cmake: clang: Support host's clang for non-MCU x86 targets on Linux

Pick host's clang if ZEPHYR_TOOLCHAIN_VARIANT=host-llvm.

Signed-off-by: Oleg Zhurakivskyy <[email protected]>

Author: ozhuraki

CMakeLists.txt

@@ -386,7 +386,8 @@ zephyr_ld_options(
   )
 
 get_property(TOPT GLOBAL PROPERTY TOPT)
-set_ifndef(  TOPT -T)
+set_ifndef(  TOPT -Wl,-T) # clang doesn't pick -T for some reason and complains,
+                          # while -Wl,-T works for both, gcc and clang
 
 if(NOT CONFIG_NATIVE_APPLICATION)
   # Funny thing is if this is set to =error, some architectures will

arch/posix/CMakeLists.txt

@@ -1,12 +1,17 @@
 zephyr_compile_options(
-  -fno-freestanding
   -m32
   -MMD
   -MP
   ${ARCH_FLAG}
   -include ${ZEPHYR_BASE}/arch/posix/include/posix_cheats.h
   )
 
+if(NOT CMAKE_C_COMPILER_ID STREQUAL "Clang") # clang errors on -fno-freestanding
+zephyr_compile_options(
+    -fno-freestanding
+  )
+endif()
+
 zephyr_include_directories(${BOARD_DIR})
 
 zephyr_compile_options_ifdef(CONFIG_COVERAGE

cmake/compiler/gcc/target_security_fortify.cmake

@@ -5,9 +5,13 @@ macro(toolchain_cc_security_fortify)
     # _FORTIFY_SOURCE: Detect common-case buffer overflows for certain functions
     # _FORTIFY_SOURCE=1 : Compile-time checks (requires -O1 at least)
     # _FORTIFY_SOURCE=2 : Additional lightweight run-time checks
-    zephyr_compile_definitions(
-      _FORTIFY_SOURCE=2
-    )
+
+    if(NOT CMAKE_C_COMPILER_ID STREQUAL "Clang")
+      # clang errors on _FORTIFY_SOURCE=2
+      zephyr_compile_definitions(
+        _FORTIFY_SOURCE=2
+	)
+    endif()
   endif()
 
 endmacro()

cmake/compiler/host-clang/generic.cmake

@@ -0,0 +1,3 @@
+# Configures CMake for using host's clang
+
+find_program(CMAKE_C_COMPILER clang)

cmake/compiler/host-clang/target.cmake

@@ -0,0 +1,20 @@
+# Configures CMake for using clang
+
+find_program(CMAKE_C_COMPILER   clang   )
+#find_program(CMAKE_CXX_COMPILER clang++ )    # Not used currently
+find_program(CMAKE_OBJCOPY      objcopy )
+#find_program(CMAKE_OBJDUMP     llvm-objdump) # Not used currently
+#find_program(CMAKE_LINKER      ld      )     # Not used currently
+find_program(CMAKE_AR           llvm-ar )
+#find_program(CMAKE_RANLILB     llvm-ranlib ) # Not used currently
+find_program(CMAKE_READELF      readelf )
+find_program(CMAKE_GDB          gdb     )
+
+# Load toolchain_cc-family macros
+# Significant overlap with freestanding gcc compiler so reuse it
+include(${ZEPHYR_BASE}/cmake/compiler/gcc/target_security_fortify.cmake)
+include(${ZEPHYR_BASE}/cmake/compiler/gcc/target_security_canaries.cmake)
+include(${ZEPHYR_BASE}/cmake/compiler/gcc/target_optimizations.cmake)
+include(${ZEPHYR_BASE}/cmake/compiler/gcc/target_cpp.cmake)
+include(${ZEPHYR_BASE}/cmake/compiler/gcc/target_asm.cmake)
+include(${ZEPHYR_BASE}/cmake/compiler/gcc/target_baremetal.cmake)

cmake/generic_toolchain.cmake

@@ -48,7 +48,9 @@ assert(ZEPHYR_TOOLCHAIN_VARIANT "Zephyr toolchain variant invalid: please set th
 
 # Pick host system's toolchain if we are targeting posix
 if((${ARCH} STREQUAL "posix") OR (${ARCH} STREQUAL "x86_64"))
-  set(ZEPHYR_TOOLCHAIN_VARIANT "host")
+  if(NOT "${ZEPHYR_TOOLCHAIN_VARIANT}" STREQUAL "host-llvm")
+    set(ZEPHYR_TOOLCHAIN_VARIANT "host")
+  endif()
 endif()
 
 # Configure the toolchain based on what SDK/toolchain is in use.

cmake/target_toolchain.cmake

@@ -30,7 +30,7 @@ set(CMAKE_SYSTEM_VERSION ${PROJECT_VERSION})
 # We are not building dynamically loadable libraries
 set(BUILD_SHARED_LIBS OFF)
 
-if(NOT (COMPILER STREQUAL "host-gcc"))
+if(NOT ((COMPILER STREQUAL "host-gcc") OR (COMPILER STREQUAL "host-clang")))
   include(${TOOLCHAIN_ROOT}/cmake/toolchain/${ZEPHYR_TOOLCHAIN_VARIANT}/target.cmake)
 endif()
 

cmake/toolchain/host-llvm/generic.cmake

@@ -0,0 +1,2 @@
+set(COMPILER host-clang)
+set(TOOLCHAIN_HAS_NEWLIB OFF CACHE BOOL "True if toolchain supports newlib")

cmake/toolchain/host-llvm/target.cmake

@@ -0,0 +1 @@
+# This file intentionally left blank.

doc/getting_started/index.rst

@@ -157,7 +157,8 @@ Set Up a Toolchain
    In some specific configurations like non-MCU x86 targets on Linux,
    you may be able to re-use the native development tools provided by
    your operating system instead of an SDK by setting
-   ``ZEPHYR_TOOLCHAIN_VARIANT=host``.
+   ``ZEPHYR_TOOLCHAIN_VARIANT=host`` for gcc or
+   ``ZEPHYR_TOOLCHAIN_VARIANT=host-llvm`` for clang.
 
    If you want, you can use the SDK host tools (such as OpenOCD) with a
    different toolchain by keeping the :envvar:`ZEPHYR_SDK_INSTALL_DIR`