Enable specifying out-of-source platform configuration cmake file (#1941)

Resolve #1935, enable specifying out-of-source platform folder with
`cmake .. -DWAMR_BUILD_PLATFORM=new-os
               -DSHARED_PLATFORM_CONFIG=/path/to/new-os/shared_platform.cmake`

build-scripts/runtime_lib.cmake

@@ -19,6 +19,11 @@ endif ()
 if (NOT DEFINED DEPS_DIR)
     set (DEPS_DIR ${WAMR_ROOT_DIR}/core/deps)
 endif ()
+if (NOT DEFINED SHARED_PLATFORM_CONFIG)
+    # CMake file for platform configuration. The PLATFORM_SHARED_SOURCE varable
+    # should point to a list of platform-specfic source files to compile.
+    set (SHARED_PLATFORM_CONFIG ${SHARED_DIR}/platform/${WAMR_BUILD_PLATFORM}/shared_platform.cmake)
+endif ()
 
 if (DEFINED EXTRA_SDK_INCLUDE_PATH)
     message(STATUS, "EXTRA_SDK_INCLUDE_PATH = ${EXTRA_SDK_INCLUDE_PATH} ")
@@ -165,7 +170,7 @@ LIST (APPEND RUNTIME_LIB_HEADER_LIST ${header})
 
 enable_language (ASM)
 
-include (${SHARED_DIR}/platform/${WAMR_BUILD_PLATFORM}/shared_platform.cmake)
+include (${SHARED_PLATFORM_CONFIG})
 include (${SHARED_DIR}/mem-alloc/mem_alloc.cmake)
 include (${IWASM_DIR}/common/iwasm_common.cmake)
 include (${SHARED_DIR}/utils/shared_utils.cmake)

doc/port_wamr.md

@@ -10,9 +10,13 @@ This document describes how to port WAMR to a new platform "**new-os**"
 # Step 1: Implement platform API layer
 
 -------------------------
-Firstly create the folder **`core/shared/platform/new-os`** for platform API layer implementations. In the folder you just created, you must provide the following files:
+Firstly create the folder for platform API layer implementations:
+* for common platforms, create a folder in **`core/shared/platform/new-os`** in WAMR repository folder, so the implementation can be upstreamed
+* for platforms that are internal and its implementation shouldn't be published, it's recommended to create a folder outside of the WAMR repository folder (e.g. have separate repository for platform API layer implementation)
 
-- `platform_internal.h`: It can be used for any platform specific definitions such as macros, data types and internal APIs.
+In the folder you just created, you must provide the following files:
+
+- `platform_internal.h`: It can be used for any platform-specific definitions such as macros, data types and internal APIs.
 
 - `shared_platform.cmake`: the cmake file will be included by the building script. It is recommended to add a definition for your platform:
 
@@ -20,16 +24,16 @@ Firstly create the folder **`core/shared/platform/new-os`** for platform API lay
     add_definitions(-DBH_PLATFORM_YOUR_NAME)
     ```
 
-Then go to implement the APIs defined in following header files for the platform abstraction layer:
+Then go to implement the APIs defined in the following header files for the platform abstraction layer:
 
-- [`platform_api_vmcore.h`](../core/shared/platform/include/platform_api_vmcore.h):   mandatory for building mini-product (vmcore only). Part of APIs are needed only for Ahead of Time compilation support. 
+- [`platform_api_vmcore.h`](../core/shared/platform/include/platform_api_vmcore.h):   mandatory for building mini-product (vmcore only). Part of the APIs is needed only for Ahead of Time compilation support.
 - [`platform_api_extension.h`](../core/shared/platform/include/platform_api_extension.h): mandatory for app-mgr and app-framework. Given that the app-mgr and app-framework are not required for your target platform, you won't have to implement the API defined in the `platform_api_extension.h`.
 
 
 
 **common/posix:**
 
-There is posix based implementation of the platform API located in the `platform/common/posix` folder. You can include it if your platform support posix API. refer to platform linux implementation.
+There is posix based implementation of the platform API located in the `platform/common/posix` folder. You can include it if your platform supports posix API. refer to platform linux implementation.
 
 
 
@@ -42,7 +46,7 @@ Some platforms such as ZephyrOS don't provide math functions e.g. sqrt, fabs and
 # Step 2: Create the mini product for the platform
 
 -------------------------
-You can build a mini WAMR product which is only the vmcore for you platform. Normally you need to implement the main function which loads a WASM file and run it with the WASM runtime. You don't have to do this step if there is no mini-product need for your platform porting.
+You can build a mini WAMR product which is only the vmcore for your platform. Normally you need to implement the main function which loads a WASM file and run it with the WASM runtime. You don't have to do this step if there is no mini-product need for your platform porting.
 
 
 
@@ -58,6 +62,11 @@ cd build
 cmake .. -DWAMR_BUILD_PLATFORM=new-os
 ```
 
+For platform implementations that are outside of the WAMR repository (e.g. internal platforms), you also need to provide `SHARED_PLATFORM_CONFIG` path:
+
+```
+cmake .. -DWAMR_BUILD_PLATFORM=new-os -DSHARED_PLATFORM_CONFIG=/path/to/new-os/shared_platform.cmake
+```
 
 
 Refer to [build_wamr.md](./build_wamr.md) for the building configurations and parameters.