Re: [DynInst_API:] BPatch_dynamicTargetExpr on return statements

[Marc Brünink <marc@xxxxxxxxx>]

On 06/10/2015 00:14, Bill Williams wrote:
> On 10/05/2015 05:09 AM, Marc Brünink wrote:
> > At the moment I have no idea where the 0x500006a1 comes from.
> Okay, this one is obvious to me, but not entirely trivial to fix: we're
> handing back the relocated address where the instrumented version of
> function_end called itself. Doing that translation directly in the
> snippet is not a good idea; there are use cases where we need to go to
> the actual control flow target and not the original address of said target.
>
> Are you doing this instrumentation dynamically or with binary rewriting?
> And if you're doing rewriting, can you get away with a post-processing
> step on your output? It should be straightforward to expose a relocated
> address->original address translation method at the BPatch_addressSpace
> level (harder in the binary rewriting case, but should Just Work(tm) in
> the process case).

I instrument dynamically. I followed Bill's suggestion and added a 
translation method to BPatch_addressSpace.
I think the post-processing approach is not optimal, though.
There is a time gap between the execution of dynamicTargetExpr and the 
post-processing. Thus, the relocation info might change in between.
But well... I suppose I can handle this.

This is another case for having the relocation info accessible in the 
instrumented process. However, I tried this once and it was really not 
trivial.

bool BPatch_addressSpace::getOrigAddr(Address relocAddr,
                                      Address& origAddr)
{
  std::vector<AddressSpace*> as;
  getAS(as);
  assert(as.size());

  Relocation::CodeTracker::RelocInfo ri;
  if (as[0]->getRelocInfo(relocAddr, ri)) {
    origAddr = ri.orig;
    return true;
  }
  return false;
}


Marc