cmake: Delay computation of linker paths until needed

With inclusion of the optimization flag into the multilib selection
process, we cannot compute the compiler library path when the compiler's
target.cmake is processed as OPTIMIZATION_FLAG is not computed until much
later.

Instead, add a function (compiler_file_path) which can be used to locate
the appropriate crtbegin.o and crtend.o files.

Delay computation of lib_include_dir and rt_library until after all
compiler flags have been computed by adding compiler_set_linker_properties
and calling that just before toolchain_linker_finalize is invoked.

Place default implementations of both of these functions in a new file,
cmake/compiler/target_template.cmake, where we assume the compiler works
like gcc or clang and handlers the --print-file-name and
--print-libgcc-file-name options. Compilers needing alternate
implementations can override these functions in their target.cmake files.

These implementations require that no generator expressions are necessary
for the compiler to compute the right library paths.

This mechanism is also used to take any additional compiler options and
pass them to the linker using toolchain_linker_add_compiler_options.

Signed-off-by: Keith Packard <keithp@keithp.com>

Author: keith-packard

CMakeLists.txt

@@ -247,7 +247,8 @@ endif()
 # Apply the final optimization flag(s)
 zephyr_compile_options($<$<COMPILE_LANGUAGE:C>:${OPTIMIZATION_FLAG}>)
 zephyr_compile_options($<$<COMPILE_LANGUAGE:CXX>:${OPTIMIZATION_FLAG}>)
-toolchain_linker_add_compiler_options(${OPTIMIZATION_FLAG})
+compiler_simple_options(simple_options)
+toolchain_linker_add_compiler_options(${OPTIMIZATION_FLAG} ${simple_options})
 
 if(CONFIG_LTO)
   zephyr_compile_options($<TARGET_PROPERTY:compiler,optimization_lto>)
@@ -2345,6 +2346,9 @@ add_subdirectory_ifdef(
   cmake/makefile_exports
   )
 
+# Ask the compiler to set the lib_include_dir and rt_library properties
+compiler_set_linker_properties()
+
 toolchain_linker_finalize()
 
 # export build information

cmake/compiler/clang/target.cmake

@@ -100,21 +100,6 @@ if(NOT "${ARCH}" STREQUAL "posix")
     endif()
   endif()
 
-  # This libgcc code is partially duplicated in compiler/*/target.cmake
-  execute_process(
-    COMMAND ${CMAKE_C_COMPILER} ${clang_target_flag} ${TOOLCHAIN_C_FLAGS}
-            --print-libgcc-file-name
-    OUTPUT_VARIABLE RTLIB_FILE_NAME
-    OUTPUT_STRIP_TRAILING_WHITESPACE
-    )
-
-  get_filename_component(RTLIB_DIR ${RTLIB_FILE_NAME} DIRECTORY)
-  get_filename_component(RTLIB_NAME_WITH_PREFIX ${RTLIB_FILE_NAME} NAME_WLE)
-  string(REPLACE lib "" RTLIB_NAME ${RTLIB_NAME_WITH_PREFIX})
-
-  set_property(TARGET linker PROPERTY lib_include_dir "-L${RTLIB_DIR}")
-  set_property(TARGET linker PROPERTY rt_library "-l${RTLIB_NAME}")
-
   list(APPEND CMAKE_REQUIRED_FLAGS -nostartfiles -nostdlib ${isystem_include_flags})
   string(REPLACE ";" " " CMAKE_REQUIRED_FLAGS "${CMAKE_REQUIRED_FLAGS}")
 

cmake/compiler/gcc/target.cmake

@@ -98,21 +98,6 @@ if(SYSROOT_DIR)
   set(LIBC_LIBRARY_DIR "\"${SYSROOT_DIR}\"/lib/${NEWLIB_DIR}")
 endif()
 
-# This libgcc code is partially duplicated in compiler/*/target.cmake
-execute_process(
-  COMMAND ${CMAKE_C_COMPILER} ${TOOLCHAIN_C_FLAGS} --print-libgcc-file-name
-  OUTPUT_VARIABLE LIBGCC_FILE_NAME
-  OUTPUT_STRIP_TRAILING_WHITESPACE
-  )
-
-assert_exists(LIBGCC_FILE_NAME)
-
-get_filename_component(LIBGCC_DIR ${LIBGCC_FILE_NAME} DIRECTORY)
-
-assert_exists(LIBGCC_DIR)
-
-set_linker_property(PROPERTY lib_include_dir "-L\"${LIBGCC_DIR}\"")
-
 # For CMake to be able to test if a compiler flag is supported by the
 # toolchain we need to give CMake the necessary flags to compile and
 # link a dummy C file.

