<div dir="ltr">Hello<div>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));".</div>
</div><div class="gmail_extra"><br><br><div class="gmail_quote">2014-04-04 16:10 GMT+08:00 Anton Korobeynikov <span dir="ltr"><<a href="mailto:anton@korobeynikov.info" target="_blank">anton@korobeynikov.info</a>></span>:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">Hello<br>
<br>
While there is a symbol in the object file, there is nothing like this<br>
in the final executable (well, you can try to export functions from<br>
PE/COFF executable, but this is pretty non-standard technique). This<br>
is the biggest difference wrt linux, where all the visible symbols are<br>
exported by default from the binary.<br>
<br>
Most probably, the best way here is to create an explicit mapping<br>
between a GlobalValue which represents your external function and the<br>
address of your function. ExecutionEngine::addGlobalMapping() is your<br>
friend here.<br>
<div><div class="h5"><br>
On Fri, Apr 4, 2014 at 9:48 AM, <a href="mailto:waxiadao@gmail.com">waxiadao@gmail.com</a> <<a href="mailto:waxiadao@gmail.com">waxiadao@gmail.com</a>> wrote:<br>
> Hi,<br>
> I have a IR file generated by Clang:<br>
><br>
> ; ModuleID = 'test_load_lib.c'<br>
> target datalayout =<br>
> "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"<br>
> target triple = "i686-pc-mingw32"<br>
><br>
> declare i32 @a_outside_func(i32)<br>
><br>
> define i32 @test_func() {<br>
> entry:<br>
> %call = call i32 @a_outside_func(i32 15)<br>
> ret i32 %call<br>
> }<br>
><br>
> where a_outside_func is a function defined on my code:<br>
><br>
> extern "C" int a_outside_func(int a)<br>
> {<br>
> return a + 50;<br>
> }<br>
><br>
> and following code is to get MCJIT work:<br>
><br>
> #define prt(x) if(x) { cout << x << endl; }<br>
> LLVMInitializeAllTargets();<br>
> LLVMInitializeAllTargetMCs();<br>
> LLVMInitializeAllTargetInfos();<br>
> LLVMInitializeAllAsmParsers();<br>
> LLVMInitializeAllAsmPrinters();<br>
> LLVMInitializeAllDisassemblers(); // just initialize them all....<br>
> prt(a_outside_func(50)); // afraid of linker optmize it out<br>
><br>
> char *err = 0;<br>
> LLVMMemoryBufferRef ll_f = 0;<br>
> LLVMModuleRef m = 0;<br>
> LLVMCreateMemoryBufferWithContentsOfFile("test_load_lib.ll",&ll_f,&err);<br>
> //read .ll<br>
> prt(err);<br>
> LLVMParseIRInContext(LLVMGetGlobalContext(),ll_f,&m,&err); // ll_f doesnt<br>
> need freeing<br>
> prt(err);<br>
> LLVMDumpModule(m);<br>
><br>
> LLVMLinkInMCJIT();<br>
> LLVMExecutionEngineRef ee = 0;<br>
> LLVMCreateMCJITCompilerForModule(&ee,m,0,0,&err);<br>
> prt(err);<br>
> using tf_t = int ();<br>
> tf_t *f =<br>
> (tf_t*)LLVMGetPointerToGlobal(ee,LLVMGetNamedFunction(m,"test_func"));<br>
><br>
> At first i got "LLVM ERROR: Incompatible object format! "<br>
> But by reading some articles I append LLVMSetTarget(m,"i686-pc-mingw32");<br>
> and it's fixed.<br>
> Then I got "LLVM ERROR: Program used external function 'a_outside_func'<br>
> which could not be resolved!".<br>
> I assumed my program didn't export the symbol properly.Thus,I use nm to<br>
> check my program's export and I found "a_outside_func" was renamed to<br>
> "_a_outside_func"<br>
> .<br>
> For it I rename the function name in the IR to "_a_outside_func".But it<br>
> seemed to make no difference: "LLVM ERROR: Program used external function<br>
> '_a_outside_func' which could not be resolved!".<br>
> .............<br>
> After a day's wasting I unconsciously packed my external function<br>
> "a_outside_func" into a shared object,called<br>
> llvm::sys::DynamicLibrary::LoadLibraryPermanently("ext_func.so"); at the<br>
> beginning of the program and named the function "_a_outside_func" in the IR.<br>
> OMG IT WORKS THEN?!<br>
> So I'd like to ask why llvm cant resolve my external function from the<br>
> program itself(in fact i dont get such problems on linux)?<br>
><br>
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><br>
<span class="HOEnZb"><font color="#888888"><br>
<br>
<br>
--<br>
With best regards, Anton Korobeynikov<br>
Faculty of Mathematics and Mechanics, Saint Petersburg State University<br>
</font></span></blockquote></div><br></div>