Setup LLVM
Installation or setting up LLVM from source
Follow the instructions on their websites:
To get the source code and setting up the environment variables:
You can grab the source directly from their repo or you can obtain it from releases.
mkdir ~/llvm
cd ~/llvm
git clone https://github.com/llvm/llvm-project.git
mkdir llvm-build
mkdir llvm-install
export LLVM_SRC="~/llvm/llvm-project"
export LLVM_BUILD="~/llvm/llvm-build"
export LLVM_PATH="~/llvm/llvm-install"
export PATH="$LLVM_PATH/bin":$PATH
export LD_LIBRARY_PATH=$LD_LIBRARY_PATH:"$LLVM_PATH/libexec"
export LD_LIBRARY_PATH=$LD_LIBRARY_PATH:"$LLVM_PATH/lib"
export LIBRARY_PATH=$LIBRARY_PATH:"$LLVM_PATH/libexec"
export LIBRARY_PATH=$LIBRARY_PATH:"$LLVM_PATH/lib"
export C_INCLUDE_PATH=$C_INCLUDE_PATH:"$LLVM_PATH/include"
export CPLUS_INCLUDE_PATH=$CPLUS_INCLUDE_PATH:"$LLVM_PATH/include"
The requirements to build from source are:
- Cmake
- Python3
- Gcc
- zlib
- GNU make
See the versions here.
LLVM on Ubuntu 16.04 x64
Almost all cmake configurations are available here.
cd $LLVM_BUILD
cmake -B build -G "Unix Makefiles" -DLLVM_TARGETS_TO_BUILD="host" \
-DLLVM_ENABLE_PROJECTS='clang;clang-tools-extra;compiler-rt' \
-DCMAKE_INSTALL_PREFIX=$LLVM_PATH -DCMAKE_BUILD_TYPE=Release \
-DLLVM_BUILD_EXAMPLES=ON -DCLANG_BUILD_EXAMPLES=ON \
-DCLANG_OPENMP_NVPTX_DEFAULT_ARCH=sm_70 \
-DLIBOMPTARGET_NVPTX_COMPUTE_CAPABILITIES=70 $LLVM_SRC/llvm
cd build
make -j8
make -j8 install
LLVM on Redhat Enterprise with PowerPC architecture (GPU-enabled)
cmake -B build -G "Unix Makefiles" -DLLVM_ENABLE_RTTI=ON \
-DLLVM_TARGETS_TO_BUILD="NVPTX;PowerPC" \
-DLLVM_ENABLE_PROJECTS='clang;clang-tools-extra;compiler-rt;libcxx;libcxxabi' \
-DCMAKE_INSTALL_PREFIX=$LLVM_PATH -DCMAKE_BUILD_TYPE=Release \
-DLLVM_BUILD_EXAMPLES=ON -DCLANG_BUILD_EXAMPLES=ON \
-DCLANG_OPENMP_NVPTX_DEFAULT_ARCH=sm_70 \
-DLIBOMPTARGET_NVPTX_COMPUTE_CAPABILITIES=70 $LLVM_SRC/llvm
cd build
make -j8
make -j8 install
Compilation simple sources with clang on PowerPC
clang++ hello.cpp -fuse-ld=lld -o hello -L/path/to/gcc/libraries/
# In my case: -L/scinet/mist/software/2020a/opt/cuda-10.2.89/gcc/8.4.0/lib/gcc/powerpc64le-unknown-linux-gnu/8.4.0
./hello
If you want to write the LLVM IR from the source, add option -S -emit-llvm to clang.
Compilation CUDA sources with clang on PowerPC
Find more details, see here, and here.
clang++ -stdlib=libc++ -Wall vectorOp.cu -o vectorOp --cuda-gpu-arch=sm_70 \
-L/scinet/mist/software/2020a/opt/cuda-10.2.89/gcc/8.4.0/lib/gcc/powerpc64le-unknown-linux-gnu/8.4.0 \
-lcudart_static -ldl -lrt -pthread
There was a weird bug that only resolved when I placed files crtbegin.o and crtend.o in the working directory. The linker was not able to find the files with -L option.
Playing around with LLVM IR
For more info, see the llvm lecture from Mike Shah.
Consider hello.cpp:
#include <stdio.h>
int main(){
printf("Bonjour!\n");
return 0;
}
You can compile this code with clang easily:
clang++ hello.cpp -o hello
To print out the LLVM IR of the code:
clang++ -S -emit-llvm hello.cpp
To run the IR with the LLVM JIT (lli):
lli hello.ll
To convert IR to Bitcode (BC); you can still run the BC with lli:
llvm-as hello.ll
lli hello.bc
To convert BC to Assembly using llc: the static compiler:
llc hello.bc
To see the available targets:
llc hello.bc --version
# The output in my case
LLVM (http://llvm.org/):
LLVM version 11.1.0
Optimized build.
Default target: powerpc64le-unknown-linux-gnu
Host CPU: pwr9
Registered Targets:
nvptx - NVIDIA PTX 32-bit
nvptx64 - NVIDIA PTX 64-bit
ppc32 - PowerPC 32
ppc64 - PowerPC 64
ppc64le - PowerPC 64 LE
Playing with Optimizer (opt) to create pass(es)
Using the previous hello.cpp, running opt with --time-pass to show timing of the passes:
# Adding the -debug-pass-manager flag to the opt commands shows what's going on.
opt hello.ll -debug-pass-manager --time-pass
Refer to this section to write passes.
Types of passes:
- Analysis Pass
- Transform Pass
Levels of passes:
- Module Pass
- Call Graph Pass
- Function Pass
- Basic Block Pass
- Immutable Pass
- Region Pass
- Machine Function Pass
Simple pass example using LLVM Hello example
Go to the directory $LLVM_BUILD/build/lib/Transforms/Hello and run make. Then you should be able to see LLVMHello.so file in $LLVM_BUILD/build/lib directory.
Then by running this command you should be able to see the results:
opt -enable-new-pm=0 -load $LLVM_BUILD/build/lib/LLVMHello.so -hello < hello.bc
How to apply a transforming pass
Take the previous example, LLVMHello.so lib:
# File instrumentation.ll contains a function we want to add to our program.
# File LLVMHello.so contains the code to transform our original code to include our new piece of code.
opt -load $LLVM_BUILD/build/lib/LLVMHello.so -hello4 -S < hello.ll > readyToBeHooked.ll
llvm-link readyToBeHooked.ll instrumentation.ll -S -o instrumentDemo.ll