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

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Date:   Tue, 9 Jul 2019 13:25:50 +0100
From:   Russell King - ARM Linux admin <linux@...linux.org.uk>
To:     Linus Walleij <linus.walleij@...aro.org>
Cc:     Arnd Bergmann <arnd@...db.de>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        clang-built-linux@...glegroups.com
Subject: Re: [PATCH] ARM: mtd-xip: work around clang/llvm bug

On Tue, Jul 09, 2019 at 02:17:58PM +0200, Linus Walleij wrote:
> On Mon, Jul 8, 2019 at 10:31 PM Arnd Bergmann <arnd@...db.de> wrote:
> 
> > -#define xip_iprefetch()        do { asm volatile (".rep 8; nop; .endr"); } while (0)
> > +#define xip_iprefetch()        do {                                            \
> > +        asm volatile ("nop; nop; nop; nop; nop; nop; nop; nop;");      \
> > +} while (0)                                                            \
> 
> This is certainly an OK fix since we use a row of inline nop at
> other places.
> 
> However after Russell explained the other nops I didn't understand I located
> these in boot/compressed/head.S as this in __start:
> 
>                 .rept   7
>                 __nop
>                 .endr
> #ifndef CONFIG_THUMB2_KERNEL
>                 mov     r0, r0
> #else
> 
> And certainly this gets compiled, right?
> 
> So does .rept/.endr work better than .rep/.endr, is it simply mis-spelled?
> 
> I.e. s/.rep/.rept/g
> ?
> 
> In that case we should explain in the commit that .rep doesn't work
> but .rept does.

According to the info pages for gas:

7.96 `.rept COUNT'
==================

Repeat the sequence of lines between the `.rept' directive and the next
`.endr' directive COUNT times.

So yes, ".rep" is mis-spelled, and it brings up the obvious question:
why isn't gas issuing an error for ".rep"?  There is no mention of
".rep" in the manual.

-- 
RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
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