[libc] Introduce a full build mode CMake option.

This option will build LLVM libc as a full libc by itself. In this mode,
it is not expected that it will be mixed with other libcs. The
non-full-build mode will be the default LLVM libc build mode. In a future
where LLVM libc is complete enough, the full libc build will be made the
default mode.

libc/CMakeLists.txt

@@ -62,6 +62,8 @@ else()
     (pass -DLLVM_LIBC_ENABLE_LINTING=ON to cmake).")
 endif()
 
+option(LLVM_LIBC_FULL_BUILD "Build and test LLVM libc as if it is the full libc" OFF)
+
 include(CMakeParseArguments)
 include(LLVMLibCRules)
 include(LLVMLibCCheckCpuFeatures)
@@ -81,18 +83,22 @@ foreach(entrypoint IN LISTS TARGET_LLVMLIBC_ENTRYPOINTS)
   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)
+if(LLVM_LIBC_FULL_BUILD)
+  # We need to set up hdrgen first since other targets depend on it.
+  add_subdirectory(utils/LibcTableGenUtil)
+  add_subdirectory(utils/HdrGen)
+endif()
 
 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)
+if(LLVM_LIBC_FULL_BUILD)
+  # The loader can potentially depend on the library components so add it
+  # after the library implementation directories.
+  add_subdirectory(loader)
+endif()
 
 # The lib and test directories are added at the very end as tests
 # and libraries potentially draw from the components present in all

libc/cmake/modules/LLVMLibCHeaderRules.cmake

@@ -58,6 +58,12 @@ function(add_gen_header target_name)
     "PARAMS;DATA_FILES;DEPENDS"     # Multi value arguments
     ${ARGN}
   )
+  get_fq_target_name(${target_name} fq_target_name)
+  if(NOT LLVM_LIBC_FULL_BUILD)
+    # We don't want to use generated headers if we are doing a non-full-build.
+    add_custom_target(${fq_target_name})
+    return()
+  endif()
   if(NOT ADD_GEN_HDR_DEF_FILE)
     message(FATAL_ERROR "`add_gen_hdr` rule requires DEF_FILE to be specified.")
   endif()
@@ -100,7 +106,6 @@ function(add_gen_header target_name)
             ${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()

libc/config/linux/x86_64/entrypoints.txt

@@ -1,7 +1,4 @@
 set(TARGET_LIBC_ENTRYPOINTS
-    # assert.h entrypoints
-    libc.src.assert.__assert_fail
-    
     # ctype.h entrypoints
     libc.src.ctype.isalnum
     libc.src.ctype.isalpha
@@ -23,23 +20,6 @@ set(TARGET_LIBC_ENTRYPOINTS
     # errno.h entrypoints
     libc.src.errno.__errno_location
 
-    # signal.h entrypoints
-    libc.src.signal.raise
-    libc.src.signal.sigaction
-    libc.src.signal.sigdelset
-    libc.src.signal.sigaddset
-    libc.src.signal.sigemptyset
-    libc.src.signal.sigprocmask
-    libc.src.signal.sigfillset
-    libc.src.signal.signal
-
-    # stdlib.h entrypoints
-    libc.src.stdlib._Exit
-    libc.src.stdlib.abort
-    libc.src.stdlib.abs
-    libc.src.stdlib.labs
-    libc.src.stdlib.llabs
-
     # string.h entrypoints
     libc.src.string.bzero
     libc.src.string.memchr
@@ -62,24 +42,6 @@ set(TARGET_LIBC_ENTRYPOINTS
     libc.src.string.strstr
     libc.src.string.strtok
     libc.src.string.strtok_r
-
-    # sys/mman.h entrypoints
-    libc.src.sys.mman.mmap
-    libc.src.sys.mman.munmap
-
-    # threads.h entrypoints
-    libc.src.threads.call_once
-    libc.src.threads.mtx_init
-    libc.src.threads.mtx_lock
-    libc.src.threads.mtx_unlock
-    libc.src.threads.thrd_create
-    libc.src.threads.thrd_join
-
-    # time.h entrypoints
-    libc.src.time.mktime
-
-    # unistd.h entrypoints
-    libc.src.unistd.write
 )
 
 set(TARGET_LIBM_ENTRYPOINTS
@@ -179,6 +141,48 @@ set(TARGET_LIBM_ENTRYPOINTS
     libc.src.math.truncl
 )
 
