[CMake][libc] Support cross-compiling libc-hdrgen

[phosek]

Summary

This is useful when cross-compiling libc to another target in which
case we first need to compile libc-hdrgen for host. We rely on the
existing LLVM CMake infrastructure for that.

[phosek]

Note that there's one additional issue right now. The TableGen cross-compilation sub-invokes CMake which fails with:

CMake Error at /src/clang-llvm/llvm-project/libc/CMakeLists.txt:49 (message):


        'clang' and 'clang-tools-extra' are required in LLVM_ENABLE_PROJECTS to
        lint llvm-libc. The linting step performs important checks to help prevent
        the introduction of subtle bugs, but it may increase build times.



        To disable linting set LLVM_LIBC_ENABLE_LINTING to OFF
        (pass -DLLVM_LIBC_ENABLE_LINTING=OFF to cmake).


-- Configuring incomplete, errors occurred!

I think we'll need some way detect when we're cross-compiling TableGen and disable the linting support in that case.

[sivachandra]

In D95205#2514656, @phosek wrote:

Note that there's one additional issue right now. The TableGen cross-compilation sub-invokes CMake which fails with:

CMake Error at /src/clang-llvm/llvm-project/libc/CMakeLists.txt:49 (message):


        'clang' and 'clang-tools-extra' are required in LLVM_ENABLE_PROJECTS to
        lint llvm-libc. The linting step performs important checks to help prevent
        the introduction of subtle bugs, but it may increase build times.



        To disable linting set LLVM_LIBC_ENABLE_LINTING to OFF
        (pass -DLLVM_LIBC_ENABLE_LINTING=OFF to cmake).


-- Configuring incomplete, errors occurred!

I think we'll need some way detect when we're cross-compiling TableGen and disable the linting support in that case.

We can take simpler route of not enabling linting by default. Developer workflow will involve testing with linting enabled of course.

[phosek]

In D95205#2521972, @sivachandra wrote:

In D95205#2514656, @phosek wrote:

Note that there's one additional issue right now. The TableGen cross-compilation sub-invokes CMake which fails with:

CMake Error at /src/clang-llvm/llvm-project/libc/CMakeLists.txt:49 (message):


        'clang' and 'clang-tools-extra' are required in LLVM_ENABLE_PROJECTS to
        lint llvm-libc. The linting step performs important checks to help prevent
        the introduction of subtle bugs, but it may increase build times.



        To disable linting set LLVM_LIBC_ENABLE_LINTING to OFF
        (pass -DLLVM_LIBC_ENABLE_LINTING=OFF to cmake).


-- Configuring incomplete, errors occurred!

I think we'll need some way detect when we're cross-compiling TableGen and disable the linting support in that case.

We can take simpler route of not enabling linting by default. Developer workflow will involve testing with linting enabled of course.

I'm fine with that, it'd also simplify integrating libc into the runtimes build where I'm also hitting this issue.

libc/CMakeLists.txt

if(COMMAND_RETURN_CODE EQUAL 0)
   message(STATUS "Set COMPILER_RESOURCE_DIR to "
                  "${COMPILER_RESOURCE_DIR} using --print-resource-dir")
 else()
   set(COMPILER_RESOURCE_DIR OFF)
   message(STATUS "COMPILER_RESOURCE_DIR not set
                   --print-resource-dir not supported by host compiler")
 endif()
 
-option(LLVM_LIBC_ENABLE_LINTING "Enables linting of libc source files" ON)
+option(LLVM_LIBC_ENABLE_LINTING "Enables linting of libc source files" OFF)
 if(LLVM_LIBC_ENABLE_LINTING)
   if("clang-tools-extra" IN_LIST LLVM_ENABLE_PROJECTS
              AND "clang" IN_LIST LLVM_ENABLE_PROJECTS)
     add_custom_target(lint-libc)
   else()
     message(FATAL_ERROR "
       'clang' and 'clang-tools-extra' are required in LLVM_ENABLE_PROJECTS to
       lint llvm-libc. The linting step performs important checks to help prevent
if(${last_dot_loc} EQUAL -1)
     message(FATAL "Invalid entrypoint target name ${entrypoint}; Expected a '.' "
                   "(dot) in the name.")
   endif()
   math(EXPR name_loc "${last_dot_loc} + 1")
   string(SUBSTRING ${entrypoint} ${name_loc} -1 entrypoint_name)
   list(APPEND TARGET_ENTRYPOINT_NAME_LIST ${entrypoint_name})
 endforeach()
 
