[libc] Implement timespec_get

`timespec_get` is C standard counterpart to POSIX `clock_gettime`. On
Linux we simply use `clock_gettime`. On baremetal we introduce a new
external API `__llvm_libc_time_utc_get` that should be implemented by
the vendor.

Author: petrhosek

libc/config/baremetal/arm/entrypoints.txt

@@ -209,6 +209,7 @@ set(TARGET_LIBC_ENTRYPOINTS
     libc.src.time.gmtime
     libc.src.time.gmtime_r
     libc.src.time.mktime
+    libc.src.time.timespec_get
 
     # internal entrypoints
     libc.startup.baremetal.init

libc/config/baremetal/riscv/entrypoints.txt

@@ -205,6 +205,7 @@ set(TARGET_LIBC_ENTRYPOINTS
     libc.src.time.gmtime
     libc.src.time.gmtime_r
     libc.src.time.mktime
+    libc.src.time.timespec_get
 
     # internal entrypoints
     libc.startup.baremetal.init

libc/config/linux/aarch64/entrypoints.txt

@@ -999,6 +999,7 @@ if(LLVM_LIBC_FULL_BUILD)
     libc.src.time.mktime
     libc.src.time.nanosleep
     libc.src.time.time
+    libc.src.time.timespec_get
 
     # unistd.h entrypoints
     libc.src.unistd.__llvm_libc_syscall

libc/config/linux/riscv/entrypoints.txt

@@ -937,6 +937,7 @@ if(LLVM_LIBC_FULL_BUILD)
     libc.src.time.mktime
     libc.src.time.nanosleep
     libc.src.time.time
+    libc.src.time.timespec_get
 
     # unistd.h entrypoints
     libc.src.unistd.__llvm_libc_syscall

libc/config/linux/x86_64/entrypoints.txt

@@ -1082,6 +1082,7 @@ if(LLVM_LIBC_FULL_BUILD)
     libc.src.time.mktime
     libc.src.time.nanosleep
     libc.src.time.time
+    libc.src.time.timespec_get
 
     # locale.h entrypoints
     libc.src.locale.localeconv

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

@@ -7,4 +7,6 @@
 #include "linux/time-macros.h"
 #endif
 
+#define TIME_UTC 1
+
 #endif // LLVM_LIBC_MACROS_TIME_MACROS_H

libc/newhdrgen/yaml/time.yaml

@@ -96,3 +96,10 @@ functions:
     return_type: time_t
     arguments:
       - type: time_t *
+  - name: timespec_get
+    standard:
+      - stdc
+    return_type: int
+    arguments:
+      - type: struct timespec *
+      - type: int

libc/src/__support/OSUtil/baremetal/CMakeLists.txt

@@ -3,8 +3,10 @@ add_object_library(
   SRCS
     io.cpp
     exit.cpp
+    time.cpp
   HDRS
     io.h
+    time.h
   DEPENDS
     libc.src.__support.common
     libc.src.__support.CPP.string_view

libc/src/__support/OSUtil/baremetal/time.cpp

@@ -0,0 +1,21 @@
+//===---------- Baremetal implementation of time utils ----------*- 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 "time.h"
+
+#include "src/__support/macros/config.h"
+
+namespace LIBC_NAMESPACE_DECL {
+
+extern "C" int __llvm_libc_time_utc_get(struct timespec *ts);
+
+int time_utc_get(struct timespec *ts) {
+  return __llvm_libc_time_utc_get(ts);
+}
+
+} // namespace LIBC_NAMESPACE_DECL

libc/src/__support/OSUtil/baremetal/time.h

@@ -0,0 +1,21 @@
+//===---------- Baremetal implementation of time utils ----------*- 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_OSUTIL_BAREMETAL_TIME_H
+#define LLVM_LIBC_SRC___SUPPORT_OSUTIL_BAREMETAL_TIME_H
+
+#include "include/llvm-libc-types/struct_timespec.h"
+#include "src/__support/macros/config.h"
+
+namespace LIBC_NAMESPACE_DECL {
+
+int time_utc_get(struct timespec *ts);
+
+} // namespace LIBC_NAMESPACE_DECL
+
+#endif // LLVM_LIBC_SRC___SUPPORT_OSUTIL_BAREMETAL_IO_H