linux-kernel - Re: [PATCH] ARM: mtd-xip: work around clang/llvm bug

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Date:   Tue, 9 Jul 2019 11:07:51 -0700
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Linus Walleij <linus.walleij@...aro.org>
Cc:     Arnd Bergmann <arnd@...db.de>,
        Russell King <linux@...linux.org.uk>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        clang-built-linux <clang-built-linux@...glegroups.com>
Subject: Re: [PATCH] ARM: mtd-xip: work around clang/llvm bug

On Tue, Jul 9, 2019 at 1:41 AM Linus Walleij <linus.walleij@...aro.org> wrote:
>
> On Mon, Jul 8, 2019 at 10:31 PM Arnd Bergmann <arnd@...db.de> wrote:
>
> > llvm gets confused by inline asm with .rep directives,
>
> Are the LLVM developers aware of the bug?
> It seems like something we can work around but should
> eventually be fixed properly in LLVM, right?

Arnd filed the bug yesterday.  I looked at it; so someone working on
LLVM is aware of it.  The kernel is definitely exercising weak points
in our inline assembly support.

> > Link: https://bugs.llvm.org/show_bug.cgi?id=42539

> I guess this brings up the old question whether the compiler should
> be worked around or just considered immature, but as it happens this

Definitely a balancing act; we prioritize work based on what's
feasible to work around vs must be implemented.  A lot of my time is
going into validation of asm goto right now, but others are ramping up
on the integrated assembler (clang itself can be invoked as a
substitute for GNU AS; but there's not enough support to do `make
AS=clang` for the kernel just yet).
-- 
Thanks,
~Nick Desaulniers