llvm dev - Jun 2012 - [LLVMdev] Cast Pointer Address to Functions

I have a function address held in an uint64_t. I would like to cast
the function address to a function prototype and create a call to the
function in LLVM. How could I do this ?

Thanks

Xin

Using uintptr_t is the way to hold pointer values. However, I seem to recall
there being an exception for function addresses.

-bw

On Jun 18, 2012, at 1:09 PM, Xin Tong wrote:
> I have a function address held in an uint64_t. I would like to cast
> the function address to a function prototype and create a call to the
> function in LLVM. How could I do this ?
> 
> Thanks
> 
> Xin
> _______________________________________________
> LLVM Developers mailing list
> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev

In fact i want to cast a uint64_t to a function address and make LLVM
generate IR to call it.

i.e. in LLVM IR, i want to generate something like this.

      the uint64_t  function prototype    function args
call 0xAABBCC    (void () (int int))        (1 , 2)

Thanks

Xin


On Mon, Jun 18, 2012 at 10:21 PM, Bill Wendling <wendling at apple.com>
wrote:
> Using uintptr_t is the way to hold pointer values. However, I seem to
recall there being an exception for function addresses.
>
> -bw
>
> On Jun 18, 2012, at 1:09 PM, Xin Tong wrote:
>
>> I have a function address held in an uint64_t. I would like to cast
>> the function address to a function prototype and create a call to the
>> function in LLVM. How could I do this ?
>>
>> Thanks
>>
>> Xin
>> _______________________________________________
>> LLVM Developers mailing list
>> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
>> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
>

> From: llvmdev-bounces at cs.uiuc.edu [mailto:llvmdev-bounces at
cs.uiuc.edu] On Behalf Of Xin Tong
> Subject: [LLVMdev] Cast Pointer Address to Functions
> I have a function address held in an uint64_t. I would like to cast
> the function address to a function prototype and create a call to the
> function in LLVM. How could I do this ?
This is what works for us:

    std::vector<Type*> margs;
    FunctionType* fType;
    PointerType* pm3_routine;
    Value* m3func;
    Value* result;

    margs.resize(1);
    margs[0] = I64;
    fType = FunctionType::get(I32, margs, false);
    pm3_routine = PointerType::get(fType, 0);
 
    m3func = Builder.CreateIntToPtr(I64_Const((uint64_t)pFunc), pm3_routine,
"pm3func");
    result = Builder.CreateCall(m3func, parameter, "m3func");

 - Chuck


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Interestingly I have something similar. but does not seem to work.

This one works.
   Value *FuncCast = EIR->CreateIntToPtr(FuncAddr, FuncTyPntr,
"FuncName");


This one does not work. it gives me an instruction with badref.
  CastInst *FuncCast = CastInst::Create(Instruction::IntToPtr,
FuncAddr, FuncTyPntr);

Anyone knows why ?

Thanks

Xin

On Mon, Jun 18, 2012 at 10:38 PM, Caldarale, Charles R
<Chuck.Caldarale at unisys.com> wrote:
>> From: llvmdev-bounces at cs.uiuc.edu [mailto:llvmdev-bounces at
cs.uiuc.edu] On Behalf Of Xin Tong
>> Subject: [LLVMdev] Cast Pointer Address to Functions
>
>> I have a function address held in an uint64_t. I would like to cast
>> the function address to a function prototype and create a call to the
>> function in LLVM. How could I do this ?
>
> This is what works for us:
>
>    std::vector<Type*> margs;
>    FunctionType* fType;
>    PointerType* pm3_routine;
>    Value* m3func;
>    Value* result;
>
>    margs.resize(1);
>    margs[0] = I64;
>    fType = FunctionType::get(I32, margs, false);
>    pm3_routine = PointerType::get(fType, 0);
>
>    m3func = Builder.CreateIntToPtr(I64_Const((uint64_t)pFunc), pm3_routine,
"pm3func");
>    result = Builder.CreateCall(m3func, parameter, "m3func");
>
>  - Chuck
>
>
> THIS COMMUNICATION MAY CONTAIN CONFIDENTIAL AND/OR OTHERWISE PROPRIETARY
MATERIAL and is thus for use only by the intended recipient. If you received
this in error, please contact the sender and delete the e-mail and its
attachments from all computers.
>
>
> _______________________________________________
> LLVM Developers mailing list
> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev