(original) (raw)

On Oct 27, 2014 10:05 AM, "CK Tan" <cktanx@gmail.com> wrote:

Does anyone have a sample code on calling a c function thru pointer? Thanks.

\> On Oct 27, 2014, at 1:37 AM, David Chisnall <David.Chisnall@cl.cam.ac.uk> wrote:
\>
\> There is at least one error here, possibly two.
\>
\>> On 27 Oct 2014, at 07:46, C K Tan <cktanx@gmail.com> wrote:
\>>
\>> I have a pointer to a function that I need to invoke without going
\>> through llvm::Module::getOrInsertFunction. This example does not work:
\>>
\>> static int add(int x, int y);
\>> llvm::Value \*one, \*two;
\>>
\>> llvm::Constant\* addfn
\>> = llvm::ConstantInt::get(JB->getIntPtrTy(DataLayout), (intptr\_t)add);
\>> llvm::Type\* args\[\] = { Int32Ty, Int32Ty };
\>> llvm::FunctionType\* ftype = llvm::FunctionType::get(Int32Ty, args);
\>
\> The type that you want is not the function type, but the function \*pointer\* type. ftype->getPointerTo() should give you the type that you need.
\>
\>> addfn = llvm::ConstantExpr::getPointerCast(addfn, ftype);
\>
\> I don't remember if this will just do casts between pointers or if it can also create inttoptrs, but you might need to be more explicit and ask for an inttoptr.
\>
\> David

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