Re: [PATCH bpf-next 4/4] selftests/bpf: Fix a user_ringbuf failure with arm64 64KB page size

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

On 6/5/25 10:52 PM, Yonghong Song wrote:
>
>
> On 6/5/25 8:23 PM, Yonghong Song wrote:
>> The ringbuf max_entries must be PAGE_ALIGNED. See kernel function
>> ringbuf_map_alloc(). So for arm64 64KB page size, adjust max_entries
>> properly.
>>
>> Signed-off-by: Yonghong Song <yonghong.song@linux.dev>
>> ---
>>   tools/testing/selftests/bpf/prog_tests/user_ringbuf.c | 6 ++++--
>>   1 file changed, 4 insertions(+), 2 deletions(-)
>>
>> diff --git a/tools/testing/selftests/bpf/prog_tests/user_ringbuf.c 
>> b/tools/testing/selftests/bpf/prog_tests/user_ringbuf.c
>> index d424e7ecbd12..f50aa8e7f6c2 100644
>> --- a/tools/testing/selftests/bpf/prog_tests/user_ringbuf.c
>> +++ b/tools/testing/selftests/bpf/prog_tests/user_ringbuf.c
>> @@ -21,8 +21,7 @@
>>   #include "../progs/test_user_ringbuf.h"
>>     static const long c_sample_size = sizeof(struct sample) + 
>> BPF_RINGBUF_HDR_SZ;
>> -static const long c_ringbuf_size = 1 << 12; /* 1 small page */
>> -static const long c_max_entries = c_ringbuf_size / c_sample_size;
>> +static long c_ringbuf_size, c_max_entries;
>>     static void drain_current_samples(void)
>>   {
>> @@ -686,6 +685,9 @@ void test_user_ringbuf(void)
>>   {
>>       int i;
>>   +    c_ringbuf_size = getpagesize(); /* 1 page */
>> +    c_max_entries = c_ringbuf_size / c_sample_size;
>> +
>>       for (i = 0; i < ARRAY_SIZE(success_tests); i++) {
>>           if (!test__start_subtest(success_tests[i].test_name))
>>               continue;
>
> CI reports a build failure error:
>
> /tmp/work/bpf/bpf/tools/testing/selftests/bpf/prog_tests/user_ringbuf.c:426:2: 
> error: call to '__compiletime_assert_0' declared with 'error' 
> attribute: BUILD_BUG_ON failed: total_samples <= c_max_entries   426 | 
> BUILD_BUG_ON(total_samples <= c_max_entries     |
>
> /tmp/work/bpf/bpf/tools/include/linux/build_bug.h:50:2: note: expanded 
> from macro 'BUILD_BUG_ON' 50 | BUILD_BUG_ON_MSG(condition, 
> "BUILD_BUG_ON failed: " #condition) | ^ 
> /tmp/work/bpf/bpf/tools/include/linux/build_bug.h:39:37: note: 
> expanded from macro 'BUILD_BUG_ON_MSG' 39 | #define 
> BUILD_BUG_ON_MSG(cond, msg) compiletime_assert(!(cond), msg) | ^ 
> /tmp/work/bpf/bpf/tools/include/linux/compiler.h:37:2: note: expanded 
> from macro 'compiletime_assert' 37 | _compiletime_assert(condition, 
> msg, __compiletime_assert_, __COUNTER__) | ^ 
> /tmp/work/bpf/bpf/tools/include/linux/compiler.h:25:2: note: expanded 
> from macro '_compiletime_assert' 25 | __compiletime_assert(condition, 
> msg, prefix, suffix) | ^ 
> /tmp/work/bpf/bpf/tools/include/linux/compiler.h:18:4: note: expanded 
> from macro '__compiletime_assert' 18 | prefix ## suffix(); \ | ^ 
> <scratch space>:60:1: note: expanded from here 60 | 
> __compiletime_assert_0
>
> | ^ This happens for the release build (RELEASE=1 in build command 
> line where -O2 is used in stead of -O0). Converting the BUILD_BUG_ON 
> to ASSERT can fix the problem. diff --git 
> a/tools/testing/selftests/bpf/prog_tests/user_ringbuf.c 
> b/tools/testing/selftests/bpf/prog_tests/user_ringbuf.c index 
> f50aa8e7f6c2..467b5b8beecc 100644 --- 
> a/tools/testing/selftests/bpf/prog_tests/user_ringbuf.c +++ 
> b/tools/testing/selftests/bpf/prog_tests/user_ringbuf.c @@ -423,7 
> +423,9 @@ static void test_user_ringbuf_loop(void) uint32_t 
> remaining_samples = total_samples; int err; - 
> BUILD_BUG_ON(total_samples <= c_max_entries); + if 
> (!ASSERT_LE(total_samples, c_max_entries, "compare_c_max_entries")) + 
> return; + err = load_skel_create_user_ringbuf(&skel, &ringbuf); I will 
> wait for some further comments before posting v2.


Sorry for mess up. Basically, need to replace a BUILD_BUG_ON with a ASSERT...
I already tried to format the code properly but somehow still messed up.
Will debug/double-check this next time.