linux-kernel - Re: [RFC PATCH v1 0/9] arm64: livepatch: Use DWARF Call Frame Information for frame pointer validation

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Message-ID: <20220408114133.GP2731@worktop.programming.kicks-ass.net>
Date:   Fri, 8 Apr 2022 13:41:33 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Josh Poimboeuf <jpoimboe@...hat.com>
Cc:     madvenka@...ux.microsoft.com, mark.rutland@....com,
        broonie@...nel.org, ardb@...nel.org, nobuta.keiya@...itsu.com,
        sjitindarsingh@...il.com, catalin.marinas@....com, will@...nel.org,
        jmorris@...ei.org, linux-arm-kernel@...ts.infradead.org,
        live-patching@...r.kernel.org, linux-kernel@...r.kernel.org,
        chenzhongjin@...wei.com
Subject: Re: [RFC PATCH v1 0/9] arm64: livepatch: Use DWARF Call Frame
 Information for frame pointer validation

Right; so not having seen the patches due to Madhaven's email being
broken, I can perhaps less appreciated the crazy involved.

On Thu, Apr 07, 2022 at 05:21:51PM -0700, Josh Poimboeuf wrote:
> 2)
> 
> If I understand correctly, objtool is converting parts of DWARF to a new
> format which can then be read by the kernel.  In that case, please don't
> call it DWARF as that will cause a lot of confusion.
> 
> There are actually several similarities between your new format and ORC,
> which is also an objtool-created DWARF alternative.  It would be
> interesting to see if they could be combined somehow.

What Josh said; please use/extend ORC.

I really don't understand where all this crazy is coming from; why does
objtool need to do something radically weird for ARM64?

There are existing ARM64 patches for objtool; in fact they have recently
been re-posted:

 https://lkml.kernel.org/r/20220407120141.43801-1-chenzhongjin@huawei.com

The only tricky bit seems to be the whole jump-table issue. Using DWARF
as input to deal with jump-tables should be possible -- exceedingly
overkill, but possible I suppose. Mandating DWARF sucks though, compile
times are so much worse with DWARVES on :/

Once objtool can properly follow/validate ARM64 code, it should be
fairly straight forward to have it generate ORC data just like it does
on x86_64.