linux-kernel - Re: [RFC PATCH 7/7] objtool: Make unwind_hints available for all architectures

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Message-ID: <c4518f15-545a-3cb5-214b-29ddc068189b@redhat.com>
Date:   Thu, 11 Jun 2020 08:20:31 +0100
From:   Julien Thierry <jthierry@...hat.com>
To:     Miroslav Benes <mbenes@...e.cz>
Cc:     linux-kernel@...r.kernel.org, jpoimboe@...hat.com,
        peterz@...radead.org, raphael.gault@....com
Subject: Re: [RFC PATCH 7/7] objtool: Make unwind_hints available for all
 architectures

Hi Miroslav,

On 6/10/20 2:20 PM, Miroslav Benes wrote:
> Hi Julien,
> 
> On Mon, 8 Jun 2020, Julien Thierry wrote:
> 
>> Unwind hints are useful to give some information about the call frame
>> or stack states in non-standard code.
>>
>> Despite unwind hints being used in arch-independent code, the
>> unwind_hint structure type itself is define in x86 kernel headers.
>>
>> This is because what an unwind hint will describe is very architecture
>> specific, both regarding the state and the affected registers.
>>
>> To get to share this concept, expose the unwind_hint structure across
>> architecutres. However, the hint types remain defined by the
>> architecture code. Objtool then needs it's arch specific code to
>> "decode" the unwind hint into a cfi_state.
> 
> I think it would be nice to split the patch. Something like.
> 
> 1. current include/linux/frame.h mixes assembly and non-assembly
> definitions, so introduce ASSEMBLY ifdef first seems like a good idea to
> me.
> 
> 2. move the relevant definitions to frame.h and add the file to
> sync-check
> 
> 3. the rest of the patch
> 
> Would it make sense?
> 

Yes, I think your approach will make it simpler to review. I wasn't sure 
how to split it but I like your suggestion, thank you for it.

I'll probably post the split patch separately if the rest of the series 
gets picked.

Cheers,

-- 
Julien Thierry