handle an unspecified return address column

Debugging PR 16155 further, I found that the DWARF unwinder found the
function in question, but thought it had no registers saved
(fs->regs.num_regs == 0).

It seems to me that if a frame does not specify the return address
column, or if the return address column is explicitly marked as
DWARF2_FRAME_REG_UNSPECIFIED, then we should set the
"undefined_retaddr" flag and let the DWARF unwinder gracefully stop.

This patch implements that idea.

With this patch the backtrace works properly:

    (gdb) bt
    #0  0x0000007fb7ed485c in nanosleep () from /lib64/libc.so.6
    #1  0x0000007fb7ed4508 in sleep () from /lib64/libc.so.6
    #2  0x00000000004008bc in thread_function (arg=0x4) at threadapply.c:73
    #3  0x0000007fb7fad950 in start_thread () from /lib64/libpthread.so.0
    #4  0x0000007fb7f0956c in clone () from /lib64/libc.so.6

2013-11-22  Tom Tromey  <tromey@redhat.com>

	PR backtrace/16155:
	* dwarf2-frame.c (dwarf2_frame_cache): Set undefined_retaddr if
	the return address column is unspecified.

2013-11-22  Tom Tromey  <tromey@redhat.com>

	* gdb.dwarf2/dw2-bad-cfi.c: New file.
	* gdb.dwarf2/dw2-bad-cfi.exp: New file.
	* gdb.dwarf2/dw2-bad-cfi.S: New file.

