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, 22 insertions, 17 deletions

diff --git a/gdb/symfile.c b/gdb/symfile.c
index f524f56..517c277 100644
--- a/gdb/symfile.c
+++ b/gdb/symfile.c
@@ -61,8 +61,7 @@
 #include <fcntl.h>
 #include <sys/stat.h>
 #include <ctype.h>
-#include <time.h>
-#include "gdb_sys_time.h"
+#include <chrono>
 
 #include "psymtab.h"
 
@@ -2066,11 +2065,15 @@ clear_memory_write_data (void *arg)
   VEC_free (memory_write_request_s, vec);
 }
 
+static void print_transfer_performance (struct ui_file *stream,
+					unsigned long data_count,
+					unsigned long write_count,
+				        std::chrono::steady_clock::duration d);
+
 void
 generic_load (const char *args, int from_tty)
 {
   bfd *loadfile_bfd;
-  struct timeval start_time, end_time;
   char *filename;
   struct cleanup *old_cleanups = make_cleanup (null_cleanup, 0);
   struct load_section_data cbdata;
@@ -2131,13 +2134,15 @@ generic_load (const char *args, int from_tty)
 
   bfd_map_over_sections (loadfile_bfd, load_section_callback, &cbdata);
 
-  gettimeofday (&start_time, NULL);
+  using namespace std::chrono;
+
+  steady_clock::time_point start_time = steady_clock::now ();
 
   if (target_write_memory_blocks (cbdata.requests, flash_discard,
 				  load_progress) != 0)
     error (_("Load failed"));
 
-  gettimeofday (&end_time, NULL);
+  steady_clock::time_point end_time = steady_clock::now ();
 
   entry = bfd_get_start_address (loadfile_bfd);
   entry = gdbarch_addr_bits_remove (target_gdbarch (), entry);
@@ -2160,32 +2165,32 @@ generic_load (const char *args, int from_tty)
 
   print_transfer_performance (gdb_stdout, total_progress.data_count,
 			      total_progress.write_count,
-			      &start_time, &end_time);
+			      end_time - start_time);
 
   do_cleanups (old_cleanups);
 }
 
-/* Report how fast the transfer went.  */
+/* Report on STREAM the performance of a memory transfer operation,
+   such as 'load'.  DATA_COUNT is the number of bytes transferred.
+   WRITE_COUNT is the number of separate write operations, or 0, if
+   that information is not available.  TIME is how long the operation
+   lasted.  */
 
-void
+static void
 print_transfer_performance (struct ui_file *stream,
 			    unsigned long data_count,
 			    unsigned long write_count,
-			    const struct timeval *start_time,
-			    const struct timeval *end_time)
+			    std::chrono::steady_clock::duration time)
 {
-  ULONGEST time_count;
+  using namespace std::chrono;
   struct ui_out *uiout = current_uiout;
 
-  /* Compute the elapsed time in milliseconds, as a tradeoff between
-     accuracy and overflow.  */
-  time_count = (end_time->tv_sec - start_time->tv_sec) * 1000;
-  time_count += (end_time->tv_usec - start_time->tv_usec) / 1000;
+  milliseconds ms = duration_cast<milliseconds> (time);
 
   ui_out_text (uiout, "Transfer rate: ");
-  if (time_count > 0)
+  if (ms.count () > 0)
     {
-      unsigned long rate = ((ULONGEST) data_count * 1000) / time_count;
+      unsigned long rate = ((ULONGEST) data_count * 1000) / ms.count ();
 
       if (ui_out_is_mi_like_p (uiout))
 	{