Re: Symbol too long for allsyms warnings on KSYM_NAME_LEN

[Arnd Bergmann]

On Thu, Mar 27, 2025, at 14:58, Peter Zijlstra wrote:
> On Thu, Mar 27, 2025 at 09:38:46AM +0100, Arnd Bergmann wrote:
>> My randconfig builds sometimes (around one in every 700 configs) run
>> into this warning on x86:
>> 
>> Symbol __pfx_snnnng1h2i3j4k5l6m7ng1h2i3j4k5l6m7nng1h2i3j4k5l6m7ng1h2i3j4k5l6m7nnng1h2i3j4k5l6m7ng1h2i3j4k5l6m7nng1h2i3j4k5l6m7ng1h2i3j4k5l6m7nnnng1h2i3j4k5l6m7ng1h2i3j4k5l6m7nng1h2i3j4k5l6m7ng1h2i3j4k5l6m7nnng1h2i3j4k5l6m7ng1h2i3j4k5l6m7nng1h2i3j4k5l6m7ng1h2i3j4k5l6m7nnnnng1h2i3j4k5l6m7ng1h2i3j4k5l6m7nng1h2i3j4k5l6m7ng1h2i3j4k5l6m7nnng1h2i3j4k5l6m7ng1h2i3j4k5l6m7nng1h2i3j4k5l6m7ng1h2i3j4k5l6m7nnnng1h2i3j4k5l6m7ng1h2i3j4k5l6m7nng1h2i3j4k5l6m7ng1h2i3j4k5l6m7nnng1h2i3j4k5l6m7ng1h2i3j4k5l6m7nng1h2i3j4k5l6m7ng1h2i3j4k5l6m7n too long for kallsyms (517 >= 512).
>> Please increase KSYM_NAME_LEN both in kernel and kallsyms.c
>> 
>> The check that gets triggered was added in commit c104c16073b
>> ("Kunit to check the longest symbol length"), see
>> https://lore.kernel.org/all/20241117195923.222145-1-sergio.collado@xxxxxxxxx/
>> 
>> and the overlong identifier seems to be the result of objtool adding
>> the six-byte "__pfx_" string to a symbol in elf_create_prefix_symbol()
>> when CONFIG_FUNCTION_PADDING_CFI is set.
>> 
>> I think the suggestion to "Please increase KSYM_NAME_LEN both in
>> kernel and kallsyms.c" is misleading here and should probably be
>> changed. I don't know if this something that objtool should work
>> around, or something that needs to be adapted in the test.
>
> Probably test needs to be fixed; objtool can't really do anything here,
> it just take the existing symname and prefixes it.

I found a workaround that avoids the problem for me now, see
https://lore.kernel.org/linux-kbuild/20250328112156.2614513-1-arnd@xxxxxxxxxx/

      Arnd