Qualcomm Hexagon LLVM Toolchain

1. Download a pre-built Hexagon LLVM cross-toolchain from the toolchain_for_hexagon releases page and extract it, for example to /opt/hexagon-toolchain. The install directory is the one holding bin/clang.

   Use a release built from LLVM 23 or newer. Earlier releases miscompile the ~BIT(n). The fix landed in #205489.

2. Set ZEPHYR_TOOLCHAIN_VARIANT to hexagon and HEXAGON_TOOLCHAIN_PATH to that directory:

   export ZEPHYR_TOOLCHAIN_VARIANT=hexagon
   export HEXAGON_TOOLCHAIN_PATH=/opt/hexagon-toolchain
   

HEXAGON_TOOLCHAIN_PATH

Install directory of the Hexagon LLVM cross-toolchain.

The toolchain is an ordinary LLVM installation, so this variant is the Host Toolchains llvm variant driving a different compiler. It has a path variable of its own because the Hexagon clang registers only the Hexagon target and so cannot build host-compiled targets such as Native simulator - native_sim; an environment that covers both has to name the two LLVM installations independently, as Zephyr’s CI does when a single Twister run spans both kinds of platform.

Building a Hexagon target with ZEPHYR_TOOLCHAIN_VARIANT=host/llvm and LLVM_TOOLCHAIN_PATH is equivalent and remains supported, as long as the installation it names is the Hexagon one.