[X86][CET] Support to build LLVM toolchain with CET enabled.

[xiongji90]

Summary

This patch is the first one of a series of patches aiming to support to build llvm toolchain(compiler, tools, libraries) with CET enabled. Currently, CET has been implemented in x86 Linux target and in order to compile source code with CET enabled, "-fcf-protection=full" should be added. CET introduces 'IBT' which restricts the target of indirect jumps and 'SHSTK' is also introduced which aims to check the return address when a function is going to return to caller. This patch introduces the option "LLVM_BUILD_CET_ENABLE", if you want to build compiler and libraries with CET enabled, you can set this option to ON:
cmake -G "Unix Makefiles" -DLLVM_BUILD_CET_ENABLE=ON ...
The default value is OFF. Not all subprojects support building with CET, so we don't add any CET build option in this patch. For those subprojects which have already supported CET, they can add CET building option based on "LLVM_BUILD_CET_ENABLE" option.

[manojgupta]

llvm/cmake/modules/HandleLLVMOptions.cmake

372

I am not an expert in CMake but I think we need to add support for this option per subproject as well since the projects can be built independent of LLVM e.g. : compiler-rt, libcxx, libcxxbi, libunwind can be built separately without compiling llvm.

[xiongji90]

llvm/cmake/modules/HandleLLVMOptions.cmake

372

Hi, @manojgupta
Agree on your suggestion. Enabling CET for each subproject one by one should be the correct practice.
I will update the patch to remove adding CET compiling options here, do you think we can keep "LLVM_BUILD_CET_ENABLE" here? When all subprojects have been enabled CET building, we can use this option to build whole llvm toolchain with CET enabled.
Thanks very much!

llvm/CMakeLists.txt

 
 # Define an option controlling whether we should build for 32-bit on 64-bit
 # platforms, where supported.
 if( CMAKE_SIZEOF_VOID_P EQUAL 8 AND NOT (WIN32 OR ${CMAKE_SYSTEM_NAME} MATCHES "AIX"))
   # TODO: support other platforms and toolchains.
   option(LLVM_BUILD_32_BITS "Build 32 bits executables and libraries." OFF)
 endif()
 
+if(NOT WIN32)
+  option(LLVM_BUILD_CET_ENABLE "Build executables and libraries with CET enabled." OFF)
+endif()
+
 # Define the default arguments to use with 'lit', and an option for the user to
 # override.
 set(LIT_ARGS_DEFAULT "-sv")
 if (MSVC_IDE OR XCODE)
   set(LIT_ARGS_DEFAULT "${LIT_ARGS_DEFAULT} --no-progress-bar")
 endif()
 set(LLVM_LIT_ARGS "${LIT_ARGS_DEFAULT}" CACHE STRING "Default options for lit")
 

llvm/cmake/modules/HandleLLVMOptions.cmake

if( LLVM_BUILD_32_BITS )
     set(CMAKE_MODULE_LINKER_FLAGS "${CMAKE_MODULE_LINKER_FLAGS} -m32")
 
     # FIXME: CMAKE_SIZEOF_VOID_P is still 8
     add_definitions(-D_LARGEFILE_SOURCE)
     add_definitions(-D_FILE_OFFSET_BITS=64)
   endif( LLVM_BUILD_32_BITS )
 endif( CMAKE_SIZEOF_VOID_P EQUAL 8 AND NOT WIN32 )
 
+# To enable CET in compilation, "-fcf-protection=full" should
+# be added. Currently, CET has been implemented in x86 GNU/Linux target.
+if(NOT WIN32)
+  if( LLVM_BUILD_CET_ENABLE)
+    add_flag_if_supported("-fcf-protection=full" CET)
+    if((NOT C_SUPPORTS_CET) OR (NOT CXX_SUPPORTS_CET))
+      message(FATAL_ERROR "The compiler used for building doesn't support CET!")
+    endif()
+  endif( LLVM_BUILD_CET_ENABLE)
+endif()
+
 # If building on a GNU specific 32-bit system, make sure off_t is 64 bits
 # so that off_t can stored offset > 2GB.
 # Android until version N (API 24) doesn't support it.
 if (ANDROID AND (ANDROID_NATIVE_API_LEVEL LESS 24))
   set(LLVM_FORCE_SMALLFILE_FOR_ANDROID TRUE)
 endif()
 if( CMAKE_SIZEOF_VOID_P EQUAL 4 AND NOT LLVM_FORCE_SMALLFILE_FOR_ANDROID)
   # FIXME: It isn't handled in LLVM_BUILD_32_BITS.

llvm/cmake/modules/LLVMConfig.cmake.in

 set(LLVM_ENABLE_DIA_SDK @LLVM_ENABLE_DIA_SDK@)
 
 set(LLVM_NATIVE_ARCH @LLVM_NATIVE_ARCH@)
 
 set(LLVM_ENABLE_PIC @LLVM_ENABLE_PIC@)
 
 set(LLVM_BUILD_32_BITS @LLVM_BUILD_32_BITS@)
 
+set(LLVM_BUILD_CET_ENABLE @LLVM_BUILD_CET_ENABLE@)
+
 if (NOT "@LLVM_PTHREAD_LIB@" STREQUAL "")
   set(LLVM_PTHREAD_LIB "@LLVM_PTHREAD_LIB@")
 endif()
 
 set(LLVM_ENABLE_PLUGINS @LLVM_ENABLE_PLUGINS@)
 set(LLVM_EXPORT_SYMBOLS_FOR_PLUGINS @LLVM_EXPORT_SYMBOLS_FOR_PLUGINS@)
 set(LLVM_PLUGIN_EXT @LLVM_PLUGIN_EXT@)
 

llvm/docs/CMake.rst

**LLVM_APPEND_VC_REV**:BOOL
   ``llvm/include/llvm/Support/VCSRevision.h``. Developers using git who don't
   need revision info can disable this option to avoid re-linking most binaries
   after a branch switch. Defaults to ON.
 
 **LLVM_BUILD_32_BITS**:BOOL
   Build 32-bit executables and libraries on 64-bit systems. This option is
   available only on some 64-bit Unix systems. Defaults to OFF.
 
+**LLVM_BUILD_CET_ENABLE**:BOOL
+  Build executables and libraries with CET enabled. CET is currently implemented
+  in x86 GNU/Linux target. Defaults to OFF.
+
 **LLVM_BUILD_BENCHMARKS**:BOOL
   Adds benchmarks to the list of default targets. Defaults to OFF.
 
 **LLVM_BUILD_DOCS**:BOOL
   Adds all *enabled* documentation targets (i.e. Doxgyen and Sphinx targets) as
   dependencies of the default build targets.  This results in all of the (enabled)
   documentation targets being as part of a normal build.  If the ``install``
   target is run then this also enables all built documentation targets to be