[llvm-dev] Building A Project Against LLVM

Sat May 16 21:21:15 PDT 2020

On Sat, May 16, 2020 at 12:07 AM Rarrum <rarrum at gmail.com> wrote:

> I've managed to get 10.0.0 working now.. there were a couple things I had
> to adjust.
>
> The Kaleidoscope example had me doing this before creating the object file:
> llvm::InitializeAllTargetInfos();
> llvm::InitializeAllTargets();
> llvm::InitializeAllTargetMCs();
> llvm::InitializeAllAsmParsers();
> llvm::InitializeAllAsmPrinters();
>
> It turns out I can get away with just this, since I'm not (yet) worried
> about targeting other machines:
> llvm::InitializeNativeTarget();
> llvm::InitializeNativeTargetAsmPrinter();
>
> Since "all" doesn't work anymore for some reason
>

Did it use to work with LLVM 9? It may be worth investigating if this is
the case.

> , I've managed to (through trial and error, guessing at different names
> shown from llvm-config --components) end up with this set of libnames:
> llvm_map_components_to_libnames(llvm_libs core executionengine support
> nativecodegen)
>
> That left me with 2 link errors referring to llvm::raw_ostream and
> llvm::raw_pwrite_stream.  After much more digging through similar
> complaints on the internet.. the last fix turned out to be adding this to
> CMakeLists.txt:
> set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -fno-rtti")
>
> I am a little worried that the rtti flag may come back and bite me later
> when I get around to building this on windows again (since I do use
> exceptions), but that's a problem for another day.
>

You can build LLVM with RTTI enable if you need it.

>
>
> One last question.. is there a good way to know which libnames I need,
> based on which #includes I pull in or which classes I'm using?  I didn't
> see anything obvious in the doxygen documentation.
>

LLVM includes are organized by subdirectory with a directory in the
`include/llvm/` folder matching directories in `lib/` in general, and the
lib name matches the component's name. If you include
"llvm/Support/raw_ostream.h" you need `support`, if you include
 "include/llvm/IRReader/IRReader.h" you need "irreader", etc. In general
for the IR-level library this is fairly straightforward I think, but it
becomes a bit more complex for the backends, jit, and these kind of things.
There are also "pseudo components" like providing the name of a target
would link all aspects of this targets, while using "AllTargetsAsmParsers"
would link only the assembly parser for all available targets... I don't
find a good doc on this unfortunately.

