linux-kernel - Re: [PATCH] scripts/mksysmap: skip objtool __pfx

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Message-ID: <ycgbf7jcq7nc62ndqiynogt6hkabgl3hld4uyelgo7rksylf32@oysq7jpchtp4>
Date: Tue, 8 Apr 2025 18:58:49 -0700
From: Josh Poimboeuf <jpoimboe@...nel.org>
To: Arnd Bergmann <arnd@...nel.org>
Cc: Masahiro Yamada <masahiroy@...nel.org>, Rae Moar <rmoar@...gle.com>, 
	Shuah Khan <skhan@...uxfoundation.org>, 
	Sergio González Collado <sergio.collado@...il.com>, David Gow <davidgow@...gle.com>, Arnd Bergmann <arnd@...db.de>, 
	Nathan Chancellor <nathan@...nel.org>, Nicolas Schier <nicolas.schier@...ux.dev>, 
	Mostafa Saleh <smostafa@...gle.com>, linux-kbuild@...r.kernel.org, linux-kernel@...r.kernel.org, 
	Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH] scripts/mksysmap: skip objtool __pfx_ symbols

On Fri, Mar 28, 2025 at 11:48:19AM +0100, Arnd Bergmann wrote:
> From: Arnd Bergmann <arnd@...db.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@...db.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