Other Cross Compilers

This toolchain variant is borrowed from the Linux kernel build system’s mechanism of using a CROSS_COMPILE environment variable to set up a GNU-based cross toolchain.

Examples of such “other cross compilers” are cross toolchains that your Linux distribution packaged, that you compiled on your own, or that you downloaded from the net. Unlike toolchains specifically listed in 3rd Party Toolchains, the Zephyr build system may not have been tested with them, and doesn’t officially support them. (Nonetheless, the toolchain set-up mechanism itself is supported.)

Follow these steps to use one of these toolchains.

Install a cross compiler suitable for your host and target systems.

For example, you might install the gcc-arm-none-eabi package on Debian-based Linux systems, or arm-none-eabi-newlib on Fedora or Red Hat:
```
# On Debian or Ubuntu
sudo apt-get install gcc-arm-none-eabi
# On Fedora or Red Hat
sudo dnf install arm-none-eabi-newlib
```
Set these environment variables:
- Set ZEPHYR_TOOLCHAIN_VARIANT to cross-compile.
- Set CROSS_COMPILE to the common path prefix which your toolchain’s binaries have, e.g. the path to the directory containing the compiler binaries plus the target triplet and trailing dash.
To check that you have set these variables correctly in your current environment, follow these example shell sessions (the CROSS_COMPILE value may be different on your system):
```
# Linux, macOS:
$ echo $ZEPHYR_TOOLCHAIN_VARIANT
cross-compile
$ echo $CROSS_COMPILE
/usr/bin/arm-none-eabi-
```
You can also set CROSS_COMPILE as a CMake variable.

When using this option, all of your toolchain binaries must reside in the same directory and have a common file name prefix. The CROSS_COMPILE variable is set to the directory concatenated with the file name prefix. In the Debian example above, the gcc-arm-none-eabi package installs binaries such as arm-none-eabi-gcc and arm-none-eabi-ld in directory /usr/bin/, so the common prefix is /usr/bin/arm-none-eabi- (including the trailing dash, -). If your toolchain is installed in /opt/mytoolchain/bin with binary names based on target triplet myarch-none-elf, CROSS_COMPILE would be set to /opt/mytoolchain/bin/myarch-none-elf-.