[patch] Fix PR tdep/12352: Handle str pc, [Rd, #imm] in displaced stepping

[Yao Qi]

On 01/22/2011 11:07 PM, Richard Earnshaw wrote:
> On 28/12/10 16:41, Yao Qi wrote:
>> When I read arm-tdep.c:copy_ldr_str_ldrb_strb, I feel pretty hard to
>> understand two lines of code,
>>
>>       dsc->modinsn[0] = 0xe58ff014;  /* str pc, [pc, #20].  */
>>       dsc->modinsn[1] = 0xe59f4010;  /* ldr r4, [pc, #16].  */
> 
> Hmm, looks like a rather convoluted way of moving the PC into R4.
> Julian, I think this patch was yours... can you remember why  "MOV R4,
> PC" wasn't sufficient?
> 

IIUC, these two instructions together with 'sub r4, r4, pc' are used to
calculate the offset of 'str pc ADDR', which is 8 or
12(implementation-dependent, but consistent for a given device).
AFAIK, 'mov r4, pc' doesn't help.

-- 
Yao (齐尧)