winedbg: Respect Thumb mode when adjusting PC on ARM

André Hentschel nerv at dawncrow.de
Sun Mar 11 07:32:29 CDT 2012


Am 11.03.2012 09:40, schrieb Eric Pouech:
> Le 11/03/2012 09:18, Eric Pouech a écrit :
>> Le 10/03/2012 18:26, André Hentschel a écrit :
>>> ---
>>>   programs/winedbg/be_arm.c |   10 ++++++----
>>>   1 files changed, 6 insertions(+), 4 deletions(-)
>>>
>>> diff --git a/programs/winedbg/be_arm.c b/programs/winedbg/be_arm.c
>>> index c39043c..6c1cc05 100644
>>> --- a/programs/winedbg/be_arm.c
>>> +++ b/programs/winedbg/be_arm.c
>>> @@ -205,13 +205,15 @@ static void be_arm_clear_watchpoint(CONTEXT* ctx, unsigned idx)
>>>
>>>   static int be_arm_adjust_pc_for_break(CONTEXT* ctx, BOOL way)
>>>   {
>>> +    INT step = (ctx->Cpsr&  0x20) ? 2 : 4;
>> hmm
>> the way winedbg works might put us in trouble here...
>>
>> when winedbg is entered with a break exception:
>> 1/ winedbg calls adjust_pc_for_break(..., TRUE) to get the PC to the real location of the break insn (and not after, as most CPU report in break exception handler)
>> 2/ user interacts with winedbg
>> 3/ user resumes execution, and winedbg calls again adjust_pc_for_break(..., FALSE)
>>
>> but, the ctx passed here is the context used to resume execution... and in ARM case Cpsr could have been changed by user in step 2/
>> leading to wrong PC computation in 3/
>>
>> therefore, if we want to plug that hole, I'd suggest having two context used in winedbg (the incoming one (never being changed), and the current/outgoing one), and that we pass the two contexts in winedbg to do the right thing here
>>
>> A+
>>
> and I forgot my question... is it possible for the user to change the cpsr value?
> A+
> 

No, he can't. That only would happen (at least for the 0x20 of cpsr) if the user moves the PC to a codepart,
which is Thumb and it was ARM before (or vise versa). AFAIK he can't do that.

-- 

Best Regards, André Hentschel



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