Re: [PATCH] scripts/mksysmap: skip objtool __pfx_ symbols

Josh Poimboeuf
2025-04-09T01:58:54Z

On Fri, Mar 28, 2025 at 11:48:19AM +0100, Arnd Bergmann wrote:
> From: Arnd Bergmann <arnd@arndb.de>
>
> The recently added testcase for overly long symbols triggers when
> CONFIG_FUNCTION_PADDING_CFI is set:
>
> Symbol __pfx_snnnng1h2i3j4k5l6m7ng1h2i3j4k5l6m7nng1h2i3j4k5l6m7ng1h2i3j4k5l6m7nnng1h2i3j4k5l6m7ng1h2i3j4k5l6m7nng1h2i3j4k5l6m7ng1h2i3j4k5l6m7nnnng1h2i3j4k5l6m7ng1h2i3j4k5l6m7nng1h2i3j4k5l6m7ng1h2i3j4k5l6m7nnng1h2i3j4k5l6m7ng1h2i3j4k5l6m7nng1h2i3j4k5l6m7ng1h2i3j4k5l6m7nnnnng1h2i3j4k5l6m7ng1h2i3j4k5l6m7nng1h2i3j4k5l6m7ng1h2i3j4k5l6m7nnng1h2i3j4k5l6m7ng1h2i3j4k5l6m7nng1h2i3j4k5l6m7ng1h2i3j4k5l6m7nnnng1h2i3j4k5l6m7ng1h2i3j4k5l6m7nng1h2i3j4k5l6m7ng1h2i3j4k5l6m7nnng1h2i3j4k5l6m7ng1h2i3j4k5l6m7nng1h2i3j4k5l6m7ng1h2i3j4k5l6m7n too long for kallsyms (517 >= 512).
> Please increase KSYM_NAME_LEN both in kernel and kallsyms.c
>
> Change the mksymtab table so the prefixed symbols are not included
> in kallsyms.
>
> Fixes: c104c16073b7 ("Kunit to check the longest symbol length")
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>

I'm not sure we want to remove the __pfx_ symbols from kallsyms. There
can be actual code there.

For example, FineIBT writes code in the __pfx area which can trigger an
#UD. And we'd want a sane backtrace for that.

Maybe objtool should error out when trying to prefix a function with a
name longer than (KSYM_NAME_LEN - 6). And the kunit test could be
adjusted accordingly for CONFIG_PREFIX_SYMBOLS.

--
Josh