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

[Song Liu <songliubraving@meta.com>]

> 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?

Thanks,
Song