cmake/compiler/icx/target.cmake

@@ -45,21 +45,6 @@ else()
   list(APPEND TOOLCHAIN_C_FLAGS "-m32")
 endif()
 
-
-# This libgcc code is partially duplicated in compiler/*/target.cmake
-execute_process(
-  COMMAND ${CMAKE_C_COMPILER} ${TOOLCHAIN_C_FLAGS} --print-libgcc-file-name
-  OUTPUT_VARIABLE LIBGCC_FILE_NAME
-  OUTPUT_STRIP_TRAILING_WHITESPACE
-  )
-
-get_filename_component(LIBGCC_DIR ${LIBGCC_FILE_NAME} DIRECTORY)
-
-list(APPEND LIB_INCLUDE_DIR "-L\"${LIBGCC_DIR}\"")
-if(LIBGCC_DIR)
-  list(APPEND TOOLCHAIN_LIBS gcc)
-endif()
-
 set(CMAKE_REQUIRED_FLAGS -nostartfiles -nostdlib ${isystem_include_flags})
 string(REPLACE ";" " " CMAKE_REQUIRED_FLAGS "${CMAKE_REQUIRED_FLAGS}")
 

cmake/compiler/target_template.cmake

@@ -0,0 +1,108 @@
+# SPDX-License-Identifier: Apache-2.0
+#
+# Copyright (c) 2025, Nordic Semiconductor ASA
+
+# Template file for optional Zephyr compiler functions.
+#
+# This file will define optional compiler functions for toolchains that are not
+# defining these functions themselves.
+
+# Extract all of the compiler options which don't involve generator
+# expressions. We hope that none of the flags required to compute compiler
+# support library paths depend upon those.
+
+function(compiler_simple_options simple_options_out)
+
+  get_property(flags TARGET zephyr_interface PROPERTY INTERFACE_COMPILE_OPTIONS)
+
+  set(simple_options "")
+
+  foreach(flag ${flags})
+
+    # Include this flag if GENEX_STRIP has no effect,
+    # otherwise skip the whole thing
+
+    string(GENEX_STRIP "${flag}" sflag)
+    if(flag STREQUAL sflag)
+      if(flag MATCHES "^SHELL:[ ]*(.*)")
+        separate_arguments(flag UNIX_COMMAND ${CMAKE_MATCH_1})
+      endif()
+      list(APPEND simple_options ${flag})
+    endif()
+
+  endforeach()
+
+  set(${simple_options_out} "${simple_options}" PARENT_SCOPE)
+endfunction()
+
+if(NOT COMMAND compiler_file_path)
+
+  # Search for filename in default compiler library path using the
+  # --print-file-name option which is common to gcc and clang.  If the
+  # file is not found, filepath_out will be set to an empty string.
+  #
+  # This only works if none of the compiler flags used to compute
+  # the library path involve generator expressions as we cannot
+  # evaluate those in this function.
+  #
+  # Compilers needing a different implementation should provide this
+  # function in their target.cmake file
+
+  function(compiler_file_path filename filepath_out)
+
+    compiler_simple_options(simple_options)
+
+    execute_process(
+      COMMAND ${CMAKE_C_COMPILER} ${TOOLCHAIN_C_FLAGS} ${OPTIMIZATION_FLAG} ${simple_options}
+      --print-file-name ${filename}
+      OUTPUT_VARIABLE filepath
+      OUTPUT_STRIP_TRAILING_WHITESPACE
+      )
+    if(${filepath} STREQUAL ${filename})
+      set(filepath "")
+    endif()
+    set(${filepath_out} "${filepath}" PARENT_SCOPE)
+  endfunction()
+
+endif()
+
+if(NOT COMMAND compiler_set_linker_properties)
+
+  # Set the lib_include_dir and rt_library linker properties
+  # by searching for the runtime library in the compiler default
+  # library search path. If no runtime library is found, these
+  # properties will remain unset
+  #
+  # Compilers needing a different implementation should provide this
+  # function in their target.cmake file
+
+  function(compiler_set_linker_properties)
+
+    compiler_simple_options(simple_options)
+
+    # Compute complete path to the runtime library using the
+    # --print-libgcc-file-name compiler flag
+    execute_process(
+      COMMAND ${CMAKE_C_COMPILER} ${TOOLCHAIN_C_FLAGS} ${OPTIMIZATION_FLAG} ${simple_options}
+      --print-libgcc-file-name
+      OUTPUT_VARIABLE library_path
+      OUTPUT_STRIP_TRAILING_WHITESPACE
+      )
+
+    # Compute the library directory name
+
+    get_filename_component(library_dir ${library_path} DIRECTORY)
+    set_linker_property(PROPERTY lib_include_dir "-L${library_dir}")
+
+    # Compute the linker option for this library
+
+    get_filename_component(library_basename ${library_path} NAME_WLE)
+
+    # Remove the leading 'lib' prefix to leave a value suitable for use with
+    # the linker -l flag
+    string(REPLACE lib "" library_name ${library_basename})
+
+    set_linker_property(PROPERTY rt_library "-l${library_name}")
+  endfunction()
+
+endif()

cmake/compiler/xcc/target.cmake

@@ -55,17 +55,6 @@ foreach(file_name include/stddef.h include-fixed/limits.h)
   endif()
 endforeach()
 
