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

From: [email-masked] (Dave Martin)
Date: Fri, 16 Aug 2013 14:24:51 +0100

On Fri, Aug 16, 2013 at 09:31:48AM +0100, Ben Dooks wrote:
> 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.

No problem, it should work fine your way.

Cheers
---Dave

> 
> >>
> >>@@ -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
> 
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