1/*
2 * Post mortem Dwarf CFI based unwinding on top of regs and stack dumps.
3 *
4 * Lots of this code have been borrowed or heavily inspired from parts of
5 * the libunwind 0.99 code which are (amongst other contributors I may have
6 * forgotten):
7 *
8 * Copyright (C) 2002-2007 Hewlett-Packard Co
9 *	Contributed by David Mosberger-Tang <davidm@hpl.hp.com>
10 *
11 * And the bugs have been added by:
12 *
13 * Copyright (C) 2010, Frederic Weisbecker <fweisbec@gmail.com>
14 * Copyright (C) 2012, Jiri Olsa <jolsa@redhat.com>
15 *
16 */
17
18#include <elf.h>
19#include <gelf.h>
20#include <fcntl.h>
21#include <string.h>
22#include <unistd.h>
23#include <sys/mman.h>
24#include <linux/list.h>
25#include <libunwind.h>
26#include <libunwind-ptrace.h>
27#include "callchain.h"
28#include "thread.h"
29#include "session.h"
30#include "perf_regs.h"
31#include "unwind.h"
32#include "symbol.h"
33#include "util.h"
34#include "debug.h"
35
36extern int
37UNW_OBJ(dwarf_search_unwind_table) (unw_addr_space_t as,
38				    unw_word_t ip,
39				    unw_dyn_info_t *di,
40				    unw_proc_info_t *pi,
41				    int need_unwind_info, void *arg);
42
43#define dwarf_search_unwind_table UNW_OBJ(dwarf_search_unwind_table)
44
45extern int
46UNW_OBJ(dwarf_find_debug_frame) (int found, unw_dyn_info_t *di_debug,
47				 unw_word_t ip,
48				 unw_word_t segbase,
49				 const char *obj_name, unw_word_t start,
50				 unw_word_t end);
51
52#define dwarf_find_debug_frame UNW_OBJ(dwarf_find_debug_frame)
53
54#define DW_EH_PE_FORMAT_MASK	0x0f	/* format of the encoded value */
55#define DW_EH_PE_APPL_MASK	0x70	/* how the value is to be applied */
56
57/* Pointer-encoding formats: */
58#define DW_EH_PE_omit		0xff
59#define DW_EH_PE_ptr		0x00	/* pointer-sized unsigned value */
60#define DW_EH_PE_udata4		0x03	/* unsigned 32-bit value */
61#define DW_EH_PE_udata8		0x04	/* unsigned 64-bit value */
62#define DW_EH_PE_sdata4		0x0b	/* signed 32-bit value */
63#define DW_EH_PE_sdata8		0x0c	/* signed 64-bit value */
64
65/* Pointer-encoding application: */
66#define DW_EH_PE_absptr		0x00	/* absolute value */
67#define DW_EH_PE_pcrel		0x10	/* rel. to addr. of encoded value */
68
69/*
70 * The following are not documented by LSB v1.3, yet they are used by
71 * GCC, presumably they aren't documented by LSB since they aren't
72 * used on Linux:
73 */
74#define DW_EH_PE_funcrel	0x40	/* start-of-procedure-relative */
75#define DW_EH_PE_aligned	0x50	/* aligned pointer */
76
77/* Flags intentionaly not handled, since they're not needed:
78 * #define DW_EH_PE_indirect      0x80
79 * #define DW_EH_PE_uleb128       0x01
80 * #define DW_EH_PE_udata2        0x02
81 * #define DW_EH_PE_sleb128       0x09
82 * #define DW_EH_PE_sdata2        0x0a
83 * #define DW_EH_PE_textrel       0x20
84 * #define DW_EH_PE_datarel       0x30
85 */
86
87struct unwind_info {
88	struct perf_sample	*sample;
89	struct machine		*machine;
90	struct thread		*thread;
91};
92
93#define dw_read(ptr, type, end) ({	\
94	type *__p = (type *) ptr;	\
95	type  __v;			\
96	if ((__p + 1) > (type *) end)	\
97		return -EINVAL;		\
