CMake cross compilation example

This project demostrates a simple example of cmake cross compilation.

The development target is a WiFi router with MTK SoC, but is is easy to cutomize it to other device, like Raspberry Pi, etc.

To custimize to other device, it could create a new toolchain file like "cmake/openwrt-mtr.cmake" and fill it suitable values for:

# toolchains
CMAKE_C_COMPILER
CMAKE_CXX_COMPILER
# root path
CMAKE_FIND_ROOT_PATH

Prerequsite

• CMake/GDB

sudo apt update
sudo apt install -y cmake gdb-multiarch

• Googletest

cd tmp
git clone https://github.com/google/googletest.git
cd googletest/
mkdir build && cd build/
cmake ..
make
sudo make install

• VSCode (Debian)

Download .deb file and install it.

dpkg -i code_xxx.deb

• PRI (Reference)

Setup toolchains:

cd /tmp
wget https://github.com/Pro/raspi-toolchain/releases/latest/download/raspi-toolchain.tar.gz
sudo mkdir /opt && cd /opt
tar xvf /tmp/raspi-toolchain.tar.gz

Copy rootfs:

cd ~ && mkdir -p raspberrypi/rootfs
rsync -vR --progress -rl --delete-after --safe-links pi@192.168.1.101:/{lib,usr,opt/vc/lib} ~/raspberrypi/rootfs

Environment (Debian/OSX)

Build

Build - Debian

mkdir deb && cd deb
cmake ..
make

Build - OSX

mkdir osx && cd osx
cmake ..
make

Build - RPI3 (cross compile)

Before building binary, it needs to modify/set the following environment variables according to your working environment.

export TARGET=root@192.168.1.101

export RPI3_C=/opt/cross-pi-gcc/bin/arm-linux-gnueabihf-gcc
export RPI3_CXX=/opt/cross-pi-gcc/bin/arm-linux-gnueabihf-g++
export RPI3_ROOTFS=$HOME/raspberrypi/rootfs

mkdir -p rpi && cd rpi
cmake -DCMAKE_TOOLCHAIN_FILE=../cmake/rpi3.cmake ..
make

Build - Openwrt MTK (cross compile)

Before building binary, it needs to modify/set the following environment variables according to your working environment.

export OPENWRT_ROOT=$HOME/workspace/official/openwrt
export STAGING_DIR=$OPENWRT_ROOT/staging_dir/toolchain-mipsel_24kc_gcc-7.5.0_musl
export TARGET=root@10.1.1.1

export MTK_C=$OPENWRT_ROOT/staging_dir/toolchain-mipsel_24kc_gcc-7.5.0_musl/bin/mipsel-openwrt-linux-musl-gcc
export MTK_CXX=$OPENWRT_ROOT/staging_dir/toolchain-mipsel_24kc_gcc-7.5.0_musl/bin/mipsel-openwrt-linux-musl-g++
export MTK_ROOTFS=$OPENWRT_ROOT/staging_dir/target-mipsel_24kc_musl/

mkdir wrt && cd wrt
cmake -DCMAKE_TOOLCHAIN_FILE=../cmake/openwrt-mtk.cmake ..
make

Build - Openwrt Package

In openwrt project folder, run "make menuconfig" and check the "Utilities/hellonux", save and exit.
make package/hellonux/compile V=s

Remote VSCode Debugging

In host machine:

1. Setup SSH to run gdbserver on target $TARGET.

   RPI:

   ssh -L9091:localhost:9091 $TARGET "gdbserver :9091 ~pi/bin/hellonux"

   or

   OpenWrt:

   ssh -L9091:localhost:9091 $TARGET "gdbserver :9091 /usr/sbin/hellonux"

2. Launch VSCode:

   code [--disable-gpu] [-n <folder>] &
   
   ex:
   
   code --disable-gpu -n hellonux

If run VSCode in VM, sometimes, it will show all white screen, it can use "--disable-gpu" to make it display correctly.

In debug console, it can issue th GDB command with "-exec" prefix, for example:

-exec info thread

3. Select "RPI3" or "MTK" debug configuration and start debugging.

Remote GDB Debugging

info thread
info shared
set sysroot
show arch
b
n
c

Q/A

mipsel-openwrt-linux-musl-gcc: warning: environment variable 'STAGING_DIR' not defined

GDB: Unable to find dynamic linker breakpoint function

Manually-specified variables were not used by the project: CMAKE_TOOLCHAIN_FILE

Just a warning, ignore it.

Cannot stop on program entry point

Try to remove all files in build folder and rebuild it.

Reply contains invalid hex digit 59

Check the output binary file format with "file" command. Setup the correct environment variables, take MTK as example, it should set 'MTK_C', 'MTK_CXX', 'MTK_ROOTFS' correctly.

Unable to stat debugging....File format is ambiguous.

Set the target architecture in GDB setupCommands section:

Ex. For RPI3:

{"text": "set gnutarget elf32-littlearm"},