From: Nick Desaulniers <ndesaulniers@google.com>
To: Arnd Bergmann <arnd@arndb.de>
Cc: Russell King <linux@armlinux.org.uk>,
Linux ARM <linux-arm-kernel@lists.infradead.org>,
LKML <linux-kernel@vger.kernel.org>,
clang-built-linux <clang-built-linux@googlegroups.com>
Subject: Re: [PATCH] ARM: mtd-xip: work around clang/llvm bug
Date: Mon, 8 Jul 2019 13:54:53 -0700 [thread overview]
Message-ID: <CAKwvOdnt5Gb8YSZ848s1RsMSJV37iJJWCxu84kFnV0yv35VKAg@mail.gmail.com> (raw)
In-Reply-To: <20190708203049.3484750-1-arnd@arndb.de>
On Mon, Jul 8, 2019 at 1:31 PM Arnd Bergmann <arnd@arndb.de> wrote:
>
> llvm gets confused by inline asm with .rep directives, which
> can lead to miscalculating the number of instructions inside it,
> and in turn lead to an overflow for relative address calculation:
>
> /tmp/cfi_cmdset_0002-539a47.s: Assembler messages:
> /tmp/cfi_cmdset_0002-539a47.s:11288: Error: bad immediate value for offset (4100)
> /tmp/cfi_cmdset_0002-539a47.s:11289: Error: bad immediate value for offset (4100)
>
> This might be fixed in future clang versions, but is not hard
> to work around by just replacing the .rep with a series of
> eight unrolled nop instructions.
Seems like this is fixable on the Clang side as well. For now, thanks
for the patch.
Acked-by: Nick Desaulniers <ndesaulniers@google.com>
>
> Link: https://bugs.llvm.org/show_bug.cgi?id=42539
> https://godbolt.org/z/DSM2Jy
^ prefix with Link: on both lines?
also, linking to clang trunk will become stale once the issue is
fixed. When possible, link to a release version of clang that's not
prone to change over time.
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>
> ---
> arch/arm/include/asm/mtd-xip.h | 4 +++-
> 1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/arch/arm/include/asm/mtd-xip.h b/arch/arm/include/asm/mtd-xip.h
> index dfcef0152e3d..5ad0325604e4 100644
> --- a/arch/arm/include/asm/mtd-xip.h
> +++ b/arch/arm/include/asm/mtd-xip.h
> @@ -15,6 +15,8 @@
> #include <mach/mtd-xip.h>
>
> /* fill instruction prefetch */
> -#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) \
--
Thanks,
~Nick Desaulniers
next prev parent reply other threads:[~2019-07-08 20:55 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-07-08 20:30 [PATCH] ARM: mtd-xip: work around clang/llvm bug Arnd Bergmann
2019-07-08 20:54 ` Nick Desaulniers [this message]
2019-07-09 8:41 ` Linus Walleij
2019-07-09 9:17 ` Russell King - ARM Linux admin
2019-07-09 11:48 ` Linus Walleij
2019-07-09 18:07 ` Nick Desaulniers
2019-07-09 18:40 ` Arnd Bergmann
2019-07-09 22:25 ` Russell King - ARM Linux admin
2019-07-10 8:33 ` Arnd Bergmann
2019-07-10 8:58 ` Russell King - ARM Linux admin
2019-07-09 12:17 ` Linus Walleij
2019-07-09 12:25 ` Russell King - ARM Linux admin
2019-07-09 18:11 ` Nick Desaulniers
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