Re: pahole v1.24: FAILED: load BTF from vmlinux: Invalid argument

[Yonghong Song <yhs@fb.com>]

On 8/25/22 7:59 PM, Vitaly Chikunov wrote:
> On Fri, Aug 26, 2022 at 05:52:20AM +0300, Vitaly Chikunov wrote:
>> Arnaldo,
>>
>> On Thu, Aug 25, 2022 at 08:16:20PM +0300, Vitaly Chikunov wrote:
>>> On Thu, Aug 25, 2022 at 01:47:59PM -0300, Arnaldo Carvalho de Melo wrote:
>>>> On Thu, Aug 25, 2022, 1:35 PM Vitaly Chikunov <vt@altlinux.org> wrote:
>>>>>
>>>>> I also noticed that after upgrading pahole to v1.24 kernel build (tested on
>>>>> v5.18.19, v5.15.63, sorry for not testing on mainline) fails with:
>>>>>
>>>>>      BTFIDS  vmlinux
>>>>>    + ./tools/bpf/resolve_btfids/resolve_btfids vmlinux
>>>>>    FAILED: load BTF from vmlinux: Invalid argument
>>>>>
>>>>> Perhaps, .tmp_vmlinux.btf is generated incorrectly? Downgrading dwarves to
>>>>> v1.23 resolves the issue.
>>>>>
>>>>
>>>> Can you try this, from Martin Reboredo (Archlinux):
>>>>
>>>> Can you try a build of the kernel or the by passing the
>>>> --skip_encoding_btf_enum64 to scripts/pahole-flags.sh?
>>>>
>>>> Here's a patch for either in tree scripts/pahole-flags.sh or
>>>> /usr/lib/modules/5.19.3-arch1-1/build/scripts/pahole-flags.sh
>>>
>>> This patch helped and kernel builds successfully after applying it.
>>> (Didn't notice this suggestion in release discussion thread.)
>>
>> Even thought it now compiles with this patch, it does not boot
>> afterwards (in virtme-like env), witch such console messages:
> 
> I'm talking here about 5.15.62. Yes, proposed patch does not apply there
> (since there is no `scripts/pahole-flags.sh`), but I updated
> `scripts/link-vmlinux.sh` with the similar `if` to append
> `--skip_encoding_btf_enum64` which lets then compilation pass.

Right, pahole v1.24 supports enum64 to correctly encode
some big 64bit values in BTF. But enum64 is only supported
in recent kernels. For old kernels, --skip_encoding_btf_enum64
is the way to workaround the issue.

> 
> Thanks,
> 
>>
>>    [    0.767649] Run /init as init process
>>    [    0.770858] BPF:[593] ENUM perf_event_task_context
>>    [    0.771262] BPF:size=4 vlen=4
>>    [    0.771511] BPF:
>>    [    0.771680] BPF:Invalid btf_info kind_flag
>>    [    0.772016] BPF:
>>    [    0.772016]
>>    [    0.772288] failed to validate module [9pnet] BTF: -22
>>    init_module '9pnet.ko' error -1
>>    [    0.785515] 9p: Unknown symbol p9_client_getattr_dotl (err -2)
>>    [    0.786005] 9p: Unknown symbol p9_client_wstat (err -2)
>>    [    0.786438] 9p: Unknown symbol p9_client_open (err -2)
>>    [    0.786863] 9p: Unknown symbol p9_client_rename (err -2)
>>    [    0.787307] 9p: Unknown symbol p9_client_remove (err -2)
>>    [    0.787749] 9p: Unknown symbol p9_client_renameat (err -2)
[...]