[libc] [llvm] Reapply "[libc][windows] start time API implementation (#117775)" (PR #118886)

Schrodinger ZHU Yifan via llvm-commits llvm-commits at lists.llvm.org
Thu Dec 5 14:14:29 PST 2024


https://github.com/SchrodingerZhu updated https://github.com/llvm/llvm-project/pull/118886

>From 4dee4c98eb5c2a84ccf4d19e6c9aaf2f3b47b86c Mon Sep 17 00:00:00 2001
From: Schrodinger ZHU Yifan <yifanzhu at rochester.edu>
Date: Thu, 5 Dec 2024 17:03:21 -0500
Subject: [PATCH 1/3] Reapply "[libc][windows] start time API implementation
 (#117775)"

This reverts commit 9fd052a1223c19245664922c68c101a79cb694f0.
---
 libc/config/windows/entrypoints.txt           |   3 +
 libc/hdr/CMakeLists.txt                       |   8 +
 libc/hdr/time_macros.h                        |   6 +
 libc/hdr/types/clockid_t.h                    |   3 +-
 .../llvm-libc-macros/windows/CMakeLists.txt   |   6 +
 .../windows/time-macros-ext.h                 |  17 ++
 libc/src/CMakeLists.txt                       |   2 +-
 libc/src/__support/time/CMakeLists.txt        |   7 +
 .../time/{linux => }/clock_gettime.h          |  10 +-
 libc/src/__support/time/linux/CMakeLists.txt  |   2 +-
 .../__support/time/linux/clock_conversion.h   |   2 +-
 .../__support/time/linux/clock_gettime.cpp    |   2 +-
 .../src/__support/time/windows/CMakeLists.txt |  16 ++
 .../__support/time/windows/clock_gettime.cpp  | 150 ++++++++++++++++++
 libc/src/time/CMakeLists.txt                  |  10 +-
 libc/src/time/linux/CMakeLists.txt            |  21 +--
 libc/src/time/linux/clock.cpp                 |   2 +-
 libc/src/time/linux/clock_gettime.cpp         |   2 +-
 libc/src/time/linux/gettimeofday.cpp          |   2 +-
 libc/src/time/linux/timespec_get.cpp          |   2 +-
 libc/src/time/{linux => }/time.cpp            |   8 +-
 libc/test/src/CMakeLists.txt                  |   2 +-
 .../threads/linux/raw_mutex_test.cpp          |   2 +-
 libc/test/src/time/CMakeLists.txt             |   2 +-
 libc/test/src/time/time_test.cpp              |   2 -
 .../llvm-project-overlay/libc/BUILD.bazel     |   6 +-
 26 files changed, 248 insertions(+), 47 deletions(-)
 create mode 100644 libc/include/llvm-libc-macros/windows/CMakeLists.txt
 create mode 100644 libc/include/llvm-libc-macros/windows/time-macros-ext.h
 rename libc/src/__support/time/{linux => }/clock_gettime.h (72%)
 create mode 100644 libc/src/__support/time/windows/CMakeLists.txt
 create mode 100644 libc/src/__support/time/windows/clock_gettime.cpp
 rename libc/src/time/{linux => }/time.cpp (83%)

diff --git a/libc/config/windows/entrypoints.txt b/libc/config/windows/entrypoints.txt
index 8f0b50bcc83ea2..d0796b85aec2af 100644
--- a/libc/config/windows/entrypoints.txt
+++ b/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
diff --git a/libc/hdr/CMakeLists.txt b/libc/hdr/CMakeLists.txt
index 93da271f5e040b..5eb311f4bb2298 100644
--- a/libc/hdr/CMakeLists.txt
+++ b/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
diff --git a/libc/hdr/time_macros.h b/libc/hdr/time_macros.h
index dc36fe66f7a802..4488a24848c359 100644
--- a/libc/hdr/time_macros.h
+++ b/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
diff --git a/libc/hdr/types/clockid_t.h b/libc/hdr/types/clockid_t.h
index 333342072a2ff2..729e580aba4384 100644
--- a/libc/hdr/types/clockid_t.h
+++ b/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"
 