98	__v = *__p++;			\
99	ptr = (typeof(ptr)) __p;	\
100	__v;				\
101	})
102
103static int __dw_read_encoded_value(u8 **p, u8 *end, u64 *val,
104				   u8 encoding)
105{
106	u8 *cur = *p;
107	*val = 0;
108
109	switch (encoding) {
110	case DW_EH_PE_omit:
111		*val = 0;
112		goto out;
113	case DW_EH_PE_ptr:
114		*val = dw_read(cur, unsigned long, end);
115		goto out;
116	default:
117		break;
118	}
119
120	switch (encoding & DW_EH_PE_APPL_MASK) {
121	case DW_EH_PE_absptr:
122		break;
123	case DW_EH_PE_pcrel:
124		*val = (unsigned long) cur;
125		break;
126	default:
127		return -EINVAL;
128	}
129
130	if ((encoding & 0x07) == 0x00)
131		encoding |= DW_EH_PE_udata4;
132
133	switch (encoding & DW_EH_PE_FORMAT_MASK) {
134	case DW_EH_PE_sdata4:
135		*val += dw_read(cur, s32, end);
136		break;
137	case DW_EH_PE_udata4:
138		*val += dw_read(cur, u32, end);
139		break;
140	case DW_EH_PE_sdata8:
141		*val += dw_read(cur, s64, end);
142		break;
143	case DW_EH_PE_udata8:
144		*val += dw_read(cur, u64, end);
145		break;
146	default:
147		return -EINVAL;
148	}
149
150 out:
151	*p = cur;
152	return 0;
153}
154
155#define dw_read_encoded_value(ptr, end, enc) ({			\
156	u64 __v;						\
157	if (__dw_read_encoded_value(&ptr, end, &__v, enc)) {	\
158		return -EINVAL;                                 \
159	}                                                       \
160	__v;                                                    \
161	})
162
163static u64 elf_section_offset(int fd, const char *name)
164{
165	Elf *elf;
166	GElf_Ehdr ehdr;
167	GElf_Shdr shdr;
168	u64 offset = 0;
169
170	elf = elf_begin(fd, PERF_ELF_C_READ_MMAP, NULL);
171	if (elf == NULL)
172		return 0;
173
174	do {
175		if (gelf_getehdr(elf, &ehdr) == NULL)
176			break;
177
178		if (!elf_section_by_name(elf, &ehdr, &shdr, name, NULL))
179			break;
180
181		offset = shdr.sh_offset;
182	} while (0);
183
184	elf_end(elf);
185	return offset;
186}
187
188#ifndef NO_LIBUNWIND_DEBUG_FRAME
189static int elf_is_exec(int fd, const char *name)
190{
191	Elf *elf;
192	GElf_Ehdr ehdr;
193	int retval = 0;
194
195	elf = elf_begin(fd, PERF_ELF_C_READ_MMAP, NULL);
196	if (elf == NULL)
197		return 0;
198	if (gelf_getehdr(elf, &ehdr) == NULL)
199		goto out;
200
201	retval = (ehdr.e_type == ET_EXEC);
202
203out:
204	elf_end(elf);
205	pr_debug("unwind: elf_is_exec(%s): %d\n", name, retval);
206	return retval;
207}
208#endif
209
210struct table_entry {
211	u32 start_ip_offset;
212	u32 fde_offset;
213};
214
215struct eh_frame_hdr {
216	unsigned char version;
217	unsigned char eh_frame_ptr_enc;
218	unsigned char fde_count_enc;
219	unsigned char table_enc;
220
221	/*
222	 * The rest of the header is variable-length and consists of the
223	 * following members:
224	 *
225	 *	encoded_t eh_frame_ptr;
226	 *	encoded_t fde_count;
227	 */
228
229	/* A single encoded pointer should not be more than 8 bytes. */
230	u64 enc[2];
231
232	/*
233	 * struct {
234	 *    encoded_t start_ip;
235	 *    encoded_t fde_addr;
236	 * } binary_search_table[fde_count];
237	 */
238	char data[0];
239} __packed;
240
241static int unwind_spec_ehframe(struct dso *dso, struct machine *machine,
