btrace, frame: fix crash in get_frame_type

In skip_artificial_frames we repeatedly call get_prev_frame_always until we get
a non-inline and non-tailcall frame assuming that there must be such a frame
eventually.

For record targets, however, we may have a frame chain that consists only of
artificial frames.  This leads to a crash in get_frame_type when dereferencing a
NULL frame pointer.

Change skip_artificial_frames and skip_tailcall_frames to return NULL in such a
case and modify each caller to cope with a NULL return.

In frame_unwind_caller_pc and frame_unwind_caller_arch, we simply assert that
the returned value is not NULL.  Their caller was supposed to check
frame_unwind_caller_id before calling those functions.

In other cases, we thrown an error.

In infcmd further move the skip_tailcall_frames call to the forward-stepping
case since we don't need a frame for reverse execution and we don't want to fail
because of that.  Reverse-finish does make sense for a tailcall frame.

gdb/
	* frame.h (skip_tailcall_frames): Update comment.
	* frame.c (skip_artificial_frames, skip_tailcall_frames): Return NULL
	if only	artificial frames are found.  Update comment.
	(frame_unwind_caller_id): Handle NULL return.
	(frame_unwind_caller_pc, frame_unwind_caller_arch): Assert that
	skip_artificial_frames does not return NULL.
	(frame_pop): Add an error if only tailcall frames are found.
	* infcmd.c (finish_command): Move skip_tailcall_frames call into forward-
	execution case.  Add an error if only tailcall frames are found.

testsuite/
	* gdb.btrace/tailcall-only.exp: New.
	* gdb.btrace/tailcall-only.c: New.
	* gdb.btrace/x86_64-tailcall-only.S: New.
	* gdb.btrace/i686-tailcall-only.S: New.

