linux-kernel - Re: [RFC PATCH v2 09/20] objtool: arm64: Implement command to invoke the decoder

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Date:   Wed, 1 Jun 2022 17:45:20 -0500
From:   "Madhavan T. Venkataraman" <madvenka@...ux.microsoft.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Mark Brown <broonie@...nel.org>, jpoimboe@...hat.com,
        chenzhongjin@...wei.com, mark.rutland@....com,
        nobuta.keiya@...itsu.com, sjitindarsingh@...il.com,
        catalin.marinas@....com, will@...nel.org,
        jamorris@...ux.microsoft.com, linux-arm-kernel@...ts.infradead.org,
        live-patching@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH v2 09/20] objtool: arm64: Implement command to invoke
 the decoder



On 5/30/22 02:51, Peter Zijlstra wrote:
> On Sun, May 29, 2022 at 09:49:44AM -0500, Madhavan T. Venkataraman wrote:
>>
>>
>> On 5/24/22 09:09, Mark Brown wrote:
>>> On Mon, May 23, 2022 at 07:16:26PM -0500, madvenka@...ux.microsoft.com wrote:
>>>> From: "Madhavan T. Venkataraman" <madvenka@...ux.microsoft.com>
>>>>
>>>> Implement a built-in command called cmd_fpv() that can be invoked as
>>>> follows:
>>>>
>>>> 	objtool fpv generate file.o
>>>>
>>>> The built-in command invokes decode_instructions() to walk each function
>>>> and decode the instructions of the function.
>>>
>>> In commit b51277eb9775ce91 ("objtool: Ditch subcommands") Josh removed
>>> subcommands so this interface is going to need a rethink.
>>
>> Thanks for mentioning this. I will sync my patchset to the latest and send out version 3.
> 
> Before you do; why are you duplicating lots of validate_branch() ? Why
> can't you use the regular code to generate ORC data?
> 
> I'm really not happy about all this.

Hi Peter,

I am preparing a detailed response to this explaining why I have not used validate_branch().
The short answer is that no validation is required for my approach. But I will send my detailed
response shortly.

Thanks.

Madhavan