[patch/RFA] multiarch INSTRUCTION_NULLIFIED

Daniel Jacobowitz drow@false.org
Wed Dec 1 17:11:00 GMT 2004


On Tue, Nov 30, 2004 at 10:19:24PM -0800, Randolph Chung wrote:
> i experimented with another proposal which is to adjust the pc when we
> are at a nullified instruction. i modified target_read_pc () to return
> the previous (or next) pc when we are at a nullified instruction. this 
> fixes some of the failures but causes new failures with the 
> "recurse.exp" test. i need to investigate that some more. but teaching 
> target_read_pc() to lie about the current pc seems to be suboptimal.
> 
> lastly a comment about sparc -- i think the sparc case is simpler
> because it doesn't have conditional nullification. so looking at a
> particular insn you can always determine if the next insn will be
> nullified or not. this is not always the case for hppa.

Randolph,

Here's an off-the-cuff idea for you.  Could you actually skip the
nullified instruction, if you had a hook in the right place?  That is,
when a thread stops, if it is stopped at a nullified instruction,
forcibly move it to the next instruction before returning control to
GDB.

This is probably not feasible if you have to use single-stepping to end
up in the right place.  If you can compute the right place and adjust
registers, though, it shouldn't be hard.

-- 
Daniel Jacobowitz



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