Clang Cross Compile For RasberryPi on Redhat 7

1. References

https://llvm.org/docs/HowToCrossCompileLLVM.html 

https://medium.com/@zw3rk/making-a-raspbian-cross-compilation-sdk-830fe56d75ba

2. Steps for setup

2.1. Select where to install clang cross compile SDK

Example:

export BASE=/opt
mkdir -p $BASE/raspbian-sdk/{prebuilt,sysroot,tmp}

2.2. Download pre-build clang+llvm

From http://releases.llvm.org/download.html, dowload clang+llvm-3.4.2-x86_64-fedora20.xz

cd $BASE/raspbian-sdk/prebuilt

wget http://releases.llvm.org/3.4.2/clang+llvm-3.4.2-x86_64-fedora20.xz 

Then extract this to $BASE/raspbian-sdk/prebuilt

tar -xvf clang+llvm-3.4.2-x86_64-fedora20.xz
rm -f clang+llvm-3.4.2-x86_64-fedora20.xz

2.3. Setup Linker and Other Utilities

cd $BASE/raspbian-sdk/tmp 

wget https://ftp.gnu.org/gnu/binutils/binutils-2.28.tar.bz2 

tar -xvf binutils-2.28.tar.bz2 

cd binutils-2.28 

./configure --prefix="${BASE}/raspbian-sdk/prebuilt" \  
        --target=arm-linux-gnueabihf \            
        --enable-gold=yes \            
        --enable-ld=yes \            
        --enable-targets=arm-linux-gnueabihf \            
        --enable-multilib \            
        --enable-interwork \            
        --disable-werror \            
        --quiet
        
make && make install

2.4. Copy Headers and Libraries from RasberryPi to cross-compile machine (Redhat 7)

cd $BASE/raspbian-sdk

rsync -rzLR --safe-links \
      pi@raspberrypi_address:/usr/lib/arm-linux-gnueabihf \
      pi@raspberrypi_address:/usr/lib/gcc/arm-linux-gnueabihf \
      pi@raspberrypi_address:/usr/include \
      pi@raspberrypi_address:/lib/arm-linux-gnueabihf \
      ./sysroot/

Notes: On RasberryPi we also need to install 'rsync' before running above command.

sudo apt-get install rsync

2.5. Remove temp folder

cd $BASE/raspbian-sdk

rm -rf tmp

After doing all above steps, now the sdk folder layout is like below.

    ├── prebuilt
	|   |── clang+llvm-3.4.2-x86_64-fedora20
	│   ├── arm-linux-gnueabihf
	│   ├── bin
	│   ├── include
	│   ├── lib
	│   ├── libexec
	│   └── share
	└── sysroot
		├── lib
		└── usr

2.6. Create shell wrappers

Do below commands before creating shell wrappers

ln -s $BASE/raspbian-sdk/prebuilt/clang+llvm-3.4.2-x86_64-fedora20/bin/clang /usr/bin/clang

ln -s /usr/bin/clang $BASE/raspbian-sdk/prebuilt/bin/clang

2.6.1. Create CC script arm-linux-gnueabihf-clang

cd $BASE
vi arm-linux-gnueabihf-clang

#------------------------------------------------------------------------
#!/bin/bash
BASE="/opt/raspbian-sdk"
SYSROOT="${BASE}/sysroot"
TARGET=arm-linux-gnueabihf
COMPILER_PATH="${SYSROOT}/usr/lib/gcc/${TARGET}/4.9"
exec env COMPILER_PATH="${COMPILER_PATH}" \
	 "${BASE}/prebuilt/bin/clang" --target=${TARGET} \
	 --sysroot="${SYSROOT}" \
	 -isysroot "${SYSROOT}" \
	 --gcc-toolchain="${BASE}/prebuilt/bin" \
	 "$@"
#------------------------------------------------------------------------`

2.6.2. Create LD script arm-linux-gnueabihf-clang-ld

cd $BASE
vi arm-linux-gnueabihf-clang-ld

#------------------------------------------------------------------------
#!/bin/bash
BASE="/opt/raspbian-sdk"
SYSROOT="${BASE}/sysroot"
TARGET=arm-linux-gnueabihf
COMPILER_PATH="${SYSROOT}/usr/lib/gcc/${TARGET}/4.9"
exec env COMPILER_PATH="${COMPILER_PATH}" \
	 "${BASE}/prebuilt/bin/clang" --target=${TARGET} \
	 --sysroot="${SYSROOT}" \
	 -isysroot "${SYSROOT}" \
	 -L"${COMPILER_PATH}" \
	 --gcc-toolchain="${BASE}/prebuilt/bin" \
	 "$@"	
#------------------------------------------------------------------------

2.6.3. Create soft links

cd $BASE
chmod +x arm-linux-gnueabihf-clang
chmod +x arm-linux-gnueabihf-clang-ld 
ln -s $BASE/arm-linux-gnueabihf-clang /usr/bin/arm-linux-gnueabihf-clang
ln -s $BASE/arm-linux-gnueabihf-clang-ld /usr/bin/arm-linux-gnueabihf-clang-ld

2.7. Test

Create file hello.c

#include <stdio.h>
int
main(int argc, char ** argv) {
  printf("Hello World!\n");
  return 0;
}

Compile hello.c:

arm-linux-gnueabihf-clang-ld -o hello hello.c

Copy executable file hello to Raspberry machine for execution.