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

[Mathieu Desnoyers <mathieu.desnoyers@efficios.com>]

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.

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@google.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@google.com>
> 

-- 
Mathieu Desnoyers
EfficiOS Inc.
https://www.efficios.com