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From: John Stultz <jstultz@google.com>
Date: Thu, 11 Apr 2024 11:11:59 -0700
Message-ID: <CANDhNCoaMX7B5_SLuo-oaYD6VGdqT7vqPw2fe8ONz7AFqO22qg@mail.gmail.com>
Subject: Re: [PATCH 2/3] selftests: timers: Fix uninitialized variable warning
 in ksft_min_kernel_version
To: Nathan Chancellor <nathan@kernel.org>
Cc: LKML <linux-kernel@vger.kernel.org>, Shuah Khan <shuah@kernel.org>, 
	Anna-Maria Behnsen <anna-maria@linutronix.de>, Frederic Weisbecker <frederic@kernel.org>, 
	Thomas Gleixner <tglx@linutronix.de>, Stephen Boyd <sboyd@kernel.org>, 
	Nick Desaulniers <ndesaulniers@google.com>, Bill Wendling <morbo@google.com>, 
	Justin Stitt <justinstitt@google.com>, Oleg Nesterov <oleg@redhat.com>, 
	Andrew Morton <akpm@linux-foundation.org>, Edward Liaw <edliaw@google.com>, 
	Carlos Llamas <cmllamas@google.com>, kernel-team@android.com, 
	linux-kselftest@vger.kernel.org
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On Thu, Apr 11, 2024 at 8:39=E2=80=AFAM Nathan Chancellor <nathan@kernel.or=
g> wrote:
> On Wed, Apr 10, 2024 at 04:26:29PM -0700, John Stultz wrote:
> > Building with clang, I see the following warning:
> >
> > In file included from posix_timers.c:17:
> > ./../kselftest.h:398:6: warning: variable 'major' is used uninitialized=
 whenever '||' condition is true [-Wsometimes-uninitialized]
> >         if (uname(&info) || sscanf(info.release, "%u.%u.", &major, &min=
or) !=3D 2)
> >             ^~~~~~~~~~~~
> > ./../kselftest.h:401:9: note: uninitialized use occurs here
> >         return major > min_major || (major =3D=3D min_major && minor >=
=3D min_minor);
> >                ^~~~~
> >
> > This is a bit of a red-herring as if the uname() call did fail,
> > we would hit ksft_exit_fail_msg() which should exit.
>
> Correct, although we have not really conveyed that to the compiler,
> right? exit() is noreturn, which means all functions that call exit()
> unconditionally are also noreturn, such as ksft_exit_fail_msg(). LLVM
> will figure this out once it performs inlining and such but that happens
> after clang's static analysis phase that this warning occurs in. I think
> a better solution would be to add __noreturn to the functions in
> tools/testing/selftests/kselftest.h that call exit(), so that the
> compiler is aware of this through all pipeline phases, maybe something
> like this? It resolves the wawrning for me.

No objection from me if this is the better approach.

Would you send that patch out?

thanks
-john