fix(cmake): add -z nostart-stop-gc for LLVM/Clang toolchains

When using LLVM-based toolchains (e.g. ST STM32CubeCLT arm-clang), ld.lld
discards __start_/__stop_ encapsulation symbols under --gc-sections, causing
undefined symbol errors for ctshell_cmd_section. Export CTSHELL_LINK_OPTIONS
with -z nostart-stop-gc automatically when LLVM linker is detected.

Also update porting docs (en/zh) to clarify GCC vs LLVM vs MDK-ARM
linker script requirements.

Author: youziLab

CMakeLists.txt

@@ -112,3 +112,13 @@ else()
 
     set(CTSHELL_DEFINITIONS ${CTSHELL_DEFINITIONS} CACHE INTERNAL "ctshell definitions")
 endif()
+
+# --- Linker options for section-based command registration ---
+# GCC (ld.bfd) handles __start_/__stop_ symbols for orphan sections automatically.
+# LLVM lld requires -z nostart-stop-gc to prevent these symbols from being
+# discarded when --gc-sections is enabled.
+set(CTSHELL_LINK_OPTIONS "")
+if(CMAKE_LINKER MATCHES "lld" OR CMAKE_C_COMPILER_ID STREQUAL "Clang" OR CMAKE_CXX_COMPILER_ID STREQUAL "Clang")
+    list(APPEND CTSHELL_LINK_OPTIONS "-z" "nostart-stop-gc")
+endif()
+set(CTSHELL_LINK_OPTIONS ${CTSHELL_LINK_OPTIONS} CACHE INTERNAL "ctshell linker options")

docs/en/quickstart/porting.rst

@@ -92,9 +92,17 @@ RTOS Environment: It is recommended to create a dedicated task to run the Shell.
 
 6. Linker Script Modification
 
-    gcc: No need to modify.
+    **GCC (ld.bfd):** No need to modify the linker script.
 
-    MDK-ARM(v5 and v6): Add in scatter file, example:
+    **LLVM/Clang (ld.lld):** If you are using an LLVM-based toolchain (e.g., ST's STM32CubeCLT with arm-clang), the linker script does not need modification either. Simply append the following to the end of your ``CMakeLists.txt``:
+
+    .. code-block:: cmake
+
+        target_link_options(${CMAKE_PROJECT_NAME} PRIVATE ${CTSHELL_LINK_OPTIONS})
+
+    ``${CTSHELL_LINK_OPTIONS}`` is exported by ctshell and automatically adds ``-z nostart-stop-gc`` when an LLVM linker is detected, preventing ``__start_ctshell_cmd_section`` and ``__stop_ctshell_cmd_section`` symbols from being discarded under ``--gc-sections``.
+
+    **MDK-ARM (v5 and v6):** Add in scatter file, example:
 
 .. code-block:: c
 

docs/zh/quickstart/porting.rst

@@ -92,9 +92,17 @@ RTOS 环境: 建议创建一个独立的任务来运行 Shell。
 
 6. 链接脚本修改
 
-    gcc：无需修改。
+    **GCC (ld.bfd)：** 无需修改链接脚本。
 
-    MDK-ARM（v5 and v6）：在scatter file中添加示例如下：
+    **LLVM/Clang (ld.lld)：** 如果你使用的是基于 LLVM 的工具链（如 ST 的 STM32CubeCLT arm-clang），则无需修改链接脚本，只需将以下内容追加到你的 ``CMakeLists.txt`` 末尾即可：
+
+    .. code-block:: cmake
+
+        target_link_options(${CMAKE_PROJECT_NAME} PRIVATE ${CTSHELL_LINK_OPTIONS})
+
+    ``${CTSHELL_LINK_OPTIONS}`` 由 ctshell 导出，会在检测到 LLVM 链接器时自动添加 ``-z nostart-stop-gc``，防止 ``__start_ctshell_cmd_section`` 和 ``__stop_ctshell_cmd_section`` 符号在 ``--gc-sections`` 下被回收。
+
+    **MDK-ARM（v5 and v6）：** 在scatter file中添加示例如下：
 
 .. code-block:: c