[DynInst_API:] Basic Blocks and Register Access

[Sergej Proskurin <prosig@xxxxxxx>]

Hello,

Within my current implementation, I am able to split and inject basic 
blocks on the basis of PatchAPI. The newly created and injected basic 
blocks are currently filled with raw bytes, as stated within the following:
InsertedCode::Ptr icode = PatchModifier::insert(post_block->object(), 
bytes, nbytes);
This method of code injection works fine. However, since it is possible 
to convert BPatch_snippets into PatchAPI::Snippets, I thought it might 
as well be possible to use predefined library functions to be 
instumented into the binary into the specified basic block. The 
following shows an idea of what I inteded to do:
---
...

BPatch_Vector<BPatch_function *> funcs;
BPatch_function *func_lib;
BPatch_image* img;

img = app->getImage();

/* look for the predefined library function 'prolog' */
funcs.clear();
img->findFunction("pprolog", funcs);
func_lib = funcs[0];

/* no arguments required for function 'pprolog' */
std::vector<BPatch_snippet *> args;
BPatch_funcCallExpr func_instr(*func_lib, args);

SnippetPtr snippet = PatchAPI::convert(func_instr);

...

/* SEGFAULT: Here, I am not quite sure how to get the right point of the 
newly created (empty) basic block */
InsertedCode::Ptr icode = PatchModifier::insert(post_block->object(), 
snippet, point);
...
---

Unfortunately, this kind of implementation crashed with a Segfault at 
the point of insertion. Which might be the result of the fact that I 
don't know exactly how to find an entry point of the type 
PatchAPI::Point* to the empty basic block. Any help would be appreciated 
at this point.
My second question aims at the use of registers:
Is it possible to change the registers of individual instructions with 
help of Dynsinst? The following should explain my idea:
---
changing registers from:
mov   edx, [esp+0x18]
e.g into:
mov   edx, [ebp-0x8]
---

My question is: is it possible to use high level constructs of 
DyninstAPI to make these kind of adjustments or is it easier to work on 
the level of raw bytes instead? Until now, I was not very successfull in 
working with registers with help of DyninstAPI. I would really 
appreciate it if someone could provide me a hint how to correctly access 
the registers.
Thank you very much in advance.

Best regards,
Sergej

--
Sometimes the problem is to discover what the problem is.

[Gordon Glegg, The Design of Design]