linux-kernel - Re: [RFC PATCH 0/5] make use of gcc 9's "asm inline()"

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Message-ID: <20190829184222.GE1312@zn.tnic>
Date:   Thu, 29 Aug 2019 20:42:22 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Nick Desaulniers <ndesaulniers@...gle.com>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        "H. Peter Anvin" <hpa@...or.com>, Nadav Amit <namit@...are.com>,
        Miguel Ojeda <miguel.ojeda.sandonis@...il.com>,
        Masahiro Yamada <yamada.masahiro@...ionext.com>,
        clang-built-linux <clang-built-linux@...glegroups.com>,
        Joe Perches <joe@...ches.com>
Subject: Re: [RFC PATCH 0/5] make use of gcc 9's "asm inline()"

On Thu, Aug 29, 2019 at 11:15:04AM -0700, Linus Torvalds wrote:
> Un-inlining a function because it contains a single inline asm
> instruction is not productive. Yes, it might result in a smaller
> binary over-all (because all those other non-code sections do take up
> some space), but it actually results in a bigger code footprint.

... and also, like one of the gcc guys said at the time, we should be
careful when using this asm inlining, because, well, if we inline it
everywhere just like always_inline functions and the code footprint
grows considerably, then we get what we deserve.

So the onus is on us to keep such sequences small.

-- 
Regards/Gruss,
    Boris.

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