Re: [RFC] bpf: Issue with bpf_fentry_test7 call

[Yonghong Song <yonghong.song@linux.dev>]

On 12/15/23 6:24 AM, Jiri Olsa wrote:
> On Fri, Dec 15, 2023 at 10:16:27AM +0100, Jiri Olsa wrote:
>> hi,
>> The bpf CI is broken due to clang emitting 2 functions for
>> bpf_fentry_test7:
>>
>>    # cat available_filter_functions | grep bpf_fentry_test7
>>    bpf_fentry_test7
>>    bpf_fentry_test7.specialized.1
>>
>> The tests attach to 'bpf_fentry_test7' while the function with
>> '.specialized.1' suffix is executed in bpf_prog_test_run_tracing.
>>
>> It looks like clang optimalization that comes from passing 0
>> as argument and returning it directly in bpf_fentry_test7.
>>
>> I'm not sure there's a way to disable this, so far I came
>> up with solution below that passes real pointer, but I think
>> that was not the original intention for the test.
>>
>> We had issue with this function back in august:
>>    32337c0a2824 bpf: Prevent inlining of bpf_fentry_test7()
>>
>> I'm not sure why it started to show now? was clang updated for CI?
>>
>> I'll try to find out more, but any clang ideas are welcome ;-)
>>
>> thanks,
>> jirka
>
> hm, there seems to be fix in bpf-next for this one:
>
>    b16904fd9f01 bpf: Fix a few selftest failures due to llvm18 change

Maybe submit a patch to https://github.com/kernel-patches/vmtest/tree/master/ci/diffs?
That is typically the place to have temporary patches to workaround ci failures.

>
> jirka
>
>>
>> ---
>> diff --git a/net/bpf/test_run.c b/net/bpf/test_run.c
>> index c9fdcc5cdce1..33208eec9361 100644
>> --- a/net/bpf/test_run.c
>> +++ b/net/bpf/test_run.c
>> @@ -543,7 +543,7 @@ struct bpf_fentry_test_t {
>>   int noinline bpf_fentry_test7(struct bpf_fentry_test_t *arg)
>>   {
>>   	asm volatile ("");
>> -	return (long)arg;
>> +	return 0;
>>   }
>>   
>>   int noinline bpf_fentry_test8(struct bpf_fentry_test_t *arg)
>> @@ -668,7 +668,7 @@ int bpf_prog_test_run_tracing(struct bpf_prog *prog,
>>   		    bpf_fentry_test4((void *)7, 8, 9, 10) != 34 ||
>>   		    bpf_fentry_test5(11, (void *)12, 13, 14, 15) != 65 ||
>>   		    bpf_fentry_test6(16, (void *)17, 18, 19, (void *)20, 21) != 111 ||
>> -		    bpf_fentry_test7((struct bpf_fentry_test_t *)0) != 0 ||
>> +		    bpf_fentry_test7(&arg) != 0 ||
>>   		    bpf_fentry_test8(&arg) != 0 ||
>>   		    bpf_fentry_test9(&retval) != 0)
>>   			goto out;
>> diff --git a/tools/testing/selftests/bpf/progs/fentry_test.c b/tools/testing/selftests/bpf/progs/fentry_test.c
>> index 52a550d281d9..95c5c34ccaa8 100644
>> --- a/tools/testing/selftests/bpf/progs/fentry_test.c
>> +++ b/tools/testing/selftests/bpf/progs/fentry_test.c
>> @@ -64,7 +64,7 @@ __u64 test7_result = 0;
>>   SEC("fentry/bpf_fentry_test7")
>>   int BPF_PROG(test7, struct bpf_fentry_test_t *arg)
>>   {
>> -	if (!arg)
>> +	if (arg)
>>   		test7_result = 1;
>>   	return 0;
>>   }
>> diff --git a/tools/testing/selftests/bpf/progs/fexit_test.c b/tools/testing/selftests/bpf/progs/fexit_test.c
>> index 8f1ccb7302e1..ffb30236ca02 100644
>> --- a/tools/testing/selftests/bpf/progs/fexit_test.c
>> +++ b/tools/testing/selftests/bpf/progs/fexit_test.c
>> @@ -65,7 +65,7 @@ __u64 test7_result = 0;
>>   SEC("fexit/bpf_fentry_test7")
>>   int BPF_PROG(test7, struct bpf_fentry_test_t *arg)
>>   {
>> -	if (!arg)
>> +	if (arg)
>>   		test7_result = 1;
>>   	return 0;
>>   }