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

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Message-Id: <0073e739-e3aa-4743-ad2d-29d7c969f454@app.fastmail.com>
Date: Fri, 11 Apr 2025 09:47:51 +0200
From: "Arnd Bergmann" <arnd@...db.de>
To: "Peter Zijlstra" <peterz@...radead.org>,
 "Josh Poimboeuf" <jpoimboe@...nel.org>
Cc: "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 Fri, Apr 11, 2025, at 08:50, Peter Zijlstra wrote:
> On Tue, Apr 08, 2025 at 06:58:49PM -0700, Josh Poimboeuf wrote:
>> On Fri, Mar 28, 2025 at 11:48:19AM +0100, Arnd Bergmann wrote:
>> 
>> For example, FineIBT writes code in the __pfx area which can trigger an
>> #UD.  And we'd want a sane backtrace for that.
>
> On top of that, clang kcfi builds do a similar thing, they will generate
> __cfi_ prefixed symbols.
>
> And yes, those symbols exist for a reason, there is code there under
> various circumstances and backtraces look really weird without these
> symbols on -- notably the code in the prefix will be attributed to
> whatever symbol comes before, most confusing.
>
> So yeah, don't remove these symbols, and fix the kunit test.

kallsyms already removes some CFI symbol names based on regular
expressions:

# CFI type identifiers
/ __kcfi_typeid_/d
/ __kvm_nvhe___kcfi_typeid_/d
/ __pi___kcfi_typeid_/d

Do you think it should not remove some of them?

I ran into another problem with generated symbols that I don't
understand yet, and added this line to avoid the build failures:

/ _GLOBAL__sub_/d

This one is 534 characters long:
_GLOBAL__sub_I_65535_1_snnnng1h2i3j4k5l6m7ng1h2i3j4k5l6m7nng1h2i3j4k5l6m7ng1h2i3j4k5l6m7nnng1h2i3j4k5l6m7ng1h2i3j4k5l6m7nng1h2i3j4k5l6m7ng1h2i3j4k5l6m7nnnng1h2i3j4k5l6m7ng1h2i3j4k5l6m7nng1h2i3j4k5l6m7ng1h2i3j4k5l6m7nnng1h2i3j4k5l6m7ng1h2i3j4k5l6m7nng1h2i3j4k5l6m7ng1h2i3j4k5l6m7nnnnng1h2i3j4k5l6m7ng1h2i3j4k5l6m7nng1h2i3j4k5l6m7ng1h2i3j4k5l6m7nnng1h2i3j4k5l6m7ng1h2i3j4k5l6m7nng1h2i3j4k5l6m7ng1h2i3j4k5l6m7nnnng1h2i3j4k5l6m7ng1h2i3j4k5l6m7nng1h2i3j4k5l6m7ng1h2i3j4k5l6m7nnng1h2i3j4k5l6m7ng1h2i3j4k5l6m7nng1h2i3j4k5l6m7ng1h2i3j4k5l6m7n

      Arnd