[llvm-dev] Since MCJIT I can't get libm functions to work

[Frank Winter via llvm-dev]

Hi Alex,

loading the symbols explicitly helped. With this the build process 
doesn't need any additional linker flags. Very nice.

Thanks,
Frank


On 06/28/2018 04:38 PM, Alex Denisov wrote:
> Hi Frank,
>
> If I am not mistaken it doesn't look in the whole process space by default.
> Please, try loading all the symbols explicitly:
>
> 	sys::DynamicLibrary::LoadLibraryPermanently(nullptr);
>
> If it doesn't help, then you may try compiling your host program with -rdynamic, otherwise dlsym may not see all the symbols. At least it was the case for me on Linux.
>
> I hope it helps.
>
> Cheers,
> Alex.
>
>> On 28. Jun 2018, at 21:40, Frank Winter via llvm-dev <llvm-dev at lists.llvm.org> wrote:
>>
>> I am upgrading our JIT application to use LLVM 6.0.0, and with this transition I am making the move to use the new MCJIT facility.
>>
>> A problem I am encountering is that the math functions from libm are not resolved/found. I am using the lambda resolver from the KaleidoscopeJIT class which first searches the present modules and, if that is unsuccessful, continues the search in the whole process space.
>>
>> The generated modules would declare external functions like
>>
>> declare float @cosf(float)
>>
>> and would call it like:
>>
>>    %17 = call float @cosf(float %16)
>>
>> The datalayout is set to
>>
>> target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
>>
>> The code snippet that adds the module is pretty much from the JIT tutorial:
>>
>>        auto Resolver = llvm::orc::createLambdaResolver(
>>                                [&](const std::string &Name) {
>>                              if (auto Sym = CompileLayer.findSymbol(Name, false))
>>                                return Sym;
>>                              return llvm::JITSymbol(nullptr);
>>                                },
>>                                [](const std::string &Name) {
>>                              if (auto SymAddr =
>> llvm::RTDyldMemoryManager::getSymbolAddressInProcess(Name))
>>                                return llvm::JITSymbol(SymAddr, llvm::JITSymbolFlags::Exported);
>>                              return llvm::JITSymbol(nullptr);
>>                                });
>>
>>        cantFail(CompileLayer.addModule(std::move(M),
>>                        std::move(Resolver)));
>>
>> When running the program I receive the following error:
>>
>> LLVM ERROR: Program used external function 'cosf' which could not be resolved!
>>
>> This is on an Intel i7 CPU with LLVM targets configured as "X86".
>>
>> Adding the '-lm' and '-ldl' option to the linker command that links the final program doesn't help. (I even called the 'cosf' function by hand in the host code to make sure it is mapped - didn't change the behavior of the MCJIT resolver.)
>>
>> Any ideas?
>>
>>
>> Best wishes,
>>
>> Frank
>>
>>
>>
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