Support WiFi as default network interface

This requires support for weak symbol override. Object files arcived in
static library don't always participate in linking, dependent on linker
and link order. To fix this, the object files which will override weak
symbols are extracted and passed to linker command line separately to
actively participate in linking.

Author: ccli8

connectivity/drivers/wifi/CMakeLists.txt

@@ -16,6 +16,35 @@ target_link_libraries(mbed-wifi
 )
 
 
+# Collect sources which need to extract from static library to override
+# weak symbols. Their paths are required to relative to this directory
+# ,so that they match with entries in static library and their corresponding
+# object files there can be found and extracted.
+set(MBED_WIFI_OVERRIDE_SOURCES "" CACHE INTERNAL "" FORCE)
+
+# Add override sources by subdirectories
+#
+# The input sources are required to relative to their subdirectories
+# and will get converted to relative to this directory herein.
+function(mbed_wifi_add_override_sources)
+    set(override_sources ${MBED_WIFI_OVERRIDE_SOURCES})
+
+    foreach(override_source ${ARGN})
+        # Convert to relative to this directory
+        file(RELATIVE_PATH
+            override_source_fix
+            ${CMAKE_CURRENT_FUNCTION_LIST_DIR}
+            ${CMAKE_CURRENT_LIST_DIR}/${override_source}
+        )
+
+        set(override_sources
+            ${override_sources}
+            ${override_source_fix}
+        )
+    endforeach()
+
+    set(MBED_WIFI_OVERRIDE_SOURCES ${override_sources} CACHE INTERNAL "" FORCE)
+endfunction()
 
 # The WICED subdirectory is for wifi drivers developed using Infineon WICED framework.
 # https://community.infineon.com/t5/Knowledge-Base-Articles/WICED-Wi-Fi-FAQ/ta-p/247356
@@ -35,3 +64,57 @@ if("COMPONENT_ESPRESSIF_ESP8266=1" IN_LIST MBED_TARGET_DEFINITIONS)
     add_subdirectory(COMPONENT_ESPRESSIF_ESP8266)
 endif()
 
+# Extract override objects from static library and pass them to
+# link options to actively participate in linking and override weak
+# symbols.
+if(TARGET mbed-wifi AND NOT "${MBED_WIFI_OVERRIDE_SOURCES}" STREQUAL "")
+    set(override_sources ${MBED_WIFI_OVERRIDE_SOURCES})
+    list(TRANSFORM override_sources APPEND ${CMAKE_CXX_OUTPUT_EXTENSION} OUTPUT_VARIABLE override_objects)
+
+    if(${MBED_TOOLCHAIN} STREQUAL "GCC_ARM")
+        # Override objects passed via target_link_options are finally
+        # de-duplicated, so we can avoid multiple definition issue caused
+        # due to cyclic target link via target_link_libraries.
+        #
+        # https://cmake.org/cmake/help/latest/command/target_link_options.html#option-de-duplication
+        target_link_options(mbed-wifi
+            INTERFACE
+                $<LIST:TRANSFORM,${override_objects},PREPEND,${CMAKE_CURRENT_BINARY_DIR}/>
+        )
+
+        # Commands for extracting override objects
+        foreach(override_object ${override_objects})
+            get_filename_component(override_object_dirname ${override_object} DIRECTORY)
+
+            # Extract object files from static library
+            #
+            # NOTE: The support has restrictions on input static library:
+            # 1. No full path match modifier ('P') is specified on creating
+            #    the static library.
+            # 2. Object file names must be different for just one-level entry
+            #    names in the static library.
+            # https://sourceware.org/binutils/docs/binutils/ar-cmdline.html
+            set(extract_commands
+                ${extract_commands}
+                COMMAND
+                    ${CMAKE_COMMAND} -E make_directory ${override_object_dirname}
+                COMMAND
+                    ${CMAKE_AR} x --output ${override_object_dirname} $<TARGET_FILE_NAME:mbed-wifi> ${override_object}
+            )
+        endforeach()
+
+        add_custom_command(
+            TARGET
+                mbed-wifi
+            POST_BUILD
+            ${extract_commands}
+            WORKING_DIRECTORY
+                ${CMAKE_CURRENT_BINARY_DIR}
+            VERBATIM
+        )
+    endif()
+
+    unset(override_sources)
+    unset(override_objects)
+    unset(extract_commands)
+endif()

connectivity/drivers/wifi/COMPONENT_ESPRESSIF_ESP8266/CMakeLists.txt

@@ -12,3 +12,10 @@ target_include_directories(mbed-wifi
         .
         ./ESP8266
 )
+
+# Add sources which contain override symbols
+if("MBED_CONF_ESP8266_PROVIDE_DEFAULT=1" IN_LIST MBED_CONFIG_DEFINITIONS)
+    mbed_wifi_add_override_sources(
+        ESP8266Interface.cpp
+    )
+endif()

connectivity/drivers/wifi/TARGET_STM/COMPONENT_EMW3080B/CMakeLists.txt

@@ -21,3 +21,10 @@ target_sources(mbed-wifi
         mx_wifi/core/mx_wifi_ipc.c
         mx_wifi/core/mx_wifi_slip.c
 )
+
+# Add sources which contain override symbols
+if("MBED_CONF_EMW3080B_PROVIDE_DEFAULT=1" IN_LIST MBED_CONFIG_DEFINITIONS)
+    mbed_wifi_add_override_sources(
+        EMW3080BInterface.cpp
+    )
+endif()