linux-kernel - Re: [PATCH v2 11/18] arm64: make mrs_s and msr

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Message-ID: <20171116171152.GH94341@samitolvanen.mtv.corp.google.com>
Date:   Thu, 16 Nov 2017 09:11:52 -0800
From:   Sami Tolvanen <samitolvanen@...gle.com>
To:     Segher Boessenkool <segher@...nel.crashing.org>
Cc:     Yury Norov <ynorov@...iumnetworks.com>,
        Will Deacon <will.deacon@....com>,
        Alex Matveev <alxmtvv@...il.com>,
        Andi Kleen <ak@...ux.intel.com>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Greg Hackmann <ghackmann@...gle.com>,
        Kees Cook <keescook@...omium.org>,
        linux-arm-kernel@...ts.infradead.org, linux-kbuild@...r.kernel.org,
        linux-kernel@...r.kernel.org, Mark Rutland <mark.rutland@....com>,
        Masahiro Yamada <yamada.masahiro@...ionext.com>,
        Maxim Kuvyrkov <maxim.kuvyrkov@...aro.org>,
        Michal Marek <michal.lkml@...kovi.net>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Matthias Kaehlcke <mka@...omium.org>
Subject: Re: [PATCH v2 11/18] arm64: make mrs_s and msr_s macros work with LTO

On Thu, Nov 16, 2017 at 11:01:44AM -0600, Segher Boessenkool wrote:
> The thing with .purgem can work.  Inelegant, sure, but it can work :-)

It works, there are already functions in the kernel that use these
macros more than once. I agree that this might not be the most elegant
solution, but at least it allows us to use the same code path for both
compilers.

> Just make sure you do the macro define, the code that uses it, and the
> undefine, all in the same inline asm statement.

Yes, that's what we're doing here. Only KVM uses msr_s/msr_s directly,
everything else uses the (read|write)_sysreg_s wrappers instead, which
means the DEFINE/UNDEFINE macros are only needed in few places.

Sami