[libc][windows] start time API implementation (llvm#117775)

Add a `clock_gettime` emulation layer and use it to implement the `time`
entrypoint.

For windows, the monotonic clock is emulated using `QPC`.
The realtime clock is emulated using `GetSystemTimePreciseAsFileTime`.

Author: SchrodingerZhu

libc/config/windows/entrypoints.txt

@@ -95,6 +95,9 @@ set(TARGET_LIBC_ENTRYPOINTS
 
     # errno.h entrypoints
     libc.src.errno.errno
+
+    # time.h entrypoints
+    libc.src.time.time
 )
 
 set(TARGET_LIBM_ENTRYPOINTS

libc/hdr/CMakeLists.txt

@@ -135,10 +135,18 @@ add_proxy_header_library(
     libc.include.llvm-libc-macros.unistd_macros
 )
 
+if (WIN32)
+  set(windows_addtional_time_macros libc.include.llvm-libc-macros.windows.time_macros_ext)
+else()
+  set(windows_addtional_time_macros "")
+endif()
+
 add_proxy_header_library(
   time_macros
   HDRS
     time_macros.h
+  DEPENDS
+    ${windows_addtional_time_macros}
   FULL_BUILD_DEPENDS
     libc.include.time
     libc.include.llvm-libc-macros.time_macros

libc/hdr/time_macros.h

@@ -19,4 +19,10 @@
 
 #endif // LLVM_LIBC_FULL_BUILD
 
+// TODO: For now, on windows, let's always include the extension header.
+// We will need to decide how to export this header.
+#ifdef _WIN32
+#include "include/llvm-libc-macros/windows/time-macros-ext.h"
+#endif // _WIN32
+
 #endif // LLVM_LIBC_HDR_TIME_MACROS_H

libc/hdr/types/clockid_t.h

@@ -9,7 +9,8 @@
 #ifndef LLVM_LIBC_HDR_TYPES_CLOCKID_T_H
 #define LLVM_LIBC_HDR_TYPES_CLOCKID_T_H
 
-#ifdef LIBC_FULL_BUILD
+// TODO: we will need to decide how to export extension to windows.
+#if defined(LIBC_FULL_BUILD) || defined(_WIN32)
 
 #include "include/llvm-libc-types/clockid_t.h"
 

libc/include/llvm-libc-macros/windows/CMakeLists.txt

@@ -0,0 +1,6 @@
+add_header(
+  time_macros_ext
+  HDR
+    time-macros-ext.h
+)
+

libc/include/llvm-libc-macros/windows/time-macros-ext.h

@@ -0,0 +1,17 @@
+//===-- Windows Time Macros Extension -------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_LIBC_MACROS_WINDOWS_TIME_MACROS_EXT_H
+#define LLVM_LIBC_MACROS_WINDOWS_TIME_MACROS_EXT_H
+
+#define CLOCK_MONOTONIC 0
+#define CLOCK_REALTIME 1
+#define CLOCK_PROCESS_CPUTIME_ID 2
+#define CLOCK_THREAD_CPUTIME_ID 3
+
+#endif // LLVM_LIBC_MACROS_WINDOWS_TIME_MACROS_EXT_H

libc/src/CMakeLists.txt

@@ -13,6 +13,7 @@ add_subdirectory(stdio)
 add_subdirectory(stdlib)
 add_subdirectory(string)
 add_subdirectory(wchar)
+add_subdirectory(time)
 
 if(${LIBC_TARGET_OS} STREQUAL "linux")
   add_subdirectory(dirent)
@@ -40,5 +41,4 @@ add_subdirectory(setjmp)
 add_subdirectory(signal)
 add_subdirectory(spawn)
 add_subdirectory(threads)
-add_subdirectory(time)
 add_subdirectory(locale)

libc/src/__support/time/CMakeLists.txt

@@ -2,6 +2,13 @@ if(EXISTS ${CMAKE_CURRENT_SOURCE_DIR}/${LIBC_TARGET_OS})
   add_subdirectory(${LIBC_TARGET_OS})
 endif()
 
+add_object_library(
+  clock_gettime
+  ALIAS
+  DEPENDS
+    libc.src.__support.time.${LIBC_TARGET_OS}.clock_gettime
+)
+
 add_header_library(
   units
   HDRS

libc/src/__support/time/linux/clock_gettime.h renamed to libc/src/__support/time/clock_gettime.h

@@ -6,21 +6,17 @@
 //
 //===----------------------------------------------------------------------===//
 
-#ifndef LLVM_LIBC_SRC___SUPPORT_TIME_LINUX_CLOCK_GETTIME_H
-#define LLVM_LIBC_SRC___SUPPORT_TIME_LINUX_CLOCK_GETTIME_H
+#ifndef LLVM_LIBC_SRC___SUPPORT_TIME_CLOCK_GETTIME_H
+#define LLVM_LIBC_SRC___SUPPORT_TIME_CLOCK_GETTIME_H
 
 #include "hdr/types/clockid_t.h"
 #include "hdr/types/struct_timespec.h"
 #include "src/__support/error_or.h"
 
-#if defined(SYS_clock_gettime64)
-#include <linux/time_types.h>
-#endif
-
 namespace LIBC_NAMESPACE_DECL {
 namespace internal {
 ErrorOr<int> clock_gettime(clockid_t clockid, timespec *ts);
 } // namespace internal
 } // namespace LIBC_NAMESPACE_DECL
 
-#endif // LLVM_LIBC_SRC___SUPPORT_TIME_LINUX_CLOCK_GETTIME_H
+#endif // LLVM_LIBC_SRC___SUPPORT_TIME_CLOCK_GETTIME_H

libc/src/__support/time/linux/CMakeLists.txt

@@ -1,7 +1,7 @@
 add_object_library(
   clock_gettime
   HDRS
-    clock_gettime.h
+    ../clock_gettime.h
   SRCS
     clock_gettime.cpp
   DEPENDS