diff --git a/libc/include/llvm-libc-macros/windows/CMakeLists.txt b/libc/include/llvm-libc-macros/windows/CMakeLists.txt
new file mode 100644
index 00000000000000..48afc795178a0d
--- /dev/null
+++ b/libc/include/llvm-libc-macros/windows/CMakeLists.txt
@@ -0,0 +1,6 @@
+add_header(
+  time_macros_ext
+  HDR
+    time-macros-ext.h
+)
+
diff --git a/libc/include/llvm-libc-macros/windows/time-macros-ext.h b/libc/include/llvm-libc-macros/windows/time-macros-ext.h
new file mode 100644
index 00000000000000..71d914b4518771
--- /dev/null
+++ b/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
diff --git a/libc/src/CMakeLists.txt b/libc/src/CMakeLists.txt
index 02c193e635362e..dd3b51886edfea 100644
--- a/libc/src/CMakeLists.txt
+++ b/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)
diff --git a/libc/src/__support/time/CMakeLists.txt b/libc/src/__support/time/CMakeLists.txt
index 89ddffb099388b..e73f2744b15a0e 100644
--- a/libc/src/__support/time/CMakeLists.txt
+++ b/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
diff --git a/libc/src/__support/time/linux/clock_gettime.h b/libc/src/__support/time/clock_gettime.h
similarity index 72%
rename from libc/src/__support/time/linux/clock_gettime.h
rename to libc/src/__support/time/clock_gettime.h
index f7f996ce7c1975..584bf546cd60cd 100644
--- a/libc/src/__support/time/linux/clock_gettime.h
+++ b/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
diff --git a/libc/src/__support/time/linux/CMakeLists.txt b/libc/src/__support/time/linux/CMakeLists.txt
index 94ed09e6521524..6fec7eeba99add 100644
--- a/libc/src/__support/time/linux/CMakeLists.txt
+++ b/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
diff --git a/libc/src/__support/time/linux/clock_conversion.h b/libc/src/__support/time/linux/clock_conversion.h
index 7a52873263a14c..ac5357d308d7c5 100644
--- a/libc/src/__support/time/linux/clock_conversion.h
+++ b/libc/src/__support/time/linux/clock_conversion.h
@@ -10,7 +10,7 @@
 #define LLVM_LIBC_SRC___SUPPORT_TIME_LINUX_CLOCK_CONVERSION_H
 
 #include "src/__support/macros/config.h"
-#include "src/__support/time/linux/clock_gettime.h"
+#include "src/__support/time/clock_gettime.h"
 #include "src/__support/time/units.h"
 
 namespace LIBC_NAMESPACE_DECL {
diff --git a/libc/src/__support/time/linux/clock_gettime.cpp b/libc/src/__support/time/linux/clock_gettime.cpp
index 3a0eca417724ac..944fc0a2b80fe7 100644
--- a/libc/src/__support/time/linux/clock_gettime.cpp
+++ b/libc/src/__support/time/linux/clock_gettime.cpp
@@ -6,7 +6,7 @@
 //
 //===----------------------------------------------------------------------===//
 
