linux-kernel - Re: [PATCH 2/2] recordmcount: Handle sections with no non-weak symbols

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Message-ID: <7c235943-4ea0-1f09-bbbb-8f23fbe8bfae@csgroup.eu>
Date:   Wed, 4 May 2022 17:10:07 +0000
From:   Christophe Leroy <christophe.leroy@...roup.eu>
To:     Steven Rostedt <rostedt@...dmis.org>
CC:     "Naveen N. Rao" <naveen.n.rao@...ux.vnet.ibm.com>,
        "llvm@...ts.linux.dev" <llvm@...ts.linux.dev>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Nathan Chancellor <nathan@...nel.org>,
        "linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>
Subject: Re: [PATCH 2/2] recordmcount: Handle sections with no non-weak
 symbols



Le 04/05/2022 à 19:06, Steven Rostedt a écrit :
> On Wed, 4 May 2022 16:50:58 +0000
> Christophe Leroy <christophe.leroy@...roup.eu> wrote:
> 
>> In vmlinux, relocations are resolved, trampolines are installed for
>> unreachable destinations and you don't anymore have a section with all
>> the relocations to mcount. It means 'recordmcount' or whatever tool we
>> use will have to read the code to find all direct calls to mcount, then
>> find all trampolines to mcount then find all calls to those trampolines.
> 
> OK, so what you are saying is that in the object file, we can see the
> site that calls mcount, but when it is linked, it may not call mcount,
> but instead it will call a trampoline that will call mcount, thus the
> tool will need to find these calls to the trampolines that call mcount
> as well as the locations that call mcount directly.
> 
> Did I get that right?
> 

Yes it is what I'm trying to say.

Christophe