btrace: pretend we're not replaying when generating a core file

When generating a core file using the "generate-core-file" command while
replaying with the btrace record target, we won't be able to access all
registers and all memory.  This leads to the following assertion:

    gdb/regcache.c:1034: internal-error: regcache_raw_supply: Assertion `regnum >= 0 && regnum < regcache->descr->nr_raw_registers' failed.
    A problem internal to GDB has been detected,
    further debugging may prove unreliable.
    Quit this debugging session? (y or n) FAIL: gdb.btrace/gcore.exp: generate-core-file core (GDB internal error)
    Resyncing due to internal error.

Pretend that we are not replaying while generating a core file.  This will
forward fetch and store registers as well as xfer memory calls to the target
beneath.

gdb/
	* record-btrace.c (record_btrace_generating_corefile)
	(record_btrace_prepare_to_generate_core)
	(record_btrace_done_generating_core): New.
	(record_btrace_xfer_partial, record_btrace_fetch_registers)
	(record_btrace_store_registers, record_btrace_prepare_to_store):
	Forward request when generating a core file.
	(record_btrace_open): Set record_btrace_generating_corefile to zero.
	(init_record_btrace_ops): Set to_prepare_to_generate_core and
	to_done_generating_core.

testsuite/
	* gdb.btrace/gcore.exp: New.

gdb/ChangeLog

@@ -1,3 +1,15 @@
+2014-06-25  Markus Metzger  <markus.t.metzger@intel.com>
+
+	* record-btrace.c (record_btrace_generating_corefile)
+	(record_btrace_prepare_to_generate_core)
+	(record_btrace_done_generating_core): New.
+	(record_btrace_xfer_partial, record_btrace_fetch_registers)
+	(record_btrace_store_registers, record_btrace_prepare_to_store):
+	Forward request when generating a core file.
+	(record_btrace_open): Set record_btrace_generating_corefile to zero.
+	(init_record_btrace_ops): Set to_prepare_to_generate_core and
+	to_done_generating_core.
+
 2014-06-25  Markus Metzger  <markus.t.metzger@intel.com>
 
 	* target.h (target_ops) <to_prepare_to_generate_core>

gdb/record-btrace.c

@@ -68,6 +68,9 @@ static enum exec_direction_kind record_btrace_resume_exec_dir = EXEC_FORWARD;
 /* The async event handler for reverse/replay execution.  */
 static struct async_event_handler *record_btrace_async_inferior_event_handler;
 
+/* A flag indicating that we are currently generating a core file.  */
+static int record_btrace_generating_corefile;
+
 /* Print a record-btrace debug message.  Use do ... while (0) to avoid
    ambiguities when used in if statements.  */
 
@@ -221,6 +224,7 @@ record_btrace_open (char *args, int from_tty)
   record_btrace_async_inferior_event_handler
     = create_async_event_handler (record_btrace_handle_async_inferior_event,
 				  NULL);
+  record_btrace_generating_corefile = 0;
 
   observer_notify_record_changed (current_inferior (),  1);
 
@@ -854,6 +858,7 @@ record_btrace_xfer_partial (struct target_ops *ops, enum target_object object,
 
   /* Filter out requests that don't make sense during replay.  */
   if (replay_memory_access == replay_memory_access_read_only
+      && !record_btrace_generating_corefile
       && record_btrace_is_replaying (ops))
     {
       switch (object)
@@ -969,7 +974,7 @@ record_btrace_fetch_registers (struct target_ops *ops,
   gdb_assert (tp != NULL);
 
   replay = tp->btrace.replay;
-  if (replay != NULL)
+  if (replay != NULL && !record_btrace_generating_corefile)
     {
       const struct btrace_insn *insn;
       struct gdbarch *gdbarch;
@@ -1010,7 +1015,7 @@ record_btrace_store_registers (struct target_ops *ops,
 {
   struct target_ops *t;
 
-  if (record_btrace_is_replaying (ops))
+  if (!record_btrace_generating_corefile && record_btrace_is_replaying (ops))
     error (_("This record target does not allow writing registers."));
 
   gdb_assert (may_write_registers != 0);
@@ -1033,7 +1038,7 @@ record_btrace_prepare_to_store (struct target_ops *ops,
 {
   struct target_ops *t;
 
-  if (record_btrace_is_replaying (ops))
+  if (!record_btrace_generating_corefile && record_btrace_is_replaying (ops))
     return;
 
   for (t = ops->beneath; t != NULL; t = t->beneath)
@@ -1939,6 +1944,22 @@ record_btrace_execution_direction (struct target_ops *self)
   return record_btrace_resume_exec_dir;
 }
 
+/* The to_prepare_to_generate_core target method.  */
+
+static void
+record_btrace_prepare_to_generate_core (struct target_ops *self)
+{
+  record_btrace_generating_corefile = 1;
+}
+
+/* The to_done_generating_core target method.  */
+
+static void
+record_btrace_done_generating_core (struct target_ops *self)
+{
+  record_btrace_generating_corefile = 0;
+}
+
 /* Initialize the record-btrace target ops.  */
 
 static void
@@ -1983,6 +2004,8 @@ init_record_btrace_ops (void)
   ops->to_can_execute_reverse = record_btrace_can_execute_reverse;
   ops->to_decr_pc_after_break = record_btrace_decr_pc_after_break;
   ops->to_execution_direction = record_btrace_execution_direction;
+  ops->to_prepare_to_generate_core = record_btrace_prepare_to_generate_core;
+  ops->to_done_generating_core = record_btrace_done_generating_core;
   ops->to_stratum = record_stratum;
   ops->to_magic = OPS_MAGIC;
 }

gdb/testsuite/ChangeLog

@@ -1,3 +1,7 @@
+2014-06-25  Markus Metzger  <markus.t.metzger@intel.com>
+
+	* gdb.btrace/gcore.exp: New.
+
 2014-06-23  Pedro Alves  <palves@redhat.com>
 
 	* gdb.base/watchpoint-reuse-slot.c: New file.

gdb/testsuite/gdb.btrace/gcore.exp

@@ -0,0 +1,41 @@
+# This testcase is part of GDB, the GNU debugger.
+#
+# Copyright 2014 Free Software Foundation, Inc.
+#
+# Contributed by Intel Corp. <markus.t.metzger@intel.com>
+#
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+# check for btrace support
+if { [skip_btrace_tests] } { return -1 }
+
+# start inferior
+standard_testfile x86-record_goto.S
+if [prepare_for_testing gcore.exp $testfile $srcfile] {
+    return -1
+}
+
+if ![runto_main] {
+    return -1
+}
+
+# trace the call to the test function
+gdb_test_no_output "record btrace"
+gdb_test "next" ".*main\.3.*"
+
+# start replaying
+gdb_test "record goto begin" ".*main\.2.*"
+
+# generate a core file - this used to assert
+gdb_test "generate-core-file core" "Saved corefile core"