`libmicroros.a` is built with a hand-maintained toolchain file that may drift from IDF's compile flags (ABI mismatch risk)

[Narukara]

From #334 (comment)

The following content was generated by AI

Cause

micro-ROS is not built as regular IDF component sources. Instead, the component's CMake configure step invokes libmicroros.mk, which runs a separate colcon build to produce libmicroros.a, and the result is linked back into the ELF via add_prebuilt_library. This separate build uses its own toolchain file (esp32_toolchain.cmake.in) that only passes through a hand-picked subset of compile options (compiler binary, C standard, sdkconfig.cmake, IDF includes, a few hardcoded flags), rather than inheriting the full set of flags IDF applies to its own components.

Impact

Some ABI-affecting flags used by the main IDF build are not propagated to the micro-ROS sub-build, so libmicroros.a can be compiled with settings inconsistent with the rest of the firmware. Known gaps:

• RISC-V -march/-mabi are not set (relies on compiler defaults) — a mismatch here breaks the calling convention/ABI.
• PSRAM cache workaround flags (e.g. -mfix-esp32-psram-cache-issue) are not forwarded.
• The hardcoded flag list in esp32_toolchain.cmake.in must be kept in sync manually and can silently drift as IDF changes.

(Note: many flags like optimization level or stack protector are not ABI-breaking, so their absence is harmless — the concern is specifically the ABI/codegen-relevant ones.)

Because the same compiler is used and sdkconfig.cmake is included, most struct-layout / config-dependent mismatches are already avoided, so this is a latent risk rather than a guaranteed failure — but it can produce hard-to-debug link/runtime issues in specific configurations (e.g. SPIRAM enabled, certain RISC-V targets).

Possible fix

Keeping micro-ROS as a separately built static library is unavoidable (it depends on the ROS 2 / colcon / rosidl build system), so the goal is not to remove this mechanism but to make the sub-build inherit IDF's ABI-relevant flags instead of hardcoding a subset:

• Query the flags IDF actually uses for its components (e.g. CMAKE_C_FLAGS / COMPILE_OPTIONS, especially RISC-V -march/-mabi and PSRAM-related flags) in the outer CMakeLists.txt and pass them through libmicroros.mk into the toolchain file.
• As a minimum/interim step, document the list of flags that are known not to be synced and must be verified manually.