Cross-compilation on Ubuntu

Setting up a cross-compilation environment for ARM and PowerPC on an x86 Ubuntu system is typically done by installing pre-built cross-compiler toolchains from the Ubuntu repositories. This is the recommended approach for standard Linux targets.

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Installing Cross-Compilers for ARM and PowerPC

You can install the necessary GCC cross-compilers and their associated binary utilities (binutils) directly using the apt package manager.

1. Update Package List

First, ensure your package list is up-to-date:

sudo apt update

2. Install ARM Cross-Compilers

For ARM (32-bit and 64-bit Linux targets), you’ll install the following packages:

Architecture	Target Triple	Compiler Package	Command
ARM 32-bit (Hard-Float)	arm-linux-gnueabihf	gcc-arm-linux-gnueabihf	sudo apt install gcc-arm-linux-gnueabihf
ARM 64-bit (AArch64)	aarch64-linux-gnu	gcc-aarch64-linux-gnu	sudo apt install gcc-aarch64-linux-gnu

You can install both with one command:

sudo apt install gcc-arm-linux-gnueabihf gcc-aarch64-linux-gnu

3. Install PowerPC Cross-Compilers

For PowerPC (32-bit and 64-bit Linux targets):

Architecture	Target Triple	Compiler Package	Command
PowerPC 32-bit	powerpc-linux-gnu	gcc-powerpc-linux-gnu	sudo apt install gcc-powerpc-linux-gnu
PowerPC 64-bit (Little-Endian)	powerpc64le-linux-gnu	gcc-powerpc64le-linux-gnu	sudo apt install gcc-powerpc64le-linux-gnu

Install them using:

sudo apt install gcc-powerpc-linux-gnu gcc-powerpc64le-linux-gnu

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Using the Cross-Compilers

Once installed, the cross-compilers and tools will have a prefix corresponding to their target triple. You’ll use these specific compiler names instead of the default gcc or g++.

Compiling a Simple C File

For a source file named hello.c:

Target Architecture	Compiler Command
ARM 32-bit	arm-linux-gnueabihf-gcc hello.c -o hello_arm32
ARM 64-bit	aarch64-linux-gnu-gcc hello.c -o hello_arm64
PowerPC 32-bit	powerpc-linux-gnu-gcc hello.c -o hello_ppc32
PowerPC 64-bit	powerpc64le-linux-gnu-gcc hello.c -o hello_ppc64

You can verify the output file type using the file command:

file hello_arm64
# Expected output: ...ELF 64-bit LSB executable, **ARM aarch64**, version 1 (SYSV)...

Compiling Universal (Cross-Platform Library)

When compiling a project like your Universal library, you’ll need to pass the appropriate compiler and configuration options to its build system (e.g., Make, CMake, Autotools).

Autotools (./configure and make)

Set the cross-compiler for C, C++, and specify the host architecture using the --host flag:

# Example for ARM 64-bit
export CC=aarch64-linux-gnu-gcc
export CXX=aarch64-linux-gnu-g++
./configure --host=aarch64-linux-gnu
make

CMake

The recommended way for CMake is to use a Toolchain File. This file, often named Toolchain-<ARCH>.cmake, tells CMake about the compilers and system roots for the target.

Example Toolchain-arm64.cmake:

set(CMAKE_SYSTEM_NAME Linux)
set(CMAKE_SYSTEM_PROCESSOR aarch64)

# Specify the cross compilers
set(CMAKE_C_COMPILER aarch64-linux-gnu-gcc)
set(CMAKE_CXX_COMPILER aarch64-linux-gnu-g++)

# Specify the sysroot (where target headers/libraries are)
# On Ubuntu, this is often the default path for the installed toolchain
# set(CMAKE_FIND_ROOT_PATH /usr/aarch64-linux-gnu)
# set(CMAKE_FIND_ROOT_PATH_MODE_PROGRAM NEVER)
# set(CMAKE_FIND_ROOT_PATH_MODE_LIBRARY ONLY)
# set(CMAKE_FIND_ROOT_PATH_MODE_INCLUDE ONLY)

Then, configure your build:

mkdir build_arm64
cd build_arm64
cmake -DCMAKE_TOOLCHAIN_FILE=../Toolchain-arm64.cmake ..
make