Change linker script handling logic to use only one linker script target

CMakeLists.txt

@@ -269,6 +269,9 @@ if(NOT MBED_IS_NATIVE_BUILD)
     # Create a distro for the microcontroller cmake target, ensuring its sources are only compiled once
     mbed_create_distro(${MBED_TARGET_CMAKE_NAME}-lib ${MBED_TARGET_CMAKE_NAME} mbed-core-flags)
 
+    # Set up the linker script and hook it up to the MCU cmake target
+    mbed_setup_linker_script(${MBED_TARGET_CMAKE_NAME}-lib)
+
     # Now make the Mbed OS code depend on the target, ensuring everything has access to the uC's flags and objects.
     target_link_libraries(mbed-core-flags INTERFACE ${MBED_TARGET_CMAKE_NAME}-lib)
 

tools/cmake/mbed_create_distro.cmake

@@ -48,6 +48,9 @@ function(mbed_create_distro NAME) # ARGN: modules...
 
 		get_property(CURR_MODULE_TYPE TARGET ${CURR_MODULE} PROPERTY TYPE)
 
+		# Pass up mbed linker script property, which is used by the top level code to select the linker script
+		copy_append_property(INTERFACE_MBED_LINKER_SCRIPT ${CURR_MODULE} ${NAME})
+
 		if("${CURR_MODULE_TYPE}" STREQUAL "STATIC_LIBRARY")
 			# Don't need to do anything other than linking it
 			target_link_libraries(${NAME} PUBLIC ${CURR_MODULE})

tools/cmake/mbed_set_linker_script.cmake

@@ -2,53 +2,88 @@
 # SPDX-License-Identifier: Apache-2.0
 
 #
-# Preprocesses and sets the linker script for an Mbed target.
-# Called once for each MCU target in the build system.
+# Sets the linker script for an Mbed target.
+# Called once by the buildscripts for each MCU target in the build system.
+# Note: Linker script path may be absolute or relative.  If relative, it will be interpreted relative to the current source dir.
 #
 function(mbed_set_linker_script input_target raw_linker_script_path)
 
-    set(LINKER_SCRIPT_PATH ${CMAKE_CURRENT_BINARY_DIR}/${input_target}.link_script.ld)
+    # Make sure that we have an absolute path so that it can be used from a different directory
+    get_filename_component(raw_linker_script_path ${raw_linker_script_path} ABSOLUTE)
+
+    # Use a custom property to store the linker script.  This property will be read and passed up by mbed_create_distro()
+    set_property(TARGET ${input_target} PROPERTY INTERFACE_MBED_LINKER_SCRIPT ${raw_linker_script_path})
+
+endfunction(mbed_set_linker_script)
+
+
+#
+# Set up the linker script for the top-level Mbed MCU target.
+# If needed, this also creates another target to preprocess the linker script.
+#
+function(mbed_setup_linker_script mbed_mcu_target)
+
+    # Find the path to the desired linker script
+    get_property(RAW_LINKER_SCRIPT_PATHS TARGET ${mbed_mcu_target} PROPERTY INTERFACE_MBED_LINKER_SCRIPT)
+
+    # Check if two (or more) different linker scripts got used
+    list(REMOVE_DUPLICATES RAW_LINKER_SCRIPT_PATHS)
+    list(LENGTH RAW_LINKER_SCRIPT_PATHS NUM_RAW_LINKER_SCRIPT_PATHS)
+    if(NUM_RAW_LINKER_SCRIPT_PATHS GREATER 1)
+        message(FATAL_ERROR "More than one linker script selected for the current MCU target.  Perhaps multiple targets with linker scripts set were linked together?")
+    endif()
+
+    # Make sure the linker script exists
+    if(NOT EXISTS "${RAW_LINKER_SCRIPT_PATHS}")
+        message(FATAL_ERROR "Selected linker script ${RAW_LINKER_SCRIPT_PATHS} does not exist!")
+    endif()
+
+    set(LINKER_SCRIPT_PATH ${CMAKE_BINARY_DIR}/${MBED_TARGET_CMAKE_NAME}.link_script.ld)
+
     # To avoid path limits on Windows, we create a "response file" and set the path to it as a
     # global property. We need this solely to pass the compile definitions to GCC's preprocessor,
     # so it can expand any macro definitions in the linker script.
-    get_property(_linker_preprocess_definitions GLOBAL PROPERTY COMPILE_DEFS_RESPONSE_FILE)
+    get_property(linker_defs_response_file GLOBAL PROPERTY COMPILE_DEFS_RESPONSE_FILE)
     if(MBED_TOOLCHAIN STREQUAL "GCC_ARM")
+
+        get_filename_component(RAW_LINKER_SCRIPT_NAME ${RAW_LINKER_SCRIPT_PATHS} NAME)
+        get_filename_component(LINKER_SCRIPT_NAME ${LINKER_SCRIPT_PATH} NAME)
         add_custom_command(
             OUTPUT
                 ${LINKER_SCRIPT_PATH}
             PRE_LINK
             COMMAND
-                ${CMAKE_C_COMPILER} ${_linker_preprocess_definitions}
+                ${CMAKE_C_COMPILER} @${linker_defs_response_file}
                 -E -x assembler-with-cpp
-                -P ${raw_linker_script_path}
+                -P ${RAW_LINKER_SCRIPT_PATHS}
                 -o ${LINKER_SCRIPT_PATH}
             DEPENDS
-                ${raw_linker_script_path}
+                ${RAW_LINKER_SCRIPT_PATHS}
+                ${linker_defs_response_file}
             WORKING_DIRECTORY
                 ${CMAKE_CURRENT_SOURCE_DIR}
             COMMENT
-                "Link line:"
+                "Preprocess linker script: ${RAW_LINKER_SCRIPT_NAME} -> ${LINKER_SCRIPT_NAME}"
             VERBATIM
         )
-        # CMake will not let us add PRE_LINK commands to INTERFACE targets, and input_target could
-        # be an INTERFACE target.
-        # To get around this we create an intermediate custom target depending on the preprocessed
-        # linker script output by CPP. We add this custom target as a dependency of input_target.
-        # This ensures CMake runs our custom command to preprocess the linker script before trying
-        # to build input_target.
-        set(LinkerScriptTarget ${input_target}LinkerScript)
-        add_custom_target(${LinkerScriptTarget} DEPENDS ${LINKER_SCRIPT_PATH} VERBATIM)
-        add_dependencies(${input_target} ${LinkerScriptTarget})
-        target_link_options(${input_target}
+
+        # The job to create the linker script gets attached to the mbed-linker-script target,
+        # which is then added as a dependency of the MCU target.  This ensures the linker script will exist
+        # by the time we need it.
+        add_custom_target(mbed-linker-script DEPENDS ${LINKER_SCRIPT_PATH} VERBATIM)
+        add_dependencies(${mbed_mcu_target} mbed-linker-script)
+
+        # Add linker flags to the MCU target to pick up the preprocessed linker script
+        target_link_options(${mbed_mcu_target}
             INTERFACE
                 "-T" "${LINKER_SCRIPT_PATH}"
         )
     elseif(MBED_TOOLCHAIN STREQUAL "ARM")
-        target_link_options(${input_target}
+        target_link_options(${mbed_mcu_target}
             INTERFACE
                 "--scatter=${raw_linker_script_path}"
                 "--predefine=${_linker_preprocess_definitions}"
                 "--map"
         )
     endif()
-endfunction()
+endfunction(mbed_setup_linker_script)