linux-kernel - Re: [PATCH v4] x86, mem: move memmove to out of line assembler

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Message-ID: <CAHk-=wgXWNx_c7XsYLRtKTpG2L0uVJuSm=hOX81m7Lb=U4PWHA@mail.gmail.com>
Date:   Fri, 30 Sep 2022 09:46:48 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Nick Desaulniers <ndesaulniers@...gle.com>
Cc:     David Laight <David.Laight@...lab.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "x86@...nel.org" <x86@...nel.org>,
        "H . Peter Anvin" <hpa@...or.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Kees Cook <keescook@...omium.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "llvm@...ts.linux.dev" <llvm@...ts.linux.dev>,
        Andy Lutomirski <luto@...nel.org>,
        Rasmus Villemoes <linux@...musvillemoes.dk>
Subject: Re: [PATCH v4] x86, mem: move memmove to out of line assembler

On Fri, Sep 30, 2022 at 9:43 AM Nick Desaulniers
<ndesaulniers@...gle.com> wrote:
>
> On Fri, Sep 30, 2022 at 2:55 AM David Laight <David.Laight@...lab.com> wrote:
> >
> > Oh - and why do all the labels have 'byteswap' in them?
>
> .Lbyteswap is swapping single bytes at a time.
> .L4_byteswap is swapping 4 bytes at a time.
> .L8_byteswap is swapping 8 bytes at a time.
> .L16_byteswap, .L16_byteswap_backwards_loop, and
> .L16_byteswap_forwards_loop are swapping 16 bytes at a time.

I think the objection here is that there is no "swap".

A "byte swap" in particular is generally a byte order operation (ie
swapping bytes within one word). And "swap" in general is about
switching the value of two things.

Here, the "byteswap" code sequences just move data in one direction.
No "swap" anywhere that I can see.

             Linus