+if(LLVM_LIBC_FULL_BUILD)
+  list(APPEND TARGET_LIBC_ENTRYPOINTS
+    # assert.h entrypoints
+    libc.src.assert.__assert_fail
+
+    # stdlib.h entrypoints
+    libc.src.stdlib._Exit
+    libc.src.stdlib.abort
+    libc.src.stdlib.abs
+    libc.src.stdlib.labs
+    libc.src.stdlib.llabs
+
+    # signal.h entrypoints
+    libc.src.signal.raise
+    libc.src.signal.sigaction
+    libc.src.signal.sigdelset
+    libc.src.signal.sigaddset
+    libc.src.signal.sigemptyset
+    libc.src.signal.sigprocmask
+    libc.src.signal.sigfillset
+    libc.src.signal.signal
+
+    # sys/mman.h entrypoints
+    libc.src.sys.mman.mmap
+    libc.src.sys.mman.munmap
+
+    # threads.h entrypoints
+    libc.src.threads.call_once
+    libc.src.threads.mtx_init
+    libc.src.threads.mtx_lock
+    libc.src.threads.mtx_unlock
+    libc.src.threads.thrd_create
+    libc.src.threads.thrd_join
+
+    # time.h entrypoints
+    libc.src.time.mktime
+
+    # unistd.h entrypoints
+    libc.src.unistd.write
+  )
+endif()
+
 set(TARGET_LLVMLIBC_ENTRYPOINTS
   ${TARGET_LIBC_ENTRYPOINTS}
   ${TARGET_LIBM_ENTRYPOINTS}

libc/src/CMakeLists.txt

@@ -1,16 +1,21 @@
-add_subdirectory(assert)
+add_subdirectory(__support)
+
 add_subdirectory(ctype)
 add_subdirectory(errno)
 add_subdirectory(fenv)
 add_subdirectory(math)
+add_subdirectory(string)
+
+if(NOT LLVM_LIBC_FULL_BUILD)
+  return()
+endif()
+
+add_subdirectory(assert)
 add_subdirectory(signal)
 add_subdirectory(stdio)
 add_subdirectory(stdlib)
-add_subdirectory(string)
 # TODO: Add this target conditional to the target OS.
 add_subdirectory(sys)
 add_subdirectory(threads)
 add_subdirectory(time)
 add_subdirectory(unistd)
-
-add_subdirectory(__support)

libc/test/CMakeLists.txt

@@ -7,7 +7,12 @@ add_header_library(
 add_custom_target(check-libc)
 add_custom_target(exhaustive-check-libc)
 
-add_subdirectory(config)
-add_subdirectory(loader)
 add_subdirectory(src)
 add_subdirectory(utils)
+
+if(NOT LLVM_LIBC_FULL_BUILD)
+  return()
+endif()
+
+add_subdirectory(config)
+add_subdirectory(loader)

libc/test/src/CMakeLists.txt

@@ -1,8 +1,13 @@
-add_subdirectory(assert)
 add_subdirectory(ctype)
 add_subdirectory(errno)
 add_subdirectory(fenv)
 add_subdirectory(math)
+
+if(NOT LLVM_LIBC_FULL_BUILD)
+  return()
+endif()
+
+add_subdirectory(assert)
 add_subdirectory(signal)
 add_subdirectory(stdio)
 add_subdirectory(stdlib)

libc/test/utils/CMakeLists.txt

@@ -1,3 +1,8 @@
 add_subdirectory(FPUtil)
 add_subdirectory(CPP)
+
+if(NOT LLVM_LIBC_FULL_BUILD)
+  return()
+endif()
+
 add_subdirectory(tools)

libc/utils/CMakeLists.txt

@@ -2,5 +2,8 @@ add_subdirectory(CPP)
 add_subdirectory(FPUtil)
 add_subdirectory(MPFRWrapper)
 add_subdirectory(testutils)
-add_subdirectory(tools)
 add_subdirectory(UnitTest)
+
+if(LLVM_LIBC_FULL_BUILD)
+  add_subdirectory(tools)
+endif()