linux-kernel - Re: [PATCH] selftests/ftrace: check for do_sys

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Date:   Thu, 1 Oct 2020 16:40:33 +0100
From:   Colin Ian King <colin.king@...onical.com>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     Ingo Molnar <mingo@...hat.com>, Shuah Khan <shuah@...nel.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Tom Zanussi <zanussi@...nel.org>,
        linux-kselftest@...r.kernel.org, kernel-janitors@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] selftests/ftrace: check for do_sys_openat2 in user-memory
 test

On 01/10/2020 15:44, Steven Rostedt wrote:
> On Thu,  1 Oct 2020 09:56:41 +0100
> Colin King <colin.king@...onical.com> wrote:
> 
>> From: Colin Ian King <colin.king@...onical.com>
>>
>> More recent libc implementations are now using openat/openat2 system
>> calls so also add do_sys_openat2 to the tracing so that the test
>> passes on these systems because do_sys_open may not be called.
>>
>> Signed-off-by: Colin Ian King <colin.king@...onical.com>
>> ---
>>  .../testing/selftests/ftrace/test.d/kprobe/kprobe_args_user.tc  | 2 ++
>>  1 file changed, 2 insertions(+)
>>
>> diff --git a/tools/testing/selftests/ftrace/test.d/kprobe/kprobe_args_user.tc b/tools/testing/selftests/ftrace/test.d/kprobe/kprobe_args_user.tc
>> index a30a9c07290d..cf1b4c3e9e6b 100644
>> --- a/tools/testing/selftests/ftrace/test.d/kprobe/kprobe_args_user.tc
>> +++ b/tools/testing/selftests/ftrace/test.d/kprobe/kprobe_args_user.tc
>> @@ -9,6 +9,8 @@ grep -A10 "fetcharg:" README | grep -q '\[u\]<offset>' || exit_unsupported
>>  :;: "user-memory access syntax and ustring working on user memory";:
>>  echo 'p:myevent do_sys_open path=+0($arg2):ustring path2=+u0($arg2):string' \
>>  	> kprobe_events  
>> +echo 'p:myevent2 do_sys_openat2 path=+0($arg2):ustring path2=+u0($arg2):string' \
>> +	> kprobe_events
>>
> 
> This still wont work, because the rest of the code only enables the myevent
> event, and not the one you just added.

Yep, I botched this and tested the wrong fix.

> 
> Did you see this broken before, and this patch fixes it?

So this test breaks with a recent libc and support tools built against
libc.  I believe the do_sys_open is not being detected because
do_sys_openat2 is being called instead.

Not sure now of the correct way to fix this.

> 
> -- Steve
> 
>  
>>  grep myevent kprobe_events | \
>>  	grep -q 'path=+0($arg2):ustring path2=+u0($arg2):string'
>