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

Fri Apr 4 09:43:43 PDT 2014

At some point LLVMAddGlobalMapping was broken/unsupported for MCJIT.  It sounds like that is still the case.

There are a couple of ways around this with the C++ interface (either add the symbol using sys::DynamicLibrary::AddSymbol() or create a custom memory manager which provides direct symbol resolution for the local functions you might use), but I don't think either of these solutions are supported in the C interface.

I don't think it would take much work to get the global mapping support added back into MCJIT.  When this last came up I believe that the other approaches were judged to be better.  Your C-interface use case might be sufficient to argue for global mapping support.

-Andy

From: llvmdev-bounces at cs.uiuc.edu [mailto:llvmdev-bounces at cs.uiuc.edu] On Behalf Of waxiadao at gmail.com
Sent: Friday, April 04, 2014 1:55 AM
To: Anton Korobeynikov
Cc: LLVM Developers Mailing List
Subject: Re: [LLVMdev] Weird problems on calling an external function from MCJIT on Windows(mingw)

I'd like to take all my code here to make things easier,they are stil unble to run properly.
cpp code: http://paste.ofcode.org/uNxEMvQTkZyjg2RTwjmXhh
IR code  : http://paste.ofcode.org/hhkFUz8weGKSUXXZZnNuEp
Thanks

2014-04-04 16:38 GMT+08:00 waxiadao at gmail.com<mailto:waxiadao at gmail.com> <waxiadao at gmail.com<mailto:waxiadao at gmail.com>>:
oh,I'm sorry to make such a stupid mistake...But I still have to tell the correct one still didnt make difference...so weird
2014-04-04 16:30 GMT+08:00 Anton Korobeynikov <anton at korobeynikov.info<mailto:anton at korobeynikov.info>>:

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<mailto:waxiadao at gmail.com> <waxiadao at gmail.com<mailto: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<mailto: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<mailto:waxiadao at gmail.com> <waxiadao at gmail.com<mailto: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<mailto: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

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