reverse-finish: turn internal error into normal error

The reverse-finish command results in an internal error if it cannot determine
the current function.

  (gdb) c
  Continuing.

  Program received signal SIGSEGV, Segmentation fault.
  0x0000000000000000 in ?? ()
  (gdb) reverse-finish
  Run back to call of #0  0x0000000000000000 in ?? ()
  gdb/infcmd.c:1576: internal-error: Finish: couldn't find function.
  A problem internal to GDB has been detected,
  further debugging may prove unreliable.
  Quit this debugging session? (y or n) y

This is not an internal error case since the command may be used in scenarios
where there is no function at the current PC, e.g. after calling through a bad
function pointer.

Turn this into a normal error.

gdb/
	* infcmd.c (finish_backward): Turn internal error into normal error.

testsuite/
	* gdb.btrace/segv.c: New.
	* gdb.btrace/segv.exp: New.

1 files changed, 32 insertions, 0 deletions

diff --git a/gdb/testsuite/gdb.btrace/segv.c b/gdb/testsuite/gdb.btrace/segv.c
new file mode 100644
index 0000000..6b3ca0a
--- /dev/null
+++ b/gdb/testsuite/gdb.btrace/segv.c
@@ -0,0 +1,32 @@
+/* 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/>.  */
+
+static int (*fun)(int);
+
+int
+test (void)
+{
+  return fun (42); /* test.call */
+}
+
+int
+main (void)
+{
+  return test ();
+}