[libc][POSIX] Add clock_settime() function for Linux (#161729)

Closes #161461
- This is my first time contributing to libc's POSIX, so for reference I
used `clock_gettime` implementation for Linux. For convenience, here is
the description of `clock_settime` function
[behavior](https://www.man7.org/linux/man-pages/man3/clock_settime.3.html)

Author: amemov

libc/config/linux/aarch64/entrypoints.txt

@@ -1144,6 +1144,7 @@ if(LLVM_LIBC_FULL_BUILD)
     libc.src.time.ctime_r
     libc.src.time.clock
     libc.src.time.clock_gettime
+    libc.src.time.clock_settime
     libc.src.time.difftime
     libc.src.time.gettimeofday
     libc.src.time.gmtime

libc/config/linux/riscv/entrypoints.txt

@@ -1273,6 +1273,7 @@ if(LLVM_LIBC_FULL_BUILD)
     libc.src.time.ctime_r
     libc.src.time.clock
     libc.src.time.clock_gettime
+    libc.src.time.clock_settime
     libc.src.time.difftime
     libc.src.time.gettimeofday
     libc.src.time.gmtime

libc/config/linux/x86_64/entrypoints.txt

@@ -1314,6 +1314,7 @@ if(LLVM_LIBC_FULL_BUILD)
     libc.src.time.ctime_r
     libc.src.time.clock
     libc.src.time.clock_gettime
+    libc.src.time.clock_settime
     libc.src.time.difftime
     libc.src.time.gettimeofday
     libc.src.time.gmtime

libc/docs/headers/time.rst

@@ -67,11 +67,11 @@ Implementation Status
 +---------------------+---------+---------+---------+-----------------+---------+---------+---------+---------+---------+---------+---------+---------+---------+
 | clock_getres        |         |         |         |                 |         |         |         |         |         |         |         |         |         |
 +---------------------+---------+---------+---------+-----------------+---------+---------+---------+---------+---------+---------+---------+---------+---------+
-| clock_gettime       | |check| | |check| |         |     |check|     |         |         |         |         |         |         |         |         |         |
+| clock_gettime       | |check| | |check| |         |     |check|     |         |         |         |         |         |         |         | |check| | |check| |
 +---------------------+---------+---------+---------+-----------------+---------+---------+---------+---------+---------+---------+---------+---------+---------+
 | clock_nanosleep     |         |         |         |                 |         |         |         |         |         |         |         |         |         |
 +---------------------+---------+---------+---------+-----------------+---------+---------+---------+---------+---------+---------+---------+---------+---------+
-| clock_settime       |         |         |         |                 |         |         |         |         |         |         |         |         |         |
+| clock_settime       | |check| | |check| |         |     |check|     |         |         |         |         |         |         |         |         |         |
 +---------------------+---------+---------+---------+-----------------+---------+---------+---------+---------+---------+---------+---------+---------+---------+
 | ctime               | |check| | |check| |         |     |check|     |         |         |         |         |         |         |         |         |         |
 +---------------------+---------+---------+---------+-----------------+---------+---------+---------+---------+---------+---------+---------+---------+---------+

libc/include/time.yaml

@@ -67,6 +67,13 @@ functions:
     arguments:
       - type: clockid_t
       - type: struct timespec *
+  - name: clock_settime
+    standard:
+      - POSIX
+    return_type: int
+    arguments:
+      - type: clockid_t
+      - type: const struct timespec *
   - name: difftime
     standard:
       - stdc

libc/src/__support/time/CMakeLists.txt

@@ -19,3 +19,12 @@ add_object_library(
   DEPENDS
     libc.src.__support.time.${LIBC_TARGET_OS}.clock_gettime
 )
+
+if(TARGET libc.src.__support.time.${LIBC_TARGET_OS}.clock_settime)  
+  add_object_library(
+    clock_settime
+    ALIAS
+    DEPENDS
+      libc.src.__support.time.${LIBC_TARGET_OS}.clock_settime
+  )
+endif()

