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

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From https://github.com/micro-ROS/micro_ros_espidf_component/pull/334#issuecomment-4829889550

> 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.

Commencez par esp32_toolchain.cmake.in, libmicroros.mk et le CMakeLists.txt externe afin de suivre comment les flags de compilation d’IDF atteignent le build colcon séparé. Comparez les flags utilisés par les composants d’IDF avec ceux transmis à libmicroros.a, en vous concentrant sur les options d’ABI RISC-V et de PSRAM. Le travail est considéré comme terminé lorsque le sous-build reçoit les flags pertinents sans liste maintenue manuellement susceptible de diverger, ou lorsque les flags non synchronisés sont explicitement documentés.

Rédigé par le modèle d'indexation à partir du texte de l'issue.