[PATCH] arm64: define BUG() instruction without CONFIG_BUG

[PATCH] arm64: define BUG() instruction without CONFIG_BUG

[Arnd Bergmann]

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>
---
 arch/arm64/include/asm/bug.h | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/include/asm/bug.h b/arch/arm64/include/asm/bug.h
index 561190d15881..461751429fc3 100644
--- a/arch/arm64/include/asm/bug.h
+++ b/arch/arm64/include/asm/bug.h
@@ -20,9 +20,10 @@
 
 #include <asm/brk-imm.h>
 
-#ifdef CONFIG_GENERIC_BUG
 #define HAVE_ARCH_BUG
 
+#ifdef CONFIG_GENERIC_BUG
+
 #ifdef CONFIG_DEBUG_BUGVERBOSE
 #define _BUGVERBOSE_LOCATION(file, line) __BUGVERBOSE_LOCATION(file, line)
 #define __BUGVERBOSE_LOCATION(file, line)				\
@@ -57,6 +58,14 @@ _BUGVERBOSE_LOCATION(__FILE__, __LINE__)		\
 
 #define __WARN_TAINT(taint) _BUG_FLAGS(BUGFLAG_TAINT(taint))
 
+#else
+
+#define BUG() do {					\
+	asm volatile("brk %[imm]"			\
+		     :: [imm] "i" (BUG_BRK_IMM));	\
+	unreachable();					\
+} while (0)
+
 #endif /* ! CONFIG_GENERIC_BUG */
 
 #include <asm-generic/bug.h>
-- 
2.9.0

[PATCH] arm64: define BUG() instruction without CONFIG_BUG

[Will Deacon]

On Tue, Feb 14, 2017 at 10:39:28PM +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>
> ---
>  arch/arm64/include/asm/bug.h | 11 ++++++++++-
>  1 file changed, 10 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/arm64/include/asm/bug.h b/arch/arm64/include/asm/bug.h
> index 561190d15881..461751429fc3 100644
> --- a/arch/arm64/include/asm/bug.h
> +++ b/arch/arm64/include/asm/bug.h
> @@ -20,9 +20,10 @@
>  
>  #include <asm/brk-imm.h>
>  
> -#ifdef CONFIG_GENERIC_BUG
>  #define HAVE_ARCH_BUG
>  
> +#ifdef CONFIG_GENERIC_BUG
> +
>  #ifdef CONFIG_DEBUG_BUGVERBOSE
>  #define _BUGVERBOSE_LOCATION(file, line) __BUGVERBOSE_LOCATION(file, line)
>  #define __BUGVERBOSE_LOCATION(file, line)				\
> @@ -57,6 +58,14 @@ _BUGVERBOSE_LOCATION(__FILE__, __LINE__)		\
>  
>  #define __WARN_TAINT(taint) _BUG_FLAGS(BUGFLAG_TAINT(taint))
>  
> +#else
> +
> +#define BUG() do {					\
> +	asm volatile("brk %[imm]"			\
> +		     :: [imm] "i" (BUG_BRK_IMM));	\
> +	unreachable();					\
> +} while (0)

Do we need to duplicate the asm, or can we reuse the existing BUG
definition in this header? The only extra thing we do is push a __bug_table
entry, but I can't see why that would be a problem.

Will

[PATCH] arm64: define BUG() instruction without CONFIG_BUG

[Arnd Bergmann]

On Wed, Feb 15, 2017 at 12:22 PM, Will Deacon <will.deacon@arm.com> wrote:
> On Tue, Feb 14, 2017 at 10:39:28PM +0100, Arnd Bergmann wrote:
>> @@ -57,6 +58,14 @@ _BUGVERBOSE_LOCATION(__FILE__, __LINE__)           \
>>
>>  #define __WARN_TAINT(taint) _BUG_FLAGS(BUGFLAG_TAINT(taint))
>>
>> +#else
>> +
>> +#define BUG() do {                                   \
>> +     asm volatile("brk %[imm]"                       \
>> +                  :: [imm] "i" (BUG_BRK_IMM));       \
>> +     unreachable();                                  \
>> +} while (0)
>
> Do we need to duplicate the asm, or can we reuse the existing BUG
> definition in this header? The only extra thing we do is push a __bug_table
> entry, but I can't see why that would be a problem.

The only reason for turning off CONFIG_BUG is to save a little extra space
in the kernel image, so I think we really don't want the __bug_table to be
generated.

However, we could split the existing asm in two and have only one definition
for the asm containing the brk instruction.

     Arnd