-#include "src/__support/time/linux/clock_gettime.h"
+#include "src/__support/time/clock_gettime.h"
 #include "hdr/types/clockid_t.h"
 #include "hdr/types/struct_timespec.h"
 #include "src/__support/OSUtil/linux/vdso.h"
diff --git a/libc/src/__support/time/windows/CMakeLists.txt b/libc/src/__support/time/windows/CMakeLists.txt
new file mode 100644
index 00000000000000..0f557ed8800802
--- /dev/null
+++ b/libc/src/__support/time/windows/CMakeLists.txt
@@ -0,0 +1,16 @@
+add_object_library(
+  clock_gettime
+  HDRS
+    ../clock_gettime.h
+  SRCS
+    clock_gettime.cpp
+  DEPENDS
+    libc.hdr.types.struct_timespec
+    libc.hdr.types.clockid_t
+    libc.hdr.errno_macros
+    libc.src.__support.common
+    libc.src.__support.error_or
+    libc.src.__support.OSUtil.osutil
+    libc.src.__support.CPP.atomic
+    libc.src.__support.CPP.limits
+)
diff --git a/libc/src/__support/time/windows/clock_gettime.cpp b/libc/src/__support/time/windows/clock_gettime.cpp
new file mode 100644
index 00000000000000..c2536acf37d799
--- /dev/null
+++ b/libc/src/__support/time/windows/clock_gettime.cpp
@@ -0,0 +1,150 @@
+//===--- clock_gettime windows implementation -------------------*- C++ -*-===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+#include "hdr/time_macros.h"
+
+#include "src/__support/CPP/atomic.h"
+#include "src/__support/CPP/bit.h"
+#include "src/__support/CPP/limits.h"
+#include "src/__support/macros/optimization.h"
+#include "src/__support/time/clock_gettime.h"
+#include "src/__support/time/units.h"
+
+#define WIN32_LEAN_AND_MEAN
+#define NOMINMAX
+#include <Windows.h>
+
+namespace LIBC_NAMESPACE_DECL {
+namespace internal {
+static long long get_ticks_per_second() {
+  static cpp::Atomic<long long> frequency = 0;
+  // Relaxed ordering is enough. It is okay to record the frequency multiple
+  // times. The store operation itself is atomic and the value must propagate
+  // as required by cache coherence.
+  auto freq = frequency.load(cpp::MemoryOrder::RELAXED);
+  if (!freq) {
+    [[clang::uninitialized]] LARGE_INTEGER buffer;
+    // On systems that run Windows XP or later, the function will always
+    // succeed and will thus never return zero.
+    ::QueryPerformanceFrequency(&buffer);
+    frequency.store(buffer.QuadPart, cpp::MemoryOrder::RELAXED);
+    return buffer.QuadPart;
+  }
+  return freq;
+}
+
+ErrorOr<int> clock_gettime(clockid_t clockid, timespec *ts) {
+  using namespace time_units;
+  constexpr unsigned long long HNS_PER_SEC = 1_s_ns / 100ULL;
+  constexpr long long SEC_LIMIT =
+      cpp::numeric_limits<decltype(ts->tv_sec)>::max();
+  ErrorOr<int> ret = 0;
+  switch (clockid) {
+  default:
+    ret = cpp::unexpected(EINVAL);
+    break;
+
+  case CLOCK_MONOTONIC: {
+    // see
+    // https://learn.microsoft.com/en-us/windows/win32/sysinfo/acquiring-high-resolution-time-stamps
+    // Is the performance counter monotonic (non-decreasing)?
+    // Yes. QPC does not go backward.
+    [[clang::uninitialized]] LARGE_INTEGER buffer;
+    // On systems that run Windows XP or later, the function will always
+    // succeed and will thus never return zero.
+    ::QueryPerformanceCounter(&buffer);
+    long long freq = get_ticks_per_second();
+    long long ticks = buffer.QuadPart;
+    long long tv_sec = ticks / freq;
+    long long tv_nsec = (ticks % freq) * 1_s_ns / freq;
+    if (LIBC_UNLIKELY(tv_sec > SEC_LIMIT)) {
+      ret = cpp::unexpected(EOVERFLOW);
+      break;
+    }
+    ts->tv_sec = static_cast<decltype(ts->tv_sec)>(tv_sec);
+    ts->tv_nsec = static_cast<decltype(ts->tv_nsec)>(tv_nsec);
+    break;
+  }
+  case CLOCK_REALTIME: {
+    // https://learn.microsoft.com/en-us/windows/win32/api/sysinfoapi/nf-sysinfoapi-getsystemtimepreciseasfiletime
+    // GetSystemTimePreciseAsFileTime
+    // This function is best suited for high-resolution time-of-day
+    // measurements, or time stamps that are synchronized to UTC
+    [[clang::uninitialized]] FILETIME file_time;
+    [[clang::uninitialized]] ULARGE_INTEGER time;
+    ::GetSystemTimePreciseAsFileTime(&file_time);
+    time.LowPart = file_time.dwLowDateTime;
+    time.HighPart = file_time.dwHighDateTime;
+
+    // adjust to POSIX epoch (from Jan 1, 1601 to Jan 1, 1970)
+    constexpr unsigned long long POSIX_TIME_SHIFT =
+        (11644473600ULL * HNS_PER_SEC);
+    if (LIBC_UNLIKELY(POSIX_TIME_SHIFT > time.QuadPart)) {
+      ret = cpp::unexpected(EOVERFLOW);
+      break;
+    }
+    time.QuadPart -= (11644473600ULL * HNS_PER_SEC);
+    unsigned long long tv_sec = time.QuadPart / HNS_PER_SEC;
+    unsigned long long tv_nsec = (time.QuadPart % HNS_PER_SEC) * 100ULL;
+    if (LIBC_UNLIKELY(tv_sec > SEC_LIMIT)) {
+      ret = cpp::unexpected(EOVERFLOW);
+      break;
+    }
+    ts->tv_sec = static_cast<decltype(ts->tv_sec)>(tv_sec);
+    ts->tv_nsec = static_cast<decltype(ts->tv_nsec)>(tv_nsec);
+    break;
+  }
+  case CLOCK_PROCESS_CPUTIME_ID:
+  case CLOCK_THREAD_CPUTIME_ID: {
+    [[clang::uninitialized]] FILETIME creation_time;
+    [[clang::uninitialized]] FILETIME exit_time;
+    [[clang::uninitialized]] FILETIME kernel_time;
+    [[clang::uninitialized]] FILETIME user_time;
+    bool success;
+    if (clockid == CLOCK_PROCESS_CPUTIME_ID) {
+      // https://learn.microsoft.com/en-us/windows/win32/api/processthreadsapi/nf-processthreadsapi-getprocesstimes
+      success = ::GetProcessTimes(::GetCurrentProcess(), &creation_time,
+                                  &exit_time, &kernel_time, &user_time);
+    } else {
+      // https://learn.microsoft.com/en-us/windows/win32/api/processthreadsapi/nf-processthreadsapi-getthreadtimes
+      success = ::GetThreadTimes(::GetCurrentThread(), &creation_time,
+                                 &exit_time, &kernel_time, &user_time);
+    }
+    if (!success) {
+      ret = cpp::unexpected(EINVAL);
+      break;
+    }
+    // https://learn.microsoft.com/en-us/windows/win32/api/minwinbase/ns-minwinbase-filetime
+    // It is not recommended that you add and subtract values from the FILETIME
+    // structure to obtain relative times. Instead, you should copy the low- and
+    // high-order parts of the file time to a ULARGE_INTEGER structure, perform
+    // 64-bit arithmetic on the QuadPart member, and copy the LowPart and
+    // HighPart members into the FILETIME structure.
+    auto kernel_time_hns = cpp::bit_cast<ULARGE_INTEGER>(kernel_time);
+    auto user_time_hns = cpp::bit_cast<ULARGE_INTEGER>(user_time);
+    unsigned long long total_time_hns =
+        kernel_time_hns.QuadPart + user_time_hns.QuadPart;
+
+    unsigned long long tv_sec = total_time_hns / HNS_PER_SEC;
+    unsigned long long tv_nsec = (total_time_hns % HNS_PER_SEC) * 100ULL;
+
+    if (LIBC_UNLIKELY(tv_sec > SEC_LIMIT)) {
+      ret = cpp::unexpected(EOVERFLOW);
+      break;
+    }
+
+    ts->tv_sec = static_cast<decltype(ts->tv_sec)>(tv_sec);
+    ts->tv_nsec = static_cast<decltype(ts->tv_nsec)>(tv_nsec);
+
+    break;
+  }
+  }
+  return ret;
+}
+} // namespace internal
+} // namespace LIBC_NAMESPACE_DECL
diff --git a/libc/src/time/CMakeLists.txt b/libc/src/time/CMakeLists.txt
index f18e74a15e6fc2..3e8e6882ffc5d4 100644
--- a/libc/src/time/CMakeLists.txt
+++ b/libc/src/time/CMakeLists.txt
@@ -106,9 +106,15 @@ add_entrypoint_object(
 
