[LLVMdev] question about ExectuionEngine::Create

[Xinglin Zhang]

I found the following problem when I try to debug "target does not support
mc emission" in linux (the same code executes OK in windows):

Below is a snippet extracted from this method,

if (UseMCJIT && ExecutionEngine::MCJITCtor) {
        ExecutionEngine *EE =
          ExecutionEngine::MCJITCtor(M, ErrorStr, JMM, OptLevel,
                                     AllocateGVsWithCode, TM);
        if (EE) return EE;
      } else if (ExecutionEngine::JITCtor) {
        ExecutionEngine *EE =
          ExecutionEngine::JITCtor(M, ErrorStr, JMM, OptLevel,
                                   AllocateGVsWithCode, TM);
        if (EE) return EE;
      }

Both ExecutionEngine::MCJITCtor and ExecutionEngine::JITCtor are function
pointers (static members in class ExecutionEngine) and are initialized at
the very beginning of ExecutionEngine.cpp to be 0 (NULL):

ExecutionEngine *(*ExecutionEngine::JITCtor)(
  Module *M,
  std::string *ErrorStr,
  JITMemoryManager *JMM,
  CodeGenOpt::Level OptLevel,
  bool GVsWithCode,
  TargetMachine *TM) = 0;
ExecutionEngine *(*ExecutionEngine::MCJITCtor)(
  Module *M,
  std::string *ErrorStr,
  JITMemoryManager *JMM,
  CodeGenOpt::Level OptLevel,
  bool GVsWithCode,
  TargetMachine *TM) = 0;


When I create the engine, I set UseMCJIT to "true" using
engineBuilder.setUseMCJIT(true);

Then I call
engineBuilder.crate()
to create the Execution engine.

In windows and Linux (Ubuntu), I got a different execution path when it
reaches the if/else structure mentioned in the very beginning of this email:
Windows: it goes into the "else if" branch, which means
that  ExecutionEngine::MCJITCtor is evaluated as 0/NULL. It then
uses ExecutionEngine::JITCtor to create the engine and successful. However,
this is not what I meant to do.
Linux: it goes into the "if" branch, which means ExecutionEngine::MCJITCtor
is not 0/NULL, and it must have been assigned a value somewhere. Then it
uses ExecutionEngine::MCJITCtor (which is what I meant to do) but fails,
giving me an error "target does not support mc emission"

In Windows, I am linking all the libraries (.lib) statically; In Linux, I
am dynamic linking libLLVM3.0.so

Question:
1. Where and when do  ExecutionEngine::MCJITCtor
and ExecutionEngine::JITCtor get assigned a different value other than
0/NULL?
2. Why the value of ExecutionEngine::MCJITCtor are different in Windows and
Linux?

Thanks.

-- 
Xinglin Zhang
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