gdb: Use C++11 std::chrono

This patch fixes a few problems with GDB's time handling.

#1 - It avoids problems with gnulib's C++ namespace support

On MinGW, the struct timeval that should be passed to gnulib's
gettimeofday replacement is incompatible with libiberty's
timeval_sub/timeval_add.  That's because gnulib also replaces "struct
timeval" with its own definition, while libiberty expects the
system's.

E.g., in code like this:

  gettimeofday (&prompt_ended, NULL);
  timeval_sub (&prompt_delta, &prompt_ended, &prompt_started);
  timeval_add (&prompt_for_continue_wait_time,
               &prompt_for_continue_wait_time, &prompt_delta);

That's currently handled in gdb by not using gnulib's gettimeofday at
all (see common/gdb_sys_time.h), but that #undef hack won't work with
if/when we enable gnulib's C++ namespace support, because that mode
adds compile time warnings for uses of ::gettimeofday, which are hard
errors with -Werror.

#2 - But there's an elephant in the room: gettimeofday is not monotonic...

We're using it to:

  a) check how long functions take, for performance analysis
  b) compute when in the future to fire events in the event-loop
  c) print debug timestamps

But that's exactly what gettimeofday is NOT meant for.  Straight from
the man page:

~~~
       The time returned by gettimeofday() is affected by
       discontinuous jumps in the system time (e.g., if the system
       administrator manually changes the system time).  If you need a
       monotonically increasing clock, see clock_gettime(2).
~~~

std::chrono (part of the C++11 standard library) has a monotonic clock
exactly for such purposes (std::chrono::steady_clock).  This commit
switches to use that instead of gettimeofday, fixing all the issues
mentioned above.

gdb/ChangeLog:
2016-11-23  Pedro Alves  <palves@redhat.com>

	* Makefile.in (SFILES): Add common/run-time-clock.c.
	(HFILES_NO_SRCDIR): Add common/run-time-clock.h.
	(COMMON_OBS): Add run-time-clock.o.
	* common/run-time-clock.c, common/run-time-clock.h: New files.
	* defs.h (struct timeval, print_transfer_performance): Delete
	declarations.
	* event-loop.c (struct gdb_timer) <when>: Now a
	std::chrono::steady_clock::time_point.
	(create_timer): use std::chrono::steady_clock instead of
	gettimeofday.  Use new instead of malloc.
	(delete_timer): Use delete instead of xfree.
	(duration_cast_timeval): New.
	(update_wait_timeout): Use std::chrono::steady_clock instead of
	gettimeofday.
	* maint.c: Include <chrono> instead of "gdb_sys_time.h", <time.h>
	and "timeval-utils.h".
	(scoped_command_stats::~scoped_command_stats)
	(scoped_command_stats::scoped_command_stats): Use
	std::chrono::steady_clock instead of gettimeofday.  Use
	user_cpu_time_clock instead of get_run_time.
	* maint.h: Include "run-time-clock.h" and <chrono>.
	(scoped_command_stats): <m_start_cpu_time>: Now a
	user_cpu_time_clock::time_point.
	<m_start_wall_time>: Now a std::chrono::steady_clock::time_point.
	* mi/mi-main.c: Include "run-time-clock.h" and <chrono> instead of
	"gdb_sys_time.h" and <sys/resource.h>.
	(rusage): Delete.
	(mi_execute_command): Use new instead of XNEW.
	(mi_load_progress): Use std::chrono::steady_clock instead of
	gettimeofday.
	(timestamp): Rewrite in terms of std::chrono::steady_clock,
	user_cpu_time_clock and system_cpu_time_clock.
	(timeval_diff): Delete.
	(print_diff): Adjust to use std::chrono::steady_clock,
	user_cpu_time_clock and system_cpu_time_clock.
	* mi/mi-parse.h: Include "run-time-clock.h" and <chrono> instead
	of "gdb_sys_time.h".
	(struct mi_timestamp): Change fields types to
	std::chrono::steady_clock::time_point, user_cpu_time_clock::time
	and system_cpu_time_clock::time_point, instead of struct timeval.
	* symfile.c: Include <chrono> instead of <time.h> and
	"gdb_sys_time.h".
	(struct time_range): New.
	(generic_load): Use std::chrono::steady_clock instead of
	gettimeofday.
	(print_transfer_performance): Replace timeval parameters with a
	std::chrono::steady_clock::duration parameter.  Adjust.
	* utils.c: Include <chrono> instead of "timeval-utils.h",
	"gdb_sys_time.h", and <time.h>.
	(prompt_for_continue_wait_time): Now a
	std::chrono::steady_clock::duration.
	(defaulted_query, prompt_for_continue): Use
	std::chrono::steady_clock instead of
	gettimeofday/timeval_sub/timeval_add.
	(reset_prompt_for_continue_wait_time): Use
	std::chrono::steady_clock::duration instead of struct timeval.
	(get_prompt_for_continue_wait_time): Return a
	std::chrono::steady_clock::duration instead of struct timeval.
	(vfprintf_unfiltered): Use std::chrono::steady_clock instead of
	gettimeofday.  Use std::string.  Use '.' instead of ':'.
	* utils.h: Include <chrono>.
	(get_prompt_for_continue_wait_time): Return a
	std::chrono::steady_clock::duration instead of struct timeval.

