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

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Message-ID: <20250415183934.46f4ed6f@pumpkin>
Date: Tue, 15 Apr 2025 18:39:34 +0100
From: David Laight <david.laight.linux@...il.com>
To: Steven Rostedt <rostedt@...dmis.org>
Cc: Peter Zijlstra <peterz@...radead.org>, Arnd Bergmann <arnd@...db.de>,
 Josh Poimboeuf <jpoimboe@...nel.org>, Arnd Bergmann <arnd@...nel.org>,
 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>, 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
Subject: Re: [PATCH] scripts/mksysmap: skip objtool __pfx_ symbols

On Sat, 12 Apr 2025 10:22:18 -0400
Steven Rostedt <rostedt@...dmis.org> wrote:

...
> I just hit this on my allyesconfig build:
> 
>   NM      .tmp_vmlinux1.syms
>   KSYMS   .tmp_vmlinux1.kallsyms.S
> Symbol __cfi_snnnng1h2i3j4k5l6m7ng1h2i3j4k5l6m7nng1h2i3j4k5l6m7ng1h2i3j4k5l6m7nnng1h2i3j4k5l6m7ng1h2i3j4k5l6m7nng1h2i3j4k5l6m7ng1h2i3j4k5l6m7nnnng1h2i3j4k5l6m7ng1h2i3j4k5l6m7nng1h2i3j4k5l6m7ng1h2i3j4k5l6m7nnng1h2i3j4k5l6m7ng1h2i3j4k5l6m7nng1h2i3j4k5l6m7ng1h2i3j4k5l6m7nnnnng1h2i3j4k5l6m7ng1h2i3j4k5l6m7nng1h2i3j4k5l6m7ng1h2i3j4k5l6m7nnng1h2i3j4k5l6m7ng1h2i3j4k5l6m7nng1h2i3j4k5l6m7ng1h2i3j4k5l6m7nnnng1h2i3j4k5l6m7ng1h2i3j4k5l6m7nng1h2i3j4k5l6m7ng1h2i3j4k5l6m7nnng1h2i3j4k5l6m7ng1h2i3j4k5l6m7nng1h2i3j4k5l6m7ng1h2i3j4k5l6m7n too long for kallsyms (517 >= 512).
> Please increase KSYM_NAME_LEN both in kernel and kallsyms.c
...
> 
> I grepped for that symbol and it lives in: lib/tests/longest_symbol_kunit.o

Looks like it is carefully counted to be 511 characters.
And then the compiler adds __cfi_ making 517.
I guess the test could be changed?

Is it possible to remove the __cfi_ symbols (to save kernel memory) and then
use a single bit to indicate that the previous few bytes (the same number for
all such symbols) belong to the following symbol?
Then stack backtraces would say "foo-n" instead "__cfi_foo+n".

	David