242			       u64 offset, u64 *table_data, u64 *segbase,
243			       u64 *fde_count)
244{
245	struct eh_frame_hdr hdr;
246	u8 *enc = (u8 *) &hdr.enc;
247	u8 *end = (u8 *) &hdr.data;
248	ssize_t r;
249
250	r = dso__data_read_offset(dso, machine, offset,
251				  (u8 *) &hdr, sizeof(hdr));
252	if (r != sizeof(hdr))
253		return -EINVAL;
254
255	/* We dont need eh_frame_ptr, just skip it. */
256	dw_read_encoded_value(enc, end, hdr.eh_frame_ptr_enc);
257
258	*fde_count  = dw_read_encoded_value(enc, end, hdr.fde_count_enc);
259	*segbase    = offset;
260	*table_data = (enc - (u8 *) &hdr) + offset;
261	return 0;
262}
263
264static int read_unwind_spec_eh_frame(struct dso *dso, struct machine *machine,
265				     u64 *table_data, u64 *segbase,
266				     u64 *fde_count)
267{
268	int ret = -EINVAL, fd;
269	u64 offset = dso->data.eh_frame_hdr_offset;
270
271	if (offset == 0) {
272		fd = dso__data_get_fd(dso, machine);
273		if (fd < 0)
274			return -EINVAL;
275
276		/* Check the .eh_frame section for unwinding info */
277		offset = elf_section_offset(fd, ".eh_frame_hdr");
278		dso->data.eh_frame_hdr_offset = offset;
279		dso__data_put_fd(dso);
280	}
281
282	if (offset)
283		ret = unwind_spec_ehframe(dso, machine, offset,
284					  table_data, segbase,
285					  fde_count);
286
287	return ret;
288}
289
290#ifndef NO_LIBUNWIND_DEBUG_FRAME
291static int read_unwind_spec_debug_frame(struct dso *dso,
292					struct machine *machine, u64 *offset)
293{
294	int fd;
295	u64 ofs = dso->data.debug_frame_offset;
296
297	if (ofs == 0) {
298		fd = dso__data_get_fd(dso, machine);
299		if (fd < 0)
300			return -EINVAL;
301
302		/* Check the .debug_frame section for unwinding info */
303		ofs = elf_section_offset(fd, ".debug_frame");
304		dso->data.debug_frame_offset = ofs;
305		dso__data_put_fd(dso);
306	}
307
308	*offset = ofs;
309	if (*offset)
310		return 0;
311
312	return -EINVAL;
313}
314#endif
315
316static struct map *find_map(unw_word_t ip, struct unwind_info *ui)
317{
318	struct addr_location al;
319
320	thread__find_addr_map(ui->thread, PERF_RECORD_MISC_USER,
321			      MAP__FUNCTION, ip, &al);
322	return al.map;
323}
324
325static int
326find_proc_info(unw_addr_space_t as, unw_word_t ip, unw_proc_info_t *pi,
327	       int need_unwind_info, void *arg)
328{
329	struct unwind_info *ui = arg;
330	struct map *map;
331	unw_dyn_info_t di;
332	u64 table_data, segbase, fde_count;
333	int ret = -EINVAL;
334
335	map = find_map(ip, ui);
336	if (!map || !map->dso)
337		return -EINVAL;
338
339	pr_debug("unwind: find_proc_info dso %s\n", map->dso->name);
340
341	/* Check the .eh_frame section for unwinding info */
342	if (!read_unwind_spec_eh_frame(map->dso, ui->machine,
343				       &table_data, &segbase, &fde_count)) {
344		memset(&di, 0, sizeof(di));
345		di.format   = UNW_INFO_FORMAT_REMOTE_TABLE;
346		di.start_ip = map->start;
347		di.end_ip   = map->end;
348		di.u.rti.segbase    = map->start + segbase;
349		di.u.rti.table_data = map->start + table_data;
350		di.u.rti.table_len  = fde_count * sizeof(struct table_entry)
