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

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Message-Id: <06639d9d-13b7-4d9a-a734-a430e91c1c27@app.fastmail.com>
Date: Fri, 28 Mar 2025 12:23:33 +0100
From: "Arnd Bergmann" <arnd@...db.de>
To: "Peter Zijlstra" <peterz@...radead.org>
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,
 "Shuah Khan" <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 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.org/

      Arnd