Re: Understanding gdb disassembly output

[Jon Masters <jcm@xxxxxxxxxx>]

On 05/01/2012 05:31 PM, Jon Masters wrote:
> On 05/01/2012 05:10 PM, Daniel Drake wrote:
> 
>> Specifically this bit looks of interest:
>>
>>    0x499fe5d4:	ldr	r8, [pc, #31461008]	; 0x499fea44
>>    0x499fe5d8:	blx	r8
>>
>> So the first instruction here says "take the data at address
>> pc+31461008 and save it in r8".
>> pc is always 8 bytes on from the address of the current instruction,
>> so at the moment pc = 0x499fe5d4 + 8 = 0x499fe5dc
> 
> I failed to spell out on IRC that the value you want for the offset is
> the one in the comment (value_in_comment). The raw #31461008 contains
> non-addressing bits taken from the ARM encoding. So actually, it's
> saying to load r8 with the value at 0x499fea44.
> 
> The gory details are in print_arm_address in gdb, which is also where
> we'll add 8 to the value of the pc in the offset so you don't need to.
> 
> Perhaps sometime someone might document gdb on ARM a little more...

Someone on #linaro told me they thought that this represented a gdb bug.
I think it's intended behavior, but I'll bring it up.

Jon.

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