Mbed OS components as OBJECT libs

CMakeLists.txt

@@ -8,9 +8,34 @@ cmake_minimum_required(VERSION 3.19.0 FATAL_ERROR)
 include(${MBED_CONFIG_PATH}/mbed_config.cmake)
 include(tools/cmake/set_linker_script.cmake)
 
+# Ensure the words that make up the Mbed target name are separated with a hyphen, lowercase, and with the `mbed-` prefix.
+set(MBED_TARGET_CONVERTED "" CACHE STRING "" FORCE)
+string(TOLOWER ${MBED_TARGET} MBED_TARGET_CONVERTED)
+string(REPLACE "_" "-" MBED_TARGET_CONVERTED ${MBED_TARGET_CONVERTED})
+string(PREPEND MBED_TARGET_CONVERTED "mbed-")
+
+# The main issue not using OBJECT for core/rtos and target libraries is their circular dependencies. 
+# They were always consider to be part of the Mbed OS as whole. To illustrate, rtos requires some 
+# core (tickers, critical section, etc) and target (MCU capabilities) functionalities. Core declares functionality that
+# target implements (hal <-> target).
+#  Known CMake issue: https://gitlab.kitware.com/cmake/cmake/-/issues/17905 for details
+#
+# We provide the main two libraries for an application: `mbed-os` and `mbed-baremetal`
+# The other libraries below like `mbed-core`, `mbed-rtos` and their `-objects` parts are internal libraries to address the above
+# limitation.
+#
+# mbed-core - flags for hal/driver/platform and MBED_TARGET
+# mbed-core-objects - only source files
 add_library(mbed-core INTERFACE)
+add_library(mbed-core-objects OBJECT EXCLUDE_FROM_ALL)
+target_link_libraries(mbed-core-objects mbed-core ${MBED_TARGET_CONVERTED})
 
+# mbed-os - application library
+# mbed-os-objects - core + rtos objects to build all together
 add_library(mbed-os INTERFACE)
+add_library(mbed-os-objects OBJECT EXCLUDE_FROM_ALL)
+
+target_sources(mbed-os INTERFACE $<TARGET_OBJECTS:mbed-os-objects> $<TARGET_OBJECTS:mbed-rtos-objects>)
 
 target_link_libraries(mbed-os
     INTERFACE
@@ -20,10 +45,13 @@ target_link_libraries(mbed-os
 
 add_library(mbed-baremetal INTERFACE)
 
+target_sources(mbed-baremetal INTERFACE $<TARGET_OBJECTS:mbed-core-objects>)
+
 target_link_libraries(mbed-baremetal
     INTERFACE
         mbed-core
 )
+
 # Validate selected C library type
 # The C library type selected has to match the library that the target can support
 if(${MBED_C_LIB} STREQUAL "small")
@@ -113,13 +141,18 @@ target_include_directories(mbed-core
 # by libraries that depend on them.
 # TODO CMake: Should the source files be moved?
 add_library(mbed-device_key INTERFACE)
+
 add_library(mbed-rtos INTERFACE)
+add_library(mbed-rtos-objects OBJECT)
+
+target_link_libraries(mbed-rtos-objects mbed-rtos mbed-core)
 
 add_subdirectory(cmsis)
 add_subdirectory(drivers)
 add_subdirectory(hal)
 add_subdirectory(platform)
 add_subdirectory(rtos)
+
 add_subdirectory(targets)
 
 # The directories below contain optional target libraries
@@ -132,12 +165,18 @@ add_subdirectory(features EXCLUDE_FROM_ALL)
 add_subdirectory(cmsis/CMSIS_5/CMSIS/RTOS2 EXCLUDE_FROM_ALL)
 add_subdirectory(cmsis/device/rtos EXCLUDE_FROM_ALL)
 
-# Ensure the words that make up the Mbed target name are separated with a hyphen, lowercase, and with the `mbed-` prefix.
-string(TOLOWER ${MBED_TARGET} MBED_TARGET_CONVERTED)
-string(REPLACE "_" "-" MBED_TARGET_CONVERTED ${MBED_TARGET_CONVERTED})
-string(PREPEND MBED_TARGET_CONVERTED "mbed-")
+# Expose linker option to an application. As we do not directly link to MBED_TARGET_CONVERTED due to built
+# object core library
+target_link_options(mbed-core INTERFACE $<TARGET_PROPERTY:${MBED_TARGET_CONVERTED},INTERFACE_LINK_OPTIONS>)
+# Expose include directories. cmsis.h/device.h and other headers are required by libraries or applications
+target_include_directories(mbed-core INTERFACE $<TARGET_PROPERTY:${MBED_TARGET_CONVERTED},INTERFACE_INCLUDE_DIRECTORIES>)
+target_compile_definitions(mbed-core INTERFACE $<TARGET_PROPERTY:${MBED_TARGET_CONVERTED},COMPILE_DEFINITIONS>)
+
+# Some of core files require MBED_CONF_RTOS_PRESENT symbol (defined in rtos). For baremetal, it's sufficient to link with mbed-core (symbol undefined = RTOS not present). For Mbed OS, this symbol must be defined and set, therefore we copy sources and build them together in mbed-os-objects
+get_property(MBED_CORE_SOURCES TARGET mbed-core-objects PROPERTY SOURCES)
+target_sources(mbed-os-objects PRIVATE ${MBED_CORE_SOURCES})
 
-target_link_libraries(mbed-core INTERFACE ${MBED_TARGET_CONVERTED})
+target_link_libraries(mbed-os-objects mbed-core mbed-rtos ${MBED_TARGET_CONVERTED})
 
 #
 # Converts output file of `target` to binary file and to Intel HEX file.

cmsis/CMSIS_5/CMSIS/RTOS2/CMakeLists.txt

@@ -8,8 +8,8 @@ target_include_directories(mbed-rtos
         Include
 )
 
-target_sources(mbed-rtos
-    INTERFACE
+target_sources(mbed-os-objects
+    PRIVATE
         Source/os_systick.c
         Source/os_tick_ptim.c
 )

cmsis/CMSIS_5/CMSIS/RTOS2/RTX/CMakeLists.txt

@@ -21,8 +21,8 @@ function(_mbed_get_cortex_m_exception_handlers toolchain_dir)
             set(STARTUP_RTX_FILE TARGET_RTOS_M4_M7/irq_cm4f.S)
         endif()
 
-        target_sources(mbed-rtos
-            INTERFACE
+        target_sources(mbed-os-objects
+            PRIVATE
                 Source/${toolchain_dir}/${STARTUP_RTX_FILE}
         )
     endforeach()
@@ -31,7 +31,7 @@ endfunction()
 function(_mbed_get_cortex_a_exception_handlers)
     foreach(key ${MBED_TARGET_LABELS})
         if(${key} STREQUAL CORTEX_A)
-            target_sources(mbed-rtos INTERFACE Config/TARGET_CORTEX_A/handlers.c)
+            target_sources(mbed-os-objects PRIVATE Config/TARGET_CORTEX_A/handlers.c)
         endif()
     endforeach()
 endfunction()
@@ -52,8 +52,8 @@ target_include_directories(mbed-rtos
         Source
 )
 
-target_sources(mbed-rtos
-    INTERFACE
+target_sources(mbed-os-objects
+    PRIVATE
         Config/RTX_Config.c
 
         Library/cmsis_os1.c

cmsis/device/rtos/CMakeLists.txt

@@ -2,13 +2,13 @@
 # SPDX-License-Identifier: Apache-2.0
 
 if(${MBED_TOOLCHAIN} STREQUAL "GCC_ARM")
-    target_sources(mbed-rtos
-        INTERFACE
+    target_sources(mbed-rtos-objects
+        PRIVATE
             TOOLCHAIN_GCC_ARM/mbed_boot_gcc_arm.c
     )
 elseif(${MBED_TOOLCHAIN} STREQUAL "ARM")
-    target_sources(mbed-rtos
-        INTERFACE
+    target_sources(mbed-rtos-objects
+        PRIVATE
             TOOLCHAIN_ARM_STD/mbed_boot_arm_std.c
     )
 endif()
@@ -18,8 +18,8 @@ target_include_directories(mbed-rtos
         include
 )
 
-target_sources(mbed-rtos
-    INTERFACE
+target_sources(mbed-os-objects
+    PRIVATE
         source/mbed_boot.c
         source/mbed_rtos_rtx.c
         source/mbed_rtx_handlers.c

connectivity/libraries/nanostack-libservice/CMakeLists.txt

@@ -31,8 +31,8 @@ target_include_directories(mbed-core
         .
         ./mbed-client-libservice
 )
-target_sources(mbed-core
-    INTERFACE
+target_sources(mbed-core-objects
+    PRIVATE
         source/libBits/common_functions.c
         source/libip6string/ip6tos.c
 )

drivers/CMakeLists.txt

@@ -9,8 +9,8 @@ target_include_directories(mbed-core
         ./include/drivers/internal
 )
 
-target_sources(mbed-core
-    INTERFACE
+target_sources(mbed-core-objects
+    PRIVATE
         source/AnalogIn.cpp
         source/AnalogOut.cpp
         source/BufferedSerial.cpp

events/CMakeLists.txt

@@ -1,18 +1,18 @@
 # Copyright (c) 2020 ARM Limited. All rights reserved.
 # SPDX-License-Identifier: Apache-2.0
 
-add_library(mbed-events INTERFACE)
+add_library(mbed-events OBJECT)
 
 target_include_directories(mbed-events
-    INTERFACE
+    PUBLIC
         .
         ./include
         ./include/events
         ./include/events/internal
 )
 
 target_sources(mbed-events
-    INTERFACE
+    PRIVATE
         source/EventQueue.cpp
         source/equeue.c
         source/equeue_mbed.cpp
@@ -21,6 +21,8 @@ target_sources(mbed-events
 )
 
 target_compile_definitions(mbed-events
-    INTERFACE
+    PUBLIC
         MBED_CONF_EVENTS_PRESENT=1
 )
+
+target_link_libraries(mbed-events PRIVATE mbed-core)

hal/CMakeLists.txt

@@ -11,8 +11,8 @@ target_include_directories(mbed-core
         include/hal
 )
 
-target_sources(mbed-core
-    INTERFACE
+target_sources(mbed-core-objects
+    PRIVATE
         source/LowPowerTickerWrapper.cpp
         source/mbed_compat.c
         source/mbed_critical_section_api.c

hal/usb/CMakeLists.txt

@@ -7,7 +7,7 @@ target_include_directories(mbed-core
         include/usb
 )
 
-target_sources(mbed-core
-    INTERFACE
+target_sources(mbed-core-objects
+    PRIVATE
         source/mbed_usb_phy.cpp
 )

platform/cxxsupport/CMakeLists.txt

@@ -6,7 +6,7 @@ target_include_directories(mbed-core
         .
 )
 
-target_sources(mbed-core
-    INTERFACE
+target_sources(mbed-core-objects
+    PRIVATE
         mstd_mutex.cpp
 )

platform/mbed-trace/CMakeLists.txt

@@ -9,7 +9,7 @@ target_include_directories(mbed-core
         include/mbed-trace
 )
 
-target_sources(mbed-core
-    INTERFACE
+target_sources(mbed-core-objects
+    PRIVATE
         source/mbed_trace.c
 )

platform/source/CMakeLists.txt

@@ -12,8 +12,8 @@ target_include_directories(mbed-core
         .
 )
 
-target_sources(mbed-core
-    INTERFACE
+target_sources(mbed-core-objects
+    PRIVATE
         ATCmdParser.cpp
         CThunkBase.cpp
         CriticalSectionLock.cpp

platform/source/TARGET_CORTEX_M/CMakeLists.txt

@@ -2,12 +2,12 @@
 # SPDX-License-Identifier: Apache-2.0
 
 if(${MBED_TOOLCHAIN} STREQUAL "GCC_ARM")
-    target_sources(mbed-core INTERFACE TOOLCHAIN_GCC/except.S)
+    target_sources(mbed-core-objects PRIVATE TOOLCHAIN_GCC/except.S)
 elseif(${MBED_TOOLCHAIN} STREQUAL "ARM")
-    target_sources(mbed-core INTERFACE TOOLCHAIN_ARM/except.S)
+    target_sources(mbed-core-objects PRIVATE TOOLCHAIN_ARM/except.S)
 endif()
 
