[libc] implement clock_gettime using vDSO (#108458)

supersedes #91805

Author: SchrodingerZhu

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

@@ -9,6 +9,7 @@ add_header_library(
     libc.src.__support.common
     libc.src.__support.error_or
     libc.src.__support.OSUtil.osutil
+    libc.src.__support.OSUtil.vdso
 )
 
 add_header_library(

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

@@ -11,26 +11,47 @@
 
 #include "hdr/types/clockid_t.h"
 #include "hdr/types/struct_timespec.h"
+#include "src/__support/OSUtil/linux/vdso.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_gettime64)
+#include <linux/time_types.h>
+#endif
+
 namespace LIBC_NAMESPACE_DECL {
 namespace internal {
 LIBC_INLINE ErrorOr<int> clock_gettime(clockid_t clockid, timespec *ts) {
-#if SYS_clock_gettime
-  int ret = LIBC_NAMESPACE::syscall_impl<int>(SYS_clock_gettime,
-                                              static_cast<long>(clockid),
-                                              reinterpret_cast<long>(ts));
+  using namespace vdso;
+  int ret;
+#if defined(SYS_clock_gettime)
+  TypedSymbol<VDSOSym::ClockGetTime> clock_gettime;
+  if (LIBC_LIKELY(clock_gettime != nullptr))
+    ret = clock_gettime(clockid, ts);
+  else
+    ret = LIBC_NAMESPACE::syscall_impl<int>(SYS_clock_gettime,
+                                            static_cast<long>(clockid),
+                                            reinterpret_cast<long>(ts));
 #elif defined(SYS_clock_gettime64)
   static_assert(
       sizeof(time_t) == sizeof(int64_t),
       "SYS_clock_gettime64 requires struct timespec with 64-bit members.");
-  int ret = LIBC_NAMESPACE::syscall_impl<int>(SYS_clock_gettime64,
-                                              static_cast<long>(clockid),
-                                              reinterpret_cast<long>(ts));
+
+  TypedSymbol<VDSOSym::ClockGetTime64> clock_gettime64;
+  __kernel_timespec ts64{};
+  if (LIBC_LIKELY(clock_gettime64 != nullptr))
+    ret = clock_gettime64(clockid, &ts64);
+  else
+    ret = LIBC_NAMESPACE::syscall_impl<int>(SYS_clock_gettime64,
+                                            static_cast<long>(clockid),
+                                            reinterpret_cast<long>(&ts64));
+  if (ret == 0) {
+    ts->tv_sec = static_cast<decltype(ts->tv_sec)>(ts64.tv_sec);
+    ts->tv_nsec = static_cast<decltype(ts->tv_nsec)>(ts64.tv_nsec);
+  }
 #else
 #error "SYS_clock_gettime and SYS_clock_gettime64 syscalls not available."
 #endif