-- 
Mehdi

>
>
> On Fri, May 15, 2020 at 8:57 PM Rarrum <rarrum at gmail.com> wrote:
>
>> I'd rather avoid updating my OS at the moment or setting up a VM.  But
>> the cmake comments were a hint.. I suspect something is going wrong in
>> there preventing it from adding the actual library files to the linker
>> commandline.
>>
>> I added this to my CMakeLists.txt:
>> set(CMAKE_VERBOSE_MAKEFILE on)
>>
>> Which shows no LLVM libs at all being passed in:
>>
>> [  8%] Linking CXX executable ../bin/CBreakCompiler
>> /usr/bin/c++     CMakeFiles/CBreakCompiler.dir/src/main.cpp.o
>> CMakeFiles/CBreakCompiler.dir/src/Parser.cpp.o
>> CMakeFiles/CBreakCompiler.dir/src/SourceTokenizer.cpp.o
>> CMakeFiles/CBreakCompiler.dir/src/IRCompiler.cpp.o
>> CMakeFiles/CBreakCompiler.dir/src/CompiledOutput.cpp.o
>> CMakeFiles/CBreakCompiler.dir/src/JIT.cpp.o  -o ../bin/CBreakCompiler
>>
>> If I change this:
>> llvm_map_components_to_libnames(llvm_libs all)
>> to:
>> llvm_map_components_to_libnames(llvm_libs core)
>>
>> Then I start to see libraries being added:
>> [  8%] Linking CXX executable ../bin/CBreakCompiler
>> /usr/bin/c++     CMakeFiles/CBreakCompiler.dir/src/main.cpp.o
>> CMakeFiles/CBreakCompiler.dir/src/Parser.cpp.o
>> CMakeFiles/CBreakCompiler.dir/src/SourceTokenizer.cpp.o
>> CMakeFiles/CBreakCompiler.dir/src/IRCompiler.cpp.o
>> CMakeFiles/CBreakCompiler.dir/src/CompiledOutput.cpp.o
>> CMakeFiles/CBreakCompiler.dir/src/JIT.cpp.o  -o ../bin/CBreakCompiler
>> /usr/local/lib/libLLVMCore.a /usr/local/lib/libLLVMBinaryFormat.a
>> /usr/local/lib/libLLVMRemarks.a /usr/local/lib/libLLVMBitstreamReader.a
>> /usr/local/lib/libLLVMSupport.a -lrt -ldl -ltinfo -lpthread -lm
>> /usr/local/lib/libLLVMDemangle.a
>>
>> Perhaps I can figure out which ones I need and manually specify them all,
>> rather than using "all".
>>
>> On Fri, May 15, 2020 at 8:17 PM Mehdi AMINI <joker.eph at gmail.com> wrote:
>>
>>>
>>>
>>> On Fri, May 15, 2020 at 6:53 PM Neil Nelson via llvm-dev <
>>> llvm-dev at lists.llvm.org> wrote:
>>>
>>>> Rarrum,
>>>>
>>>> Kubuntu 20.04 LTS is available. You may be able to upgrade to 19.10,
>>>> and then to 20.04 without reinstalling. It can be done on Xubuntu. A direct
>>>> upgrade to 20.04 should become available. LLVM 10 then installs from the
>>>> distribution packages. I put all this on a VM using KVM/QEMU to keep it
>>>> isolated from my primary desktop environment. Building a 20.04 VM after
>>>> upgrading to 20.04 appears to give a faster VM. Use llvm's linker lld.
>>>>
>>>> The cmake version for 20.04 is 3.16.3 which should help with llvm's
>>>> recommended version.
>>>>
>>>
>>> Do you believe the error listed have to do with the CMake version?
>>>
>>>
>>>
>>>
>>>> Neil
>>>> On 5/15/20 12:05 AM, Rarrum via llvm-dev wrote:
>>>>
>>>> I decided to start playing around with building my own programming
>>>> language recently, and to use LLVM to handle the assembly-level details.
>>>> I'm on Kubuntu 18.04, and I started out using LLVM 6.0 from Kubuntu's
>>>> packages.  I put together code for dealing with my language, then went over
>>>> the Kaleidoscope tutorials (which have been extremely helpful btw!).  I was
>>>> able to successfully get my own compiler to generate IR using LLVM, use
>>>> PassManager to write that to a native .o file, use gcc to link that, and
>>>> execute a tiny program written in my own language.
>>>>
>>>> I also decided it was a good time to learn CMake, so I set up my
>>>> project using that.  The CMakeLists.txt file I'm using is essentially just
>>>> taken from:
>>>> https://llvm.org/docs/CMake.html#embedding-llvm-in-your-project -
>>>> though originally it would not link.  From scouring the internet I made 2
>>>> changes to get that working: replaced "support core irreader" with "all",
>>>> and replaced "${llvm_libs}" with just "LLVM".
>>>>
>>>> However as I was starting to play with setting up JIT, I hit more
>>>> differences between the version of LLVM in Kubuntu and the version the
>>>> examples and documentation were written against.  So I decided to try to
