casaroli opened a new pull request, #19507:
URL: https://github.com/apache/nuttx/pull/19507
## Summary
CMake validates a compiler by building **and linking** a small test program.
For a bare-metal cross toolchain that link cannot succeed on its own terms —
no
start files, no default linker script, no libc — and the flags NuttX supplies
for it assume a toolchain shipped with newlib. `arch/arm/src/cmake/gcc.cmake`
sets:
```cmake
set(CMAKE_EXE_LINKER_FLAGS_INIT "--specs=nosys.specs")
```
A perfectly usable `arm-none-eabi-gcc` built without those specs therefore
fails configuration before a single NuttX source file is considered.
Setting `CMAKE_TRY_COMPILE_TARGET_TYPE` to `STATIC_LIBRARY` in the ARM
toolchain file makes the detection step compile without linking. This is the
approach CMake documents for cross-compiling to bare metal, and NuttX does
not
currently set it anywhere in the tree.
## Impact
- **Users:** the CMake build becomes usable with any ARM toolchain that lacks
`nosys.specs`, including the Homebrew `arm-none-eabi-gcc` and other
newlib-less builds. Previously it could not configure at all.
- **Toolchains that do ship `nosys.specs`:** unaffected. The setting applies
only to CMake's own compiler-detection step, not to the NuttX link.
- **Build process:** no change to any produced artifact.
- **Documentation / hardware / security / compatibility:** unaffected.
## Testing
Board: `mps3-an547:picostest`, CMake + Ninja generator.
Before (master `7df7c6ee`):
```
$ cmake -B build -DBOARD_CONFIG=mps3-an547:picostest -GNinja
arm-none-eabi-gcc: fatal error: cannot read spec file 'nosys.specs': No
such file or directory
compilation terminated.
ninja: build stopped: subcommand failed.
CMake will not be able to correctly generate this project.
Call Stack (most recent call first):
CMakeLists.txt:481 (project)
-- Configuring incomplete, errors occurred!
```
After this patch, configuration succeeds:
```
$ cmake -B build -DBOARD_CONFIG=mps3-an547:picostest -GNinja
-- Check for working CXX compiler: /opt/homebrew/bin/arm-none-eabi-g++ -
skipped
-- Detecting CXX compile features - done
-- Configuring done (2.5s)
-- Generating done (0.1s)
-- Build files have been written to: build
```
and the tree then compiles — **1248 objects built**:
```
$ ninja -k 0
...
$ grep -c "Building C object" ninja.log
1248
```
The build stops at the final link, for a reason this patch does not address
and
does not introduce:
```
FAILED: [code=1] nuttx
arm-none-eabi-g++: fatal error: cannot read spec file 'nosys.specs': No such
file or directory
```
That is the NuttX link itself passing `--specs=nosys.specs`
(`gcc.cmake:277`), not CMake's detection step. Whether that flag is needed at
all for a `-nostdlib` NuttX link is a separate question I have deliberately
left alone. With this patch the compile phase is fully exercised on a
newlib-less toolchain, where before nothing could be configured.
(`CONFIG_LIBM=y` / `CONFIG_LIBM_TOOLCHAIN=n` was set for the run above, for
the
same missing-newlib reason.)
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