Re: [PATCH v2] module/kallsyms: Filter out local mapping symbols during module load

[Tiezhu Yang <yangtiezhu@loongson.cn>]

On 2026/8/11 下午10:22, Huacai Chen wrote:
> Hi, Petr,
> 
> On Tue, Aug 11, 2026 at 8:20 PM Petr Pavlu <petr.pavlu@suse.com> wrote:
>>
>> On 8/11/26 9:15 AM, Tiezhu Yang wrote:
>>> The compiler toolchains generate internal local labels on certain
>>> architectures (such as LoongArch) for optimizations and relocations.
>>>
>>> While these local labels are filtered out during runtime lookups in
>>> find_kallsyms_symbol(), they still leak into the permanent symbol
>>> tables of loaded modules, because layout_symtab() and add_kallsyms()
>>> do not check for the mapping symbols during layout generation.
>>>
>>> Consequently, tracing tools like bpftrace resolve identical addresses
>>> into confusing local labels instead of actual clear C function names.
>>>
>>> Fix this by adding is_mapping_symbol() checks directly into the symbol
>>> tracking loops of layout_symtab() and add_kallsyms(). This prevents the
>>> mapping symbols from entering the module's memory symbol arrays at load
>>> time.
>>
>> This optimization looks sensible to me. Kallsyms in vmlinux also
>> normally doesn't include information about local labels (.L<xyz>) and
>> mapping symbols ($a, $d, ...), so it should be ok not to track them in
>> modules either.
>>
>> Note that the patch description mixes up these two symbol categories,
>> presumably because the existing is_mapping_symbol() function conflates
>> them as well.

...

>> It is better to avoid duplicating the same logic in layout_symtab() and
>> add_kallsyms(). The function is_core_symbol() can be renamed to
>> something like is_kept_symbol() and can be solely responsible for
>> deciding what to keep.
> I'm sorry but I think Tiezhu's patch is simpler and cleaner. :)

Hi Petr and Huacai,

Thanks for your feedback! To make the code cleaner, I plan to split the
changes into the following three patches for v3:

1. module/kallsyms: Rename is_mapping_symbol() to is_local_mapping_symbol()
2. module/kallsyms: Refactor current symbol filtering into is_kept_symbol()
3. module/kallsyms: Filter out local and mapping symbols during module load

I will send out the v3 patch series soon.

Thanks,
Tiezhu