Re: [rvm-research] Instrumenting machine codes to find memory addresses

Hi,

I investigated my code better, and I seem to have found the main problems.
For each instruction that uses a memory address, i also add my code to the
machine code array which pushed the value of the address on the stack and
also moved it to EAX, and called a function inside JIKES which right now
prints it on the screen. This was creating a problem, as i was modifying
the register state. To fix this, I saved the registers EAX, ECX, and EDX on
the stack and later restore them, and this seems to have solved the problem
for cases I tried. Do i need to save other registers as well and restore
them as well, like ESI, EDI etc ? And are there any other things i need to
care about, like EFLAGS register?

Also, I extended my trace to include the instruction trace, basically i am
trying to get all the instructions executed as well. For this I pushed the
instruction that is going to be executed on the stack and again call a
function inside JIKES with that as argument. However, this is creating
problems in the forwardShortBranch function as now due to the extra machine
codes added the offset to the label to branch to becomes too large  and
can't fit into 8 bits, giving a VM assertion fail during compile . Right
now I temporarily turn off instrumentation during the forwardShortBranch
function, but is there any better way around for this?

Thanks

On Wed, May 1, 2013 at 6:22 PM, Michael Bond <[email protected]>wrote:

>  Hi Shashank,
>
> It's hard to say without seeing exactly how you instrumented "new." It
> seems tricky (or at least different from instrumenting other accesses)
> since the instrumentation presumably occurs after the allocation, whereas
> read/write instrumentation occurs before the access if you're following
> Pacer's approach. To instrument after an allocation, it seems like you'd
> want the instrumentation to push the address (which is on the stack) onto
> the stack *again* so it's both the top and next element on the stack, and
> then call your instrumentation method. For better feedback, please show the
> code for exactly how you instrumented "new." :)
>
> Cheers,
> Mike
>
>
> On 04/28/2013 02:14 PM, Shashank Gupta wrote:
>
>   Hi,
>
>  We are inserting some machine codes in the machine code array of a sample
> Java program running on Jikes RVM dynamically. We want to find the memory
> addresses accessed, and hence inserted our own instructions to calls a
> function within Jikes passing address as an argument. We are using an
> approach almost similar as done in Pacer Patch in Jikes Archive.
>
>  It was working for simple programs without constructors of a separate
> class being called. However in case of using "new" operator for creating
> instance of a class, we are either getting sysFail error or a Null Pointer
> Exception.
>
>  What might be possible reasons for this?
>
>  Thanks
>
>  --
> Shashank Gupta
> 4th Year, B.Tech
> Department of Computer Science and Engineering
> Indian Institute of Technology Delhi
>
>
>
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-- 
Shashank Gupta
4th Year, B.Tech
Department of Computer Science and Engineering
Indian Institute of Technology Delhi

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