[LLVMdev] Weird problems on calling an external function from MCJIT on Windows(mingw)

waxiadao@gmail.com
Fri, 04 Apr 2014 05:48:07 -0000

Hi,
I have a IR file generated by Clang:

; ModuleID = 'test_load_lib.c'
target datalayout
"e-p:32:32:32-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f32:32:32-f64:64:64-f80:128:128-v64:64:64-v128:128:128-a0:0:64-f80:32:32-n8:16:32-S32"
target triple = "i686-pc-mingw32"

declare i32 @a_outside_func(i32)

define i32 @test_func() {
entry:
  %call = call i32 @a_outside_func(i32 15)
  ret i32 %call
}

where a_outside_func is a function defined on my code:

extern "C" int a_outside_func(int a)
{
  return a + 50;
}

and following code is to get MCJIT work:

#define prt(x) if(x) { cout << x << endl; }
LLVMInitializeAllTargets();
  LLVMInitializeAllTargetMCs();
  LLVMInitializeAllTargetInfos();
  LLVMInitializeAllAsmParsers();
  LLVMInitializeAllAsmPrinters();
  LLVMInitializeAllDisassemblers(); // just initialize them all....
  prt(a_outside_func(50));               // afraid of linker optmize it out

  char *err = 0;
  LLVMMemoryBufferRef ll_f = 0;
  LLVMModuleRef m = 0;

LLVMCreateMemoryBufferWithContentsOfFile("test_load_lib.ll",&ll_f,&err);
  //read .ll
  prt(err);
  LLVMParseIRInContext(LLVMGetGlobalContext(),ll_f,&m,&err); // ll_f
doesnt
need freeing
  prt(err);
  LLVMDumpModule(m);

  LLVMLinkInMCJIT();
  LLVMExecutionEngineRef ee = 0;
  LLVMCreateMCJITCompilerForModule(&ee,m,0,0,&err);
  prt(err);
  using tf_t = int ();
  tf_t *f
(tf_t*)LLVMGetPointerToGlobal(ee,LLVMGetNamedFunction(m,"test_func"));

At first i got "LLVM ERROR: Incompatible object format! "
But by reading some articles I append
LLVMSetTarget(m,"i686-pc-mingw32");
and it's fixed.
Then I got "LLVM ERROR: Program used external function
'a_outside_func'
which could not be resolved!".
I assumed my program didn't export the symbol properly.Thus,I use nm to
check my program's export and I found "a_outside_func" was renamed
to
"_a_outside_func"
.
For it I rename the function name in the IR to "_a_outside_func".But
it
seemed to make no difference: "LLVM ERROR: Program used external function
'_a_outside_func' which could not be resolved!".
.............
After a day's wasting I unconsciously packed my external function
"a_outside_func" into a shared object,called
llvm::sys::DynamicLibrary::LoadLibraryPermanently("ext_func.so"); at
the
beginning of the program and named the function "_a_outside_func" in
the IR.
OMG IT WORKS THEN?!
So I'd like to ask why llvm cant resolve my external function from the
program itself(in fact i dont get such problems on linux)?
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