grep -s $f available_filter_functions; then
> +			echo $f
> +			break
> +		fi
> +	done
> +}
> +
> +FUNC=`find_dot_func | tail -n 1`
>  [ "x" != "x$FUNC" ] || exit_unresolved
>  echo "p $FUNC" > kprobe_events
>  EVENT=`grep $FUNC kprobe_events | cut -f 1 -d " " | cut -f 2 -d:`