Re: [PATCH bpf-next v3] selftests/bpf: replace fall through comment by fallthrough pseudo-keyword

[Ruan Jinjie <ruanjinjie@huawei.com>]

On 2023/8/1 23:40, Yonghong Song wrote:
> 
> 
> On 8/1/23 2:48 AM, Ruan Jinjie wrote:
>> Replace the existing /* fall through */ comments with the
>> new pseudo-keyword macro fallthrough[1].
>>
>> [1]
>> https://www.kernel.org/doc/html/v5.7/process/deprecated.html?highlight=fallthrough#implicit-switch-case-fall-through
>>
>> Signed-off-by: Ruan Jinjie <ruanjinjie@huawei.com>
>> ---
>> v3:
>> - Update the subject prefix and fix the 'fallthrough' undeclared build
>> error.
>> ---
>> v2:
>> - Update the subject and commit message.
>> ---
>>   tools/testing/selftests/bpf/prog_tests/kfunc_call.c          | 4 ++--
>>   tools/testing/selftests/bpf/progs/test_cls_redirect.c        | 2 +-
>>   tools/testing/selftests/bpf/progs/test_cls_redirect_dynptr.c | 2 +-
>>   tools/testing/selftests/bpf/test_verifier.c                  | 3 ++-
>>   4 files changed, 6 insertions(+), 5 deletions(-)
>>
>> diff --git a/tools/testing/selftests/bpf/prog_tests/kfunc_call.c
>> b/tools/testing/selftests/bpf/prog_tests/kfunc_call.c
>> index a543742cd7bd..0fd08172965a 100644
>> --- a/tools/testing/selftests/bpf/prog_tests/kfunc_call.c
>> +++ b/tools/testing/selftests/bpf/prog_tests/kfunc_call.c
>> @@ -101,7 +101,7 @@ static void verify_success(struct
>> kfunc_test_params *param)
>>       case syscall_test:
>>           topts.ctx_in = &args;
>>           topts.ctx_size_in = sizeof(args);
>> -        /* fallthrough */
>> +        fallthrough;
> 
> This won't work for clang built kernel/selftests:
> 
> In file included from progs/test_cls_redirect_subprogs.c:2:
> progs/test_cls_redirect.c:303:4: error: use of undeclared identifier
> 'fallthrough'
>   303 |                         fallthrough;
>       |                         ^
>   CLNG-BPF [test_maps] netns_cookie_prog.bpf.o
>   CLNG-BPF [test_maps] test_skmsg_load_helpers.bpf.o
>   CLNG-BPF [test_maps] bpf_iter_setsockopt.bpf.o
>   CLNG-BPF [test_maps] timer.bpf.o
> progs/test_cls_redirect.c:303:4: error: use of undeclared identifier
> 'fallthrough'
>   303 |                         fallthrough;
Thank you very much! I'll fix it in v4.

>       |                         ^
> 
> Try to build the kernel with:
>   make -j LLVM=1
>   make headers_install
> 
> and then build the selftests with
>   make -C tools/testing/selftests/bpf -j LLVM=1
> 
> [~/work/bpf-next/tools/include (master)]$ egrep -r fallthrough
> egrep: warning: egrep is obsolescent; using grep -E
> linux/compiler-gcc.h:#if __has_attribute(__fallthrough__)
> linux/compiler-gcc.h:# define fallthrough __attribute__((__fallthrough__))
> linux/compiler-gcc.h:# define fallthrough                    do {} while
> (0)  /* fallthrough */
> [~/work/bpf-next/tools/include (master)]$
> 
> Looks like 'fallthrough' is not defined for clang build tools/selftests.
> 
>>       case syscall_null_ctx_test:
>>           break;
>>       case tc_test:
>> @@ -167,7 +167,7 @@ static void verify_fail(struct kfunc_test_params
>> *param)
>>       case syscall_test:
>>           topts.ctx_in = &args;
>>           topts.ctx_size_in = sizeof(args);
>> -        /* fallthrough */
>> +        fallthrough;
>>       case syscall_null_ctx_test:
>>           break;
>>       case tc_test:
> [...]