linux-kernel - Re: [PATCH] kbuild, x86: revert macros in extended asm workarounds

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Message-ID: <20181216100042.GA815@zn.tnic>
Date:   Sun, 16 Dec 2018 11:00:42 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     Nadav Amit <namit@...are.com>,
        Masahiro Yamada <yamada.masahiro@...ionext.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        "H . Peter Anvin" <hpa@...or.com>, X86 ML <x86@...nel.org>,
        Richard Biener <rguenther@...e.de>,
        Logan Gunthorpe <logang@...tatee.com>,
        Sedat Dilek <sedat.dilek@...il.com>,
        Segher Boessenkool <segher@...nel.crashing.org>,
        linux-arch <linux-arch@...r.kernel.org>,
        Arnd Bergmann <arnd@...db.de>,
        Luc Van Oostenryck <luc.vanoostenryck@...il.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "virtualization@...ts.linux-foundation.org" 
        <virtualization@...ts.linux-foundation.org>,
        Michal Marek <michal.lkml@...kovi.net>,
        "linux-sparse@...r.kernel.org" <linux-sparse@...r.kernel.org>,
        Alok Kataria <akataria@...are.com>,
        Juergen Gross <jgross@...e.com>,
        Andy Lutomirski <luto@...nel.org>,
        Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>
Subject: Re: [PATCH] kbuild, x86: revert macros in extended asm workarounds

On Sun, Dec 16, 2018 at 02:33:39AM +0000, Nadav Amit wrote:
> In general, I think that from the start it was clear that the motivation for
> the patch-set is not just performance and also better code. For example, I
> see no reason to revert the PV-changes or the lock-prefix changes that
> improved the code readability.

One thing that has caught my eye with the asm macros, which actually
decreases readability, is that I can't see the macro properly expanded
when I do

make <filename>.s

For example, I get

#APP
# 164 "./arch/x86/include/asm/cpufeature.h" 1
        STATIC_CPU_HAS bitnum=$8 cap_byte="boot_cpu_data+35(%rip)" feature=123 t_yes=.L75 t_no=.L78 always=117  #, MEM[(const char *)&boot_cpu_data + 35B],,,,
# 0 "" 2
        .loc 11 164 2 view .LVU480
#NO_APP

but I'd like to see the actual asm as it is really helpful when hacking
on inline asm stuff. And I haven't found a way to make gcc expand asm
macros in .s output.

Now, assuming the gcc inline patch will be backported to gcc8, I think
we should be covered on all modern distros going forward. So I think we
should revert at least the more complex macros.

-- 
Regards/Gruss,
    Boris.

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