Subject: [PATCH 2/3] ARM: fix BUG() detection

From: [email-masked] (Ben Dooks)
Date: Fri, 16 Aug 2013 09:31:48 +0100

On 15/08/13 16:09, Dave Martin wrote:
> On Wed, Aug 14, 2013 at 05:42:42PM +0100, Ben Dooks wrote:
>> The detection of the instruction used by BUG() did not take into account
>> the differences in endian-ness between instruction and data. Change the
>> code to use the relevant helpers in<asm/opcodes.h>  to translate the
>> endian-ness of the instructions.
>>
>> Fixes issue reported by Dave Martin<[email-masked]>
>
> It probably makes sense to fold this with the preceding patch.
>
>>
>> Signed-off-by: Ben Dooks<[email-masked]>
>> ---
>>   arch/arm/include/asm/bug.h |   10 ++++++----
>>   arch/arm/kernel/traps.c    |    8 +++++---
>>   2 files changed, 11 insertions(+), 7 deletions(-)
>>
>> diff --git a/arch/arm/include/asm/bug.h b/arch/arm/include/asm/bug.h
>> index b95da52..b274bde 100644
>> --- a/arch/arm/include/asm/bug.h
>> +++ b/arch/arm/include/asm/bug.h
>> @@ -2,6 +2,8 @@
>>   #define _ASMARM_BUG_H
>>
>>   #include<linux/linkage.h>
>> +#include<linux/types.h>
>> +#include<asm/opcodes.h>
>>
>>   #ifdef CONFIG_BUG
>>
>> @@ -12,10 +14,10 @@
>>    */
>>   #ifdef CONFIG_THUMB2_KERNEL
>>   #define BUG_INSTR_VALUE 0xde02
>> -#define BUG_INSTR_TYPE ".inst.w "
>> +#define BUG_INSTR(__value) __inst_thumb16(__value)
>>   #else
>>   #define BUG_INSTR_VALUE 0xe7f001f2
>> -#define BUG_INSTR_TYPE ".inst "
>> +#define BUG_INSTR(__value) __inst_arm(__value)
>>   #endif
>
> Looks OK.  You could make things a bit less verbose by
>
> 	#define BUG_INSTR __inst_thumb16(BUG_INSTR_VALUE)
> #else
> ...
> 	#define BUG_INSTR __inst_arm(BUG_INSTR_VALUE)

I was trying to keep the macro as similar as possible, although
there is only one bug instruction value at the moment the __BUG()
code seems to assume that in the future there may be more of them
and that it should be able to handle them.

>>
>> @@ -33,7 +35,7 @@
>>
>>   #define __BUG(__file, __line, __value)				\
>>   do {								\
>> -	asm volatile("1:\t" BUG_INSTR_TYPE #__value "\n"	\
>> +	asm volatile("1:\t" BUG_INSTR(__value) "\n"  \
>>   		".pushsection .rodata.str, \"aMS\", %progbits, 1\n" \
>>   		"2:\t.asciz " #__file "\n" 			\
>>   		".popsection\n" 				\
>> @@ -48,7 +50,7 @@ do {								\
>>
>>   #define __BUG(__file, __line, __value)				\
>>   do {								\
>> -	asm volatile(BUG_INSTR_TYPE #__value);			\
>> +	asm volatile(BUG_INSTR(__value) "\n");			\
>>   	unreachable();						\
>>   } while (0)
>>   #endif  /* CONFIG_DEBUG_BUGVERBOSE */
>> diff --git a/arch/arm/kernel/traps.c b/arch/arm/kernel/traps.c
>> index cb67b04..ae2d828 100644
>> --- a/arch/arm/kernel/traps.c
>> +++ b/arch/arm/kernel/traps.c
>> @@ -344,15 +344,17 @@ void arm_notify_die(const char *str, struct pt_regs *regs,
>>   int is_valid_bugaddr(unsigned long pc)
>>   {
>>   #ifdef CONFIG_THUMB2_KERNEL
>> -	unsigned short bkpt;
>> +	u16 bkpt;
>> +	u16 insn = __opcode_to_mem_thumb16(BUG_INSTR_VALUE);
>>   #else
>> -	unsigned long bkpt;
>> +	u32 bkpt;
>> +	u32 insn = __opcode_to_mem_arm(BUG_INSTR_VALUE);
>>   #endif
>>
>>   	if (probe_kernel_address((unsigned *)pc, bkpt))
>
> Hmm, the (unsigned *) actually looks weird here now I look at it.
>
> probe_kernel_address does (__force typeof(bkpt) __user *) on it anyway,
> so I guess that's harmless.  void * might make more sense, though this
> patch may not be the place to fix it.
>
> Cheers
> ---Dave
>
>>   		return 0;
>>
>> -	return bkpt == BUG_INSTR_VALUE;
>> +	return bkpt == insn;
>>   }
>>
>>   #endif
>> --
>> 1.7.10.4
>>
>>
>> _______________________________________________
>> linux-arm-kernel mailing list
>> linux-arm-kernel at lists.infradead.org
>> http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

-- 
Ben Dooks				http://www.codethink.co.uk/
Senior Engineer				Codethink - Providing Genius