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Created: Saturday, January 20 2007 22:49.00 CST

Modified: Sunday, January 21 2007 15:04.30 CST

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BinNavis basic block handling

Author: ero

# Views: 2786

A while back I talked about the problem of highly optimized code and the resulting problems when we want to store it in a database while allowing for all possible constructs.
In this post Ill show how the recently released BinNavi 1.2 handles some cases where code is shared among functions and basic blocks exhibit non-typical characteristics.

Note: I could not get the Microsoft or Intel compilers to produce compiled code with functions sharing basic blocks as an example for this post. Using PGO (Profiling Guided Optimization) and other optimizations proved fun but the furthest I could go was producing multi-chunked functions. I might need to play more with it in order to get chunks to be shared... Anyway, I just picked a Microsoft DLL for the example. Specifically wkssvc.dll.

In this DLL there are two functions sharing some blocks on their exit paths. The shared code is shown in green in this graphic exported from BinNavi.

Interestingly enough, those blocks share exactly the same code but one function has six of them while the other has seven. I previously commented on the issue here and happends because of a reference in one of the functions that targets the shared code and causes a block to split.

Here one can see the shared code grouped and highlighted. Click on the image for a larger view.

Now a zoomed version of the block on the left:

And the one on the right:

Within the database, BinNavi handles this by allowing instructions to belong to multiple basic blocks, as well as basic blocks to belong to multiple functions. And it just works...

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