Fix "info frame" in the outermost frame.

Doing "info frame" in the outermost frame, when that was indicated by
the next frame saying the unwound PC is undefined/not saved, results
in error and incomplete output:

 (gdb) bt
 #0  thread_function0 (arg=0x0) at threads.c:63
 #1  0x00000034cf407d14 in start_thread (arg=0x7ffff7fcb700) at pthread_create.c:309
 #2  0x000000323d4f168d in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:115

 (gdb) frame 2
 #2  0x000000323d4f168d in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:115
 115             call    *%rax

 (gdb) info frame
 Stack level 2, frame at 0x0:
  rip = 0x323d4f168d in clone (../sysdeps/unix/sysv/linux/x86_64/clone.S:115); saved rip Register 16 was not saved
 (gdb)

Not saved register values are treated as optimized out values
internally throughout.  stack.c:frame_info is handing unvailable
values, but not optimized out ones.  The patch deletes the
frame_unwind_caller_pc_if_available wrapper function and instead lets
errors propagate to frame_info (it's only user).

As frame_unwind_pc now needs to be able to handle and cache two
different error scenarios, the prev_pc.p variable is replaced with an
enumeration.

(FWIW, I looked into making gdbarch_unwind_pc or a variant return
struct value's instead, but it results in lots of boxing and unboxing
for no real gain -- e.g., the mips and arm implementations need to do
computation on the unboxed PC value.  Might as well throw an error on
first attempt to get at invalid contents.)

After the patch, we get:

 (gdb) info frame
 Stack level 2, frame at 0x0:
  rip = 0x323d4f168d in clone (../sysdeps/unix/sysv/linux/x86_64/clone.S:115); saved rip = <not saved>
  Outermost frame: outermost
  caller of frame at 0x7ffff7fcafc0
  source language asm.
  Arglist at 0x7ffff7fcafb8, args:
  Locals at 0x7ffff7fcafb8, Previous frame's sp is 0x7ffff7fcafc8
 (gdb)

A new test is added.  It's based off dw2-reg-undefined.exp, and tweaked to
mark the return address (rip) of "stop_frame" as undefined.

Tested on x86_64 Fedora 17.

gdb/
2013-12-06  Pedro Alves  <palves@redhat.com>

	* frame.c (enum cached_copy_status): New enum.
	(struct frame_info) <prev_pc.p>: Change type to enum
	cached_copy_status.
	(fprint_frame): Handle not saved and unavailable prev_pc values.
	(frame_unwind_pc_if_available): Delete and merge contents into ...
	(frame_unwind_pc): ... here.  Handle OPTIMIZED_OUT_ERROR.  Adjust
	to use enum cached_copy_status.
	(frame_unwind_caller_pc_if_available): Delete.
	(create_new_frame): Adjust.
	* frame.h (frame_unwind_caller_pc_if_available): Delete
	declaration.
	* stack.c (frame_info): Use frame_unwind_caller_pc instead of
	frame_unwind_caller_pc_if_available, and handle
	NOT_AVAILABLE_ERROR and OPTIMIZED_OUT_ERROR errors.
	* valprint.c (val_print_optimized_out): Use val_print_not_saved.
	(val_print_not_saved): New function.
	* valprint.h (val_print_not_saved): Declare.

gdb/testsuite/
2013-12-06  Pedro Alves  <palves@redhat.com>

	* gdb.dwarf2/dw2-undefined-ret-addr.S: New file.
	* gdb.dwarf2/dw2-undefined-ret-addr.c: New file.
	* gdb.dwarf2/dw2-undefined-ret-addr.exp: New file.

1 files changed, 58 insertions, 0 deletions

diff --git a/gdb/testsuite/gdb.dwarf2/dw2-undefined-ret-addr.exp b/gdb/testsuite/gdb.dwarf2/dw2-undefined-ret-addr.exp
new file mode 100644
index 0000000..40ac356
--- /dev/null
+++ b/gdb/testsuite/gdb.dwarf2/dw2-undefined-ret-addr.exp
@@ -0,0 +1,58 @@
+# Copyright 2013 Free Software Foundation, Inc.
+
+# 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/>.
+load_lib dwarf.exp
+
+standard_testfile .S
+
+# This test can only be run on targets which support DWARF-2 and use gas.
+if ![dwarf2_support] {
+    return 0
+}
+
+# This test can only be run on x86-64 targets.
+if {![istarget x86_64-*] || ![is_lp64_target]} {
+    return 0
+}
+
+if {[prepare_for_testing "$testfile.exp" "$testfile" $srcfile {nodebug}]} {
+    return -1
+}
+
+if ![runto "stop_frame"] {
+    return -1
+}
+
+# stop_frame should be the outermost frame.
+
+# Check that backtrace shows only frame #0.
+gdb_test "bt" "#0\[ \]\+stop_frame \[^\r\n\]\+"
+
+# And that "up" doesn't work.
+gdb_test "up" \
+    "Initial frame selected; you cannot go up\\." \
+    "up refuses to go up"
+
+# "info frame" unwinds the PC for "saved ... = ".  Make sure that
+# doesn't cause an error, and shows "<not saved>".
+gdb_test "info frame" [join [list \
+    "Stack level 0, frame at $hex\:" \
+    " rip = $hex in stop_frame \\(dw2-undefined-ret-addr\\.c:22\\); saved rip = <not saved>" \
+    " Outermost frame: outermost" \
+    " source language c\\." \
+    " Arglist at $hex, args\: " \
+    " Locals at $hex, Previous frame's sp is $hex" \
+    " Saved registers\:" \
+    "  rbp at $hex.*" \
+] "\r\n"]