Re: [RFC bpf-next 06/15] bpftool: Handle multi-split BTF by supporting multiple base BTFs

[Alan Maguire <alan.maguire@oracle.com>]

On 16/10/2025 19:36, Andrii Nakryiko wrote:
> On Wed, Oct 8, 2025 at 10:35 AM Alan Maguire <alan.maguire@oracle.com> wrote:
>>
>> For bpftool to be able to dump .BTF.extra data in /sys/kernel/btf_extra
>> for modules, it needs to support multi-split BTF because the
>> parent-child relationship of BTF extra data for modules is
>>
>> vmlinux BTF data
>>         module BTF data
>>                 module BTF extra data
>>
>> So for example to dump BTF extra info for xfs we would run
>>
>> $ bpftool btf dump -B /sys/kernel/btf/vmlinux -B /sys/kernel/btf/xfs file /sys/kernel/btf_extra/xfs
>>
>> Multiple bases are specified with the vmlinux base BTF first (parent)
>> followed by the xfs BTF (child), and finally the XFS BTF extra.
>>
>> Signed-off-by: Alan Maguire <alan.maguire@oracle.com>
>> ---
>>  tools/bpf/bpftool/main.c | 3 ++-
>>  1 file changed, 2 insertions(+), 1 deletion(-)
>>
> 
> we'll need to update documentation to mention that order of -B matters
> and how it is treated
>

yep, good point, I'll add a documentation patch in the next round.

> 
>> diff --git a/tools/bpf/bpftool/main.c b/tools/bpf/bpftool/main.c
>> index a829a6a49037..aa16560b4157 100644
>> --- a/tools/bpf/bpftool/main.c
>> +++ b/tools/bpf/bpftool/main.c
>> @@ -514,7 +514,8 @@ int main(int argc, char **argv)
>>                         verifier_logs = true;
>>                         break;
>>                 case 'B':
>> -                       base_btf = btf__parse(optarg, NULL);
>> +                       /* handle multi-split BTF */
>> +                       base_btf = btf__parse_split(optarg, base_btf);
>>                         if (!base_btf) {
>>                                 p_err("failed to parse base BTF at '%s': %d\n",
>>                                       optarg, -errno);
>> --
>> 2.39.3
>>