Subject: [PATCH 2/4] ARM: traps: use <asm/opcodes.h> to get correct instruction order

From: [email-masked] (Dave Martin)
Date: Fri, 26 Jul 2013 17:04:42 +0100

On Thu, Jul 25, 2013 at 12:17:59PM +0100, Ben Dooks wrote:
> On 24/07/13 18:34, Dave Martin wrote:
> >On Mon, Jul 22, 2013 at 05:33:51PM +0100, Ben Dooks wrote:
> >>The trap handler needs to take into account the endian configuration of
> >>the system when loading instructions. Use<asm/opcodes.h>  to provide the
> >>necessary conversion functions.
> >>
> >>Signed-off-by: Ben Dooks<[email-masked]>
> >>---
> >>  arch/arm/kernel/traps.c |   10 ++++++----
> >>  1 file changed, 6 insertions(+), 4 deletions(-)
> >>
> >>diff --git a/arch/arm/kernel/traps.c b/arch/arm/kernel/traps.c
> >>index 1c08911..0a56e13 100644
> >>--- a/arch/arm/kernel/traps.c
> >>+++ b/arch/arm/kernel/traps.c
> >>@@ -34,6 +34,7 @@
> >>  #include<asm/unwind.h>
> >>  #include<asm/tls.h>
> >>  #include<asm/system_misc.h>
> >>+#include<asm/opcodes.h>
> >>
> >>  #include "signal.h"
> >
> >Looks like is_valid_bugaddr() might need fixing too?
> >
> >That will need __mem_to_opcode_thumb16() or __mem_to_opcode_arm()
> >depending on CONFIG_THUMB2_KERNEL.
> 
> I was looking at that, and was considering if this is the right
> thing to do or to change the value of BUG_INSTR_VALUE depending
> on this.
> 
> It is possible the linker may try and change the ordering of the
> BUG() instruction as it is being placed in the output with either
> a .hword or .word value. I will go and check this as soon as possible.

I guess the way would be to leave BUG_INSTR_VALUE as-is, and
inject it into the code using the appropriate __inst (similarly to the
KGDB case).

> 
> >>@@ -411,23 +412,24 @@ asmlinkage void __exception do_undefinstr(struct pt_regs *regs)
> >>  	if (processor_mode(regs) == SVC_MODE) {
> >>  #ifdef CONFIG_THUMB2_KERNEL
> >>  		if (thumb_mode(regs)) {
> >>-			instr = ((u16 *)pc)[0];
> >>+			instr = __mem_to_opcode_thumb16(((u16 *)pc)[0]);
> >>  			if (is_wide_instruction(instr)) {
> >>  				instr<<= 16;
> >>-				instr |= ((u16 *)pc)[1];
> >>+				instr |= __mem_to_opcode_thumb16(((u16 *)pc)[1]);
> >
> >Could use __opcode_thumb32_compose(), in which case it might look like
> >
> >			if (is_wide_instruction(instr)) {
> >				unsigned int instr2 = __mem_to_opcode_thumb16(
> >					((u16 *)pc)[1]);
> >				instr = __opcode_thumb32_compose(instr, instr2);
> >
> >(Hmmm, I just noticed that is_wide_instruction and __opcode_is_thumb16()
> >kinda duplicate each other.  Could change that too, but it would look
> >more like pointless churn...  is_wide_instruction() is used in a fair
> >few places already.)
> 
> It is possible that it could be changed, but I will avoid that for this
> particular patch

No problem, that was just cosmetic.

> 
> >>  			}
> >>  		} else
> >>  #endif
> >>-			instr = *(u32 *) pc;
> >>+			instr = __mem_to_opcode_arm(*(u32 *) pc);
> >>  	} else if (thumb_mode(regs)) {
> >>  		if (get_user(instr, (u16 __user *)pc))
> >>  			goto die_sig;
> >>+		instr = __mem_to_opcode_thumb16(instr);
> >>  		if (is_wide_instruction(instr)) {
> >>  			unsigned int instr2;
> >>  			if (get_user(instr2, (u16 __user *)pc+1))
> >>  				goto die_sig;
> >>  			instr<<= 16;
> >>-			instr |= instr2;
> >>+			instr |= __mem_to_opcode_thumb16(instr2);
> >>  		}
> >>  	} else if (get_user(instr, (u32 __user *)pc)) {
> >
> >This also needs mem-to-opcode'ing.
> 
> Thanks, will check.

OK.

Cheers
---Dave