Fix PR threads/19422 - show which thread caused stop

This commit changes GDB like this:

 - Program received signal SIGINT, Interrupt.
 + Thread 1 "main" received signal SIGINT, Interrupt.

 - Breakpoint 1 at 0x40087a: file threads.c, line 87.
 + Thread 3 "bar" hit Breakpoint 1 at 0x40087a: file threads.c, line 87.

 ... once the program goes multi-threaded.  Until GDB sees a second
thread spawn, the output is still the same as before, per the
discussion back in 2012:

  https://www.sourceware.org/ml/gdb/2012-11/msg00010.html

This helps non-stop mode, where you can't easily tell which thread hit
a breakpoint or received a signal:

 (gdb) info threads
   Id   Target Id         Frame
 * 1    Thread 0x7ffff7fc1740 (LWP 19362) "main" (running)
   2    Thread 0x7ffff7fc0700 (LWP 19366) "foo" (running)
   3    Thread 0x7ffff77bf700 (LWP 19367) "bar" (running)
 (gdb)
 Program received signal SIGUSR1, User defined signal 1.
 0x0000003616a09237 in pthread_join (threadid=140737353877248, thread_return=0x7fffffffd5b8) at pthread_join.c:92
 92          lll_wait_tid (pd->tid);
 (gdb) b threads.c:87
 Breakpoint 1 at 0x40087a: file threads.c, line 87.
 (gdb)
 Breakpoint 1, thread_function1 (arg=0x1) at threads.c:87
 87              usleep (1);  /* Loop increment.  */

The best the user can do is run "info threads" and try to figure
things out.

It actually also affects all-stop mode, in case of "handle SIG print
nostop":

...
  Program received signal SIGUSR1, User defined signal 1.

  Program received signal SIGUSR1, User defined signal 1.

  Program received signal SIGUSR1, User defined signal 1.

  Program received signal SIGUSR1, User defined signal 1.
...

The above doesn't give any clue that these were different threads
getting the SIGUSR1 signal.

I initially thought of lowercasing "breakpoint" in

  "Thread 3 hit Breakpoint 1"

but then after trying it I realized that leaving "Breakpoint"
uppercase helps the eye quickly find the relevant information.  It's
also easier to implement not showing anything about threads until the
program goes multi-threaded this way.

Here's a larger example session in non-stop mode:

  (gdb) c -a&
  Continuing.
  (gdb) interrupt -a
  (gdb)
  Thread 1 "main" stopped.
  0x0000003616a09237 in pthread_join (threadid=140737353877248, thread_return=0x7fffffffd5b8) at pthread_join.c:92
  92          lll_wait_tid (pd->tid);

  Thread 2 "foo" stopped.
  0x0000003615ebc6ed in nanosleep () at ../sysdeps/unix/syscall-template.S:81
  81      T_PSEUDO (SYSCALL_SYMBOL, SYSCALL_NAME, SYSCALL_NARGS)

  Thread 3 "bar" stopped.
  0x0000003615ebc6ed in nanosleep () at ../sysdeps/unix/syscall-template.S:81
  81      T_PSEUDO (SYSCALL_SYMBOL, SYSCALL_NAME, SYSCALL_NARGS)
  b threads.c:87
  Breakpoint 4 at 0x40087a: file threads.c, line 87.
  (gdb) b threads.c:67
  Breakpoint 5 at 0x400811: file threads.c, line 67.
  (gdb) c -a&
  Continuing.
  (gdb)
  Thread 3 "bar" hit Breakpoint 4, thread_function1 (arg=0x1) at threads.c:87
  87              usleep (1);  /* Loop increment.  */

  Thread 2 "foo" hit Breakpoint 5, thread_function0 (arg=0x0) at threads.c:68
  68              (*myp) ++;
  info threads
    Id   Target Id         Frame
  * 1  Thread 0x7ffff7fc1740 (LWP 31957) "main" (running)
    2  Thread 0x7ffff7fc0700 (LWP 31961) "foo" thread_function0 (arg=0x0) at threads.c:68
    3  Thread 0x7ffff77bf700 (LWP 31962) "bar" thread_function1 (arg=0x1) at threads.c:87
  (gdb) shell kill -SIGINT 31957
  (gdb)
  Thread 1 "main" received signal SIGINT, Interrupt.
  0x0000003616a09237 in pthread_join (threadid=140737353877248, thread_return=0x7fffffffd5b8) at pthread_join.c:92
  92          lll_wait_tid (pd->tid);
  info threads
    Id   Target Id         Frame
  * 1  Thread 0x7ffff7fc1740 (LWP 31957) "main" 0x0000003616a09237 in pthread_join (threadid=140737353877248, thread_return=0x7fffffffd5b8) at pthread_join.c:92
    2  Thread 0x7ffff7fc0700 (LWP 31961) "foo" thread_function0 (arg=0x0) at threads.c:68
    3  Thread 0x7ffff77bf700 (LWP 31962) "bar" thread_function1 (arg=0x1) at threads.c:87
  (gdb) t 2
  [Switching to thread 2, Thread 0x7ffff7fc0700 (LWP 31961)]
  #0  thread_function0 (arg=0x0) at threads.c:68
  68              (*myp) ++;
  (gdb) catch syscall
  Catchpoint 6 (any syscall)
  (gdb) c&
  Continuing.
  (gdb)
  Thread 2 "foo" hit Catchpoint 6 (call to syscall nanosleep), 0x0000003615ebc6ed in nanosleep () at ../sysdeps/unix/syscall-template.S:81
  81      T_PSEUDO (SYSCALL_SYMBOL, SYSCALL_NAME, SYSCALL_NARGS)

I'll work on documentation next if this looks agreeable.

This patch applies on top of the star wildcards thread IDs series:

  https://sourceware.org/ml/gdb-patches/2016-01/msg00291.html

For convenience, I've pushed this to the
users/palves/show-which-thread-caused-stop branch.

gdb/doc/ChangeLog:
2016-01-18  Pedro Alves  <palves@redhat.com>

	* gdb.texinfo (Threads): Mention that GDB displays the ID and name
	of the thread that hit a breakpoint or received a signal.

gdb/ChangeLog:
2016-01-18  Pedro Alves  <palves@redhat.com>

	* NEWS: Mention that GDB now displays the ID and name of the
	thread that hit a breakpoint or received a signal.
	* break-catch-sig.c (signal_catchpoint_print_it): Use
	maybe_print_thread_hit_breakpoint.
	* break-catch-syscall.c (print_it_catch_syscall): Likewise.
	* break-catch-throw.c (print_it_exception_catchpoint): Likewise.
	* breakpoint.c (maybe_print_thread_hit_breakpoint): New function.
	(print_it_catch_fork, print_it_catch_vfork, print_it_catch_solib)
	(print_it_catch_exec, print_it_ranged_breakpoint)
	(print_it_watchpoint, print_it_masked_watchpoint, bkpt_print_it):
	Use maybe_print_thread_hit_breakpoint.
	* breakpoint.h (maybe_print_thread_hit_breakpoint): Declare.
	* gdbthread.h (show_thread_that_caused_stop): Declare.
	* infrun.c (print_signal_received_reason): Print which thread
	received signal.
	* thread.c (show_thread_that_caused_stop): New function.

gdb/testsuite/ChangeLog:
2016-01-18  Pedro Alves  <palves@redhat.com>

	* gdb.base/async-shell.exp: Adjust expected output.
	* gdb.base/dprintf-non-stop.exp: Adjust expected output.
	* gdb.base/siginfo-thread.exp: Adjust expected output.
	* gdb.base/watchpoint-hw-hit-once.exp: Adjust expected output.
	* gdb.java/jnpe.exp: Adjust expected output.
	* gdb.threads/clone-new-thread-event.exp: Adjust expected output.
	* gdb.threads/continue-pending-status.exp: Adjust expected output.
	* gdb.threads/leader-exit.exp: Adjust expected output.
	* gdb.threads/manythreads.exp: Adjust expected output.
	* gdb.threads/pthreads.exp: Adjust expected output.
	* gdb.threads/schedlock.exp: Adjust expected output.
	* gdb.threads/siginfo-threads.exp: Adjust expected output.
	* gdb.threads/signal-command-multiple-signals-pending.exp: Adjust
	expected output.
	* gdb.threads/signal-delivered-right-thread.exp: Adjust expected
	output.
	* gdb.threads/sigthread.exp: Adjust expected output.
	* gdb.threads/watchpoint-fork.exp: Adjust expected output.

1 files changed, 5 insertions, 0 deletions

diff --git a/gdb/gdbthread.h b/gdb/gdbthread.h
index 37c2837b20..bdd2bb0d49 100644
--- a/gdb/gdbthread.h
+++ b/gdb/gdbthread.h
@@ -630,6 +630,11 @@ extern void thread_cancel_execution_command (struct thread_info *thr);
    executing).  */
 extern void validate_registers_access (void);
 
+/* Returns whether to show which thread hit the breakpoint, received a
+   signal, etc. and ended up causing a user-visible stop.  This is
+   true iff we ever detected multiple threads.  */
+extern int show_thread_that_caused_stop (void);
+
 extern struct thread_info *thread_list;
 
 #endif /* GDBTHREAD_H */