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SubjectRe: [PATCH] [v2] arm64: define BUG() instruction without CONFIG_BUG
Hi Arnd,

On Tue, Mar 14, 2017 at 10:39:21PM +0100, Arnd Bergmann wrote:
> This mirrors commit e9c38ceba8d9 ("ARM: 8455/1: define __BUG as
> asm(BUG_INSTR) without CONFIG_BUG") to make the behavior of
> arm64 consistent with arm and x86, and avoids lots of warnings in
> randconfig builds, such as:
>
> kernel/seccomp.c: In function '__seccomp_filter':
> kernel/seccomp.c:666:1: error: no return statement in function returning non-void [-Werror=return-type]
>
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>
> ---
> Originally submitted v1 on Feb 14 as a simple addition of a few lines.
> v2 is a new version doing the same thing with a cleaner rewrite of
> the file, using three lines less, after a suggested from Will Deacon.
>
> No need to get this into v4.11 though, especially as the rewrite
> makes it a bit risky. Please queue this for v4.12 if you like the
> new version.
> ---
> arch/arm64/include/asm/bug.h | 34 ++++++++++++++++++++--------------
> 1 file changed, 20 insertions(+), 14 deletions(-)

Thanks for updating this. It looks correct to me, but I have one question
below.

> diff --git a/arch/arm64/include/asm/bug.h b/arch/arm64/include/asm/bug.h
> index 561190d15881..bfc6021760e5 100644
> --- a/arch/arm64/include/asm/bug.h
> +++ b/arch/arm64/include/asm/bug.h
> @@ -20,9 +20,6 @@
>
> #include <asm/brk-imm.h>
>
> -#ifdef CONFIG_GENERIC_BUG
> -#define HAVE_ARCH_BUG
> -
> #ifdef CONFIG_DEBUG_BUGVERBOSE
> #define _BUGVERBOSE_LOCATION(file, line) __BUGVERBOSE_LOCATION(file, line)
> #define __BUGVERBOSE_LOCATION(file, line) \
> @@ -36,28 +33,37 @@
> #define _BUGVERBOSE_LOCATION(file, line)
> #endif
>
> -#define _BUG_FLAGS(flags) __BUG_FLAGS(flags)
> +#ifdef CONFIG_GENERIC_BUG
>
> -#define __BUG_FLAGS(flags) asm volatile ( \
> +#define __BUG_ENTRY(flags) \
> ".pushsection __bug_table,\"a\"\n\t" \
> ".align 2\n\t" \
> "0: .long 1f - 0b\n\t" \
> _BUGVERBOSE_LOCATION(__FILE__, __LINE__) \
> ".short " #flags "\n\t" \
> ".popsection\n" \
> - \
> - "1: brk %[imm]" \
> - :: [imm] "i" (BUG_BRK_IMM) \
> -)
> + "1: "
> +#else
> +#define __BUG_ENTRY(flags) ""
> +#endif
> +
> +#define __BUG_FLAGS(flags) \
> + asm volatile ( \
> + __BUG_ENTRY(0) \
> + "brk %[imm]" :: [imm] "i" (BUG_BRK_IMM) \
> + );
>
> -#define BUG() do { \
> - _BUG_FLAGS(0); \
> - unreachable(); \
> +#define _BUG_FLAGS(flags) __BUG_FLAGS(flags)

What is this for? I don't see _BUG_FLAGS used anywhere, but I could
be missing some macro expansion.

Will

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