 add_entrypoint_object(
   time
-  ALIAS
+  SRCS
+    time.cpp
+  HDRS
+    time_func.h
   DEPENDS
-    .${LIBC_TARGET_OS}.time
+    libc.hdr.time_macros
+    libc.hdr.types.time_t
+    libc.src.__support.time.clock_gettime
+    libc.src.errno.errno
 )
 
 add_entrypoint_object(
diff --git a/libc/src/time/linux/CMakeLists.txt b/libc/src/time/linux/CMakeLists.txt
index 31fd7d1e64c85c..314623f9f425e7 100644
--- a/libc/src/time/linux/CMakeLists.txt
+++ b/libc/src/time/linux/CMakeLists.txt
@@ -1,16 +1,3 @@
-add_entrypoint_object(
-  time
-  SRCS
-    time.cpp
-  HDRS
-    ../time_func.h
-  DEPENDS
-    libc.hdr.time_macros
-    libc.hdr.types.time_t
-    libc.src.__support.time.linux.clock_gettime
-    libc.src.errno.errno
-)
-
 add_entrypoint_object(
   timespec_get
   SRCS
@@ -20,7 +7,7 @@ add_entrypoint_object(
   DEPENDS
     libc.hdr.time_macros
     libc.hdr.types.struct_timespec
-    libc.src.__support.time.linux.clock_gettime
+    libc.src.__support.time.clock_gettime
     libc.src.errno.errno
 )
 
@@ -34,7 +21,7 @@ add_entrypoint_object(
     libc.hdr.time_macros
     libc.hdr.types.clock_t
     libc.src.__support.time.units
-    libc.src.__support.time.linux.clock_gettime
+    libc.src.__support.time.clock_gettime
     libc.src.__support.CPP.limits
     libc.src.errno.errno
 )
@@ -62,7 +49,7 @@ add_entrypoint_object(
   DEPENDS
     libc.hdr.types.clockid_t
     libc.hdr.types.struct_timespec
-    libc.src.__support.time.linux.clock_gettime
+    libc.src.__support.time.clock_gettime
     libc.src.errno.errno
 )
 