351				      / sizeof(unw_word_t);
352		ret = dwarf_search_unwind_table(as, ip, &di, pi,
353						need_unwind_info, arg);
354	}
355
356#ifndef NO_LIBUNWIND_DEBUG_FRAME
357	/* Check the .debug_frame section for unwinding info */
358	if (ret < 0 &&
359	    !read_unwind_spec_debug_frame(map->dso, ui->machine, &segbase)) {
360		int fd = dso__data_get_fd(map->dso, ui->machine);
361		int is_exec = elf_is_exec(fd, map->dso->name);
362		unw_word_t base = is_exec ? 0 : map->start;
363		const char *symfile;
364
365		if (fd >= 0)
366			dso__data_put_fd(map->dso);
367
368		symfile = map->dso->symsrc_filename ?: map->dso->name;
369
370		memset(&di, 0, sizeof(di));
371		if (dwarf_find_debug_frame(0, &di, ip, base, symfile,
372					   map->start, map->end))
373			return dwarf_search_unwind_table(as, ip, &di, pi,
374							 need_unwind_info, arg);
375	}
376#endif
377
378	return ret;
379}
380
381static int access_fpreg(unw_addr_space_t __maybe_unused as,
382			unw_regnum_t __maybe_unused num,
383			unw_fpreg_t __maybe_unused *val,
384			int __maybe_unused __write,
385			void __maybe_unused *arg)
386{
387	pr_err("unwind: access_fpreg unsupported\n");
388	return -UNW_EINVAL;
389}
390
391static int get_dyn_info_list_addr(unw_addr_space_t __maybe_unused as,
392				  unw_word_t __maybe_unused *dil_addr,
393				  void __maybe_unused *arg)
394{
395	return -UNW_ENOINFO;
396}
397
398static int resume(unw_addr_space_t __maybe_unused as,
399		  unw_cursor_t __maybe_unused *cu,
400		  void __maybe_unused *arg)
401{
402	pr_err("unwind: resume unsupported\n");
403	return -UNW_EINVAL;
404}
405
406static int
407get_proc_name(unw_addr_space_t __maybe_unused as,
408	      unw_word_t __maybe_unused addr,
409		char __maybe_unused *bufp, size_t __maybe_unused buf_len,
410		unw_word_t __maybe_unused *offp, void __maybe_unused *arg)
411{
412	pr_err("unwind: get_proc_name unsupported\n");
413	return -UNW_EINVAL;
414}
415
416static int access_dso_mem(struct unwind_info *ui, unw_word_t addr,
417			  unw_word_t *data)
418{
419	struct addr_location al;
420	ssize_t size;
421
422	thread__find_addr_map(ui->thread, PERF_RECORD_MISC_USER,
423			      MAP__FUNCTION, addr, &al);
424	if (!al.map) {
425		pr_debug("unwind: no map for %lx\n", (unsigned long)addr);
426		return -1;
427	}
428
429	if (!al.map->dso)
430		return -1;
431
432	size = dso__data_read_addr(al.map->dso, al.map, ui->machine,
433				   addr, (u8 *) data, sizeof(*data));
434
435	return !(size == sizeof(*data));
436}
437
438static int access_mem(unw_addr_space_t __maybe_unused as,
439		      unw_word_t addr, unw_word_t *valp,
440		      int __write, void *arg)
441{
442	struct unwind_info *ui = arg;
443	struct stack_dump *stack = &ui->sample->user_stack;
444	u64 start, end;
445	int offset;
446	int ret;
447
448	/* Don't support write, probably not needed. */
449	if (__write || !stack || !ui->sample->user_regs.regs) {
450		*valp = 0;
451		return 0;
452	}
453
454	ret = perf_reg_value(&start, &ui->sample->user_regs, PERF_REG_SP);
455	if (ret)
456		return ret;
457
458	end = start + stack->size;
459
460	/* Check overflow. */
