record-btrace: extend unwinder

Extend the always failing unwinder to provide the PC based on the call
structure detected in the branch trace.

The unwinder supports normal frames and tailcall frames.
Inline frames are not supported.

2014-01-16  Markus Metzger  <markus.t.metzger@intel.com>

	* record.h (record_btrace_frame_unwind)
	(record_btrace_tailcall_frame_unwind): New declarations.
	* dwarf2-frame: Include record.h
	(dwarf2_frame_cfa): Throw an error for btrace frames.
	* record-btrace.c: Include hashtab.h.
	(btrace_get_bfun_name): New.
	(btrace_call_history): Call btrace_get_bfun_name.
	(struct btrace_frame_cache): New.
	(bfcache): New.
	(bfcache_hash, bfcache_eq, bfcache_new): New.
	(btrace_get_frame_function): New.
	(record_btrace_frame_unwind_stop_reason): Allow unwinding.
	(record_btrace_frame_this_id): Compute own id.
	(record_btrace_frame_prev_register): Provide PC, throw_error
	for all other registers.
	(record_btrace_frame_sniffer): Detect btrace frames.
	(record_btrace_tailcall_frame_sniffer): New.
	(record_btrace_frame_dealloc_cache): New.
	(record_btrace_frame_unwind): Add new functions.
	(record_btrace_tailcall_frame_unwind): New.
	(_initialize_record_btrace): Allocate cache.
	* btrace.c (btrace_clear): Call reinit_frame_cache.
	* NEWS: Announce it.

testsuite/
	* gdb.btrace/record_goto.exp: Add backtrace test.
	* gdb.btrace/tailcall.exp: Add backtrace test.

gdb/btrace.c

@@ -765,6 +765,10 @@ btrace_clear (struct thread_info *tp)
 
   DEBUG ("clear thread %d (%s)", tp->num, target_pid_to_str (tp->ptid));
 
+  /* Make sure btrace frames that may hold a pointer into the branch
+     trace data are destroyed.  */
+  reinit_frame_cache ();
+
   btinfo = &tp->btrace;
 
   it = btinfo->begin;