@@ -75,7 +62,7 @@ add_entrypoint_object(
   DEPENDS
     libc.hdr.time_macros
     libc.hdr.types.suseconds_t
-    libc.src.__support.time.linux.clock_gettime
+    libc.src.__support.time.clock_gettime
     libc.src.__support.time.units
     libc.src.errno.errno
 )
diff --git a/libc/src/time/linux/clock.cpp b/libc/src/time/linux/clock.cpp
index f43e1bcad6a3a1..ee4fa82b4f8944 100644
--- a/libc/src/time/linux/clock.cpp
+++ b/libc/src/time/linux/clock.cpp
@@ -11,7 +11,7 @@
 #include "src/__support/CPP/limits.h"
 #include "src/__support/common.h"
 #include "src/__support/macros/config.h"
-#include "src/__support/time/linux/clock_gettime.h"
+#include "src/__support/time/clock_gettime.h"
 #include "src/__support/time/units.h"
 #include "src/errno/libc_errno.h"
 
diff --git a/libc/src/time/linux/clock_gettime.cpp b/libc/src/time/linux/clock_gettime.cpp
index a2b20a6dbc9879..743c644d65d024 100644
--- a/libc/src/time/linux/clock_gettime.cpp
+++ b/libc/src/time/linux/clock_gettime.cpp
@@ -9,7 +9,7 @@
 #include "src/time/clock_gettime.h"
 #include "src/__support/common.h"
 #include "src/__support/macros/config.h"
-#include "src/__support/time/linux/clock_gettime.h"
+#include "src/__support/time/clock_gettime.h"
 #include "src/errno/libc_errno.h"
 
 namespace LIBC_NAMESPACE_DECL {
diff --git a/libc/src/time/linux/gettimeofday.cpp b/libc/src/time/linux/gettimeofday.cpp
index 19d9988ae73a6e..e8ddf482fc9840 100644
--- a/libc/src/time/linux/gettimeofday.cpp
+++ b/libc/src/time/linux/gettimeofday.cpp
@@ -11,7 +11,7 @@
 #include "hdr/types/suseconds_t.h"
 #include "src/__support/common.h"
 #include "src/__support/macros/config.h"
-#include "src/__support/time/linux/clock_gettime.h"
+#include "src/__support/time/clock_gettime.h"
 #include "src/__support/time/units.h"
 #include "src/errno/libc_errno.h"
 
diff --git a/libc/src/time/linux/timespec_get.cpp b/libc/src/time/linux/timespec_get.cpp
index ba9f8eb2e4426b..cf5174523aa4f9 100644
--- a/libc/src/time/linux/timespec_get.cpp
+++ b/libc/src/time/linux/timespec_get.cpp
@@ -10,7 +10,7 @@
 #include "hdr/time_macros.h"
 #include "src/__support/common.h"
 #include "src/__support/macros/config.h"
-#include "src/__support/time/linux/clock_gettime.h"
+#include "src/__support/time/clock_gettime.h"
 #include "src/errno/libc_errno.h"
 
 namespace LIBC_NAMESPACE_DECL {
diff --git a/libc/src/time/linux/time.cpp b/libc/src/time/time.cpp
similarity index 83%
rename from libc/src/time/linux/time.cpp
rename to libc/src/time/time.cpp
index 20fb86e8e29dbb..4a0b614a68ef5f 100644
--- a/libc/src/time/linux/time.cpp
+++ b/libc/src/time/time.cpp
@@ -9,14 +9,14 @@
 #include "hdr/time_macros.h"
 #include "src/__support/common.h"
 #include "src/__support/macros/config.h"
-#include "src/__support/time/linux/clock_gettime.h"
+#include "src/__support/time/clock_gettime.h"
 #include "src/errno/libc_errno.h"
 #include "src/time/time_func.h"
 
 namespace LIBC_NAMESPACE_DECL {
-
-LLVM_LIBC_FUNCTION(time_t, time, (time_t * tp)) {
-  // TODO: Use the Linux VDSO to fetch the time and avoid the syscall.
+// avoid inconsitent clang-format behavior
+using time_ptr_t = time_t *;
+LLVM_LIBC_FUNCTION(time_t, time, (time_ptr_t tp)) {
   struct timespec ts;
   auto result = internal::clock_gettime(CLOCK_REALTIME, &ts);
   if (!result.has_value()) {
diff --git a/libc/test/src/CMakeLists.txt b/libc/test/src/CMakeLists.txt
index 8ac8f91e98d4cc..606f6d837e4fe7 100644
--- a/libc/test/src/CMakeLists.txt
+++ b/libc/test/src/CMakeLists.txt
@@ -59,6 +59,7 @@ add_subdirectory(stdio)
 add_subdirectory(stdlib)
 add_subdirectory(string)
 add_subdirectory(wchar)
+add_subdirectory(time)
 
