Re: [PATCH bpf-next] libbpf: Silence newly-added and unused sections

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

On 9/20/25 8:56 AM, Alexei Starovoitov wrote:
> On Sat, Sep 20, 2025 at 8:35 AM Yonghong Song <yonghong.song@linux.dev> wrote:
>> With latest llvm22, when building bpf selftest, I got the following info
>> emitted by libbpf:
>>    ...
>>    libbpf: elf: skipping unrecognized data section(14) .comment
>>    libbpf: elf: skipping section(15) .note.GNU-stack (size 0)
>>    ...
>>
>> The reason is due to llvm patch [1]. Previously, bpf class BPFMCAsmInfo
>> inherits class MCAsmInfo. With [1], BPFMCAsmInfo inherits class
>> MCAsmInfoELF. Such a change added two more sections in the bpf binary, e.g.
>>    [Nr] Name              Type            Address          Off    Size   ES Flg Lk Inf Al
>>    ...
>>    [23] .comment          PROGBITS        0000000000000000 0035ac 00006d 01  MS  0   0  1
>>    [24] .note.GNU-stack   PROGBITS        0000000000000000 003619 000000 00      0   0  1
>>    ...
>>
>> Adding the above two sections in elf section ignore list can avoid the
>> above info dump during selftest build.
>>
>>    [1] https://github.com/llvm/llvm-project/commit/d9489fd073c0e100c6fbb1e5aef140b00cf62b81
> Can we revert this instead?
> Why do we need these sections if we're not doing anything with them?

Yes, we can revert at llvm side. It does not add any value to libbpf.
Will submit a llvm pull request soon.

>
>> Signed-off-by: Yonghong Song <yonghong.song@linux.dev>
>> ---
>>   tools/lib/bpf/libbpf.c | 8 ++++++++
>>   1 file changed, 8 insertions(+)
>>
>> diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
>> index 5161c2b39875..34aed7904039 100644
>> --- a/tools/lib/bpf/libbpf.c
>> +++ b/tools/lib/bpf/libbpf.c
>> @@ -3788,6 +3788,14 @@ static bool ignore_elf_section(Elf64_Shdr *hdr, const char *name)
>>          if (is_sec_name_dwarf(name))
>>                  return true;
>>
>> +       /* .comment section */
>> +       if (strcmp(name, ".comment") == 0)
>> +               return true;
>> +
>> +       /* .note.GNU-stack section */
>> +       if (strcmp(name, ".note.GNU-stack") == 0)
>> +               return true;
>> +
>>          if (str_has_pfx(name, ".rel")) {
>>                  name += sizeof(".rel") - 1;
>>                  /* DWARF section relocations */
>> --
>> 2.47.3
>>