3 files changed, 286 insertions, 0 deletions

diff --git a/gdb/testsuite/gdb.dwarf2/dw2-bad-cfi.S b/gdb/testsuite/gdb.dwarf2/dw2-bad-cfi.S
new file mode 100644
index 0000000..9a97889
--- /dev/null
+++ b/gdb/testsuite/gdb.dwarf2/dw2-bad-cfi.S
@@ -0,0 +1,216 @@
+# This file was created by running dw2-bad-cfi.c
+# through 'gcc -g -dA -S', and then hand-editing
+# the CFI in "callee" to suit.
+
+	.file	"dw2-bad-cfi.c"
+	.text
+.Ltext0:
+	.globl	callee
+	.type	callee, @function
+callee:
+.LFB0:
+	.file 1 "dw2-bad-cfi.c"
+	# dw2-bad-cfi.c:20
+	.loc 1 20 0
+	.cfi_startproc
+# BLOCK 2 seq:0
+# PRED: ENTRY (fallthru)
+	pushq	%rbp
+/*
+	.cfi_def_cfa_offset 16
+	.cfi_offset 6, -16
+*/
+	movq	%rsp, %rbp
+/*	.cfi_def_cfa_register 6 */
+	# dw2-bad-cfi.c:21
+	.loc 1 21 0
+	popq	%rbp
+/*	.cfi_def_cfa 7, 8 */
+	# Our little lies.
+	.cfi_undefined 6
+	.cfi_return_column 6
+# SUCC: EXIT [100.0%] 
+	ret
+	.cfi_endproc
+.LFE0:
+	.size	callee, .-callee
+	.globl	main
+	.type	main, @function
+main:
+.LFB1:
+	# dw2-bad-cfi.c:25
+	.loc 1 25 0
+	.cfi_startproc
+# BLOCK 2 seq:0
+# PRED: ENTRY (fallthru)
+	pushq	%rbp
+	.cfi_def_cfa_offset 16
+	.cfi_offset 6, -16
+	movq	%rsp, %rbp
+	.cfi_def_cfa_register 6
+	# dw2-bad-cfi.c:26
+	.loc 1 26 0
+	call	callee
+	# dw2-bad-cfi.c:27
+	.loc 1 27 0
+	movl	$0, %eax
+	# dw2-bad-cfi.c:28
+	.loc 1 28 0
+	popq	%rbp
+	.cfi_def_cfa 7, 8
+# SUCC: EXIT [100.0%] 
+	ret
+	.cfi_endproc
+.LFE1:
+	.size	main, .-main
+.Letext0:
+	.section	.debug_info,"",@progbits
+.Ldebug_info0:
+	.long	0x67	# Length of Compilation Unit Info
+	.value	0x4	# DWARF version number
+	.long	.Ldebug_abbrev0	# Offset Into Abbrev. Section
+	.byte	0x8	# Pointer Size (in bytes)
+	.uleb128 0x1	# (DIE (0xb) DW_TAG_compile_unit)
+	.long	.LASF0	# DW_AT_producer: "GNU C 4.7.2 20121109 (Red Hat 4.7.2-8) -mtune=generic -march=x86-64 -g"
+	.byte	0x1	# DW_AT_language
+	.long	.LASF1	# DW_AT_name: "dw2-bad-cfi.c"
+	.long	.LASF2	# DW_AT_comp_dir: "/home/tromey/gnu/gdb/devel/binutils-gdb/gdb/testsuite/gdb.dwarf2"
+	.quad	.Ltext0	# DW_AT_low_pc
+	.quad	.Letext0	# DW_AT_high_pc
+	.long	.Ldebug_line0	# DW_AT_stmt_list
+	.uleb128 0x2	# (DIE (0x2d) DW_TAG_subprogram)
+			# DW_AT_external
+	.long	.LASF3	# DW_AT_name: "callee"
+	.byte	0x1	# DW_AT_decl_file (dw2-bad-cfi.c)
+	.byte	0x13	# DW_AT_decl_line
+			# DW_AT_prototyped
+	.quad	.LFB0	# DW_AT_low_pc
+	.quad	.LFE0	# DW_AT_high_pc
+	.uleb128 0x1	# DW_AT_frame_base
+	.byte	0x9c	# DW_OP_call_frame_cfa
+			# DW_AT_GNU_all_call_sites
+	.uleb128 0x3	# (DIE (0x46) DW_TAG_subprogram)
+			# DW_AT_external
+	.long	.LASF4	# DW_AT_name: "main"
+	.byte	0x1	# DW_AT_decl_file (dw2-bad-cfi.c)
+	.byte	0x18	# DW_AT_decl_line
+			# DW_AT_prototyped
+	.long	0x63	# DW_AT_type
+	.quad	.LFB1	# DW_AT_low_pc
+	.quad	.LFE1	# DW_AT_high_pc
+	.uleb128 0x1	# DW_AT_frame_base
+	.byte	0x9c	# DW_OP_call_frame_cfa
+			# DW_AT_GNU_all_tail_call_sites
+	.uleb128 0x4	# (DIE (0x63) DW_TAG_base_type)
+	.byte	0x4	# DW_AT_byte_size
+	.byte	0x5	# DW_AT_encoding
+	.ascii "int\0"	# DW_AT_name
+	.byte	0	# end of children of DIE 0xb
+	.section	.debug_abbrev,"",@progbits
+.Ldebug_abbrev0:
+	.uleb128 0x1	# (abbrev code)
+	.uleb128 0x11	# (TAG: DW_TAG_compile_unit)
+	.byte	0x1	# DW_children_yes
+	.uleb128 0x25	# (DW_AT_producer)
+	.uleb128 0xe	# (DW_FORM_strp)
+	.uleb128 0x13	# (DW_AT_language)
+	.uleb128 0xb	# (DW_FORM_data1)
+	.uleb128 0x3	# (DW_AT_name)
+	.uleb128 0xe	# (DW_FORM_strp)
+	.uleb128 0x1b	# (DW_AT_comp_dir)
+	.uleb128 0xe	# (DW_FORM_strp)
+	.uleb128 0x11	# (DW_AT_low_pc)
+	.uleb128 0x1	# (DW_FORM_addr)
+	.uleb128 0x12	# (DW_AT_high_pc)
+	.uleb128 0x1	# (DW_FORM_addr)
+	.uleb128 0x10	# (DW_AT_stmt_list)
+	.uleb128 0x17	# (DW_FORM_sec_offset)
+	.byte	0
