LLVM-C: Calling functions contained in other libraries


I have a question concerning llvm-c.
I have set up a function that needs to invoke an external method, in a other library. It has the following signature: void* NSFullUserName(void);
The void* can be replaced with a i8*, that far I was able to get, but when my call is invoked, the engine gives me the following message:

LLVM ERROR: Tried to execute an unknown external function: i8* ()* NSFullUserName

I have dumped the module (without the clutter):

declare i8* @NSFullUserName()

define i8* @MyFunction() {
%myCall = call i8* @NSFullUserName() ; <i8*> [#uses=1]
ret i8* %myCall

Where am I going wrong here?

To add some code to my previous question:

LLVMTypeRef i8Ptr(void) {
return LLVMPointerType(LLVMInt8Type(), 0);

LLVMValueRef d(LLVMModuleRef module) {
LLVMValueRef result;
LLVMBasicBlockRef block;
LLVMBuilderRef builder = LLVMCreateBuilder();

LLVMValueRef fullUsername = LLVMAddFunction(module, “NSFullUserName”, LLVMFunctionType(LLVMPointerType(LLVMInt8Type(), 0), NULL, 0, 0));
LLVMSetLinkage(fullUsername, LLVMExternalLinkage);

result = LLVMAddFunction(module, “MyFunction”, LLVMFunctionType(i8Ptr(), NULL, 0, 0));
block = LLVMAppendBasicBlock(result, “entrypoint”);
LLVMPositionBuilderAtEnd(builder, block);

LLVMValueRef returnVal = LLVMBuildCall(builder, fullUsername, NULL, 0, “myCall”);
LLVMBuildRet(builder, returnVal);

return result;

int main (int argc, const char * argv[]) {
NSAutoreleasePool * pool = [[NSAutoreleasePool alloc] init];

char * error = NULL;
LLVMExecutionEngineRef engine;
LLVMModuleRef module = LLVMModuleCreateWithName(“MyModule”);

LLVMValueRef toCall = d(module);


LLVMCreateInterpreterForModule(&engine, module, &error);

LLVMGenericValueRef result = LLVMRunFunction(engine, toCall, 0, NULL);

[pool drain];
return 0;

Thank you,


Did you link against the library that contains the function?


The function is called in my code, just to be sure it is reachable...

This might be a bug (or feature depending on vision of the software).

I have tried this with the global mapping, and it still won't work.
But by replacing the calling code with the JIT:

    LLVMCreateJITCompilerForModule(&engine, module, 0, &error);
    //LLVMAddGlobalMapping(engine, toCall, (void*)&NSFullUserName);
    LLVMGenericValueRef result = LLVMRunFunction(engine, toCall, 0, NULL);
    NSLog(@"Second attempt: %@", LLVMGenericValueToPointer(result));

It suddenly works like a charm, without any global mapping required.