Calling virtual elf functions under windows

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Calling virtual elf functions under windows

Sam McCall via cfe-dev
Hello everyone reading this,

I'm totally confused and need an explanation. I'm also not sure if it's a clang or a LLVM subject.

I'm working with Visual Studio 2015, LLVM 5.0.1 and Windows 7 64bit.

I have a simple project. With 2 Header files and 1 cpp file.
"Interface.h"
This file defines a simple class with two pure virtual member functions.


"SimpleResult.h"
This file defines a struct holding an integer

"CM_Elf.cpp"
This file defines a class (CM_Elf) implementing the interface from Interface.h
Also there is an instance of the class (named "elf").

I compile the CM_Elf.cpp to a CM_Elf.bc file via clang-cl but with target "x86_64-pc-windows-elf"


In another application I use LLVM to parse the BC file and use the ExecutionEngine to get some addresses.
What I want to archive is:

I want to call the implemented member functions of "elf".

1.) I execute all the global constructors collected by the ExecutionEngine
-> The constructor of elf gets called
2.) I use ExecutionEngine to get the address of "elf"
3.) I use the interface to execute Interface::init
-> Init gets called
4.) I use the interface to execute Interface::shutdown
-> CRASH!

When I swap the calls to init and shutdown, then everything works. So the virtual call to init seems to corrupt my stack - maybe it's the return value. Could it be a calling convention problem? But my target is still "windows" only msvc changed to elf...
When I compile CM_Elf for target "x86_64-pc-windows-msvc19.0.24215" then it works.

When I get the address of CM_Elf::init and CM_Elf::shutdown via the ExecutionEngine and call them without using the virtual table, then again everything works.

SO! Is it not possible to call virtual elf functions via there interface? But why does normal functions work? Also I reach the functions which are stored in the vTable of CM_Elf so the vTable is correct.

I append some pictures of the code... I hope someone could help me with this.

Kind regards
Björn


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SimpleResult_H.PNG (7K) Download Attachment