Build: CMake compiler flags will be set, regardless of the cache status

Defining CMake variables from the command-line or from another CMake project,
such as `-DCMAKE_C_FLAGS= -DCMAKE_CXX_FLAGS=`, caused a link failure as ESP
CMake was unable to set its proper compilation flags.
Additional CMake compiler flags can now be provided by another project.

* Closes https://github.com/espressif/esp-idf/issues/7507

CMakeLists.txt

@@ -7,11 +7,8 @@ if(CMAKE_CURRENT_LIST_DIR STREQUAL CMAKE_SOURCE_DIR)
     "again.")
 endif()
 
-unset(compile_options)
-unset(c_compile_options)
-unset(cxx_compile_options)
-unset(compile_definitions)
-unset(link_options)
+# Variables compile_options, c_compile_options, cxx_compile_options, compile_definitions, link_options shall
+# not be unset as they may already contain flags, set by toolchain-TARGET.cmake files.
 
 # Add the following build specifications here, since these seem to be dependent
 # on config values on the root Kconfig.
@@ -215,6 +212,7 @@ endif()
 idf_build_set_property(COMPILE_OPTIONS "${compile_options}" APPEND)
 idf_build_set_property(C_COMPILE_OPTIONS "${c_compile_options}" APPEND)
 idf_build_set_property(CXX_COMPILE_OPTIONS "${cxx_compile_options}" APPEND)
+idf_build_set_property(ASM_COMPILE_OPTIONS "${asm_compile_options}" APPEND)
 idf_build_set_property(COMPILE_DEFINITIONS "${compile_definitions}" APPEND)
 idf_build_set_property(LINK_OPTIONS "${link_options}" APPEND)
 

tools/ci/test_build_system_cmake.sh

@@ -351,6 +351,24 @@ function run_tests()
     rm sdkconfig
     rm sdkconfig.defaults
 
+    print_status "Compiler flags on build command line are taken into account"
+    clean_build_dir
+    # Backup original source file
+    cp main/main.c main/main.c.bak
+    # Alter source file to check user flag
+    echo -e "\n#ifndef USER_FLAG \n \
+#error \"USER_FLAG is not defined!\" \n \
+#endif\n" >> main/main.c
+    idf.py build -DCMAKE_C_FLAGS=-DUSER_FLAG || failure "User flags should have been taken into account"
+    # Restore original file
+    mv main/main.c.bak main/main.c
+
+    print_status "Compiler flags cannot be overwritten"
+    clean_build_dir
+    # If the compiler flags are overriden, the following build command will
+    # cause issues at link time.
+    idf.py build -DCMAKE_C_FLAGS= -DCMAKE_CXX_FLAGS= || failure "CMake compiler flags have been overriden"
+
     # the next tests use the esp32s2 target
     export other_target=esp32s2
 

tools/cmake/component.cmake

@@ -446,12 +446,14 @@ function(idf_component_register)
     idf_build_get_property(compile_options COMPILE_OPTIONS GENERATOR_EXPRESSION)
     idf_build_get_property(c_compile_options C_COMPILE_OPTIONS GENERATOR_EXPRESSION)
     idf_build_get_property(cxx_compile_options CXX_COMPILE_OPTIONS GENERATOR_EXPRESSION)
+    idf_build_get_property(asm_compile_options ASM_COMPILE_OPTIONS GENERATOR_EXPRESSION)
     idf_build_get_property(common_reqs ___COMPONENT_REQUIRES_COMMON)
 
     include_directories("${include_directories}")
     add_compile_options("${compile_options}")
     add_c_compile_options("${c_compile_options}")
     add_cxx_compile_options("${cxx_compile_options}")
+    add_asm_compile_options("${asm_compile_options}")
 
