linux-kernel - Re: [PATCH v9 02/10] Makefile: Prepare for using macros for inline asm

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Date:   Wed, 7 Nov 2018 11:53:02 -0700
From:   Logan Gunthorpe <logang@...tatee.com>
To:     Nadav Amit <namit@...are.com>, Ingo Molnar <mingo@...hat.com>
Cc:     LKML <linux-kernel@...r.kernel.org>, X86 ML <x86@...nel.org>,
        Sam Ravnborg <sam@...nborg.org>,
        Michal Marek <michal.lkml@...kovi.net>,
        Thomas Gleixner <tglx@...utronix.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>,
        Stephen Bates <sbates@...thlin.com>
Subject: Re: [PATCH v9 02/10] Makefile: Prepare for using macros for inline
 asm



On 2018-11-07 11:01 a.m., Nadav Amit wrote:
> Ideas? Do people care about it?

Just spit balling, but is there a reason we didn't just put the macros
for inline assembly directly in the header? Something like this:

asm(".macro ANNOTATE_UNREACHABLE counter:req\n\t"
    "\\counter:\n\t"
        ".pushsection .discard.unreachable\n\t"
        ".long \\counter\\()b -.\n\t"
        ".popsection\n\t"
    ".endm\n");

#define annotate_unreachable() ({                   \
    asm volatile("ANNOTATE_UNREACHABLE counter=%c0" \
                 : : "i" (__COUNTER__));            \
})

It does mean the macros won't be usable in non-inline assembly, without
duplicating them, but do we care about that?

I would have expected people compiling the kernel with distcc to be
fairly common -- it certainly speeds up my kernel compiles quite
significantly and thus saves me a lot of time.

Logan