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

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

On 9/20/25 5:30 PM, Eduard Zingerman wrote:
> On Sat, 2025-09-20 at 08:35 -0700, Yonghong Song 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
> This section is generated by MCELFStreamer::emitIdent(), virtual
> function.
>
>>    [24] .note.GNU-stack   PROGBITS        0000000000000000 003619 000000 00      0   0  1
> And this one is generated by MCELFStreamer::initSections() virtual
> function and is controlled by NoExecStack formal parameter.
>
> MCELFStreamer instance for BPF backend is created by function
> BPFMCTargetDesc.cpp:createBPFMCStreamer().
>
> I think we can define a sub-class BPFMCELFStreamer, override the above
> virtual functions and suppress generation of the sections above.
>
> [...]

Two llvm pull request:
   to avoid generating .comment section:
     https://github.com/llvm/llvm-project/pull/159958
   to avoid generating .note.GNU-stack section:
     https://github.com/llvm/llvm-project/pull/159960