Re: Disassembling ARM and Thumb code

[Shaun Jackman <sjackman at gmail dot com>]

On 5/5/05, Daniel Jacobowitz <drow@false.org> wrote:
> On Thu, May 05, 2005 at 05:05:56PM -0700, Shaun Jackman wrote:
> > My ARM7TDMI processor is currently in Thumb mode, but the x/i command
> > dissects the instruction as an ARM instruction. The symbol
> > rdp_getargvsp is a Thumb symbol added using add-symbol-file [elf
> > binary here]. What is the command to disassemble a given memory
> > location as a Thumb instruction?
> 
> How is it marked as Thumb in the binary?

It's marked with a $t symbol at the same address.

$ nm busybox | grep 020004dd
020004dd t $t
020004dd t rdp_getargvsp

I haven't read this in documentation; only noticed it from empirical
evidence. For example, here's a symbol compiled for ARM marked with a
$a symbol at the same address.

$ nm hello | grep 000081f8
000081f8 t $a
000081f8 T main

> GDB does not use the current CPSR value when disassembling; that way
> lies madness.

Hehe. I agree, that's probably not the best plan. However, for the
unique case of 'x/i $pc' it does make a certain amount of sense to use
the CPSR as a hint. I'm not sure if it's worth the special case
though. An explicit switch to the x/i and disas commands to specify
ARM or Thumb dissection is very much a good idea though.

Cheers,
Shaun