 # Depends on utilities in stdlib
 add_subdirectory(inttypes)
@@ -82,7 +83,6 @@ add_subdirectory(network)
 add_subdirectory(setjmp)
 add_subdirectory(signal)
 add_subdirectory(spawn)
-add_subdirectory(time)
 add_subdirectory(locale)
 
 if(${LIBC_TARGET_OS} STREQUAL "linux")
diff --git a/libc/test/src/__support/threads/linux/raw_mutex_test.cpp b/libc/test/src/__support/threads/linux/raw_mutex_test.cpp
index 918f5d35c94f42..dadc706421d06e 100644
--- a/libc/test/src/__support/threads/linux/raw_mutex_test.cpp
+++ b/libc/test/src/__support/threads/linux/raw_mutex_test.cpp
@@ -12,7 +12,7 @@
 #include "src/__support/OSUtil/syscall.h"
 #include "src/__support/threads/linux/raw_mutex.h"
 #include "src/__support/threads/sleep.h"
-#include "src/__support/time/linux/clock_gettime.h"
+#include "src/__support/time/clock_gettime.h"
 #include "src/stdlib/exit.h"
 #include "src/sys/mman/mmap.h"
 #include "src/sys/mman/munmap.h"
diff --git a/libc/test/src/time/CMakeLists.txt b/libc/test/src/time/CMakeLists.txt
index 7151526b72b26d..d2a98677a55435 100644
--- a/libc/test/src/time/CMakeLists.txt
+++ b/libc/test/src/time/CMakeLists.txt
@@ -157,8 +157,8 @@ add_libc_unittest(
   SRCS
     time_test.cpp
   DEPENDS
-    libc.include.time
     libc.src.time.time
+    libc.src.__support.time.clock_gettime
     libc.src.errno.errno
 )
 
diff --git a/libc/test/src/time/time_test.cpp b/libc/test/src/time/time_test.cpp
index d3d4dc9a285158..7cdb4e834633e5 100644
--- a/libc/test/src/time/time_test.cpp
+++ b/libc/test/src/time/time_test.cpp
@@ -9,8 +9,6 @@
 #include "src/time/time_func.h"
 #include "test/UnitTest/Test.h"
 
-#include <time.h>
-
 TEST(LlvmLibcTimeTest, SmokeTest) {
   time_t t1;
   time_t t2 = LIBC_NAMESPACE::time(&t1);
diff --git a/utils/bazel/llvm-project-overlay/libc/BUILD.bazel b/utils/bazel/llvm-project-overlay/libc/BUILD.bazel
index c5a0076d2ef308..957b49fe6afe8e 100644
--- a/utils/bazel/llvm-project-overlay/libc/BUILD.bazel
+++ b/utils/bazel/llvm-project-overlay/libc/BUILD.bazel
@@ -1471,13 +1471,13 @@ libc_support_library(
     }),
     deps = [
         ":__support_time",
-        ":__support_time_linux_clock_gettime",
+        ":__support_time_clock_gettime",
     ],
 )
 
 libc_support_library(
-    name = "__support_time_linux_clock_gettime",
-    hdrs = ["src/__support/time/linux/clock_gettime.h"],
+    name = "__support_time_clock_gettime",
+    hdrs = ["src/__support/time/clock_gettime.h"],
     target_compatible_with = select({
         "@platforms//os:linux": [],
         "//conditions:default": ["@platforms//:incompatible"],

>From 67e357e4ccfedfb1dc81579eb4ae370ba0a80e14 Mon Sep 17 00:00:00 2001
From: Schrodinger ZHU Yifan <i at zhuyi.fan>
Date: Thu, 5 Dec 2024 12:02:56 -0800
Subject: [PATCH 2/3] [libc][gpu] unify time implementation style and fix build

---
 libc/src/__support/time/CMakeLists.txt        | 20 ++++++-----
 libc/src/__support/time/gpu/CMakeLists.txt    | 22 ++++++++++++
 libc/src/__support/time/gpu/clock_gettime.cpp | 33 +++++++++++++++++
 .../{ => __support}/time/gpu/time_utils.cpp   |  0
 .../src/{ => __support}/time/gpu/time_utils.h |  0
 libc/src/time/gpu/CMakeLists.txt              | 36 ++++++++-----------
 libc/src/time/gpu/clock.cpp                   |  2 +-
 libc/src/time/gpu/clock_gettime.cpp           | 19 ++++------
 libc/src/time/gpu/nanosleep.cpp               |  2 +-
 9 files changed, 88 insertions(+), 46 deletions(-)
 create mode 100644 libc/src/__support/time/gpu/CMakeLists.txt
 create mode 100644 libc/src/__support/time/gpu/clock_gettime.cpp
 rename libc/src/{ => __support}/time/gpu/time_utils.cpp (100%)
 rename libc/src/{ => __support}/time/gpu/time_utils.h (100%)

