Re: [DynInst_API:] Call Redirection to a Library Function

[Sergej Proskurin <prosig@xxxxxxx>]

Dear Bill,

First of all, thank you very much for the fast reply. I really 
appreciate your help.
> There are many things that could go wrong with code modification in 
> general, but this is also functionality that's supported through 
> Dyninst's BPatch layer directly. There are function replacement (all 
> calls to foo now call bar), function wrapping (all calls to foo call 
> bar, which then calls foo), and callsite replacement (this call to foo 
> now calls bar) primitives available, and one of those is likely to be 
> easier to work with than PatchAPI code modification for a simple 
> function-level graft.
I am familiar with Dyninst's Bpatch function replacement functionality. 
Unfortunately, I believe that I am not able to use its functionality 
within my implementation, since my case is probably somewhat unusual:
What I am trying to achieve is a modification of the function's prologue 
and epilogue. Therefore, my implementation looks for the associated 
parts of the affected function(s) and inserts the associated code 
(currently in form of raw data) into these points. I am working on the 
PatchAPI level, since I didn't find a solution how implement 
modifications of the function's pro- and epilogue on the BPatch level. 
If you tell me that it is possible to perform such fine grained 
modifications on the higher abstraction layer of BPatchAPI, I will 
definitely give it a try.
So, the presented call redirection code within the initial issue 
description affects the epilogue of the function. Within the epilog to 
be modified, I would like to include a call to a function (included 
within the mentined library), which is performed after a certain 
condition is met; Otherwise simply proceed operation. As already 
mentioned, I have already injected raw binary data into the epilogue, 
which can be seen in the following simplified assembly code snippet:
---
...
cmp    %ebx, %eax
jz     _pseudo_jump_to_be_redirected
call   _peudo_call_to_be_redirected
---

Because of the fact that I am calling a "pseudo function" from the 
assembly code (from the raw data), I believe that it is not possible to 
track this function down on the BPatch level - am I right? But as 
already said, if you tell me that it is possible to perform such fine 
grained modifications on the prolog and epilog of a function, I would 
rather use the higher abstraction layer of BPatchAPI.
Thanks again.

Best regards,
Sergej