1 files changed, 447 insertions, 0 deletions

diff --git a/gdb/testsuite/gdb.btrace/i686-tailcall-only.S b/gdb/testsuite/gdb.btrace/i686-tailcall-only.S
new file mode 100644
index 0000000..a89f2f2
--- /dev/null
+++ b/gdb/testsuite/gdb.btrace/i686-tailcall-only.S
@@ -0,0 +1,447 @@
+/* This testcase is part of GDB, the GNU debugger.
+
+   Copyright 2016 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/>.
+
+
+   This file has been generated using:
+   gcc -m32 -march=i686 -S -O2 -dA -g tailcall-only.c -o i686-tailcall-only.S
+ */
+
+	.file	"tailcall-only.c"
+	.text
+.Ltext0:
+	.p2align 4,,15
+	.type	bar_1, @function
+bar_1:
+.LFB0:
+	.file 1 "tailcall-only.c"
+	# tailcall-only.c:22
+	.loc 1 22 0
+	.cfi_startproc
+# BLOCK 2 freq:10000 seq:0
+# PRED: ENTRY [100.0%]  (FALLTHRU)
+	# tailcall-only.c:24
+	.loc 1 24 0
+	movl	$42, %eax
+# SUCC: EXIT [100.0%]
+	ret
+	.cfi_endproc
+.LFE0:
+	.size	bar_1, .-bar_1
+	.p2align 4,,15
+	.type	bar, @function
+bar:
+.LFB1:
+	# tailcall-only.c:28
+	.loc 1 28 0
+	.cfi_startproc
+# BLOCK 2 freq:10000 seq:0
+# PRED: ENTRY [100.0%]  (FALLTHRU)
+	# tailcall-only.c:29
+	.loc 1 29 0
+	jmp	bar_1
+# SUCC: EXIT [100.0%]  (ABNORMAL,SIBCALL)
+.LVL0:
+	.cfi_endproc
+.LFE1:
+	.size	bar, .-bar
+	.p2align 4,,15
+	.type	foo_1, @function
+foo_1:
+.LFB2:
+	# tailcall-only.c:34
+	.loc 1 34 0
+	.cfi_startproc
+# BLOCK 2 freq:10000 seq:0
+# PRED: ENTRY [100.0%]  (FALLTHRU)
+	# tailcall-only.c:35
+	.loc 1 35 0
+	jmp	bar
+# SUCC: EXIT [100.0%]  (ABNORMAL,SIBCALL)
+.LVL1:
+	.cfi_endproc
+.LFE2:
+	.size	foo_1, .-foo_1
+	.p2align 4,,15
+	.type	foo, @function
+foo:
+.LFB3:
+	# tailcall-only.c:40
+	.loc 1 40 0
+	.cfi_startproc
+# BLOCK 2 freq:10000 seq:0
+# PRED: ENTRY [100.0%]  (FALLTHRU)
+	# tailcall-only.c:41
+	.loc 1 41 0
+	jmp	foo_1
+# SUCC: EXIT [100.0%]  (ABNORMAL,SIBCALL)
+.LVL2:
+	.cfi_endproc
+.LFE3:
+	.size	foo, .-foo
+	.section	.text.startup,"ax",@progbits
+	.p2align 4,,15
+	.globl	main
+	.type	main, @function
+main:
+.LFB4:
+	# tailcall-only.c:46
+	.loc 1 46 0
+	.cfi_startproc
+# BLOCK 2 freq:10000 seq:0
+# PRED: ENTRY [100.0%]  (FALLTHRU)
+	# tailcall-only.c:49
+	.loc 1 49 0
+	call	foo
+.LVL3:
+	# tailcall-only.c:50
+	.loc 1 50 0
+	addl	$1, %eax
+.LVL4:
+# SUCC: EXIT [100.0%]
+	# tailcall-only.c:53
+	.loc 1 53 0
+	ret
+	.cfi_endproc
+.LFE4:
+	.size	main, .-main
+	.text
+.Letext0:
+	.section	.debug_info,"",@progbits
+.Ldebug_info0:
+	.long	0xd5	# Length of Compilation Unit Info
+	.value	0x4	# DWARF version number
+	.long	.Ldebug_abbrev0	# Offset Into Abbrev. Section
+	.byte	0x4	# Pointer Size (in bytes)
+	.uleb128 0x1	# (DIE (0xb) DW_TAG_compile_unit)
+	.long	.LASF1	# DW_AT_producer: "GNU C 4.8.3 20140911 (Red Hat 4.8.3-9) -m32 -march=i686 -g -O2"
+	.byte	0x1	# DW_AT_language
+	.long	.LASF2	# DW_AT_name: "tailcall-only.c"
+	.long	.LASF3	# DW_AT_comp_dir: ""
+	.long	.Ldebug_ranges0+0	# DW_AT_ranges
+	.long	0	# DW_AT_low_pc
+	.long	.Ldebug_line0	# DW_AT_stmt_list
+	.uleb128 0x2	# (DIE (0x25) DW_TAG_subprogram)
+	.long	.LASF4	# DW_AT_name: "bar_1"
+	.byte	0x1	# DW_AT_decl_file (tailcall-only.c)
+	.byte	0x15	# DW_AT_decl_line
+			# DW_AT_prototyped
+	.long	0x3a	# DW_AT_type
+	.long	.LFB0	# DW_AT_low_pc
+	.long	.LFE0-.LFB0	# 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 (0x3a) DW_TAG_base_type)
