linux-kernel - Re: [PATCH 1/3] Compiler attributes: Introduce the __preserve

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Date:   Wed, 2 Aug 2023 19:08:51 +0200
From:   Miguel Ojeda <miguel.ojeda.sandonis@...il.com>
To:     Marco Elver <elver@...gle.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Kees Cook <keescook@...omium.org>,
        Guenter Roeck <linux@...ck-us.net>,
        Marc Zyngier <maz@...nel.org>,
        Oliver Upton <oliver.upton@...ux.dev>,
        James Morse <james.morse@....com>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        Zenghui Yu <yuzenghui@...wei.com>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>, Miguel Ojeda <ojeda@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Nathan Chancellor <nathan@...nel.org>,
        Tom Rix <trix@...hat.com>,
        linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.linux.dev,
        linux-kernel@...r.kernel.org, llvm@...ts.linux.dev,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Alexander Potapenko <glider@...gle.com>,
        kasan-dev@...glegroups.com, linux-toolchains@...r.kernel.org,
        Mark Rutland <mark.rutland@....com>,
        Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH 1/3] Compiler attributes: Introduce the __preserve_most
 function attribute

On Wed, Aug 2, 2023 at 6:51 PM Marco Elver <elver@...gle.com> wrote:
>
> Mark says that there may be an issue with using this in combination
> with ftrace because arm64 tracing relies on AAPCS. Probably not just
> arm64, but also other architectures (x86?).
>
> To make this safe, I'm going to move __preserve_most to
> compiler_types.h and always pair it with notrace and some comments in
> v2.

Sounds good, thanks! The patch here was otherwise good in terms of
`compiler_attributes.h`.

I was also thinking about the implications for Rust. I guess if we
need to call them, we will go through a C helper for the moment, and
later on if we get cross-language LTO (or the LLVM IR hacks), it will
hopefully not be a performance penalty.

Cheers,
Miguel