On 13/5/26 00:23, [email protected] wrote:
>> diff --git a/tools/lib/bpf/bpf.c b/tools/lib/bpf/bpf.c
>> index 5846de364209..9d8740761b7a 100644
>> --- a/tools/lib/bpf/bpf.c
>> +++ b/tools/lib/bpf/bpf.c
>
> [ ... ]
>
>> +int probe_sys_bpf_ext(void)
>> +{
>> + const size_t attr_sz = offsetofend(union bpf_attr, prog_token_fd);
>> + union bpf_attr attr;
>> + int fd;
>> +
>> + memset(&attr, 0, attr_sz);
>> + fd = syscall(__NR_bpf, BPF_PROG_LOAD | BPF_COMMON_ATTRS, &attr,
>> attr_sz, NULL,
>> + sizeof(struct bpf_common_attr));
>> + if (fd >= 0) {
>> + close(fd);
>> + return -EINVAL;
> ^^^^^^
>
> Should probe_sys_bpf_ext() return 1 instead of -EINVAL when fd >= 0?
>
> The probe function detects kernel support for extended BPF syscall
> attributes by calling the BPF syscall with the BPF_COMMON_ATTRS flag
> and a NULL pointer for common attributes.
>
> The expected outcomes are:
> - New kernel with support: errno=EFAULT (can't copy from NULL) -> return 1
> - Old kernel without support: errno!=EFAULT (invalid command) -> return 0
>
> If the syscall succeeds (fd >= 0), that definitively proves the kernel
> accepts the extended syscall format and supports BPF_COMMON_ATTRS. The
> function should return 1 (supported) rather than -EINVAL (error).
>
> Returning -EINVAL causes feat_supported() in features.c to print a
> warning "Detection of kernel BPF syscall common attributes support
> support failed: Invalid argument" and mark the feature as MISSING,
> incorrectly reporting that the kernel doesn't support the feature when
> the successful syscall proves it does.
>
Should not return 1.
This return was discussed in v5 and v6.
Cite Andrii's review in v5:
But fd should really not be >= 0, and if it is -- it's some problem,
so I'd return an error in that case to keep us aware, which is why I'm
saying I'd just return inside if (fd >= 0) { }
Thanks,
Leon
>> + }
>> + return errno == EFAULT ? 1 : 0;
>> +}
>
> [ ... ]
>
>
> ---
> AI reviewed your patch. Please fix the bug or email reply why it's not a bug.
> See: https://github.com/kernel-patches/vmtest/blob/master/ci/claude/README.md
>
> CI run summary: https://github.com/kernel-patches/bpf/actions/runs/25745661172