+	.byte	0
+	.uleb128 0x2	# (abbrev code)
+	.uleb128 0x2e	# (TAG: DW_TAG_subprogram)
+	.byte	0	# DW_children_no
+	.uleb128 0x3f	# (DW_AT_external)
+	.uleb128 0x19	# (DW_FORM_flag_present)
+	.uleb128 0x3	# (DW_AT_name)
+	.uleb128 0xe	# (DW_FORM_strp)
+	.uleb128 0x3a	# (DW_AT_decl_file)
+	.uleb128 0xb	# (DW_FORM_data1)
+	.uleb128 0x3b	# (DW_AT_decl_line)
+	.uleb128 0xb	# (DW_FORM_data1)
+	.uleb128 0x27	# (DW_AT_prototyped)
+	.uleb128 0x19	# (DW_FORM_flag_present)
+	.uleb128 0x11	# (DW_AT_low_pc)
+	.uleb128 0x1	# (DW_FORM_addr)
+	.uleb128 0x12	# (DW_AT_high_pc)
+	.uleb128 0x1	# (DW_FORM_addr)
+	.uleb128 0x40	# (DW_AT_frame_base)
+	.uleb128 0x18	# (DW_FORM_exprloc)
+	.uleb128 0x2117	# (DW_AT_GNU_all_call_sites)
+	.uleb128 0x19	# (DW_FORM_flag_present)
+	.byte	0
+	.byte	0
+	.uleb128 0x3	# (abbrev code)
+	.uleb128 0x2e	# (TAG: DW_TAG_subprogram)
+	.byte	0	# DW_children_no
+	.uleb128 0x3f	# (DW_AT_external)
+	.uleb128 0x19	# (DW_FORM_flag_present)
+	.uleb128 0x3	# (DW_AT_name)
+	.uleb128 0xe	# (DW_FORM_strp)
+	.uleb128 0x3a	# (DW_AT_decl_file)
+	.uleb128 0xb	# (DW_FORM_data1)
+	.uleb128 0x3b	# (DW_AT_decl_line)
+	.uleb128 0xb	# (DW_FORM_data1)
+	.uleb128 0x27	# (DW_AT_prototyped)
+	.uleb128 0x19	# (DW_FORM_flag_present)
+	.uleb128 0x49	# (DW_AT_type)
+	.uleb128 0x13	# (DW_FORM_ref4)
+	.uleb128 0x11	# (DW_AT_low_pc)
+	.uleb128 0x1	# (DW_FORM_addr)
+	.uleb128 0x12	# (DW_AT_high_pc)
+	.uleb128 0x1	# (DW_FORM_addr)
+	.uleb128 0x40	# (DW_AT_frame_base)
+	.uleb128 0x18	# (DW_FORM_exprloc)
+	.uleb128 0x2116	# (DW_AT_GNU_all_tail_call_sites)
+	.uleb128 0x19	# (DW_FORM_flag_present)
+	.byte	0
+	.byte	0
+	.uleb128 0x4	# (abbrev code)
+	.uleb128 0x24	# (TAG: DW_TAG_base_type)
+	.byte	0	# DW_children_no
+	.uleb128 0xb	# (DW_AT_byte_size)
+	.uleb128 0xb	# (DW_FORM_data1)
+	.uleb128 0x3e	# (DW_AT_encoding)
+	.uleb128 0xb	# (DW_FORM_data1)
+	.uleb128 0x3	# (DW_AT_name)
+	.uleb128 0x8	# (DW_FORM_string)
+	.byte	0
+	.byte	0
+	.byte	0
+	.section	.debug_aranges,"",@progbits
+	.long	0x2c	# Length of Address Ranges Info
+	.value	0x2	# DWARF Version
+	.long	.Ldebug_info0	# Offset of Compilation Unit Info
+	.byte	0x8	# Size of Address
+	.byte	0	# Size of Segment Descriptor
+	.value	0	# Pad to 16 byte boundary
+	.value	0
+	.quad	.Ltext0	# Address
+	.quad	.Letext0-.Ltext0	# Length
+	.quad	0
+	.quad	0
+	.section	.debug_line,"",@progbits
+.Ldebug_line0:
+	.section	.debug_str,"MS",@progbits,1
+.LASF3:
+	.string	"callee"
+.LASF1:
+	.string	"dw2-bad-cfi.c"
+.LASF2:
+	.string	"/home/tromey/gnu/gdb/devel/binutils-gdb/gdb/testsuite/gdb.dwarf2"
+.LASF4:
+	.string	"main"
+.LASF0:
+	.string	"GNU C 4.7.2 20121109 (Red Hat 4.7.2-8) -mtune=generic -march=x86-64 -g"
+	.ident	"GCC: (GNU) 4.7.2 20121109 (Red Hat 4.7.2-8)"
+	.section	.note.GNU-stack,"",@progbits
diff --git a/gdb/testsuite/gdb.dwarf2/dw2-bad-cfi.c b/gdb/testsuite/gdb.dwarf2/dw2-bad-cfi.c
new file mode 100644
index 0000000..f5b415b
--- /dev/null
+++ b/gdb/testsuite/gdb.dwarf2/dw2-bad-cfi.c
@@ -0,0 +1,28 @@
+/* This testcase is part of GDB, the GNU debugger.
+
+   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/>.  */
+
+void
+callee (void)
+{
+}
+
+int
+main(void)
+{
+  callee ();
+  return 0;
+}
diff --git a/gdb/testsuite/gdb.dwarf2/dw2-bad-cfi.exp b/gdb/testsuite/gdb.dwarf2/dw2-bad-cfi.exp
new file mode 100644
index 0000000..12b1275
--- /dev/null
+++ b/gdb/testsuite/gdb.dwarf2/dw2-bad-cfi.exp
@@ -0,0 +1,42 @@
+# 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_main] {
+    return -1
+}
+
+gdb_breakpoint "callee"
+gdb_continue_to_breakpoint "callee"
+
+# This test ensures that the backtrace does not go past "callee".
+gdb_test "bt" ".*callee .. at [file rootname $srcfile]\\.c:\[0-9\]*"