[PATCH 1/4] ARM: ftrace: use canonical Thumb-2 wide instruction format

[Dave Martin]

On Tue, Nov 22, 2011 at 11:30:11PM +0530, Rabin Vincent wrote:
> On Tue, Nov 22, 2011 at 17:32, Dave Martin <dave.martin at linaro.org> wrote:
> > On Mon, Nov 21, 2011 at 08:43:46PM +0530, Rabin Vincent wrote:
> >> +#ifndef __ARMEB__
> >> +     if (IS_ENABLED(CONFIG_THUMB2_KERNEL)) {
> >> +             old = (old >> 16) | (old << 16);
> >> +             new = (new >> 16) | (new << 16);
> >
> > I think swahw32() in <linux/swab.h> can be used for this operation.
> 
> Yes.
> 
> > Really though, we need a common set of "load and store instruction"
> > macros, rather than duplicating this knowledge everywhere.
> 
> Yes, though this ftrace code may not be able to use them directly since
> it uses probe_kernel_read()/write().

In that case what we would want are macros to convert instructions between
integer and in-memory representation, rather than conflating all that
together in some memory accessor macros.

How about:

#include <linux/swab.h>

#ifdef __ARMEB__
#define insn_to_mem_arm(insn) swab32(insn)
#define insn_to_mem_thumb16(insn) swab16(insn)
#define insn_to_mem_thumb32(insn) swab16(insn)
#else
#define insn_to_mem_arm(insn) (insn)
#define insn_to_mem_thumb16(insn) (insn)
#define insn_to_mem_thumb32(insn) shahw32(insn)
#endif

#define mem_to_insn_arm(insn) insn_to_mem_asm(insn)
#define mem_to_insn_thumb16(insn) insn_to_mem_thumb16(insn)
#define mem_to_insn_thumb32(insn) insn_to_mem_thumb32(insn)

Because these are all straightforward swap operations, we don't really
need separate forwards and backwards operations, but having the separate
names may make calling code easier to read.

I'm still not sure exactly which header this belongs in, but it's a core
ARM thing; not local to kprobes or ftrace, etc.


If this looks sensible, it would also make sense for Junxiao Bi to build
his big-endian fixes on it.

Cheers
---Dave