-# This libgcc code is partially duplicated in compiler/*/target.cmake
-execute_process(
-  COMMAND ${CMAKE_C_COMPILER} ${TOOLCHAIN_C_FLAGS} --print-libgcc-file-name
-  OUTPUT_VARIABLE LIBGCC_FILE_NAME
-  OUTPUT_STRIP_TRAILING_WHITESPACE
-  )
-
-get_filename_component(LIBGCC_DIR ${LIBGCC_FILE_NAME} DIRECTORY)
-
-list(APPEND LIB_INCLUDE_DIR "-L\"${LIBGCC_DIR}\"")
-
 # For CMake to be able to test if a compiler flag is supported by the
 # toolchain we need to give CMake the necessary flags to compile and
 # link a dummy C file.

cmake/linker/ld/target.cmake

@@ -159,10 +159,12 @@ macro(toolchain_linker_finalize)
 
   set(cpp_link "${common_link}")
   if(NOT "${ZEPHYR_TOOLCHAIN_VARIANT}" STREQUAL "host")
-    if(CONFIG_CPP_EXCEPTIONS AND LIBGCC_DIR)
+    compiler_file_path(crtbegin.o CRTBEGIN_PATH)
+    compiler_file_path(crtend.o CRTEND_PATH)
+    if(CONFIG_CPP_EXCEPTIONS AND CRTBEGIN_PATH AND CRTEND_PATH)
       # When building with C++ Exceptions, it is important that crtbegin and crtend
       # are linked at specific locations.
-      set(cpp_link "<LINK_FLAGS> ${LIBGCC_DIR}/crtbegin.o ${link_libraries} ${LIBGCC_DIR}/crtend.o")
+      set(cpp_link "<LINK_FLAGS> ${CRTBEGIN_PATH} ${link_libraries} ${CRTEND_PATH}")
     endif()
   endif()
   set(CMAKE_CXX_LINK_EXECUTABLE "<CMAKE_CXX_COMPILER> <FLAGS> <CMAKE_CXX_LINK_FLAGS> ${cpp_link}")

cmake/linker/xt-ld/target.cmake

@@ -11,14 +11,16 @@ find_program(CMAKE_LINKER xt-ld ${LD_SEARCH_PATH})
 
 set_ifndef(LINKERFLAGPREFIX -Wl)
 
-if(CONFIG_CPP_EXCEPTIONS)
+compiler_file_path(crtbegin.o CRTBEGIN_PATH)
+compiler_file_path(crtend.o CRTEND_PATH)
+if(CONFIG_CPP_EXCEPTIONS AND CRTBEGIN_PATH AND CRTEND_PATH)
   # When building with C++ Exceptions, it is important that crtbegin and crtend
   # are linked at specific locations.
   # The location is so important that we cannot let this be controlled by normal
   # link libraries, instead we must control the link command specifically as
   # part of toolchain.
   set(CMAKE_CXX_LINK_EXECUTABLE
-      "<CMAKE_CXX_COMPILER> <FLAGS> <CMAKE_CXX_LINK_FLAGS> <LINK_FLAGS> ${LIBGCC_DIR}/crtbegin.o <OBJECTS> -o <TARGET> <LINK_LIBRARIES> ${LIBGCC_DIR}/crtend.o")
+      "<CMAKE_CXX_COMPILER> <FLAGS> <CMAKE_CXX_LINK_FLAGS> <LINK_FLAGS> ${CRTBEGIN_PATH} <OBJECTS> -o <TARGET> <LINK_LIBRARIES> ${CRTEND_PATH}")
 endif()
 
 # Run $LINKER_SCRIPT file through the C preprocessor, producing ${linker_script_gen}

cmake/modules/FindTargetTools.cmake

@@ -106,6 +106,7 @@ include(${ZEPHYR_BASE}/cmake/bintools/bintools_template.cmake)
 include(${TOOLCHAIN_ROOT}/cmake/bintools/${BINTOOLS}/target.cmake OPTIONAL)
 
 include(${TOOLCHAIN_ROOT}/cmake/linker/target_template.cmake)
+include(${TOOLCHAIN_ROOT}/cmake/compiler/target_template.cmake)
 
 set(TargetTools_FOUND TRUE)
 set(TARGETTOOLS_FOUND TRUE)