[libc] Add clock_gettime for Darwin

This patch adds support for clock_gettime for Darwin. Darwin syscall
'gettimeofday' is used to query the time from the system.

Many headers in llvm-libc-types, namely clockid_t, struct_timespec,
struct_timeval, suseconds_t, time_t_32, time_t_64, are modified to include
header guards as Darwin has its own implementation of primitive types.

Author: bojle

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

@@ -0,0 +1,5 @@
+add_header(
+  time_macros
+  HDR
+    time-macros.h
+)

libc/include/llvm-libc-macros/darwin/time-macros.h

@@ -0,0 +1,14 @@
+//===-- Definition of macros from time.h ---------------------------------===//
+//
+// 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_LINUX_TIME_MACROS_H
+#define LLVM_LIBC_MACROS_LINUX_TIME_MACROS_H
+
+#include <_time.h>
+
+#endif // LLVM_LIBC_MACROS_LINUX_TIME_MACROS_H

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

@@ -7,6 +7,8 @@
 #include "linux/time-macros.h"
 #elif defined(__ELF__)
 #include "baremetal/time-macros.h"
+#elif defined(__APPLE__)
+#include "darwin/time-macros.h"
 #else
 #define CLOCKS_PER_SEC 1000000
 #endif

libc/include/llvm-libc-types/clockid_t.h

@@ -9,6 +9,12 @@
 #ifndef LLVM_LIBC_TYPES_CLOCKID_T_H
 #define LLVM_LIBC_TYPES_CLOCKID_T_H
 
+#if defined(__APPLE__)
+// Darwin provides its own defintion for clockid_t . Use that to prevent
+// redeclaration errors and correctness.
+#include <_time.h>
+#else
 typedef int clockid_t;
+#endif // __APPLE__
 
 #endif // LLVM_LIBC_TYPES_CLOCKID_T_H

libc/include/llvm-libc-types/struct_timespec.h

@@ -9,12 +9,18 @@
 #ifndef LLVM_LIBC_TYPES_STRUCT_TIMESPEC_H
 #define LLVM_LIBC_TYPES_STRUCT_TIMESPEC_H
 
+#if defined(__APPLE__)
+// Darwin provides its own definition for struct timespec. Include it directly
+// to ensure type compatibility and avoid redefinition errors.
+#include <sys/_types/_timespec.h>
+#else
 #include "time_t.h"
 
 struct timespec {
   time_t tv_sec; /* Seconds.  */
   /* TODO: BIG_ENDIAN may require padding. */
   long tv_nsec; /* Nanoseconds.  */
 };
+#endif // __APPLE__
 
 #endif // LLVM_LIBC_TYPES_STRUCT_TIMESPEC_H

libc/include/llvm-libc-types/struct_timeval.h

@@ -12,9 +12,15 @@
 #include "suseconds_t.h"
 #include "time_t.h"
 
+#if defined(__APPLE__)
+// Darwin provides its own definition for struct timeval. Include it directly
+// to ensure type compatibility and avoid redefinition errors.
+#include <sys/_types/_timeval.h>
+#else
 struct timeval {
   time_t tv_sec;       // Seconds
   suseconds_t tv_usec; // Micro seconds
 };
+#endif // __APPLE__
 
 #endif // LLVM_LIBC_TYPES_STRUCT_TIMEVAL_H

libc/include/llvm-libc-types/suseconds_t.h

@@ -14,6 +14,12 @@
 // types...] and suseconds_t are no greater than the width of type long.
 
 // The kernel expects 64 bit suseconds_t at least on x86_64.
+#if defined(__APPLE__)
+// Darwin provides its own definition for suseconds_t. Include it directly
+// to ensure type compatibility and avoid redefinition errors.
+#include <sys/_types/_suseconds_t.h>
+#else
 typedef long suseconds_t;
+#endif // __APPLE__
 
 #endif // LLVM_LIBC_TYPES_SUSECONDS_T_H

libc/include/llvm-libc-types/time_t_32.h

@@ -9,6 +9,12 @@
 #ifndef LLVM_LIBC_TYPES_TIME_T_32_H
 #define LLVM_LIBC_TYPES_TIME_T_32_H
 
+#if defined(__APPLE__)
+// Darwin provides its own definition for time_t. Include it directly
+// to ensure type compatibility and avoid redefinition errors.
+#include <sys/_types/_time_t.h>
+#else
 typedef __INT32_TYPE__ time_t;
+#endif // __APPLE__
 
 #endif // LLVM_LIBC_TYPES_TIME_T_32_H

libc/include/llvm-libc-types/time_t_64.h

@@ -9,6 +9,12 @@
 #ifndef LLVM_LIBC_TYPES_TIME_T_64_H
 #define LLVM_LIBC_TYPES_TIME_T_64_H
 
+#if defined(__APPLE__)
+// Darwin provides its own definition for time_t. Include it directly
+// to ensure type compatibility and avoid redefinition errors.
+#include <sys/_types/_time_t.h>
+#else
 typedef __INT64_TYPE__ time_t;
+#endif // __APPLE__
 
 #endif // LLVM_LIBC_TYPES_TIME_T_64_H

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

@@ -0,0 +1,12 @@
+add_object_library(
+  clock_gettime
+  SRCS
+    clock_gettime.cpp
+  HDRS
+    ../clock_gettime.h
+  DEPENDS
+    libc.src.__support.common
+    libc.src.__support.error_or
+    libc.hdr.types.struct_timeval
+    libc.hdr.types.struct_timespec
+)