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@gmail.com...

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@kernel.or...

Arnd