cross-gcc

# C
aarch64-linux-gnu-gcc -O2 -o hello hello.c
 
# C++
aarch64-linux-gnu-g++ -O2 -std=c++17 -o hello hello.cpp
 
# Bare-metal (no stdlib, no OS)
arm-none-eabi-gcc -mcpu=cortex-m4 -mthumb -mfloat-abi=hard -mfpu=fpv4-sp-d16 \
    -ffreestanding -nostdlib -T linker.ld -o firmware.elf startup.s main.c

# Use a sysroot
aarch64-linux-gnu-gcc --sysroot=/path/to/aarch64-sysroot -O2 -o prog main.c
 
# Common sysroot sources:
# - Raspberry Pi: download from raspbian/raspios
# - Debian multiarch: debootstrap --arch arm64 bullseye /tmp/sysroot
# - Yocto/Buildroot: generated automatically in build output

aarch64-linux-gnu-gcc --sysroot=/path/to/sysroot -v -E - < /dev/null 2>&1 | grep sysroot

export PKG_CONFIG_SYSROOT_DIR=/path/to/sysroot
export PKG_CONFIG_LIBDIR=${PKG_CONFIG_SYSROOT_DIR}/usr/lib/aarch64-linux-gnu/pkgconfig:${PKG_CONFIG_SYSROOT_DIR}/usr/share/pkgconfig
export PKG_CONFIG_PATH=   # clear host path
 
pkg-config --libs libssl  # now returns target paths

set(CMAKE_SYSTEM_NAME Linux)
set(CMAKE_SYSTEM_PROCESSOR aarch64)
 
set(CMAKE_C_COMPILER   aarch64-linux-gnu-gcc)
set(CMAKE_CXX_COMPILER aarch64-linux-gnu-g++)
 
set(CMAKE_SYSROOT /path/to/aarch64-sysroot)
set(CMAKE_FIND_ROOT_PATH_MODE_PROGRAM NEVER)
set(CMAKE_FIND_ROOT_PATH_MODE_LIBRARY ONLY)
set(CMAKE_FIND_ROOT_PATH_MODE_INCLUDE ONLY)

cmake -S . -B build -DCMAKE_TOOLCHAIN_FILE=aarch64.cmake
cmake --build build

# User-mode emulation (Linux binaries, no full OS)
sudo apt install qemu-user-static
 
qemu-aarch64-static ./hello
# Or set binfmt_misc for transparent execution:
# Then just: ./hello
 
# GDB remote debug via QEMU
qemu-aarch64-static -g 1234 ./hello &
aarch64-linux-gnu-gdb -ex "target remote :1234" ./hello

# Tell build systems to use cross-compiler
export CC=aarch64-linux-gnu-gcc
export CXX=aarch64-linux-gnu-g++
export AR=aarch64-linux-gnu-ar
export STRIP=aarch64-linux-gnu-strip
export OBJDUMP=aarch64-linux-gnu-objdump
 
# For autoconf projects
./configure --host=aarch64-linux-gnu --prefix=/usr