linux-kernel - Re: [PATCH v3 4/4] objtool: orc_gen: Move orc

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Date:   Thu, 30 Jul 2020 15:33:43 +0200
From:   peterz@...radead.org
To:     Julien Thierry <jthierry@...hat.com>
Cc:     linux-kernel@...r.kernel.org, jpoimboe@...hat.com,
        mhelsley@...are.com, mbenes@...e.cz
Subject: Re: [PATCH v3 4/4] objtool: orc_gen: Move orc_entry out of
 instruction structure

On Thu, Jul 30, 2020 at 01:40:48PM +0100, Julien Thierry wrote:
> 
> 
> On 7/30/20 11:03 AM, peterz@...radead.org wrote:
> > On Thu, Jul 30, 2020 at 10:41:43AM +0100, Julien Thierry wrote:
> > > One orc_entry is associated with each instruction in the object file,
> > > but having the orc_entry contained by the instruction structure forces
> > > architectures not implementing the orc subcommands to provide a dummy
> > > definition of the orc_entry.

> I guess I forgot about the usecase of running objtool on vmlinux...

Right, and LTO builds will even do ORC at that level.

> On a kernel build for x86_64 defconfig, the difference in time seems to be
> withing the noise.

Good.

> But I agree the proposed code is not ideal and on the other we've tried
> avoiding #ifdef in the code. Ideally I'd have an empty orc_entry definition
> when SUBCMD_ORC is not implemented.
> 
> Would you have a suggested approach to do that?

How ugly is having that:

struct orc_entry { };

?