diff --git a/libc/src/__support/time/CMakeLists.txt b/libc/src/__support/time/CMakeLists.txt
index e73f2744b15a0e..8247e792e84105 100644
--- a/libc/src/__support/time/CMakeLists.txt
+++ b/libc/src/__support/time/CMakeLists.txt
@@ -1,5 +1,16 @@
+add_header_library(
+  units
+  HDRS
+    units.h
+  DEPENDS
+    libc.src.__support.common
+    libc.hdr.types.time_t
+)
+
 if(EXISTS ${CMAKE_CURRENT_SOURCE_DIR}/${LIBC_TARGET_OS})
   add_subdirectory(${LIBC_TARGET_OS})
+else()
+  return()
 endif()
 
 add_object_library(
@@ -8,12 +19,3 @@ add_object_library(
   DEPENDS
     libc.src.__support.time.${LIBC_TARGET_OS}.clock_gettime
 )
-
-add_header_library(
-  units
-  HDRS
-    units.h
-  DEPENDS
-    libc.src.__support.common
-    libc.hdr.types.time_t
-)
diff --git a/libc/src/__support/time/gpu/CMakeLists.txt b/libc/src/__support/time/gpu/CMakeLists.txt
new file mode 100644
index 00000000000000..efa6cd32454cc0
--- /dev/null
+++ b/libc/src/__support/time/gpu/CMakeLists.txt
@@ -0,0 +1,22 @@
+add_object_library(
+  time_utils
+  SRCS
+    time_utils.cpp
+  HDRS
+    time_utils.h
+  DEPENDS
+    libc.hdr.types.clock_t
+    libc.hdr.time_macros
+)
+
+add_entrypoint_object(
+  clock_gettime
+  SRCS
+    clock_gettime.cpp
+  HDRS
+    ../clock_gettime.h
+  DEPENDS
+    libc.hdr.types.clockid_t
+    libc.hdr.types.struct_timespec
+    .time_utils
+)
diff --git a/libc/src/__support/time/gpu/clock_gettime.cpp b/libc/src/__support/time/gpu/clock_gettime.cpp
new file mode 100644
index 00000000000000..cede72a1f35da4
--- /dev/null
+++ b/libc/src/__support/time/gpu/clock_gettime.cpp
@@ -0,0 +1,33 @@
+//===---------- GPU implementation of the clock_gettime function ----------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+#include "src/time/clock_gettime.h"
+
+#include "src/__support/common.h"
+#include "src/__support/macros/config.h"
+#include "src/__support/time/clock_gettime.h"
+#include "src/__support/time/gpu/time_utils.h"
+
+namespace LIBC_NAMESPACE_DECL {
+namespace internal {
+constexpr uint64_t TICKS_PER_SEC = 1000000000UL;
+
+ErrorOr<int> clock_gettime(clockid_t clockid, timespec *ts) {
+  if (clockid != CLOCK_MONOTONIC || !ts)
+    return cpp::unexpected(-1);
+
+  uint64_t ns_per_tick = TICKS_PER_SEC / GPU_CLOCKS_PER_SEC;
+  uint64_t ticks = gpu::fixed_frequency_clock();
+
+  ts->tv_nsec = (ticks * ns_per_tick) % TICKS_PER_SEC;
+  ts->tv_sec = (ticks * ns_per_tick) / TICKS_PER_SEC;
+
+  return 0;
+}
+} // namespace internal
+} // namespace LIBC_NAMESPACE_DECL
diff --git a/libc/src/time/gpu/time_utils.cpp b/libc/src/__support/time/gpu/time_utils.cpp
similarity index 100%
rename from libc/src/time/gpu/time_utils.cpp
rename to libc/src/__support/time/gpu/time_utils.cpp
diff --git a/libc/src/time/gpu/time_utils.h b/libc/src/__support/time/gpu/time_utils.h
similarity index 100%
rename from libc/src/time/gpu/time_utils.h
rename to libc/src/__support/time/gpu/time_utils.h
diff --git a/libc/src/time/gpu/CMakeLists.txt b/libc/src/time/gpu/CMakeLists.txt
index 8da5d3a22f5a09..31a60595d68ff3 100644
--- a/libc/src/time/gpu/CMakeLists.txt
+++ b/libc/src/time/gpu/CMakeLists.txt
@@ -1,14 +1,3 @@
-add_object_library(
-  time_utils
-  SRCS
-    time_utils.cpp
-  HDRS
-    time_utils.h
-  DEPENDS
-    libc.hdr.types.clock_t
-    libc.hdr.time_macros
-)
-
 add_entrypoint_object(
   clock
   SRCS
@@ -18,7 +7,8 @@ add_entrypoint_object(
   DEPENDS
     libc.include.time
     libc.src.__support.GPU.utils
-    .time_utils
+    libc.src.__support.time.clock_gettime
+    libc.src.__support.time.gpu.time_utils
 )
 
 add_entrypoint_object(
@@ -30,29 +20,31 @@ add_entrypoint_object(
   DEPENDS
     libc.include.time
     libc.src.__support.GPU.utils
-    .time_utils
+    libc.src.__support.time.gpu.time_utils
 )
 
