linux-kernel - Re: [PATCH v2] x86/lib: Do not use local symbols with SYM_CODE_START

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Message-ID: <20230526204559.GAZHEahxxnQaHhSUul@nazgul.local>
Date:   Fri, 26 May 2023 22:45:59 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     Nadav Amit <nadav.amit@...il.com>
Cc:     Dave Hansen <dave.hansen@...el.com>,
        Jiri Slaby <jirislaby@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        X86 ML <x86@...nel.org>, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] x86/lib: Do not use local symbols with
 SYM_CODE_START_LOCAL()

On Fri, May 26, 2023 at 10:29:29AM -0700, Nadav Amit wrote:
> Can you give me some examples for code whose address cannot be mapped
> back to a symbol?

No, this is not what I'm talking about.

I'm talking about all the local labels the compiler uses. For example:

$ make kernel/sched/core.s
$ grep -E "^\.L" kernel/sched/core.s | wc -l
2799

All those local labels are not in the symbol table (get discarded) and
the addresses they represent are shown as belonging to the containing
function.

> I did not ask to make them global. Just to keep them as local after
> linkage in the executable, like all other functions in the kernel.

Ok, not global. But local and present in the symbol table:

105185: ffffffff81b89330    17 NOTYPE  LOCAL  DEFAULT    1 bad_get_user_clac

And again, this helps how exactly?

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette