record-btrace: indicate gaps

Indicate gaps in the trace due to decode errors.  Internally, a gap is
represented as a btrace function segment without instructions and with a
non-zero format-specific error code.

Show the gap when traversing the instruction or function call history.
Also indicate gaps in "info record".

It looks like this:

  (gdb) info record
  Active record target: record-btrace
  Recording format: Branch Trace Store.
  Buffer size: 64KB.
  Recorded 32 instructions in 5 functions (1 gaps) for thread 1 (process 7182).
  (gdb) record function-call-history /cli
  1	fib	inst 1,9	at src/fib.c:9,14
  2	  fib	inst 10,20	at src/fib.c:6,14
  3	[decode error (1): instruction overflow]
  4	fib	inst 21,28	at src/fib.c:11,14
  5	  fib	inst 29,33	at src/fib.c:6,9
  (gdb) record instruction-history 20,22
  20	   0x000000000040062f <fib+47>:	sub    $0x1,%rax
  [decode error (1): instruction overflow]
  21	   0x0000000000400613 <fib+19>:	add    $0x1,%rax
  22	   0x0000000000400617 <fib+23>:	mov    %rax,0x200a3a(%rip)
  (gdb)

Gaps are ignored during reverse execution and replay.

2015-02-09  Markus Metzger  <markus.t.metzger@intel.com>

	* btrace.c (ftrace_find_call): Skip gaps.
	(ftrace_new_function): Initialize level.
	(ftrace_new_call, ftrace_new_tailcall, ftrace_new_return)
	(ftrace_new_switch): Update
	level computation.
	(ftrace_new_gap): New.
	(ftrace_update_function): Create new function after gap.
	(btrace_compute_ftrace_bts): Create gap on error.
	(btrace_stitch_bts): Update parameters.  Clear trace if it
	becomes empty.
	(btrace_stitch_trace): Update parameters.  Update callers.
	(btrace_clear): Reset the number of gaps.
	(btrace_insn_get): Return NULL if the iterator points to a gap.
	(btrace_insn_number): Return zero if the iterator points to a gap.
	(btrace_insn_end): Allow gaps at the end.
	(btrace_insn_next, btrace_insn_prev, btrace_insn_cmp): Handle gaps.
	(btrace_find_insn_by_number): Assert that the found iterator does
	not point to a gap.
	(btrace_call_next, btrace_call_prev): Assert that the last function
	is not a gap.
	* btrace.h (btrace_bts_error): New.
	(btrace_function): Update comment.
	(btrace_function) <insn, insn_offset, number>: Update comment.
	(btrace_function) <errcode>: New.
	(btrace_thread_info) <ngaps>: New.
	(btrace_thread_info) <replay>: Update comment.
	(btrace_insn_get): Update comment.
	* record-btrace.c (btrace_ui_out_decode_error): New.
	(record_btrace_info): Print number of gaps.
	(btrace_insn_history, btrace_call_history): Call
	btrace_ui_out_decode_error for gaps.
	(record_btrace_step_thread, record_btrace_start_replaying): Skip gaps.

testsuite/
	* gdb.btrace/buffer-size.exp: Update "info record" output.
	* gdb.btrace/delta.exp: Update "info record" output.
	* gdb.btrace/enable.exp: Update "info record" output.
	* gdb.btrace/finish.exp: Update "info record" output.
	* gdb.btrace/instruction_history.exp: Update "info record" output.
	* gdb.btrace/next.exp: Update "info record" output.
	* gdb.btrace/nexti.exp: Update "info record" output.
	* gdb.btrace/step.exp: Update "info record" output.
	* gdb.btrace/stepi.exp: Update "info record" output.
	* gdb.btrace/nohist.exp: Update "info record" output.

1 files changed, 1 insertions, 1 deletions

diff --git a/gdb/testsuite/gdb.btrace/enable.exp b/gdb/testsuite/gdb.btrace/enable.exp
index 1122884..d447bd9 100644
--- a/gdb/testsuite/gdb.btrace/enable.exp
+++ b/gdb/testsuite/gdb.btrace/enable.exp
@@ -58,7 +58,7 @@ gdb_test "record full" "The process is already being recorded\\.  Use \"record s
 # no trace recorded yet
 gdb_test "info record" "Active record target: record-btrace\r
 .*\r
-Recorded 0 instructions in 0 functions for thread 1.*\\." "info record without trace"
+Recorded 0 instructions in 0 functions \\\(0 gaps\\\) for thread 1.*\\." "info record without trace"
 
 # stop btrace record
 gdb_test "record stop" "Process record is stopped and all execution logs are deleted\\." "record stop"