Compilation and Building

Compilation Environment Setup

Set up the basic environment by following instructions in Quick Start Overview. Both the user space and LiteOS Cortex-A kernel space are compiled using the LLVM compiler. If you choose to port the Linux kernel, run the following command to install the gcc-arm-linux-gnueabi cross compiler for compiling the Linux kernel-space image:

sudo apt-get install gcc-arm-linux-gnueabi

Introduction to the Compilation and Building Subsystem

To learn more about the Compilation and Building subsystem, including the compilation and building process, build scripts, and directory structure, see Compilation and Building Guide.

Adding a Chipset Solution

After learning the compilation framework and setting up the compilation environment, perform the following steps to create a chipset solution:

Create a category.

The directory structure is as follows: device/{chipset solution vendor}/{development board}. For example, if you are using the hispark_taurus development board from HiSilicon, create the following directory in the root directory of the code:

mkdir -p device/hisilicon/hispark_taurus

The chipset solution directory tree is as follows:

device                                      
└── company                         # Chipset solution vendor
    └── board                       # Name of the development board
        ├── BUILD.gn                # Build script
        ├── hals                    # OS device API adaptation
        ├── linux                   # (Optional) Linux kernel version
        │   └── config.gni          # Linux build configuration
        └── liteos_a                # (Optional) LiteOS kernel version
            └── config.gni          # LiteOS_A build configuration

For example, if you are porting the Linux kernel to the hispark_taurus development board, the directory tree is as follows:

device                  
└── hisilicon             
    └── hispark_taurus          
        ├── BUILD.gn    
        ├── hals        
        ├── ......      
        └── linux    
            └── config.gni

After the directory tree is created, store the source code related to the development board in the hispark_taurus directory.

Configure the build options of the development board.

You can configure the build options in the config.gni file described in step 1. The compilation and building framework will then compile all OS components in the user space based on your configuration. The config.gni file contains the following key fields:

kernel_type: Kernel used by the development board, for example, LiteOS_A, LiteOS_M, or Linux.
kernel_version: Kernel version used by the development board, for example, 4.19.
board_cpu: CPU of the development board, for example, Cortex-A7 or RISCV32.
board_arch: Chipset architecture of the development board, for example, armv7-a or rv32imac.
board_toolchain: Name of the customized build toolchain used by the development board, for example, gcc-arm-none-eabi. If this field is not specified, ohos-clang will be used.
board_toolchain_prefix: Prefix of the toolchain, for example, gcc-arm-none-eabi.
board_toolchain_type: Toolchain type. Currently, only GCC and clang are supported.
board_cflags: Build options of the .c file configured for the development board.
board_cxx_flags: Build options of the .cpp file configured for the development board.
board_ld_flags: Linking options configured for the development board.

For HiSilicon's hispark_taurus development board, the content in device/hisilicon/hispark_taurus/config.gni is as follows:

# Board CPU type, e.g. "cortex-a7", "riscv32".
board_cpu = "cortex-a7"

# Name of the toolchain used for system building
# E.g. gcc-arm-none-eabi, arm-linux-harmonyeabi-gcc, ohos-clang,  riscv32-unknown-elf.
# Note: The "ohos-clang" toolchain is used by default. You can also customize the toolchain.
board_toolchain = "mips-linux-gnu-gcc"

# Path where the toolchain is installed, which can be left blank if the installation path has been added to ~/.bashrc.
board_toolchain_path = 
    rebase_path("//prebuilts/gcc/linux-x86/arm/arm-linux-ohoseabi-gcc/bin",
                root_build_dir)

# Prefix of the toolchain
board_toolchain_prefix = "arm-linux-ohoseabi-"

# Type of the compiler, which can be gcc or clang
board_toolchain_type = "gcc"

# Build options related to the development board
board_cflags = [
]
board_cxx_flags = [
]
board_ld_flags = []

# Board related headfiles search path.
board_include_dirs = []
board_include_dirs += [ rebase_path(
        "//prebuilts/gcc/linux-x86/arm/arm-linux-ohoseabi-gcc/target/usr/include",
        root_build_dir) ]

# Board adapter dir for OHOS components.
board_adapter_dir = ""

# Sysroot path.
board_configed_sysroot = ""

# Board storage type, it used for file system generation.
storage_type = "emmc"

Edit the build script of the development board.

In the BUILD.gn file described in step 1, build code related to the development board, such as code for the on-device driver, on-device interface adaptation (media and graphics), and SDK on the development board.

For example, edit the device/hisilicon/hispark_taurus/BUILD.gn file as follows:
```
# It is recommended that the group name be the same as the development board name.
group("hispark_taurus") {   
  deps = [ "//kernel/linux/patches:linux_kernel" ] # Start kernel compilation.
  deps += [
  ...... # Other compilation units of the development board
  ]
}
```
Start building and debugging.

In the directory of the development board, run the hb set and hb build commands to start building the chipset solution. The compilation and building framework starts the building with the BUILD.gn file in the directory as the entry.