>>>> update to a newer version of LLVM.. and this is where I've been stuck for
>>>> several days now.  Here are the steps I've taken:
>>>>
>>>> * Uninstalled any llvm packages I could find from Kubuntu's package
>>>> manager.
>>>> * Followed the getting started guide:
>>>> https://llvm.org/docs/GettingStarted.html - I git cloned LLVM, checked
>>>> out the 10.0.0 tag, ran cmake as instructed, with the Release type.  When
>>>> that completed successfully I ran sudo ninja install.
>>>> * I then went back to my project and adjusted a couple places to
>>>> successfully compile against the new version.
>>>> * At this point I put "${llvm_libs}" in the CMakeLists.txt file back to
>>>> match the example.  However I was getting a massive wall of link errors.
>>>> * I assumed I must have built LLVM incorrectly somehow, so in an effort
>>>> to undo that install, I deleted everything I could find under /usr/local
>>>> that had LLVM in its name, downloaded the 10.0 release from
>>>> https://releases.llvm.org/download.html for ubuntu 18.04, and
>>>> extracted that all to /usr/local.
>>>> * I can still successfully compile, but not link.
>>>>
>>>> At this point I'm not sure what to try next.  Is there additional
>>>> documentation somewhere for how to "install" a current release of LLVM
>>>> correctly?
>>>>
>>>>
>>>> For reference here's my final CMakeLists.txt file:
>>>>
>>>> cmake_minimum_required(VERSION 3.10)
>>>>
>>>> project(CBreakCompiler)
>>>>
>>>> set(CMAKE_CXX_STANDARD 17)
>>>> set(CMAKE_CXX_STANDARD_REQUIRED True)
>>>> add_compile_options(-Wall)
>>>>
>>>> find_package(LLVM 10.0.0 REQUIRED CONFIG)
>>>>
>>>> message(STATUS "Found LLVM ${LLVM_PACKAGE_VERSION}")
>>>> message(STATUS "Using LLVMConfig.cmake in: ${LLVM_DIR}")
>>>>
>>>> include_directories(${LLVM_INCLUDE_DIRS})
>>>> add_definitions(${LLVM_DEFINITIONS})
>>>>
>>>> add_executable(CBreakCompiler
>>>>     src/main.cpp
>>>>     src/Parser.cpp
>>>>     src/SourceTokenizer.cpp
>>>>     src/IRCompiler.cpp
>>>>     src/CompiledOutput.cpp)
>>>>
>>>> llvm_map_components_to_libnames(llvm_libs all)
>>>> target_link_libraries(CBreakCompiler ${llvm_libs})
>>>>
>>>>
>>>> And a snippet from the cmake output corresponding to those message
>>>> lines:
>>>>
>>>> -- Found LLVM 10.0.0
>>>> -- Using LLVMConfig.cmake in: /usr/local/lib/cmake/llvm
>>>>
>>>>
>>>> There are dozens of link errors.. the first few and last few are:
>>>>
>>>> CMakeFiles/CBreakCompiler.dir/src/main.cpp.o:(.data.rel+0x0): undefined
>>>> reference to `llvm::DisableABIBreakingChecks'
>>>> CMakeFiles/CBreakCompiler.dir/src/main.cpp.o: In function
>>>> `std::default_delete<llvm::LLVMContext>::operator()(llvm::LLVMContext*)
>>>> const':
>>>> main.cpp:(.text._ZNKSt14default_deleteIN4llvm11LLVMContextEEclEPS1_[_ZNKSt14default_deleteIN4llvm11LLVMContextEEclEPS1_]+0x1e):
>>>> undefined reference to `llvm::LLVMContext::~LLVMContext()'
>>>> ...
>>>> CMakeFiles/CBreakCompiler.dir/src/CompiledOutput.cpp.o:(.data.rel.ro+0xe0):
>>>> undefined reference to `llvm::raw_ostream::anchor()'
>>>> CMakeFiles/CBreakCompiler.dir/src/CompiledOutput.cpp.o:(.data.rel.ro+0xf8):
>>>> undefined reference to `typeinfo for llvm::raw_pwrite_stream'
>>>> CMakeFiles/CBreakCompiler.dir/src/CompiledOutput.cpp.o:(.data.rel.ro+0x110):
>>>> undefined reference to `typeinfo for llvm::raw_ostream'
>>>>
>>>>
>>> Seems like `llvm_map_components_to_libnames` wasn't populated well?
>>> I'd start by printing `${llvm_libs}` in your CMake to check the output
>>> of llvm_map_components_to_libnames, I don't know how the "all" works for
>>> external builds? You may have to list the components you need more
>>> explicitly instead?
>>>
>>> --
>>> Mehdi
>>>
>>>
>>>
>>>
>>>
>>>
>>>>
>>>> _______________________________________________
>>>> LLVM Developers mailing listllvm-dev at lists.llvm.orghttps://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>>>>
>>>> _______________________________________________
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>>>>
>>>
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