gdb/gdbserver/ChangeLog:
2016-11-23  Pedro Alves  <palves@redhat.com>

	* debug.c: Include <chrono> instead of "gdb_sys_time.h".
	(debug_vprintf): Use std::chrono::steady_clock instead of
	gettimeofday.  Use '.' instead of ':'.
	* tracepoint.c: Include <chrono> instead of "gdb_sys_time.h".
	(get_timestamp): Use std::chrono::steady_clock instead of
	gettimeofday.

2 files changed, 133 insertions, 0 deletions

diff --git a/gdb/common/run-time-clock.c b/gdb/common/run-time-clock.c
new file mode 100644
index 0000000..f9dc7a0
--- /dev/null
+++ b/gdb/common/run-time-clock.c
@@ -0,0 +1,58 @@
+/* User/system CPU time clocks that follow the std::chrono interface.
+   Copyright (C) 2016 Free Software Foundation, Inc.
+
+   This file is part of GDB.
+
+   This program is free software; you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; either version 3 of the License, or
+   (at your option) any later version.
+
+   This program 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 General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
+
+#include "common-defs.h"
+#include "run-time-clock.h"
+#if defined HAVE_SYS_RESOURCE_H
+#include <sys/resource.h>
+#endif
+
+using namespace std::chrono;
+
+run_time_clock::time_point
+run_time_clock::now () noexcept
+{
+  return time_point (microseconds (get_run_time ()));
+}
+
+#ifdef HAVE_GETRUSAGE
+static std::chrono::microseconds
+timeval_to_microseconds (struct timeval *tv)
+{
+  return (seconds (tv->tv_sec) + microseconds (tv->tv_usec));
+}
+#endif
+
+void
+run_time_clock::now (user_cpu_time_clock::time_point &user,
+		     system_cpu_time_clock::time_point &system) noexcept
+{
+#ifdef HAVE_GETRUSAGE
+  struct rusage rusage;
+
+  getrusage (RUSAGE_SELF, &rusage);
+
+  microseconds utime = timeval_to_microseconds (&rusage.ru_utime);
+  microseconds stime = timeval_to_microseconds (&rusage.ru_stime);
+  user = user_cpu_time_clock::time_point (utime);
+  system = system_cpu_time_clock::time_point (stime);
+#else
+  user = user_cpu_time_clock::time_point (microseconds (get_run_time ()));
+  system = system_cpu_time_clock::time_point (microseconds::zero ());
+#endif
+}
diff --git a/gdb/common/run-time-clock.h b/gdb/common/run-time-clock.h
new file mode 100644
index 0000000..ee531bb
--- /dev/null
+++ b/gdb/common/run-time-clock.h
@@ -0,0 +1,75 @@
+/* User/system CPU time clocks that follow the std::chrono interface.
+   Copyright (C) 2016 Free Software Foundation, Inc.
+
+   This file is part of GDB.
+
+   This program is free software; you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; either version 3 of the License, or
+   (at your option) any later version.
+
+   This program 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 General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
+
+#ifndef RUN_TIME_CLOCK_H
+#define RUN_TIME_CLOCK_H
+
+#include <chrono>
+
+/* Count the total amount of time spent executing in user mode.  */
+
+struct user_cpu_time_clock
+{
+  using duration = std::chrono::microseconds;
+  using rep = duration::rep;
+  using period = duration::period;
+  using time_point = std::chrono::time_point<user_cpu_time_clock>;
+
+  static constexpr bool is_steady = true;
+
+  /* Use run_time_clock::now instead.  */
+  static time_point now () noexcept = delete;
+};
+
+/* Count the total amount of time spent executing in kernel mode.  */
+
+struct system_cpu_time_clock
+{
+  using duration = std::chrono::microseconds;
+  using rep = duration::rep;
+  using period = duration::period;
+  using time_point = std::chrono::time_point<system_cpu_time_clock>;
+
+  static constexpr bool is_steady = true;
+
+  /* Use run_time_clock::now instead.  */
+  static time_point now () noexcept = delete;
+};
+
+/* Count the total amount of time spent executing in userspace+kernel
+   mode.  */
+
+struct run_time_clock
+{
+  using duration = std::chrono::microseconds;
+  using rep = duration::rep;
+  using period = duration::period;
+  using time_point = std::chrono::time_point<run_time_clock>;
+
+  static constexpr bool is_steady = true;
+
+  static time_point now () noexcept;
+
+  /* Return the user/system time as separate time points, if
+     supported.  If not supported, then the combined user+kernel time
+     is returned in USER and SYSTEM is set to zero.  */
+  static void now (user_cpu_time_clock::time_point &user,
+		   system_cpu_time_clock::time_point &system) noexcept;
+};
+
+#endif