[llvm-dev] creating a callinst to an external function

[marwayusuf@feng.bu.edu.eg via llvm-dev]

Thanks a million!

I've finally went to the object file containing foo function and using objdump tool I found the exact used name in its symbol table. Using this mangled name in my pass, solved the resolve issue and my foo function is finally called correctly.


Regards,
Marwa Yusuf
Teaching Assistant - Computer Engineering Department
Faculty of Engineering - Benha University
E-JUST PhD Student
Computer Science & Engineering Dept.


________________________________
From: mats.o.petersson at googlemail.com <mats.o.petersson at googlemail.com> on behalf of mats petersson <mats at planetcatfish.com>
Sent: Wednesday, September 2, 2015 4:36 PM
To: marwayusuf at feng.bu.edu.eg
Cc: llvm-dev
Subject: Re: [llvm-dev] creating a callinst to an external function

If you look at the computer output of the file that provides the function `myclass::foo` (-S -emit-llvm if you use clang), you should see that the name of the function (probably) isn't `foo`. You need to precisely match the name between the caller and the actual function.

--
Mats



On 2 September 2015 at 15:17, marwayusuf at feng.bu.edu.eg<mailto:marwayusuf at feng.bu.edu.eg> via llvm-dev <llvm-dev at lists.llvm.org<mailto:llvm-dev at lists.llvm.org>> wrote:

I tried to remove parameters from the called function "foo". So I got a different error.

LLVM ERROR: Program used external function 'foo' which could not be resolved!

Any help?


Regards,
Marwa Yusuf
Teaching Assistant - Computer Engineering Department
Faculty of Engineering - Benha University
E-JUST PhD Student
Computer Science & Engineering Dept.


________________________________
From: llvm-dev <llvm-dev-bounces at lists.llvm.org<mailto:llvm-dev-bounces at lists.llvm.org>> on behalf of marwayusuf at feng.bu.edu.eg<mailto:marwayusuf at feng.bu.edu.eg> via llvm-dev <llvm-dev at lists.llvm.org<mailto:llvm-dev at lists.llvm.org>>
Sent: Thursday, August 20, 2015 12:42 AM
To: llvm-dev at lists.llvm.org<mailto:llvm-dev at lists.llvm.org>
Subject: [llvm-dev] creating a callinst to an external function


Dear All

I'm making an instrumentation pass. The pass is supposed to modify the given IR in a specefic way. One of the required modifications is to insert a call to a function at a specific location.

This is the signature of the called function:

      void myclass::foo(Function *f, BasicBlock* b)

This function's prototype is in an foofile.h file in include/llvm

And the function definition is in foofile.cpp file in the MCJIT folder.

and running "make" at this folder works fine and the foofile.cpp is compiled with MCJIT.cpp and another function in the same file works just fine as expected.

Not back to the instrumentation pass. How can I insert a callinst to the foo function in the given IR?

Here is the snippet that inserts the call:

           Type* retTy = Type::getInt32Ty(C);

            FunctionType* FuncTy = FunctionType::get(retTy, false);

            PointerType* PtrToFuncTy = PointerType::get(FuncTy, 0);

            Constant *fun = M->getOrInsertFunction("foo", Type::getVoidTy(C), PtrToFuncTy, Type::getLabelTy(C), nullptr);

            Function *dofoo = cast<Function>(fun);

            Instruction* dofooCall = CallInst::Create(fun, Args2, "", bb);


Note: Args2 is an arraylist containing 2 value pointers to a function and a basicblock, bb is the basicblock to insert the call in.


When I run the pass using op on a given IR, it produces a declaration and a call correctly like this:

 declaration:       declare void @foo(i32 ()*, label)

 call:                   call void @foo(i32 ()* @main, label %for.cond)

But when I try to run the resulting .ll file using lli, everything explodes! This the first 2 lines before the stacktrace:

    Can't get register for value!

    UNREACHABLE executed at /home/marwayusuf/llvm-env/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp:1158!



I concluded that the problem is it can't find the foo function. If this is the problem, how can I create the callinst correctly?




Regards,
Marwa Yusuf
Teaching Assistant - Computer Engineering Department
Faculty of Engineering - Benha University
E-JUST PhD Student
Computer Science & Engineering Dept.

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