Swatantra-66 opened a new pull request, #20874:
URL: https://github.com/apache/nuttx/pull/20874
## Summary
When NuttX is embedded into a parent CMake project via `add_subdirectory()`,
several issues previously prevented cross-compiling non-sim architectures:
1. In `arch/{arm,arm64,risc-v,tricore,x86_64,xtensa}/src/CMakeLists.txt` and
`boards/CMakeLists.txt`, `add_subdirectory()` inverted the `EXCLUDE_FROM_ALL`
and `binary_dir` arguments, violating CMake syntax `add_subdirectory(source_dir
binary_dir [EXCLUDE_FROM_ALL])`.
2. `arch/arm/src/cmake/Toolchain.cmake` and
`arch/arm64/src/cmake/Toolchain.cmake` used `include()` without
`${CMAKE_CURRENT_LIST_DIR}`, failing to locate sibling toolchain files when
`CMAKE_MODULE_PATH` was not inherited.
3. In subproject mode, `CMAKE_TOOLCHAIN_FILE` is resolved using a
deduplicated macro (`nuttx_resolve_toolchain_file`) against `CMAKE_BINARY_DIR`,
`CMAKE_SOURCE_DIR`, and `CMAKE_CURRENT_SOURCE_DIR` per CMake lookup rules, and
safely evaluated after NuttX configuration is loaded.
4. Active compiler detection prioritizes `CMAKE_C_COMPILER` over
`$CACHE{CMAKE_C_COMPILER}` to ensure normal-scope toolchain definitions from
the parent project take precedence over stale cache entries.
5. Added a diagnostic check inspecting the active compiler basename against
`TOOLCHAIN_PREFIX` (or verifying `clang`/`armclang` for Clang-based targets).
If a host compiler was inadvertently initialized by a parent `project()` call,
a clear `FATAL_ERROR` is raised advising how to configure
`CMAKE_TOOLCHAIN_FILE` before the parent's first `project()` call.
6. Exported `CMAKE_TOOLCHAIN_FILE`, `CMAKE_MODULE_PATH`, and all `CONFIG_*`
variables to `PARENT_SCOPE`.
Fixes #19697.
## Impact
- **Is new feature added? Is existing feature changed?**
Yes, enables cross-compilation support when NuttX is embedded as a
subproject via `add_subdirectory()`.
- **User impact:**
Users can now embed NuttX into larger CMake projects (e.g. multi-component
firmware or SDKs) targeting embedded architectures (ARM, ARM64, RISC-V, Xtensa,
TriCore, etc.).
- **Build process:**
- Standalone NuttX CMake builds (`cmake -B build -DBOARD_CONFIG=...`) and
GNU Make builds are completely unaffected.
- Subproject builds now correctly resolve toolchain files, inherit
compiler definitions, and export configuration variables (`CONFIG_*`) to the
parent project scope.
- **Hardware:**
Applies to all architectures when building with CMake, specifically fixing
embedded targets (`arm`, `arm64`, `risc-v`, `xtensa`, `tricore`, `x86_64`).
- **Documentation / Diagnostics:**
Adds a clear diagnostic `FATAL_ERROR` guiding users to set
`CMAKE_TOOLCHAIN_FILE` before `project()` if a parent build inadvertently
initializes a host compiler.
- **Security / Compatibility:**
No security implications. Fully backward-compatible.
## Testing
- **Build Host:**
- OS: Windows 11 / Linux
- CMake: 3.20+
- **Verification:**
1. **Syntax & whitespace:** Verified with `git diff --check`.
2. **Standalone CMake build:** Confirmed standalone configuration behavior
remains unchanged (`cmake -B build -DBOARD_CONFIG=...`).
3. **Embedded subproject (`add_subdirectory`):**
- Verified that chip and board subdirectories are registered with valid
binary directories in parent projects without syntax errors (`exclude_chip`,
`exclude_board`, etc.).
- Tested `CMAKE_TOOLCHAIN_FILE` resolution for both relative and
absolute paths via the new `nuttx_resolve_toolchain_file` macro.
- Verified active compiler evaluation: confirms correct precedence
(`CMAKE_C_COMPILER` before `$CACHE{CMAKE_C_COMPILER}`) and verifies that
matching cross-compilers (`arm-none-eabi-*`, `riscv64-unknown-elf-*`, `clang`,
`armclang`) pass.
- Verified diagnostic error: tested with mismatched host compilers to
confirm clear, actionable guidance is produced without empty string artifacts.
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