linux-kernel - Re: [PATCH v2 4/6] compiler-gcc.h: add asm

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Message-ID: <20190920005044.GN9749@gate.crashing.org>
Date:   Thu, 19 Sep 2019 19:50:44 -0500
From:   Segher Boessenkool <segher@...nel.crashing.org>
To:     Nick Desaulniers <ndesaulniers@...gle.com>
Cc:     Jakub Jelinek <jakub@...hat.com>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        Miguel Ojeda <miguel.ojeda.sandonis@...il.com>,
        "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        "gcc-patches@....gnu.org" <gcc-patches@....gnu.org>,
        clang-built-linux <clang-built-linux@...glegroups.com>
Subject: Re: [PATCH v2 4/6] compiler-gcc.h: add asm_inline definition

On Thu, Sep 12, 2019 at 02:54:50PM -0700, Nick Desaulniers wrote:
> I have seen instances where instruction selection fails to select the
> appropriate way to branch when inline asm size is misjudged, resulting
> in un-encodeable jumps (as in the branch target is too far to be
> encoded in the number of bits of a single jump/branch instruction).

"asm inline" *only* influences the estimated size *for inlining
purposes*.  Not for anything else.  Everything else still uses
conservative estimates.


Segher