linux-kernel - Re: [PATCH v2 2/2] selftests/ftrace: Add new test case which checks for optimized probes

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Date:   Tue, 25 Apr 2023 09:10:39 +0900
From:   Masami Hiramatsu (Google) <mhiramat@...nel.org>
To:     Akanksha J N <akanksha@...ux.ibm.com>
Cc:     linux-kselftest@...r.kernel.org,
        linux-trace-kernel@...r.kernel.org, linux-kernel@...r.kernel.org,
        rostedt@...dmis.org, mhiramat@...nel.org, shuah@...nel.org,
        naveen.n.rao@...ux.ibm.com
Subject: Re: [PATCH v2 2/2] selftests/ftrace: Add new test case which checks
 for optimized probes

On Tue, 18 Apr 2023 15:25:57 +0530
Akanksha J N <akanksha@...ux.ibm.com> wrote:

> Add new test case kprobe_opt_types.tc which enables and checks
> if each probe has been optimized in order to test potential issues with
> optimized probes.
> The '|| continue' is added with the echo statement to ignore errors that
> are caused by trying to add kprobes to non probeable lines and continue
> with the test.
> Signed-off-by: Akanksha J N <akanksha@...ux.ibm.com>
> ---
>  .../ftrace/test.d/kprobe/kprobe_opt_types.tc  | 34 +++++++++++++++++++
>  1 file changed, 34 insertions(+)
>  create mode 100644 tools/testing/selftests/ftrace/test.d/kprobe/kprobe_opt_types.tc
> 
> diff --git a/tools/testing/selftests/ftrace/test.d/kprobe/kprobe_opt_types.tc b/tools/testing/selftests/ftrace/test.d/kprobe/kprobe_opt_types.tc
> new file mode 100644
> index 000000000000..54e4800b8a13
> --- /dev/null
> +++ b/tools/testing/selftests/ftrace/test.d/kprobe/kprobe_opt_types.tc
> @@ -0,0 +1,34 @@
> +#!/bin/sh
> +# SPDX-License-Identifier: GPL-2.0-or-later
> +# Copyright (C) 2023 Akanksha J N, IBM corporation
> +# description: Register/unregister optimized probe
> +# requires: kprobe_events
> +
> +case `uname -m` in
> +x86_64)
> +;;
> +arm*)
> +;;
> +ppc*)
> +;;
> +*)
> +  echo "Please implement other architecture here"
> +  exit_unsupported
> +esac
> +
> +DEFAULT=$(cat /proc/sys/debug/kprobes-optimization)
> +echo 1 > /proc/sys/debug/kprobes-optimization
> +for i in `seq 0 255`; do
> +        echo  "p:testprobe $FUNCTION_FORK+${i}" > kprobe_events || continue
> +        echo 1 > events/kprobes/enable || continue
> +        (echo "forked")
> +        PROBE_TYPE=$(cat /sys/kernel/debug/kprobes/list | grep $FUNCTION_FORK | awk '{print $4}' | awk '{print substr($0,2,length($0)-2)}')

I think we can make it simply;

PROBE=$(grep $FUNCTION_FORK /sys/kernel/debug/kprobes/list)

> +        echo 0 > events/kprobes/enable
> +        echo > kprobe_events
> +        if [ $PROBE_TYPE = "OPTIMIZED" ]; then

and

if echo $PROBE | grep -q OPTIMIZED; then

> +                echo "$DEFAULT" >  /proc/sys/debug/kprobes-optimization
> +                exit_pass
> +        fi
> +done
> +echo "$DEFAULT" >  /proc/sys/debug/kprobes-optimization
> +echo "Done"

Hmm, this test does NOT return any error. It always returns success.
I understand that optimization may not be possible within 256 bytes
from the beginning of the function. In that case, you can return
"unresolved", and not echoing "Done" but the reason why it is
unresolved.

Thank you,

> -- 
> 2.31.1
> 


-- 
Masami Hiramatsu (Google) <mhiramat@...nel.org>