linux-kernel - Re: [PATCH] selftests: kselftest.h: mark functions with 'noreturn'

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Date:   Fri, 29 Oct 2021 12:19:26 -0600
From:   Shuah Khan <skhan@...uxfoundation.org>
To:     Anders Roxell <anders.roxell@...aro.org>, shuah@...nel.org
Cc:     fenghua.yu@...el.com, reinette.chatre@...el.com,
        john.stultz@...aro.org, tglx@...utronix.de,
        akpm@...ux-foundation.org, nathan@...nel.org,
        ndesaulniers@...gle.com, linux-kernel@...r.kernel.org,
        linux-kselftest@...r.kernel.org, linux-mm@...ck.org,
        llvm@...ts.linux.dev, Shuah Khan <skhan@...uxfoundation.org>
Subject: Re: [PATCH] selftests: kselftest.h: mark functions with 'noreturn'

On 10/29/21 5:43 AM, Anders Roxell wrote:
> When building kselftests/capabilities the following warning shows up:
> 
> clang -O2 -g -std=gnu99 -Wall    test_execve.c -lcap-ng -lrt -ldl -o test_execve
> test_execve.c:121:13: warning: variable 'have_outer_privilege' is used uninitialized whenever 'if' condition is false [-Wsometimes-uninitialized]
>          } else if (unshare(CLONE_NEWUSER | CLONE_NEWNS) == 0) {
>                     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> test_execve.c:136:9: note: uninitialized use occurs here
>          return have_outer_privilege;
>                 ^~~~~~~~~~~~~~~~~~~~
> test_execve.c:121:9: note: remove the 'if' if its condition is always true
>          } else if (unshare(CLONE_NEWUSER | CLONE_NEWNS) == 0) {
>                 ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> test_execve.c:94:27: note: initialize the variable 'have_outer_privilege' to silence this warning
>          bool have_outer_privilege;
>                                   ^
>                                    = false
> 
> Rework so all the ksft_exit_*() functions have attribue
> '__attribute__((noreturn))' so the compiler knows that there wont be
> any return from the function. That said, without
> '__attribute__((noreturn))' the compiler warns about the above issue
> since it thinks that it will get back from the ksft_exit_skip()
> function, which it wont.
> Cleaning up the callers that rely on ksft_exit_*() return code, since
> the functions ksft_exit_*() have never returned anything.
> 
> Signed-off-by: Anders Roxell <anders.roxell@...aro.org>

Lot of changes to fix this warning. Is this necessary? I would
like to explore if there is an easier and localized change that
can fix the problem.

thanks,
-- Shuah