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Subject: Re: [PATCH v3 4/4] objtool: orc_gen: Move orc_entry out of
 instruction structure
To:     peterz@infradead.org
Cc:     linux-kernel@vger.kernel.org, jpoimboe@redhat.com,
        mhelsley@vmware.com, mbenes@suse.cz
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 <e4e239ad-120e-bd8f-4128-6976146c8512@redhat.com>
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From:   Julien Thierry <jthierry@redhat.com>
Message-ID: <0280367f-3839-acad-799a-ecc2756c1846@redhat.com>
Date:   Thu, 30 Jul 2020 14:45:46 +0100
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On 7/30/20 2:33 PM, peterz@infradead.org wrote:
> On Thu, Jul 30, 2020 at 01:40:48PM +0100, Julien Thierry wrote:
>>
>>
>> On 7/30/20 11:03 AM, peterz@infradead.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 { };
> 
> ?

Not sure I am understanding the suggestion. Without #ifdef this will 
conflict with the definition in <asm/orc_types.h> for x86. Or every arch 
needs to provide their own <asm/orc_types.h> and definition of struct 
orc_entry, even if they don't implement the orc subcommand.

Which would be preferable? #ifdef? or arch provided definition? (or 
something I have not thought of)

-- 
Julien Thierry