linux-kernel - Re: [PATCH 0/6] objtool: Add support for Arm64

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Date:   Tue, 9 Apr 2019 22:37:32 -0500
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     Ard Biesheuvel <ard.biesheuvel@...aro.org>
Cc:     Raphael Gault <raphael.gault@....com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        Julien Thierry <julien.thierry@....com>,
        Peter Zijlstra <peterz@...radead.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>
Subject: Re: [PATCH 0/6] objtool: Add support for Arm64

On Tue, Apr 09, 2019 at 10:43:18AM -0700, Ard Biesheuvel wrote:
> On Tue, 9 Apr 2019 at 06:53, Raphael Gault <raphael.gault@....com> wrote:
> >
> > Hi,
> >
> > As of now, objtool only supports the x86_64 architecture but the
> > groundwork has already been done in order to add support for other
> > architecture without too much effort.
> >
> > This series of patches adds support for the arm64 architecture
> > based on the Armv8.5 Architecture Reference Manual.
> >
> 
> I think it makes sense to clarify *why* we want this on arm64. Also,
> we should identify things that objtool does today that maybe we don't
> want on arm64, rather than buy into all of it by default.

Agreed, the "why" should at least be in the cover letter.  From my
perspective, the "why" includes:

- Live patching - objtool stack validation is the foundation for a
  reliable unwinder

- ORC unwinder - benefits include presumed improved overall performance
  from disabling frame pointers, and the ability to unwind across
  interrupts and exceptions

- PeterZ's new uaccess validation?

-- 
Josh