Command-line compilation is suitable for CI/CD pipelines or headless server environments, using the same toolchain and sysroot as Qt Creator. This chapter covers three scenarios: bare g++ toolchain verification, CMake cross-compilation, and qmake cross-compilation.

Prerequisites: The SDK is located at /home/lckfb/TaishanPi-3-Linux, and Buildroot has completed its first build (see Buildroot Qt Build Environment). If you need to deploy compiled binaries to the board, please complete the Communication Channel Configuration first.

Cross-Compilation Toolchain Overview

Toolchain Description

Important: The Buildroot route must use the Buildroot-bundled toolchain

After a full Buildroot build, a GCC 12.4.0 toolchain (prefix aarch64-buildroot-linux-gnu-) is generated under buildroot/output/rockchip_rk3576/host/bin/. Qt 5.15.11 and all libraries in the sysroot are built with this compiler.

The SDK-bundled GCC 10.3.1 (under prebuilts/gcc/, prefix aarch64-rockchip1031-linux-gnu-) is used for compiling the kernel and u-boot, and cannot be used to compile Qt applications — the two have incompatible C++ ABIs (libstdc++ symbol version mismatch).

Item	Value
Compiler path	buildroot/output/rockchip_rk3576/host/bin/
Compiler prefix	aarch64-buildroot-linux-gnu-
GCC version	12.4.0
sysroot	buildroot/output/rockchip_rk3576/host/aarch64-buildroot-linux-gnu/sysroot (staging/ is a symlink to it)

Configuring PATH

Execute the following each time you open a new terminal:

export PATH=/home/lckfb/TaishanPi-3-Linux/buildroot/output/rockchip_rk3576/host/bin:$PATH

Verification:

aarch64-buildroot-linux-gnu-gcc --version
# Expected output contains: aarch64-buildroot-linux-gnu-gcc.br_real (Buildroot -g8c544b52-dirty) 12.4.0

It is not recommended to add this path to ~/.bashrc, as it will conflict with the SDK-bundled toolchain. Manually export it when needed.

Verifying the Toolchain with g++

First, use the simplest program to confirm the toolchain works properly:

// hello.cpp
#include <iostream>
int main() {
    std::cout << "Hello from TaishanPi-3M!" << std::endl;
    return 0;
}

aarch64-buildroot-linux-gnu-g++ hello.cpp -o hello
file hello
# Expected output: ELF 64-bit LSB executable, ARM aarch64, ...

Seeing ARM aarch64 means the toolchain is working. If the output shows x86-64, the PATH has not taken effect — re-run the export command from the previous section.

CMake Cross-Compilation for Qt Programs

CMake is the recommended build method. Buildroot includes a toolchainfile.cmake, so there is no need to write a toolchain file manually.

Project Structure

tspi-sysmonitor/
├── CMakeLists.txt
├── tspi-sysmonitor.pro
├── main.cpp
├── sysmonitor.h
└── sysmonitor.cpp

For the complete source code, refer to the sample project tspi-sysmonitor.

CMakeLists.txt

cmake_minimum_required(VERSION 3.16)
project(tspi-sysmonitor LANGUAGES CXX)

set(CMAKE_CXX_STANDARD 17)
set(CMAKE_CXX_STANDARD_REQUIRED ON)
set(CMAKE_AUTOMOC ON)

find_package(Qt5 REQUIRED COMPONENTS Widgets Network)

add_executable(tspi-sysmonitor
    main.cpp
    sysmonitor.cpp
)

target_link_libraries(tspi-sysmonitor PRIVATE Qt5::Widgets Qt5::Network)

Configuration and Compilation

cd tspi-sysmonitor
mkdir build && cd build
cmake .. \
    -DCMAKE_TOOLCHAIN_FILE=/home/lckfb/TaishanPi-3-Linux/buildroot/output/rockchip_rk3576/host/share/buildroot/toolchainfile.cmake \
    -DCMAKE_PREFIX_PATH=/home/lckfb/TaishanPi-3-Linux/buildroot/output/rockchip_rk3576/staging/usr/lib/cmake \
    -DCMAKE_BUILD_TYPE=Release
make -j$(nproc)

Key parameter descriptions:

Parameter	Purpose
CMAKE_TOOLCHAIN_FILE	Buildroot auto-generated toolchain file containing all configurations including compiler and sysroot
CMAKE_PREFIX_PATH	Points to the directory containing Qt5 CMake config files, allowing find_package(Qt5) to locate Qt

Verifying Build Artifacts

$ file build/tspi-sysmonitor
tspi-sysmonitor: ELF 64-bit LSB executable, ARM aarch64, dynamically linked, ...

$ aarch64-buildroot-linux-gnu-readelf -d build/tspi-sysmonitor | grep NEEDED
 (NEEDED) Shared library: [libQt5Widgets.so.5]
 (NEEDED) Shared library: [libQt5Network.so.5]
 (NEEDED) Shared library: [libQt5Core.so.5]
 (NEEDED) Shared library: [libc.so.6]

ARM aarch64 + dependency on libQt5Widgets.so.5 confirms a successful build.

qmake Cross-Compilation

The qmake provided by Buildroot has cross-compilation configuration built in — just call it directly.

Source code reuses the sample project tspi-sysmonitor

Build Commands

Note

If qmake is not found, check the Configuring PATH section at the beginning of this document to confirm that host/bin/ has been added to PATH.

# Confirm Buildroot qmake is in PATH
$ which qmake
/home/lckfb/TaishanPi-3-Linux/buildroot/output/rockchip_rk3576/host/bin/qmake

# Generate Makefile and compile
qmake tspi-sysmonitor.pro
make -j$(nproc)

Verifying Artifacts

$ file tspi-sysmonitor
tspi-sysmonitor: ELF 64-bit LSB executable, ARM aarch64, version 1 (GNU/Linux), dynamically linked, ...

If you accidentally use the qmake installed via apt on the development machine, you will get an Unknown spec error — use which qmake to confirm the path points to Buildroot's host/bin/qmake.

Troubleshooting Build Issues

1. command not found: aarch64-buildroot-linux-gnu-g++

The toolchain is not in PATH. Re-run export PATH=.../host/bin:$PATH.

2. Could not find a package configuration file provided by "Qt5"

find_package(Qt5) cannot find Qt5Config.cmake. Confirm the file exists:

find /home/lckfb/TaishanPi-3-Linux/buildroot/output/rockchip_rk3576/staging -name "Qt5Config.cmake"

Once found, pass its directory to -DCMAKE_PREFIX_PATH. If not found, it means Buildroot has not enabled Qt — go back to ./build.sh bconfig and confirm BR2_PACKAGE_QT5 is selected.

3. cannot find -lQt5Widgets

The linker cannot find the Qt libraries. Check if the libraries exist in the sysroot:

ls buildroot/output/rockchip_rk3576/staging/usr/lib/libQt5Widgets*

4. relocation R_X86_64_... error

x86_64 libraries from the development machine were linked, meaning CMAKE_TOOLCHAIN_FILE did not take effect. Confirm the cmake command correctly specifies the toolchainfile.cmake path.

5. Build artifact is x86-64 instead of ARM64

The development machine's compiler was used. Run which g++ to confirm the Buildroot toolchain has higher priority in PATH than the system path.

Next Steps

The core of command-line cross-compilation comes down to two things: the Buildroot toolchain PATH is correct, and CMake specifies toolchainfile.cmake and the Qt PREFIX_PATH. CMake is the universal approach; qmake is simpler but tied to Buildroot. After compilation, use file and readelf to confirm the artifact architecture and dependencies.

Next step: Deployment and Debugging