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

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Message-ID: <6d5ff91a-560e-56ea-0047-175f712872c2@csgroup.eu>
Date:   Tue, 3 May 2022 11:20:22 +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 03/05/2022 à 01:52, Steven Rostedt a écrit :
> On Mon, 2 May 2022 14:44:56 +0000
> Christophe Leroy <christophe.leroy@...roup.eu> wrote:
> 
>> If we do that after the linking, won't it be a nightmare with the
>> trampolines installed by the linker when the destination is over the 24
>> bits limit ?
> 
> Not sure what you mean. The locations I'm talking about is the full
> address saved in the __mcount_loc table (data section).
> 

Maybe I misunderstood. When you say 'after linking', do you mean vmlinux 
or vmlinux.o ?

In vmlinux, the addresses to be saved in __mcount_loc table might not 
contain anymore a call to _mcount but a call to a trampoline that jumps 
to _mcount, in case _mcount is too far from the said location at link 
time. That's what I meant.

Christophe