 add_entrypoint_object(
-  clock_gettime
+  timespec_get
   SRCS
-    clock_gettime.cpp
+    timespec_get.cpp
   HDRS
-    ../clock_gettime.h
+    ../timespec_get.h
   DEPENDS
-    libc.hdr.types.clockid_t
+    libc.hdr.time_macros
     libc.hdr.types.struct_timespec
-    .time_utils
+    libc.src.__support.time.gpu.time_utils
 )
 
 add_entrypoint_object(
-  timespec_get
+  clock_gettime
   SRCS
-    timespec_get.cpp
+    clock_gettime.cpp
   HDRS
-    ../timespec_get.h
+    ../clock_gettime.h
   DEPENDS
     libc.hdr.time_macros
+    libc.hdr.types.clockid_t
     libc.hdr.types.struct_timespec
-    .time_utils
+    libc.src.__support.time.gpu.time_utils
+    libc.src.__support.time.clock_gettime
 )
diff --git a/libc/src/time/gpu/clock.cpp b/libc/src/time/gpu/clock.cpp
index 4cdb1d505aed2b..add5b2725ef8f0 100644
--- a/libc/src/time/gpu/clock.cpp
+++ b/libc/src/time/gpu/clock.cpp
@@ -8,7 +8,7 @@
 
 #include "src/time/clock.h"
 #include "src/__support/macros/config.h"
-#include "src/time/gpu/time_utils.h"
+#include "src/__support/time/gpu/time_utils.h"
 
 namespace LIBC_NAMESPACE_DECL {
 
diff --git a/libc/src/time/gpu/clock_gettime.cpp b/libc/src/time/gpu/clock_gettime.cpp
index de7899a2a17cc0..81547ef7f1ca68 100644
--- a/libc/src/time/gpu/clock_gettime.cpp
+++ b/libc/src/time/gpu/clock_gettime.cpp
@@ -10,23 +10,16 @@
 
 #include "src/__support/common.h"
 #include "src/__support/macros/config.h"
-#include "time_utils.h"
+#include "src/__support/time/clock_gettime.h"
+#include "src/__support/time/gpu/time_utils.h"
 
 namespace LIBC_NAMESPACE_DECL {
 
-constexpr uint64_t TICKS_PER_SEC = 1000000000UL;
-
 LLVM_LIBC_FUNCTION(int, clock_gettime, (clockid_t clockid, timespec *ts)) {
-  if (clockid != CLOCK_MONOTONIC || !ts)
-    return -1;
-
-  uint64_t ns_per_tick = TICKS_PER_SEC / GPU_CLOCKS_PER_SEC;
-  uint64_t ticks = gpu::fixed_frequency_clock();
-
-  ts->tv_nsec = (ticks * ns_per_tick) % TICKS_PER_SEC;
-  ts->tv_sec = (ticks * ns_per_tick) / TICKS_PER_SEC;
-
-  return 0;
+  ErrorOr<int> result = internal::clock_gettime(clockid, ts);
+  if (result)
+    return result.value();
+  return result.error();
 }
 
 } // namespace LIBC_NAMESPACE_DECL
diff --git a/libc/src/time/gpu/nanosleep.cpp b/libc/src/time/gpu/nanosleep.cpp
index 3f4a609dd40eba..25a22d5703fa78 100644
--- a/libc/src/time/gpu/nanosleep.cpp
+++ b/libc/src/time/gpu/nanosleep.cpp
@@ -9,7 +9,7 @@
 #include "src/time/nanosleep.h"
 
 #include "src/__support/macros/config.h"
-#include "time_utils.h"
+#include "src/__support/time/gpu/time_utils.h"
 
 namespace LIBC_NAMESPACE_DECL {
 

>From ea35f2a0cdc3b02d3299e49204d7b7fdd58a5456 Mon Sep 17 00:00:00 2001
From: Schrodinger ZHU Yifan <yifanzhu at rochester.edu>
Date: Thu, 5 Dec 2024 17:14:15 -0500
Subject: [PATCH 3/3] fix

---
 libc/src/__support/time/gpu/CMakeLists.txt | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/libc/src/__support/time/gpu/CMakeLists.txt b/libc/src/__support/time/gpu/CMakeLists.txt
index efa6cd32454cc0..fc465e0cea25ff 100644
--- a/libc/src/__support/time/gpu/CMakeLists.txt
+++ b/libc/src/__support/time/gpu/CMakeLists.txt
@@ -9,7 +9,7 @@ add_object_library(
     libc.hdr.time_macros
 )
 
-add_entrypoint_object(
+add_object_library(
   clock_gettime
   SRCS
     clock_gettime.cpp



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