linux-kernel - Re: [PATCH RFC] selftests/rseq: fix kselftest Clang build warnings

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Date:   Mon, 11 Sep 2023 09:53:42 -0700
From:   Justin Stitt <justinstitt@...gle.com>
To:     Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        "Paul E. McKenney" <paulmck@...nel.org>,
        Boqun Feng <boqun.feng@...il.com>,
        Shuah Khan <shuah@...nel.org>,
        Nathan Chancellor <nathan@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Tom Rix <trix@...hat.com>, linux-kernel@...r.kernel.org,
        linux-kselftest@...r.kernel.org, llvm@...ts.linux.dev
Subject: Re: [PATCH RFC] selftests/rseq: fix kselftest Clang build warnings

On Sat, Sep 9, 2023 at 5:37 AM Mathieu Desnoyers
<mathieu.desnoyers@...icios.com> wrote:
>
> On 9/8/23 19:03, Justin Stitt wrote:
> > Hi,
> >
> > I am experiencing many warnings when trying to build tools/testing/selftests.
> >
> > Here's one such example from rseq tree:
> > |  param_test.c:1234:10: error: address argument to atomic operation must be a pointer to _Atomic type ('intptr_t *' (aka 'long *') invalid)
> > |   1234 |         while (!atomic_load(&args->percpu_list_ptr)) {}
> > |        |                 ^           ~~~~~~~~~~~~~~~~~~~~~~
> > |  /usr/local/google/home/justinstitt/repos/tc-build/build/llvm/final/lib/clang/18/include/stdatomic.h:140:29: note: expanded from macro 'atomic_load'
> > |    140 | #define atomic_load(object) __c11_atomic_load(object, __ATOMIC_SEQ_CST)
> > |        |                             ^                 ~~~~~~
> >
> > I added the _Atomic type in various locations to silence _all_ (10) of these
> > warnings. I'm wondering, though, perhaps the absence of these _Atomic
> > types in the first place is on purpose? Am I on the right track to fix
> > these warnings without damaging the legitimacy of the tests at hand?
> >
> > I'd like some feedback about where to go from here and if others are
> > experiencing the same issues. Thanks!
> >
> > FWIW here's my specific build incantation on Clang-18 (49d41de57896e935cd5726719c5208bce22694ae):
> > $ make LLVM=1 -j128 ARCH=x86_64 mrproper headers defconfig kselftest-merge
> > $ make LLVM=1 ARCH=x86_64 -C tools/testing/selftests
>
> I should have used the __atomic_load_n() compiler builtin rather than
> atomic_load(), mainly because it does not require the _Atomic annotation
> to each type it touches.

Would you like me to send a patch in with this change?

>
> Thanks,
>
> Mathieu
>
>
> >
> > Link: https://github.com/ClangBuiltLinux/linux/issues/1698
> > Link: https://github.com/ClangBuiltLinux/continuous-integration2/issues/61
> > Signed-off-by: Justin Stitt <justinstitt@...gle.com>
> > ---
> >   tools/testing/selftests/rseq/param_test.c | 8 ++++----
> >   1 file changed, 4 insertions(+), 4 deletions(-)
> >
> > diff --git a/tools/testing/selftests/rseq/param_test.c b/tools/testing/selftests/rseq/param_test.c
> > index bf951a490bb4..94802aeed2c6 100644
> > --- a/tools/testing/selftests/rseq/param_test.c
> > +++ b/tools/testing/selftests/rseq/param_test.c
> > @@ -356,7 +356,7 @@ struct inc_thread_test_data {
> >   };
> >
> >   struct percpu_list_node {
> > -     intptr_t data;
> > +     _Atomic intptr_t data;
> >       struct percpu_list_node *next;
> >   };
> >
> > @@ -1212,8 +1212,8 @@ static int set_signal_handler(void)
> >   /* Test MEMBARRIER_CMD_PRIVATE_RESTART_RSEQ_ON_CPU membarrier command. */
> >   #ifdef TEST_MEMBARRIER
> >   struct test_membarrier_thread_args {
> > -     int stop;
> > -     intptr_t percpu_list_ptr;
> > +     _Atomic int stop;
> > +     _Atomic intptr_t percpu_list_ptr;
> >   };
> >
> >   /* Worker threads modify data in their "active" percpu lists. */
> > @@ -1240,7 +1240,7 @@ void *test_membarrier_worker_thread(void *arg)
> >                       int cpu = get_current_cpu_id();
> >
> >                       ret = rseq_offset_deref_addv(RSEQ_MO_RELAXED, RSEQ_PERCPU,
> > -                             &args->percpu_list_ptr,
> > +                             (intptr_t*)&args->percpu_list_ptr,
> >                               sizeof(struct percpu_list_entry) * cpu, 1, cpu);
> >               } while (rseq_unlikely(ret));
> >       }
> >
> > ---
> > base-commit: 2dde18cd1d8fac735875f2e4987f11817cc0bc2c
> > change-id: 20230908-kselftest-param_test-c-1763b62e762f
> >
> > Best regards,
> > --
> > Justin Stitt <justinstitt@...gle.com>
> >
>
> --
> Mathieu Desnoyers
> EfficiOS Inc.
> https://www.efficios.com
>