Re: [patch/RFA] multiarch INSTRUCTION_NULLIFIED

Paul Schlie
2004-12-01T13:32:29Z

> Randolph wrote:
>> >well, first i want to understand the problem. because i'm still not
>> >yet 100% convinced that step_through_delay will work. simply using the
>> >"instruction_nullified" method in hppa-tdep as the "step_through_delay"
>> >method certainly is not working...
>>
>> When doing a stepi? step_through_delay certainly won't help when it
>> comes to doing a backtrace from the nullified instruction.
>
> when doing a step.

A point that may be worth considering is that on architectures which support
jump/branch delay slots, the branch and delay slot is actually logically
executed as single compound instruction, treated by the machine as a unified
whole.

i.e. if an interrupt is received, the machine will break either at the
jump/branch, or at it's target (after logically completing execution of
it's delay slot, conditionally or otherwise, but never in between, as the
control flow through the delay slot is bound to the preceding jump/branch.)

Therefore it's likely ill advised to attempt to logically single step
through a corresponding instruction pair any differently, as although coded
as two separate instructions, execution can't be literally interrupted
between the jump/branch and it's delay slot on most machines, I believe.