linux-kernel - Re: Symbol too long for allsyms warnings on KSYM_NAME

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Message-ID: <20250327135847.GE31358@noisy.programming.kicks-ass.net>
Date: Thu, 27 Mar 2025 14:58:47 +0100
From: Peter Zijlstra <peterz@...radead.org>
To: Arnd Bergmann <arnd@...db.de>
Cc: Sergio González Collado <sergio.collado@...il.com>,
	Brendan Higgins <brendan.higgins@...ux.dev>,
	David Gow <davidgow@...gle.com>, Miguel Ojeda <ojeda@...nel.org>,
	Alex Gaynor <alex.gaynor@...il.com>,
	linux-kselftest@...r.kernel.org, kunit-dev@...glegroups.com,
	Dave Hansen <dave.hansen@...uax.intel.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Josh Poimboeuf <jpoimboe@...nel.org>,
	Boqun Feng <boqun.feng@...il.com>, Gary Guo <gary@...yguo.net>,
	Björn Roy Baron <bjorn3_gh@...tonmail.com>,
	Benno Lossin <benno.lossin@...ton.me>,
	Andreas Hindborg <a.hindborg@...sung.com>,
	Alice Ryhl <aliceryhl@...gle.com>,
	David Rheinsberg <david@...dahead.eu>,
	rust-for-linux@...r.kernel.org, skhan@...uxfoundation.org,
	ricardo.marliere@...e.com, Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
	Martin Rodriguez Reboredo <yakoyoku@...il.com>,
	linux-kernel@...r.kernel.org
Subject: Re: Symbol too long for allsyms warnings on KSYM_NAME_LEN

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.