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.

1 files changed, 14 insertions, 17 deletions

diff --git a/gdb/maint.c b/gdb/maint.c
index 738571c..b43dbf9 100644
--- a/gdb/maint.c
+++ b/gdb/maint.c
@@ -24,8 +24,6 @@
 #include "arch-utils.h"
 #include <ctype.h>
 #include <signal.h>
-#include "gdb_sys_time.h"
-#include <time.h>
 #include "command.h"
 #include "gdbcmd.h"
 #include "symtab.h"
@@ -39,7 +37,6 @@
 #include "objfiles.h"
 #include "value.h"
 #include "top.h"
-#include "timeval-utils.h"
 #include "maint.h"
 #include "selftest.h"
 
@@ -822,23 +819,21 @@ scoped_command_stats::~scoped_command_stats ()
 
   if (m_time_enabled && per_command_time)
     {
-      long cmd_time = get_run_time () - m_start_cpu_time;
-      struct timeval now_wall_time, delta_wall_time, wait_time;
+      using namespace std::chrono;
 
-      gettimeofday (&now_wall_time, NULL);
-      timeval_sub (&delta_wall_time,
-		   &now_wall_time, &m_start_wall_time);
+      run_time_clock::duration cmd_time
+	= run_time_clock::now () - m_start_cpu_time;
 
+      steady_clock::duration wall_time
+	= steady_clock::now () - m_start_wall_time;
       /* Subtract time spend in prompt_for_continue from walltime.  */
-      wait_time = get_prompt_for_continue_wait_time ();
-      timeval_sub (&delta_wall_time, &delta_wall_time, &wait_time);
+      wall_time -= get_prompt_for_continue_wait_time ();
 
       printf_unfiltered (!m_msg_type
-			 ? _("Startup time: %ld.%06ld (cpu), %ld.%06ld (wall)\n")
-			 : _("Command execution time: %ld.%06ld (cpu), %ld.%06ld (wall)\n"),
-			 cmd_time / 1000000, cmd_time % 1000000,
-			 (long) delta_wall_time.tv_sec,
-			 (long) delta_wall_time.tv_usec);
+			 ? _("Startup time: %.6f (cpu), %.6f (wall)\n")
+			 : _("Command execution time: %.6f (cpu), %.6f (wall)\n"),
+			 duration<double> (cmd_time).count (),
+			 duration<double> (wall_time).count ());
     }
 
   if (m_space_enabled && per_command_space)
@@ -892,8 +887,10 @@ scoped_command_stats::scoped_command_stats (bool msg_type)
 
   if (msg_type == 0 || per_command_time)
     {
-      m_start_cpu_time = get_run_time ();
-      gettimeofday (&m_start_wall_time, NULL);
+      using namespace std::chrono;
+
+      m_start_cpu_time = run_time_clock::now ();
+      m_start_wall_time = steady_clock::now ();
       m_time_enabled = 1;
     }
   else