Re: [PATCH] kallsyms: let kallsyms_on_each_match_symbol match symbols exactly

["Leizhen (ThunderTown)" <thunder.leizhen@huawei.com>]

On 2023/6/16 16:11, Leizhen (ThunderTown) wrote:
> 
> 
> On 2023/6/16 13:01, Song Liu wrote:
>>
>>
>>> On Jun 15, 2023, at 7:19 PM, Leizhen (ThunderTown) <thunder.leizhen@huawei.com> wrote:
>>>
>>> On 2023/6/16 1:00, Song Liu wrote:
>>>> With CONFIG_LTO_CLANG, kallsyms.c:cleanup_symbol_name() removes symbols
>>>> suffixes during comparison. This is problematic for livepatch, as
>>>> kallsyms_on_each_match_symbol may find multiple matches for the same
>>>> symbol, and fail with:
>>>>
>>>>  livepatch: unresolvable ambiguity for symbol 'xxx' in object 'yyy'
>>>
>>> Did you forget to specify 'old_sympos'? When there are multiple symbols with
>>> the same name, we need to specify the sequence number of the symbols to be
>>> matched.
>>
>>
>> old_sympos is indeed 0 here. However, the issue with CONFIG_LTO_CLANG 
>> is different. Here is an example:
>>
>> $ grep bpf_verifier_vlog /proc/kallsyms
>> ffffffff81549f60 t bpf_verifier_vlog
>> ffffffff8268b430 d bpf_verifier_vlog._entry
>> ffffffff8282a958 d bpf_verifier_vlog._entry_ptr
>> ffffffff82e12a1f d bpf_verifier_vlog.__already_done
>>
>> kallsyms_on_each_match_symbol matches "bpf_verifier_vlog" to all of 
>> these because of cleanup_symbol_name(). IOW, we only have one 
>> function called bpf_verifier_vlog, but kallsyms_on_each_match_symbol() 
>> matches it to bpf_verifier_vlog.*. 
>>
>> Does this make sense?
> 
> Sorry. I mistakenly thought you were operating a static function.
> 
> These suffixes are not mentioned in the comments in the function
> cleanup_symbol_name(). So I didn't notice it.
We can keep these three suffixes on the kallsyms tool end.

> 
>>
>> Thanks,
>> Song
>>
>>
>> .
>>
> 

-- 
Regards,
  Zhen Lei