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

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Message-ID: <CACRpkdZO6to2UsJ64FCYi3aOC79PEb9pxOBABBkgcmR_d82dYg@mail.gmail.com>
Date:   Tue, 9 Jul 2019 14:17:58 +0200
From:   Linus Walleij <linus.walleij@...aro.org>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     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@...glegroups.com
Subject: Re: [PATCH] ARM: mtd-xip: work around clang/llvm bug

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.

Yours,
Linus Walleij