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

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Message-Id: <1651166416.afl3n7tts7.naveen@linux.ibm.com>
Date:   Thu, 28 Apr 2022 22:54:38 +0530
From:   "Naveen N. Rao" <naveen.n.rao@...ux.vnet.ibm.com>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        llvm@...ts.linux.dev, Michael Ellerman <mpe@...erman.id.au>,
        Nathan Chancellor <nathan@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>
Subject: Re: [PATCH 2/2] recordmcount: Handle sections with no non-weak
 symbols

Steven Rostedt wrote:
> On Thu, 28 Apr 2022 13:15:22 +0530
> "Naveen N. Rao" <naveen.n.rao@...ux.vnet.ibm.com> wrote:
> 
>> Indeed, plain old -pg will be a problem. I'm not sure there is a generic 
>> way to address this. I suppose architectures will have to validate the 
>> mcount locations, something like this?
> 
> Perhaps another solution is to make the mcount locations after the linking
> is done. The main downside to that is that it takes time to go over the
> entire vmlinux, and will slow down a compile that only modified a couple of
> files.

Yes, and I think that is also very useful with LTO. So, that would be a 
good one to consider in the longer term.

For now, I have posted a v2 of this series with your comments addressed.  
It is working well in my tests on powerpc in the different 
configurations, including the older elf abi v1 that uses -pg. If it 
looks ok to you, we can use this approach for now.


Thanks,
Naveen