What can be the reason of `LLVM ERROR: Target does not support MC emission!`?

Question

I'm working on LLVM tutorial in Rust now. I have implemented some parts of Kaleidoscope REPL already. It worked for me well, but suddenly it stopped to work and every attempt to calculate a value ends in LLVM ERROR: Target does not support MC emission! now. It seems it happend after updating of Rust compiler to the latest nightly (but I am not sure here).

Relevant pieces of code follow.

Initialization function:

#[allow(non_snake_case)]
pub unsafe fn LLVMInitializeNativeTarget() {
    llvm::LLVMInitializeX86TargetInfo();
    llvm::LLVMInitializeX86Target();
    llvm::LLVMInitializeX86TargetMC();
}

Module creation:

        let module = llvm::LLVMModuleCreateWithNameInContext(module_name.to_c_str().as_ptr(), context);

Execution engine creation:

        let mut exec_engine = 0 as llvm::ExecutionEngineRef;
        let mut error = 0 as *const c_char;
        LLVMCreateExecutionEngineForModule(&mut exec_engine, module, &mut error);
        assert!(exec_engine != 0 as llvm::ExecutionEngineRef);

Compilation and running of function:

pub fn run(value: llvm::ValueRef, context: &Context) -> f64 {
    unsafe {
        let result = LLVMRunFunction(context.exec_engine,
                                     value,
                                     0,
                                     0 as *const GenericValueRef);
        let ty = llvm::LLVMDoubleTypeInContext(context.context);
        LLVMGenericValueToFloat(ty, result)
    }
}

LLVM functions prefexed by llvm:: are imported by rustc, those not prefexed by llvm:: are imported by my code, see https://github.com/jauhien/iron-kaleidoscope/blob/master/src/missing_llvm_bindings/mod.rs.

To see full code listing, look at https://github.com/jauhien/iron-kaleidoscope/blob/master/src/builder.rs

I'm using the latest nightly Rust and LLVM 3.5.0.

UPD: After commenting out of the call to LLVMInitializeNativeTarget, JIT started to work again. But I am still wondering what is the reason of the problem and how JIT should be used correctly.

UPD2: after commenting out line with initialization not everything started to work again: calls to the function defined in the Rust code fail with LLVM ERROR: Tried to execute an unknown external function now.

Function I'm trying to call (this worked before):

#[no_mangle]
pub extern fn print(x: f64) -> f64 {
    println!("> {} <", x);
    x
}

Example session:

jauhien@zcj iron-repl % ./target/iron_kaleidoscope
>extern print(x)

declare double @print(double)

>print(1)
LLVM ERROR: Tried to execute an unknown external function: print

Answer 1

I had the same problem and could solve it by also running

LLVMInitializeNativeAsmPrinter();
LLVMInitializeNativeAsmParser();

after initializing X86Target. I found this in the source code of lli.