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Date:   Tue, 25 Apr 2023 10:58:30 +0530
From:   "Naveen N. Rao" <naveen.n.rao@linux.ibm.com>
Subject: Re: [PATCH v2 2/2] selftests/ftrace: Add new test case which checks
 for optimized probes
To:     Akanksha J N <akanksha@linux.ibm.com>,
        Masami Hiramatsu <mhiramat@kernel.org>
Cc:     linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org,
        linux-trace-kernel@vger.kernel.org, rostedt@goodmis.org,
        shuah@kernel.org
References: <20230418095557.19061-1-akanksha@linux.ibm.com>
        <20230418095557.19061-3-akanksha@linux.ibm.com>
        <20230425091039.9fd523dfdf7be5e800bac4fe@kernel.org>
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Masami Hiramatsu wrote:
> On Tue, 18 Apr 2023 15:25:57 +0530
> Akanksha J N <akanksha@linux.ibm.com> wrote:
>=20
>> 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@linux.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
>>=20
>> diff --git a/tools/testing/selftests/ftrace/test.d/kprobe/kprobe_opt_typ=
es.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=3D$(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 || cont=
inue
>> +        echo 1 > events/kprobes/enable || continue
>> +        (echo "forked")
>> +        PROBE_TYPE=3D$(cat /sys/kernel/debug/kprobes/list | grep $FUNCT=
ION_FORK | awk '{print $4}' | awk '{print substr($0,2,length($0)-2)}')
>=20
> I think we can make it simply;
>=20
> PROBE=3D$(grep $FUNCTION_FORK /sys/kernel/debug/kprobes/list)
>=20
>> +        echo 0 > events/kprobes/enable
>> +        echo > kprobe_events
>> +        if [ $PROBE_TYPE =3D "OPTIMIZED" ]; then
>=20
> and
>=20
> if echo $PROBE | grep -q OPTIMIZED; then
>=20
>> +                echo "$DEFAULT" >  /proc/sys/debug/kprobes-optimization
>> +                exit_pass
>> +        fi
>> +done
>> +echo "$DEFAULT" >  /proc/sys/debug/kprobes-optimization
>> +echo "Done"
>=20
> Hmm, this test does NOT return any error. It always returns success.

Good catch!

> I understand that optimization may not be possible within 256 bytes
> from the beginning of the function.

Is that true in practice? Looking at x86 and ppc64le, it looks like we=20
will almost always be able to optimize at least one of the instructions=20
within the first 256 bytes of kernel_clone(). That's one of the primary=20
purposes of this test.

Are there valid reasons why we may not be able to optimize instructions?

> In that case, you can return
> "unresolved", and not echoing "Done" but the reason why it is
> unresolved.


- Naveen