libc/src/__support/time/clock_settime.h

@@ -0,0 +1,22 @@
+//===--- clock_settime linux 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
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_LIBC_SRC___SUPPORT_TIME_CLOCK_SETTIME_H
+#define LLVM_LIBC_SRC___SUPPORT_TIME_CLOCK_SETTIME_H
+
+#include "hdr/types/clockid_t.h"
+#include "hdr/types/struct_timespec.h"
+#include "src/__support/error_or.h"
+
+namespace LIBC_NAMESPACE_DECL {
+namespace internal {
+ErrorOr<int> clock_settime(clockid_t clockid, const timespec *ts);
+} // namespace internal
+} // namespace LIBC_NAMESPACE_DECL
+
+#endif // LLVM_LIBC_SRC___SUPPORT_TIME_CLOCK_SETTIME_H

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

@@ -14,6 +14,21 @@ add_object_library(
     libc.src.__support.OSUtil.linux.vdso
 )
 
+add_object_library(
+  clock_settime
+  HDRS
+    ../clock_settime.h
+  SRCS
+    clock_settime.cpp
+  DEPENDS
+    libc.include.sys_syscall
+    libc.hdr.types.struct_timespec
+    libc.hdr.types.clockid_t
+    libc.src.__support.common
+    libc.src.__support.error_or
+    libc.src.__support.OSUtil.osutil
+)
+
 add_header_library(
   clock_conversion
   HDRS

libc/src/__support/time/linux/clock_settime.cpp

@@ -0,0 +1,53 @@
+//===--- clock_settime linux 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 "src/__support/time/clock_settime.h"
+#include "hdr/types/clockid_t.h"
+#include "hdr/types/struct_timespec.h"
+#include "src/__support/OSUtil/syscall.h"
+#include "src/__support/common.h"
+#include "src/__support/error_or.h"
+#include "src/__support/macros/config.h"
+#include <sys/syscall.h>
+
+#if defined(SYS_clock_settime64)
+#include <linux/time_types.h>
+#endif
+
+namespace LIBC_NAMESPACE_DECL {
+namespace internal {
+ErrorOr<int> clock_settime(clockid_t clockid, const timespec *ts) {
+  int ret;
+#if defined(SYS_clock_settime)
+  ret = LIBC_NAMESPACE::syscall_impl<int>(SYS_clock_settime,
+                                          static_cast<long>(clockid),
+                                          reinterpret_cast<long>(ts));
+#elif defined(SYS_clock_settime64)
+  static_assert(
+      sizeof(time_t) == sizeof(int64_t),
+      "SYS_clock_settime64 requires struct timespec with 64-bit members.");
+
+  __kernel_timespec ts64{};
+
+  // Populate the 64-bit kernel structure from the user-provided timespec
+  ts64.tv_sec = static_cast<decltype(ts64.tv_sec)>(ts->tv_sec);
+  ts64.tv_nsec = static_cast<decltype(ts64.tv_nsec)>(ts->tv_nsec);
+
+  ret = LIBC_NAMESPACE::syscall_impl<int>(SYS_clock_settime64,
+                                          static_cast<long>(clockid),
+                                          reinterpret_cast<long>(&ts64));
+#else
+#error "SYS_clock_settime and SYS_clock_settime64 syscalls not available."
+#endif
+  if (ret < 0)
+    return Error(-ret);
+  return ret;
+}
+
+} // namespace internal
+} // namespace LIBC_NAMESPACE_DECL

libc/src/time/CMakeLists.txt

@@ -245,3 +245,11 @@ add_entrypoint_object(
   DEPENDS
     .${LIBC_TARGET_OS}.clock_getres
 )
+
+add_entrypoint_object(
+  clock_settime
+  ALIAS
+  DEPENDS
+    .${LIBC_TARGET_OS}.clock_settime
+)
+