linux-kernel - Re: [RFC][PATCH 00/36] objtool: Make recordmcount a subcommand

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Date:   Tue, 14 Apr 2020 15:17:39 +0100
From:   Julien Thierry <jthierry@...hat.com>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     Matt Helsley <mhelsley@...are.com>, linux-kernel@...r.kernel.org,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>, Miroslav Benes <mbenes@...e.cz>
Subject: Re: [RFC][PATCH 00/36] objtool: Make recordmcount a subcommand



On 4/14/20 2:35 PM, Steven Rostedt wrote:
> On Tue, 14 Apr 2020 08:24:15 +0100
> Julien Thierry <jthierry@...hat.com> wrote:
> 
>> If all you need from objtool it the elf parsing code, wouldn't it make
>> more sense to move that out of objtool, as a utility library that both
>> objtool and recordmcount could use (and perhaps other tools in the future?)
>>
>> In patch 3 you seem to mention that other tools already have their own
>> code to parse elf. So instead of converting everything as an objtool
>> subcommand, maybe just have the library with the required functionality.
>>
>> Any opinions on the above? What do people prefer?
> 
> I think we discussed this before (and originally that was the plan), but I
> believe one of the goals for bringing recordmcount into objtool is to speed
> up the processing. Instead of having to read the elf sections for each use
> case, we do it once, and then execute all the necessary operations for that
> build.
> 
> If we just have a elf parsing library, then each object file is going to
> have that read redundantly for each operation that is done on it.
> 
> I was hoping to have objtool handle all the operations needed that required
> reading elf headers.
> 

That makes sense, however, having each operation as an objtool 
subcommand doesn't solve that issue, right? Each invocation of objtool 
will re-read the elf object.

I guess having all the relevant code in objtool as subcommand would be a 
first step towards that goal.

> But if that's not what objtool maintainers want, then we can certainly go
> back to looking at pulling out the elf headers, and have each tool be a
> standalone again.
> 

I'm no maintainer nor know their feeling about this and I haven't been 
part of the initial discussion. My main concern was about the approach 
of moving existing subcommand code to arch specific folders.

Thanks for the explanations.

Cheers,

-- 
Julien Thierry