+	.byte	0x4	# DW_AT_byte_size
+	.byte	0x5	# DW_AT_encoding
+	.ascii "int\0"	# DW_AT_name
+	.uleb128 0x4	# (DIE (0x41) DW_TAG_subprogram)
+	.ascii "bar\0"	# DW_AT_name
+	.byte	0x1	# DW_AT_decl_file (tailcall-only.c)
+	.byte	0x1b	# DW_AT_decl_line
+			# DW_AT_prototyped
+	.long	0x3a	# DW_AT_type
+	.long	.LFB1	# DW_AT_low_pc
+	.long	.LFE1-.LFB1	# DW_AT_high_pc
+	.uleb128 0x1	# DW_AT_frame_base
+	.byte	0x9c	# DW_OP_call_frame_cfa
+			# DW_AT_GNU_all_call_sites
+	.long	0x64	# DW_AT_sibling
+	.uleb128 0x5	# (DIE (0x5a) DW_TAG_GNU_call_site)
+	.long	.LVL0	# DW_AT_low_pc
+			# DW_AT_GNU_tail_call
+	.long	0x25	# DW_AT_abstract_origin
+	.byte	0	# end of children of DIE 0x41
+	.uleb128 0x6	# (DIE (0x64) DW_TAG_subprogram)
+	.long	.LASF0	# DW_AT_name: "foo_1"
+	.byte	0x1	# DW_AT_decl_file (tailcall-only.c)
+	.byte	0x21	# DW_AT_decl_line
+			# DW_AT_prototyped
+	.long	0x3a	# DW_AT_type
+	.long	.LFB2	# DW_AT_low_pc
+	.long	.LFE2-.LFB2	# DW_AT_high_pc
+	.uleb128 0x1	# DW_AT_frame_base
+	.byte	0x9c	# DW_OP_call_frame_cfa
+			# DW_AT_GNU_all_call_sites
+	.long	0x87	# DW_AT_sibling
+	.uleb128 0x5	# (DIE (0x7d) DW_TAG_GNU_call_site)
+	.long	.LVL1	# DW_AT_low_pc
+			# DW_AT_GNU_tail_call
+	.long	0x41	# DW_AT_abstract_origin
+	.byte	0	# end of children of DIE 0x64
+	.uleb128 0x4	# (DIE (0x87) DW_TAG_subprogram)
+	.ascii "foo\0"	# DW_AT_name
+	.byte	0x1	# DW_AT_decl_file (tailcall-only.c)
+	.byte	0x27	# DW_AT_decl_line
+			# DW_AT_prototyped
+	.long	0x3a	# DW_AT_type
+	.long	.LFB3	# DW_AT_low_pc
+	.long	.LFE3-.LFB3	# DW_AT_high_pc
+	.uleb128 0x1	# DW_AT_frame_base
+	.byte	0x9c	# DW_OP_call_frame_cfa
+			# DW_AT_GNU_all_call_sites
+	.long	0xaa	# DW_AT_sibling
+	.uleb128 0x5	# (DIE (0xa0) DW_TAG_GNU_call_site)
+	.long	.LVL2	# DW_AT_low_pc
+			# DW_AT_GNU_tail_call
+	.long	0x64	# DW_AT_abstract_origin
+	.byte	0	# end of children of DIE 0x87
+	.uleb128 0x7	# (DIE (0xaa) DW_TAG_subprogram)
+			# DW_AT_external
+	.long	.LASF5	# DW_AT_name: "main"
+	.byte	0x1	# DW_AT_decl_file (tailcall-only.c)
+	.byte	0x2d	# DW_AT_decl_line
+			# DW_AT_prototyped
+	.long	0x3a	# DW_AT_type
+	.long	.LFB4	# DW_AT_low_pc
+	.long	.LFE4-.LFB4	# DW_AT_high_pc
+	.uleb128 0x1	# DW_AT_frame_base
+	.byte	0x9c	# DW_OP_call_frame_cfa
+			# DW_AT_GNU_all_call_sites
+	.uleb128 0x8	# (DIE (0xbf) DW_TAG_variable)
+	.long	.LASF6	# DW_AT_name: "answer"
+	.byte	0x1	# DW_AT_decl_file (tailcall-only.c)
+	.byte	0x2f	# DW_AT_decl_line
+	.long	0x3a	# DW_AT_type
+	.long	.LLST0	# DW_AT_location
+	.uleb128 0x9	# (DIE (0xce) DW_TAG_GNU_call_site)
+	.long	.LVL3	# DW_AT_low_pc
+	.long	0x87	# DW_AT_abstract_origin
+	.byte	0	# end of children of DIE 0xaa
+	.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 0x55	# (DW_AT_ranges)
+	.uleb128 0x17	# (DW_FORM_sec_offset)
+	.uleb128 0x11	# (DW_AT_low_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 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 0x6	# (DW_FORM_data4)
+	.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 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
+	.uleb128 0x4	# (abbrev code)
+	.uleb128 0x2e	# (TAG: DW_TAG_subprogram)
+	.byte	0x1	# DW_children_yes
+	.uleb128 0x3	# (DW_AT_name)
+	.uleb128 0x8	# (DW_FORM_string)
