Re: [PATCH] selftests/ftrace: check for do_sys_openat2 in user-memory test

From: Masami Hiramatsu
Date: Fri Oct 02 2020 - 03:33:01 EST


On Thu, 1 Oct 2020 16:40:33 +0100
Colin Ian King <colin.king@xxxxxxxxxxxxx> wrote:

> On 01/10/2020 15:44, Steven Rostedt wrote:
> > On Thu, 1 Oct 2020 09:56:41 +0100
> > Colin King <colin.king@xxxxxxxxxxxxx> wrote:
> >
> >> From: Colin Ian King <colin.king@xxxxxxxxxxxxx>
> >>
> >> 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@xxxxxxxxxxxxx>
> >> ---
> >> .../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.

Hmm, this actually just try to catch the user-string. So the another
function which accepts any user-string, is OK.
Let me try to use another one.

Thank you for reporting!


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


--
Masami Hiramatsu <mhiramat@xxxxxxxxxx>