LLVM JIT segfaults. What am I doing wrong?
- by bugspy.net
It is probably something basic because I am just starting to learn LLVM..
The following creates a factorial function and tries to git and execute it (I know the generated func is correct because I was able to static compile and execute it).
But I get segmentation fault upon execution of the function (in EE-runFunction(TheF, Args))
#include <iostream>
#include "llvm/Module.h"
#include "llvm/Function.h"
#include "llvm/PassManager.h"
#include "llvm/CallingConv.h"
#include "llvm/Analysis/Verifier.h"
#include "llvm/Assembly/PrintModulePass.h"
#include "llvm/Support/IRBuilder.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/ExecutionEngine/JIT.h"
#include "llvm/ExecutionEngine/GenericValue.h"
using namespace llvm;
Module* makeLLVMModule() {
// Module Construction
LLVMContext& ctx = getGlobalContext();
Module* mod = new Module("test", ctx);
Constant* c = mod->getOrInsertFunction("fact64",
/*ret type*/ IntegerType::get(ctx,64),
IntegerType::get(ctx,64),
/*varargs terminated with null*/ NULL);
Function* fact64 = cast<Function>(c);
fact64->setCallingConv(CallingConv::C);
/* Arg names */
Function::arg_iterator args = fact64->arg_begin();
Value* x = args++;
x->setName("x");
/* Body */
BasicBlock* block = BasicBlock::Create(ctx, "entry", fact64);
BasicBlock* xLessThan2Block= BasicBlock::Create(ctx, "xlst2_block", fact64);
BasicBlock* elseBlock = BasicBlock::Create(ctx, "else_block", fact64);
IRBuilder<> builder(block);
Value *One = ConstantInt::get(Type::getInt64Ty(ctx), 1);
Value *Two = ConstantInt::get(Type::getInt64Ty(ctx), 2);
Value* xLessThan2 = builder.CreateICmpULT(x, Two, "tmp");
//builder.CreateCondBr(xLessThan2, xLessThan2Block, cond_false_2);
builder.CreateCondBr(xLessThan2, xLessThan2Block, elseBlock);
/* Recursion */
builder.SetInsertPoint(elseBlock);
Value* xMinus1 = builder.CreateSub(x, One, "tmp");
std::vector<Value*> args1;
args1.push_back(xMinus1);
Value* recur_1 = builder.CreateCall(fact64, args1.begin(), args1.end(), "tmp");
Value* retVal = builder.CreateBinOp(Instruction::Mul, x, recur_1, "tmp");
builder.CreateRet(retVal);
/* x<2 */
builder.SetInsertPoint(xLessThan2Block);
builder.CreateRet(One);
return mod;
}
int main(int argc, char**argv) {
long long x;
if(argc > 1)
x = atol(argv[1]);
else
x = 4;
Module* Mod = makeLLVMModule();
verifyModule(*Mod, PrintMessageAction);
PassManager PM;
PM.add(createPrintModulePass(&outs()));
PM.run(*Mod);
// Now we going to create JIT
ExecutionEngine *EE = EngineBuilder(Mod).create();
// Call the function with argument x:
std::vector<GenericValue> Args(1);
Args[0].IntVal = APInt(64, x);
Function* TheF = cast<Function>(Mod->getFunction("fact64")) ;
/* The following CRASHES.. */
GenericValue GV = EE->runFunction(TheF, Args);
outs() << "Result: " << GV.IntVal << "\n";
delete Mod;
return 0;
}