+# We need to set up hdrgen first since other targets depend on it.
+add_subdirectory(utils/LibcTableGenUtil)
+add_subdirectory(utils/HdrGen)
+
 add_subdirectory(include)
 add_subdirectory(config)
 add_subdirectory(src)
 add_subdirectory(utils)
 
 # The loader can potentially depend on the library components so add it
 # after the library implementation directories.
 add_subdirectory(loader)

libc/cmake/modules/LLVMLibCHeaderRules.cmake

function(add_gen_header target_name)
 
   file(GLOB td_includes ${LIBC_SOURCE_DIR}/spec/*.td)
 
   set(ENTRYPOINT_NAME_LIST_ARG ${TARGET_ENTRYPOINT_NAME_LIST})
   list(TRANSFORM ENTRYPOINT_NAME_LIST_ARG PREPEND "--e=")
 
   add_custom_command(
     OUTPUT ${out_file}
-    COMMAND $<TARGET_FILE:libc-hdrgen> -o ${out_file} --header ${ADD_GEN_HDR_GEN_HDR}
+    COMMAND ${LIBC_TABLEGEN_EXE} -o ${out_file} --header ${ADD_GEN_HDR_GEN_HDR}
             --def ${in_file} ${replacement_params} -I ${LIBC_SOURCE_DIR}
            ${ENTRYPOINT_NAME_LIST_ARG}
            ${LIBC_SOURCE_DIR}/config/${LIBC_TARGET_OS}/api.td
 
     WORKING_DIRECTORY ${CMAKE_CURRENT_SOURCE_DIR}
     DEPENDS ${in_file} ${fq_data_files} ${td_includes}
-            ${LIBC_SOURCE_DIR}/config/${LIBC_TARGET_OS}/api.td libc-hdrgen
+            ${LIBC_SOURCE_DIR}/config/${LIBC_TARGET_OS}/api.td
+            ${LIBC_TABLEGEN_EXE} ${LIBC_TABLEGEN_TARGET}
   )
 
   get_fq_target_name(${target_name} fq_target_name)
   if(ADD_GEN_HDR_DEPENDS)
     get_fq_deps_list(fq_deps_list ${ADD_GEN_HDR_DEPENDS})
   endif()
   add_custom_target(
     ${fq_target_name}
     DEPENDS ${out_file} ${fq_deps_list}
   )
 endfunction(add_gen_header)

libc/utils/CMakeLists.txt

 add_subdirectory(CPP)
 add_subdirectory(FPUtil)
-add_subdirectory(LibcTableGenUtil)
-add_subdirectory(HdrGen)
 add_subdirectory(MPFRWrapper)
 add_subdirectory(testutils)
 add_subdirectory(tools)
 add_subdirectory(UnitTest)

libc/utils/HdrGen/CMakeLists.txt

 set(LLVM_LINK_COMPONENTS Support)
 
-add_tablegen(libc-hdrgen llvm-libc
+add_tablegen(libc-hdrgen LIBC
   Command.h
   Command.cpp
   Generator.cpp
   Generator.h
   IncludeFileCommand.cpp
   IncludeFileCommand.h
   Main.cpp
   PublicAPICommand.cpp
   PublicAPICommand.h
 )
 
 target_include_directories(libc-hdrgen PRIVATE ${LIBC_SOURCE_DIR})
 target_link_libraries(libc-hdrgen PRIVATE LibcTableGenUtil)
 
 add_subdirectory(PrototypeTestGen)