llvm dev - Jan 2013 - [LLVMdev] Passing an array to an external function

Hi all,

I am new to LLVM, and I am learning how to use LLVM for profiling. I need to
pass an array to an external method, and insert a call instruction to the
method in the code.

After reading a few source files, I've tried using GetElementPtrInst to pass
an array, but it fails at llvm::GetElementPtrInst::hasAllZeroIndices() const
+ 0

			std::vector<Value*> Args(1);
                          	
                        //Vector with array values
                        SmallVector<Constant*, 2> counts;
                       
counts.push_back(ConstantInt::get(Type::getInt32Ty(BB->getContext()),32,
false));
                       
counts.push_back(ConstantInt::get(Type::getInt32Ty(BB->getContext()),12,
false));

			//Array with 2 integers
			ArrayType* ar_type
llvm::ArrayType::get(llvm::Type::getInt32Ty(BI->getContext()),2);
                        Value* array = ConstantArray::get(&(*ar_type),
counts);
                            
                        //Indicies
  			std::vector<Value*> ids(1);
                       
ids.push_back(ConstantInt::get(Type::getInt32Ty(BB->getContext()),1));
                       
ids.push_back(ConstantInt::get(Type::getInt32Ty(BB->getContext()),2));
                            
                        Args[1] = GetElementPtrInst::Create(array, ids, "
");

                        //Instrument the branch target instructions
                        CallInst::Create(hook, Args,  "",CI);


Also, I 'hook' is defined as M.getOrInsertFunction("hook",
Type::getVoidTy(M.getContext()), 
                                                   
PointerType::get(Type::getInt32PtrTy(M.getContext()),0),  //??
                                                    (Type*)0); 

Could someone kindly keep me a few pointers on passing arrays to an external
function (say with the signature void hook(int abc[]) ). I am probably wrong
all the way through, and would really appreciate some help.


Thanks!




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On Jan 26, 2013, at 19:24 , SArora <silkyar at umich.edu> wrote:
> Hi all,
> 
> I am new to LLVM, and I am learning how to use LLVM for profiling. I need
to
> pass an array to an external method, and insert a call instruction to the
> method in the code.
> 
> After reading a few source files, I've tried using GetElementPtrInst to
pass
> an array, but it fails at llvm::GetElementPtrInst::hasAllZeroIndices()
const
> + 0
I'm fairly new to LLVM myself, but I'm not sure why you're using GEP
at all, let alone with two indices. Does it work to just pass the array value?
If not, try using GEP with a single index of 0. The second index would try to
index off of element 1 (the second), and then the third element of that, which
is an int, and doesn't have sub elements.

-- 
Rick

Hi,

I tried passing the array directly using and changing the
getorInsertFunction accordingly but this didn't work. It fails with
Assertion `(i >= FTy->getNumParams() || FTy->getParamType(i)
=Args[i]->getType()) && "Calling a function with a bad
signature!"' failed.

hookFunc = M.getOrInsertFunction("hook",
Type::getVoidTy(M.getContext()),
llvm::ArrayType::get(llvm::Type::getInt32Ty(M.getContext()),2), (Type*)0);
.....
Args[0]
ConstantArray::get(llvm::ArrayType::get(llvm::Type::getInt32Ty(BI->getContext()),2),
arr);

I tried using index 0 in the GEP, but it fails with

7  opt             0x00000000006c59f5 bool llvm::isa<llvm::Constant,
llvm::Value*>(llvm::Value* const&) + 24
8  opt             0x00000000006c5a0f llvm::cast_retty<llvm::Constant,
llvm::Value*>::ret_type llvm::cast<llvm::Constant,
llvm::Value*>(llvm::Value* const&) + 24
9  opt             0x0000000000b2b22f
10 opt             0x0000000000b2a4fe
llvm::ConstantFoldGetElementPtr(llvm::Constant*, bool,
llvm::ArrayRef<llvm::Value*>) + 55
11 opt             0x0000000000b33df2
llvm::ConstantExpr::getGetElementPtr(llvm::Constant*,
llvm::ArrayRef<llvm::Value*>, bool) + 82

Probably the ConstantArray could't be casted to Value*. Any ideas? 
Thanks!




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