     # Unfortunately add_definitions() does not support generator expressions. A new command
     # add_compile_definition() does but is only available on CMake 3.12 or newer. This uses

tools/cmake/toolchain-clang-esp32.cmake

@@ -1,3 +1,5 @@
+include($ENV{IDF_PATH}/tools/cmake/utilities.cmake)
+
 set(CMAKE_SYSTEM_NAME Generic)
 
 set(CMAKE_C_COMPILER clang)
@@ -11,6 +13,6 @@ set(CMAKE_OBJDUMP xtensa-esp32-elf-objdump)
 # -freestanding is a hack to force Clang to use its own stdatomic.h,
 # without falling back to the (incompatible) GCC stdatomic.h
 # https://github.com/espressif/llvm-project/blob/d9341b81/clang/lib/Headers/stdatomic.h#L13-L18
-set(CMAKE_C_FLAGS "--target=xtensa -mcpu=esp32 -ffreestanding" CACHE STRING "C Compiler Base Flags")
-set(CMAKE_CXX_FLAGS "--target=xtensa -mcpu=esp32 -ffreestanding" CACHE STRING "C++ Compiler Base Flags")
-set(CMAKE_ASM_FLAGS "--target=xtensa -mcpu=esp32" CACHE STRING "Assembler Base Flags")
+list(APPEND c_compile_options "--target=xtensa" "-mcpu=esp32" "-ffreestanding")
+list(APPEND cxx_compile_options "--target=xtensa" "-mcpu=esp32" "-ffreestanding")
+list(APPEND asm_compile_options "--target=xtensa" "-mcpu=esp32")

tools/cmake/toolchain-clang-esp32s2.cmake

@@ -11,6 +11,6 @@ set(CMAKE_OBJDUMP xtensa-esp32-elf-objdump)
 # -freestanding is a hack to force Clang to use its own stdatomic.h,
 # without falling back to the (incompatible) GCC stdatomic.h
 # https://github.com/espressif/llvm-project/blob/d9341b81/clang/lib/Headers/stdatomic.h#L13-L18
-set(CMAKE_C_FLAGS "--target=xtensa -mcpu=esp32s2 -ffreestanding" CACHE STRING "C Compiler Base Flags")
-set(CMAKE_CXX_FLAGS "--target=xtensa -mcpu=esp32s2 -ffreestanding" CACHE STRING "C++ Compiler Base Flags")
-set(CMAKE_ASM_FLAGS "--target=xtensa -mcpu=esp32s2" CACHE STRING "Assembler Base Flags")
+list(APPEND c_compile_options "--target=xtensa" "-mcpu=esp32s2" "-ffreestanding")
+list(APPEND cxx_compile_options "--target=xtensa" "-mcpu=esp32s2" "-ffreestanding")
+list(APPEND asm_compile_options "--target=xtensa" "-mcpu=esp32s2")

tools/cmake/toolchain-esp32.cmake

@@ -4,5 +4,4 @@ set(CMAKE_C_COMPILER xtensa-esp32-elf-gcc)
 set(CMAKE_CXX_COMPILER xtensa-esp32-elf-g++)
 set(CMAKE_ASM_COMPILER xtensa-esp32-elf-gcc)
 
-set(CMAKE_C_FLAGS "-mlongcalls -Wno-frame-address" CACHE STRING "C Compiler Base Flags")
-set(CMAKE_CXX_FLAGS "-mlongcalls -Wno-frame-address" CACHE STRING "C++ Compiler Base Flags")
+list(APPEND compile_options "-mlongcalls" "-Wno-frame-address")

tools/cmake/toolchain-esp32c3.cmake

@@ -4,6 +4,10 @@ set(CMAKE_C_COMPILER riscv32-esp-elf-gcc)
 set(CMAKE_CXX_COMPILER riscv32-esp-elf-g++)
 set(CMAKE_ASM_COMPILER riscv32-esp-elf-gcc)
 
-set(CMAKE_C_FLAGS "-march=rv32imc" CACHE STRING "C Compiler Base Flags")
-set(CMAKE_CXX_FLAGS "-march=rv32imc" CACHE STRING "C++ Compiler Base Flags")
-set(CMAKE_EXE_LINKER_FLAGS "-nostartfiles -march=rv32imc --specs=nosys.specs" CACHE STRING "Linker Base Flags")
+list(APPEND compile_options "-march=rv32imc")
+
+# Option `--specs` must only be defined ONCE in the final linker command, else GCC will complain:
+# "attempt to rename spec 'link_gcc_c_sequence' to already defined spec 'nosys_link_gcc_c_sequence'"
+# so unset `link_options` first.
+unset(link_options)
+list(APPEND link_options "-nostartfiles" "-march=rv32imc" "--specs=nosys.specs")

tools/cmake/toolchain-esp32h2.cmake

@@ -4,6 +4,10 @@ set(CMAKE_C_COMPILER riscv32-esp-elf-gcc)
 set(CMAKE_CXX_COMPILER riscv32-esp-elf-g++)
 set(CMAKE_ASM_COMPILER riscv32-esp-elf-gcc)
 
