[llvm-dev] Kaleidoscope tutorial: extern functions failing

[Eli Baum via llvm-dev]

Hi Lang,

Here you go:

[c34n09 kaleidoscope] ./kld
kaleidoscope interpreter
kld> extern putchard(x); putchard(120);
kaleidoscope error:Symbols not found: { putchard }
pure virtual method called
terminate called without an active exception
Aborted (core dumped)

Also, I'm on Linux (RHEL 7.4). I did see in a source file some kind of
Windows extern issue, but that's not relevant here... :/

Thanks so much for your help,
Eli

On Tue, Jan 8, 2019 at 3:49 PM Lang Hames <lhames at gmail.com> wrote:

> Hi Eli,
>
> Could you replace this code:
>
> double (*FP)() = (double (*)())(intptr_t)cantFail(ExprSymbol.getAddress());
>
> with:
>
> double (*FP)() = nullptr;
> if (auto ExprAddr = ExprSymbol.getAddress())
>   FP = (double(*)())*ExprAddr;
> else {
>   logAllUnhandledErrors(ExprAddr.takeError(), llvm::errs(), "kaleidoscope
> error:");
>   exit(1);
> }
>
> Then reproduce the error?
>
> That should allow us to log the error that RuntimeDyld is returning from
> processRelocationRef. I guess this will be an unimplemented relocation on
> Windows. It will be helpful to know which one it is.
>
> Cheers,
> Lang.
>
>
> On Sun, Jan 6, 2019 at 6:45 PM Eli Baum via llvm-dev <
> llvm-dev at lists.llvm.org> wrote:
>
>> Hi all,
>>
>> I am new to LLVM and have been working through the Kaleidoscope tutorial.
>> Everything is working fine so far except for local externs (as opposed to
>> things like the math functions, which are working). Note that I have seen
>> this bug with the reference code listing, as well as my own code. link to
>> code: https://llvm.org/docs/tutorial/LangImpl05.html#full-code-listing
>>
>> [c34n10 kaleidoscope] ./toy
>> ready> extern sin(x); sin(1);
>> ready> Read extern:
>> declare double @sin(double)
>>
>> ready> ready> Evaluated to 0.841471
>> ready> extern putchard(x); putchard(120);
>> ready> Read extern:
>> declare double @putchard(double)
>>
>> ready> ready> Failure value returned from cantFail wrapped call
>> UNREACHABLE executed at ~/project/llvm/include/llvm/Support/Error.h:732!
>> Aborted (core dumped)
>>
>> sin is, of course, defined in libm. putchard is declared in my code, per
>> the tutorial, as
>>
>> /// putchard - putchar that takes a double and returns 0.
>> extern "C" DLLEXPORT double putchard(double X) {
>>   fputc((char)X, stderr);
>>   return 0;
>> }
>>
>> Other posts online suggest that this issue could be caused by not
>> compiling with -rdynamic, but I am.
>>
>> The actual error is occuring with the following code (on the cantFail
>> line)
>>
>> auto ExprSymbol = TheJIT->findSymbol("__anon_expr");
>> assert(ExprSymbol && "Function not found");
>>
>> // cast to double-returning function
>> double (*FP)() = (double
>> (*)())(intptr_t)cantFail(ExprSymbol.getAddress());
>> fprintf(stderr, "Evaluated to %f\n", FP());
>>
>> and some investigation with GDB reveals that the hasError flag of
>> ExprSymbol.getAddress() is true, which is why the cantFail is failing. As
>> to why that flag is set, I'm at a loss. I have run through GDB with both
>> the sin and putchard examples, to try and see where they are diverging. I'm
>> not totally sure, but I think the divergence might be happening on line 347
>> of RuntimeDyld.cpp:
>>
>> if (auto IOrErr = processRelocationRef(SectionID, I, Obj, LocalSections,
>> Stubs))
>>
>> That is, in the sin example, this expression is false; in the putchard
>> example, it is true. However there may be something earlier on that I
>> missed – there were a few thousand lines of GDB logging to diff through.
>>
>> It appears not to be an issue with the function itself, nor the
>> compilation/link process: from within GDB, I can successfully run call
>> putchard(120), so the symbol is definitely being included in the
>> executable. Just for some reason the JIT can't find it.
>>
>> Finally, my makefile looks like
>>
>> LIBS=core orcjit native analysis executionengine instcombine object
>> runtimedyld scalaropts support
>> FLAGS=`llvm-config --cxxflags --ldflags --system-libs --libs $(LIBS)`
>>
>> %: %.cpp
>>         clang++ -v -g3 -O0 $^ -o $@ $(FLAGS) -rdynamic
>>
>> Please let me know if I can provide any additional code or debug
>> information. I don't know a ton about LLVM so am a bit lost as to where to
>> go from here.
>>
>> (Note: I also have posted this question on the LLVM IRC channel, and on
>> Stack
>> <https://stackoverflow.com/questions/54048268/llvm-kaleidoscope-tutorial-failing-on-local-extern>
>> .)
>>
>> Thank you so much! I'm very excited to start working with LLVM and have
>> just been stuck on this issue for a couple of days.
>>
>> Best,
>> Eli Baum
>> eli.baum at yale.edu
>>
>> _______________________________________________
>> LLVM Developers mailing list
>> llvm-dev at lists.llvm.org
>> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>>
>
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