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

[Anton Korobeynikov]

Are you sure, that LLVMGetNamedFunction(m,"_a_outside_func") does not
return NULL? I believe it should be
LLVMGetNamedFunction(m,"a_outside_func")

On Fri, Apr 4, 2014 at 12:25 PM, waxiadao at gmail.com <waxiadao at gmail.com> wrote:
> Hello
> I quite thank you for your advice,but I have to tell that it made no
> difference too calling
> "LLVMAddGlobalMapping(ee,LLVMGetNamedFunction(m,"_a_outside_func"),(void*)(&a_outside_func));".
>
>
> 2014-04-04 16:10 GMT+08:00 Anton Korobeynikov <anton at korobeynikov.info>:
>
>> Hello
>>
>> While there is a symbol in the object file, there is nothing like this
>> in the final executable (well, you can try to export functions from
>> PE/COFF executable, but this is pretty non-standard technique). This
>> is the biggest difference wrt linux, where all the visible symbols are
>> exported by default from the binary.
>>
>> Most probably, the best way here is to create an explicit mapping
>> between a GlobalValue which represents your external function and the
>> address of your function. ExecutionEngine::addGlobalMapping() is your
>> friend here.
>>
>> On Fri, Apr 4, 2014 at 9:48 AM, waxiadao at gmail.com <waxiadao at gmail.com>
>> wrote:
>> > 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)?
>> >
>> > _______________________________________________
>> > LLVM Developers mailing list
>> > LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
>> > http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
>> >
>>
>>
>>
>> --
>> With best regards, Anton Korobeynikov
>> Faculty of Mathematics and Mechanics, Saint Petersburg State University
>
>



-- 
With best regards, Anton Korobeynikov
Faculty of Mathematics and Mechanics, Saint Petersburg State University