-set(CMAKE_C_FLAGS "-march=rv32imc" CACHE STRING "C Compiler Base Flags")
-set(CMAKE_CXX_FLAGS "-march=rv32imc" CACHE STRING "C++ Compiler Base Flags")
-set(CMAKE_EXE_LINKER_FLAGS "-nostartfiles -march=rv32imc --specs=nosys.specs" CACHE STRING "Linker Base Flags")
+list(APPEND compile_options "-march=rv32imc")
+
+# Option `--specs` must only be defined ONCE in the final linker command, else GCC will complain:
+# "attempt to rename spec 'link_gcc_c_sequence' to already defined spec 'nosys_link_gcc_c_sequence'"
+# so unset `link_options` first.
+unset(link_options)
+list(APPEND link_options "-nostartfiles" "-march=rv32imc" "--specs=nosys.specs")

tools/cmake/toolchain-esp32s2.cmake

@@ -4,5 +4,5 @@ set(CMAKE_C_COMPILER xtensa-esp32s2-elf-gcc)
 set(CMAKE_CXX_COMPILER xtensa-esp32s2-elf-g++)
 set(CMAKE_ASM_COMPILER xtensa-esp32s2-elf-gcc)
 
-set(CMAKE_C_FLAGS "-mlongcalls" CACHE STRING "C Compiler Base Flags")
-set(CMAKE_CXX_FLAGS "-mlongcalls" CACHE STRING "C++ Compiler Base Flags")
+
+list(APPEND compile_options "-mlongcalls")

tools/cmake/toolchain-esp32s3.cmake

@@ -4,5 +4,4 @@ set(CMAKE_C_COMPILER xtensa-esp32s3-elf-gcc)
 set(CMAKE_CXX_COMPILER xtensa-esp32s3-elf-g++)
 set(CMAKE_ASM_COMPILER xtensa-esp32s3-elf-gcc)
 
-set(CMAKE_C_FLAGS "-mlongcalls" CACHE STRING "C Compiler Base Flags")
-set(CMAKE_CXX_FLAGS "-mlongcalls" CACHE STRING "C++ Compiler Base Flags")
+list(APPEND compile_options "-mlongcalls")

tools/cmake/toolchain-esp8684.cmake

@@ -4,6 +4,10 @@ set(CMAKE_C_COMPILER riscv32-esp-elf-gcc)
 set(CMAKE_CXX_COMPILER riscv32-esp-elf-g++)
 set(CMAKE_ASM_COMPILER riscv32-esp-elf-gcc)
 
-set(CMAKE_C_FLAGS "-march=rv32imc" CACHE STRING "C Compiler Base Flags")
-set(CMAKE_CXX_FLAGS "-march=rv32imc" CACHE STRING "C++ Compiler Base Flags")
-set(CMAKE_EXE_LINKER_FLAGS "-nostartfiles -march=rv32imc --specs=nosys.specs" CACHE STRING "Linker Base Flags")
+list(APPEND compile_options "-march=rv32imc")
+
+# Option `--specs` must only be defined ONCE in the final linker command, else GCC will complain:
+# "attempt to rename spec 'link_gcc_c_sequence' to already defined spec 'nosys_link_gcc_c_sequence'"
+# so unset `link_options` first.
+unset(link_options)
+list(APPEND link_options "-nostartfiles" "-march=rv32imc" "--specs=nosys.specs")

tools/cmake/utilities.cmake

@@ -283,6 +283,17 @@ function(add_c_compile_options)
     endforeach()
 endfunction()
 
+# add_compile_options variant for ASM code only
+#
+# This adds global options, set target properties for
+# component-specific flags
+function(add_asm_compile_options)
+    foreach(option ${ARGV})
+        # note: the Visual Studio Generator doesn't support this...
+        add_compile_options($<$<COMPILE_LANGUAGE:ASM>:${option}>)
+    endforeach()
+endfunction()
+
 
 # add_prebuild_library
 #