+	.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 0x6	# (DW_FORM_data4)
+	.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)
+	.uleb128 0x1	# (DW_AT_sibling)
+	.uleb128 0x13	# (DW_FORM_ref4)
+	.byte	0
+	.byte	0
+	.uleb128 0x5	# (abbrev code)
+	.uleb128 0x4109	# (TAG: DW_TAG_GNU_call_site)
+	.byte	0	# DW_children_no
+	.uleb128 0x11	# (DW_AT_low_pc)
+	.uleb128 0x1	# (DW_FORM_addr)
+	.uleb128 0x2115	# (DW_AT_GNU_tail_call)
+	.uleb128 0x19	# (DW_FORM_flag_present)
+	.uleb128 0x31	# (DW_AT_abstract_origin)
+	.uleb128 0x13	# (DW_FORM_ref4)
+	.byte	0
+	.byte	0
+	.uleb128 0x6	# (abbrev code)
+	.uleb128 0x2e	# (TAG: DW_TAG_subprogram)
+	.byte	0x1	# DW_children_yes
+	.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 0x6	# (DW_FORM_data4)
+	.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)
+	.uleb128 0x1	# (DW_AT_sibling)
+	.uleb128 0x13	# (DW_FORM_ref4)
+	.byte	0
+	.byte	0
+	.uleb128 0x7	# (abbrev code)
+	.uleb128 0x2e	# (TAG: DW_TAG_subprogram)
+	.byte	0x1	# DW_children_yes
+	.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 0x6	# (DW_FORM_data4)
+	.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 0x8	# (abbrev code)
+	.uleb128 0x34	# (TAG: DW_TAG_variable)
+	.byte	0	# DW_children_no
+	.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 0x49	# (DW_AT_type)
+	.uleb128 0x13	# (DW_FORM_ref4)
+	.uleb128 0x2	# (DW_AT_location)
+	.uleb128 0x17	# (DW_FORM_sec_offset)
+	.byte	0
+	.byte	0
+	.uleb128 0x9	# (abbrev code)
+	.uleb128 0x4109	# (TAG: DW_TAG_GNU_call_site)
+	.byte	0	# DW_children_no
+	.uleb128 0x11	# (DW_AT_low_pc)
+	.uleb128 0x1	# (DW_FORM_addr)
+	.uleb128 0x31	# (DW_AT_abstract_origin)
+	.uleb128 0x13	# (DW_FORM_ref4)
+	.byte	0
+	.byte	0
+	.byte	0
+	.section	.debug_loc,"",@progbits
+.Ldebug_loc0:
+.LLST0:
+	.long	.LVL3	# Location list begin address (*.LLST0)
+	.long	.LVL4	# Location list end address (*.LLST0)
+	.value	0x3	# Location expression size
+	.byte	0x70	# DW_OP_breg0
+	.sleb128 1
+	.byte	0x9f	# DW_OP_stack_value
+	.long	.LVL4	# Location list begin address (*.LLST0)
+	.long	.LFE4	# Location list end address (*.LLST0)
+	.value	0x1	# Location expression size
+	.byte	0x50	# DW_OP_reg0
+	.long	0	# Location list terminator begin (*.LLST0)
+	.long	0	# Location list terminator end (*.LLST0)
+	.section	.debug_aranges,"",@progbits
+	.long	0x24	# Length of Address Ranges Info
+	.value	0x2	# DWARF Version
+	.long	.Ldebug_info0	# Offset of Compilation Unit Info
+	.byte	0x4	# Size of Address
+	.byte	0	# Size of Segment Descriptor
+	.value	0	# Pad to 8 byte boundary
+	.value	0
+	.long	.Ltext0	# Address
+	.long	.Letext0-.Ltext0	# Length
+	.long	.LFB4	# Address
+	.long	.LFE4-.LFB4	# Length
+	.long	0
+	.long	0
+	.section	.debug_ranges,"",@progbits
+.Ldebug_ranges0:
+	.long	.Ltext0	# Offset 0
+	.long	.Letext0
+	.long	.LFB4	# Offset 0x8
+	.long	.LFE4
+	.long	0
+	.long	0
+	.section	.debug_line,"",@progbits
+.Ldebug_line0:
+	.section	.debug_str,"MS",@progbits,1
+.LASF4:
+	.string	"bar_1"
+.LASF2:
+	.string	"tailcall-only.c"
+.LASF1:
+	.string	"GNU C 4.8.3 20140911 (Red Hat 4.8.3-9) -m32 -march=i686 -g -O2"
+.LASF6:
+	.string	"answer"
+.LASF5:
+	.string	"main"
+.LASF3:
+	.string	""
+.LASF0:
+	.string	"foo_1"
+	.ident	"GCC: (GNU) 4.8.3 20140911 (Red Hat 4.8.3-9)"
+	.section	.note.GNU-stack,"",@progbits