-target_sources(mbed-core
-    INTERFACE
+target_sources(mbed-core-objects
+    PRIVATE
         mbed_fault_handler.c
 )

platform/source/minimal-printf/CMakeLists.txt

@@ -6,8 +6,8 @@ target_include_directories(mbed-core
         .
 )
 
-target_sources(mbed-core
-    INTERFACE
+target_sources(mbed-core-objects
+    PRIVATE
         mbed_printf_armlink_overrides.c
         mbed_printf_implementation.c
         mbed_printf_wrapper.c

rtos/CMakeLists.txt

@@ -10,8 +10,8 @@ target_include_directories(mbed-core
         ./source
 )
 
-target_sources(mbed-core
-    INTERFACE
+target_sources(mbed-core-objects
+    PRIVATE
         source/EventFlags.cpp
         source/Kernel.cpp
         source/Mutex.cpp

targets/TARGET_Maxim/CMakeLists.txt

@@ -1,7 +1,6 @@
 # Copyright (c) 2020-2021 ARM Limited. All rights reserved.
 # SPDX-License-Identifier: Apache-2.0
 
-
 add_subdirectory(TARGET_MAX32620C EXCLUDE_FROM_ALL)
 add_subdirectory(TARGET_MAX32625 EXCLUDE_FROM_ALL)
 add_subdirectory(TARGET_MAX32630 EXCLUDE_FROM_ALL)

targets/TARGET_Maxim/TARGET_MAX32620C/CMakeLists.txt

@@ -75,7 +75,4 @@ target_sources(mbed-maxim-max32620c
         ${STARTUP_FILE}
 )
 
-target_link_libraries(mbed-maxim-max32620c 
-    INTERFACE 
-        mbed-maxim
-)
+target_link_libraries(mbed-maxim-max32620c INTERFACE mbed-maxim)

tools/cmake/README.md

@@ -126,3 +126,45 @@ Notes:
 - words separated by hyphens
 
 For example: `mbed-ble-cordio`
+
+## Mbed libraries
+
+This section provides description for all CMake targets within Mbed OS repository.
+
+### mbed-os and mbed-baremetal libraries
+
+An application links to either mbed-os or mbed-baremetal.
+
+| Target  | Function |
+| ------------- | ------------- |
+| mbed-os | Interface library that attaches Mbed OS to a target (objects from mbed-core and mbed-rtos) |
+| mbed-baremetal | Interface library that attaches Mbed baremetal to a target (objects from mbed-core) |
+
+These are internal targets. They are subject to change. An application should not link to any of these.
+
+| Target  | Function |
+| ------------- | ------------- |
+| mbed-cmsis-cortex-m | CMSIS library for Cortex-M |
+| mbed-cmsis-cortex-a | CMSIS library for Cortex-A |
+| mbed-core  | Contains flags from Mbed baremetal.  All Mbed OS libraries link to this.  |
+| mbed-core-objects  | Builds objects for Mbed baremetal  |
+| mbed-rtos | Contains flags that turn Mbed baremetal into Mbed OS |
+| mbed-rtos-objects | Builds objects for RTOS |
+| mbed-os-objects | Build objects for Mbed OS (objects from mbed-core and mbed-rtos) |
+| ${MBED_TARGET_CONVERTED} | Contains interface flags and sources that adapt Mbed OS for a target |
+
+### Additional Mbed OS libraries
+
+An application must explicitely link them using `target_link_libraries()`.
+
+| Target  | Function |
+| ------------- | ------------- |
+| mbed-events  | Events library
+| mbed-ble  | Bluetooth library
+| mbed-storage  | Storage library
+| mbed-mbedtls  | TLS  library
+| mbed-nfc  | NFC library
+| mbed-nanostack  | Nanostack library
+| mbed-netsocket | Netsocket library
+| mbed-lorawan | Lorawan library
+| mbed-wifi | Wifi library