Use clock_gettime to implement gettimeofday.

Consolidate generic gettimeofday implementation to use clock_gettime.
Linux ports that still provide gettimeofday through vDSO are not
changed.

Remove sysdeps/unix/clock_gettime.c, which implemented clock_gettime
using gettimeofday; new OS ports must provide a real implementation of
clock_gettime.

Rename sysdeps/mach/gettimeofday.c to sysdeps/mach/clock_gettime.c and
convert into an implementation of clock_gettime.  It only supports
CLOCK_REALTIME; Mach does not appear to have any support for monotonic
clocks.  It uses __host_get_time, which provides at best microsecond
resolution.  Hurd is currently using sysdeps/posix/clock_getres.c for
clock_getres; its output for CLOCK_REALTIME is based on
sysconf (_SC_CLK_TCK), and I do not know whether that gives the
correct result.

Unlike settimeofday, there are no known uses of gettimeofday's
vestigial "get time zone" feature that are not bugs.  (The per-process
timezone support in localtime and friends is unrelated, and the
programs that set the kernel's offset between the hardware clock and
UTC do not need to read it back.)  Therefore, this feature is dummied
out.  Henceforth, if gettimeofday's "struct timezone" argument is not
NULL, it will write zeroes to both fields.  Any program that is
actually looking at this data will thus think it is running in UTC,
which is probably more correct than whatever it was doing before.

[__]gettimeofday no longer has any internal callers, so we can now
remove its internal prototype and PLT bypass aliases.  The
__gettimeofday@GLIBC_2.0 export remains, in case it is used by any
third-party code.

It also allows to simplify the arch-specific implementation on x86 and
powerpc to remove the hack to disable the internal route to non iFUNC
variant for internal symbol.

This patch also fixes a missing optimization on aarch64, powerpc, and
x86 where the code used on static build do not use the vDSO.

Checked on x86_64-linux-gnu, i686-linux-gnu, powerpc64le-linux-gnu,
powerpc64-linux-gnu, powerpc-linux-gnu, and aarch64-linux-gnu.

Co-authored-by: Zack Weinberg <zackw@panix.com>
Reviewed-by: Lukasz Majewski <lukma@denx.de>

3 files changed, 36 insertions, 3 deletions

diff --git a/sysdeps/unix/sysv/linux/alpha/gettimeofday.c b/sysdeps/unix/sysv/linux/alpha/gettimeofday.c
new file mode 100644
index 0000000000..262a3c2352
--- /dev/null
+++ b/sysdeps/unix/sysv/linux/alpha/gettimeofday.c
@@ -0,0 +1,22 @@
+/* gettimeofday -- Get the current time of day.  Linux/Alpha/tv64 version.
+   Copyright (C) 2019 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <https://www.gnu.org/licenses/>.  */
+
+/* We can use the generic implementation, but we have to override its
+   default symbol version.  */
+#define VERSION_gettimeofday GLIBC_2.1
+#include <time/gettimeofday.c>
diff --git a/sysdeps/unix/sysv/linux/alpha/osf_gettimeofday.c b/sysdeps/unix/sysv/linux/alpha/osf_gettimeofday.c
index 59fc614523..4698c8a5db 100644
--- a/sysdeps/unix/sysv/linux/alpha/osf_gettimeofday.c
+++ b/sysdeps/unix/sysv/linux/alpha/osf_gettimeofday.c
@@ -20,6 +20,8 @@
 
 #if SHLIB_COMPAT (libc, GLIBC_2_0, GLIBC_2_1)
 
+#include <string.h>
+#include <time.h>
 #include <sys/time.h>
 #include <tv32-compat.h>
 
@@ -30,10 +32,13 @@ int
 attribute_compat_text_section
 __gettimeofday_tv32 (struct timeval32 *restrict tv32, void *restrict tz)
 {
-  struct timeval tv;
-  __gettimeofday (&tv, tz);
+  if (__glibc_unlikely (tz != 0))
+    memset (tz, 0, sizeof (struct timezone));
 
-  *tv32 = valid_timeval64_to_timeval (tv);
+  struct timespec ts;
+  __clock_gettime (CLOCK_REALTIME, &ts);
+
+  *tv32 = valid_timespec_to_timeval32 (ts);
   return 0;
 }
 
diff --git a/sysdeps/unix/sysv/linux/alpha/tv32-compat.h b/sysdeps/unix/sysv/linux/alpha/tv32-compat.h
index 5f86e66e08..0fbf284bb5 100644
--- a/sysdeps/unix/sysv/linux/alpha/tv32-compat.h
+++ b/sysdeps/unix/sysv/linux/alpha/tv32-compat.h
@@ -89,6 +89,12 @@ valid_timeval32_to_timespec (const struct timeval32 tv)
   return (struct timespec) { tv.tv_sec, tv.tv_usec * 1000 };
 }
 
+static inline struct timeval32
+valid_timespec_to_timeval32 (const struct timespec ts)
+{
+  return (struct timeval32) { (time_t) ts.tv_sec, ts.tv_nsec / 1000 };
+}
+
 static inline void
 rusage64_to_rusage32 (struct rusage32 *restrict r32,
                       const struct rusage *restrict r64)