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

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Date:   Fri, 26 May 2023 14:17:20 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     Nadav Amit <nadav.amit@...il.com>, Borislav Petkov <bp@...en8.de>
Cc:     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 5/26/23 14:10, Nadav Amit wrote:
>>> 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?
> Allowing debuggers, tracers, disassemblers and instrumentation tools to
> work the same way they work as they work with any other piece of code in
> the kernel.
> 
> I personally work on code instrumentation and this makes my life hard for
> no good reason.
> 
> [ Perhaps the question should go the other way around: why addresses of
> code in these functions should not be mapped to any symbol? ]

Nadav, is there a chance you could give us a real-life example of how
this affects you as an end user?  What's a specific tool that you were
using or a specific problem that you were trying to solve where these
local symbols caused a problem?  How would the global symbol have helped?

I can certainly _imagine_ some, but I'm curious what you saw that
prompted you to send this patch.