Re: [DynInst_API:] Binary Rewriting using wrapFunction

[Bill Williams <bill@xxxxxxxxxxx>]

On 12/14/2014 04:04 PM, Sergej Proskurin wrote:
> Hello,
>
> currently, I am developing a software that should be able to rewrite
> binaries (as the name suggests, the process of rewriting should be
> performed statically). One of the goals I am trying to achieve, is to
> wrap library function calls with custom implementations.
>
> To achieve this, I am using the function:
> BPatch_addressSpace::wrapFunction(...)
>
> This works fine for functions compiled statically into binary objects.
> However, I have encountered the issue that the wrapping of dynamically
> loaded functions (such as printf) works only dynamically. This means, if
> the binary object is opened with BPatch_addressSpace::openBinary(...),
> it will not create persistent wrappers for dynamic library function
> calls within the binary object on BPatch_binaryEdit::writeFile(...).
>
> Is there any way to manipulate the ELF file by using the tools provided
> by Dyninst so that the binary will behave as presented? Thank you very
> much in advance.
There are at least two approaches here, depending on your precise goals:

1) Open the binary, including all of its shared libraries, and rewrite 
the shared libraries in which you want to wrap functions.
2) For calls to functions outside the main executable, wrap the call 
site with pre-call and post-call instrumentation.
Obviously there are tradeoffs between keeping a rewritten (e.g.) libc 
around and performing the instrumentation on a callsite basis. 
Unfortunately, we can't play the symbol games that we rely on in order 
to wrap functions without modifying the shared library that they're in...
> Best regards,
> Sergej
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--
--bw

Bill Williams
Paradyn Project
bill@xxxxxxxxxxx