[llvm-dev] Building A Project Against LLVM

[Rarrum via llvm-dev]

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'
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