461	if (addr + sizeof(unw_word_t) < addr)
462		return -EINVAL;
463
464	if (addr < start || addr + sizeof(unw_word_t) >= end) {
465		ret = access_dso_mem(ui, addr, valp);
466		if (ret) {
467			pr_debug("unwind: access_mem %p not inside range"
468				 " 0x%" PRIx64 "-0x%" PRIx64 "\n",
469				 (void *) (uintptr_t) addr, start, end);
470			*valp = 0;
471			return ret;
472		}
473		return 0;
474	}
475
476	offset = addr - start;
477	*valp  = *(unw_word_t *)&stack->data[offset];
478	pr_debug("unwind: access_mem addr %p val %lx, offset %d\n",
479		 (void *) (uintptr_t) addr, (unsigned long)*valp, offset);
480	return 0;
481}
482
483static int access_reg(unw_addr_space_t __maybe_unused as,
484		      unw_regnum_t regnum, unw_word_t *valp,
485		      int __write, void *arg)
486{
487	struct unwind_info *ui = arg;
488	int id, ret;
489	u64 val;
490
491	/* Don't support write, I suspect we don't need it. */
492	if (__write) {
493		pr_err("unwind: access_reg w %d\n", regnum);
494		return 0;
495	}
496
497	if (!ui->sample->user_regs.regs) {
498		*valp = 0;
499		return 0;
500	}
501
502	id = libunwind__arch_reg_id(regnum);
503	if (id < 0)
504		return -EINVAL;
505
506	ret = perf_reg_value(&val, &ui->sample->user_regs, id);
507	if (ret) {
508		pr_err("unwind: can't read reg %d\n", regnum);
509		return ret;
510	}
511
512	*valp = (unw_word_t) val;
513	pr_debug("unwind: reg %d, val %lx\n", regnum, (unsigned long)*valp);
514	return 0;
515}
516
517static void put_unwind_info(unw_addr_space_t __maybe_unused as,
518			    unw_proc_info_t *pi __maybe_unused,
519			    void *arg __maybe_unused)
520{
521	pr_debug("unwind: put_unwind_info called\n");
522}
523
524static int entry(u64 ip, struct thread *thread,
525		 unwind_entry_cb_t cb, void *arg)
526{
527	struct unwind_entry e;
528	struct addr_location al;
529
530	thread__find_addr_location(thread, PERF_RECORD_MISC_USER,
531				   MAP__FUNCTION, ip, &al);
532
533	e.ip = ip;
534	e.map = al.map;
535	e.sym = al.sym;
536
537	pr_debug("unwind: %s:ip = 0x%" PRIx64 " (0x%" PRIx64 ")\n",
538		 al.sym ? al.sym->name : "''",
539		 ip,
540		 al.map ? al.map->map_ip(al.map, ip) : (u64) 0);
541
542	return cb(&e, arg);
543}
544
545static void display_error(int err)
546{
547	switch (err) {
548	case UNW_EINVAL:
549		pr_err("unwind: Only supports local.\n");
550		break;
551	case UNW_EUNSPEC:
552		pr_err("unwind: Unspecified error.\n");
553		break;
554	case UNW_EBADREG:
555		pr_err("unwind: Register unavailable.\n");
556		break;
557	default:
558		break;
559	}
560}
561
562static unw_accessors_t accessors = {
563	.find_proc_info		= find_proc_info,
564	.put_unwind_info	= put_unwind_info,
565	.get_dyn_info_list_addr	= get_dyn_info_list_addr,
566	.access_mem		= access_mem,
567	.access_reg		= access_reg,
568	.access_fpreg		= access_fpreg,
569	.resume			= resume,
570	.get_proc_name		= get_proc_name,
571};
572
573int unwind__prepare_access(struct thread *thread)
574{
575	unw_addr_space_t addr_space;
576
577	if (callchain_param.record_mode != CALLCHAIN_DWARF)
578		return 0;
579
580	addr_space = unw_create_addr_space(&accessors, 0);
581	if (!addr_space) {
582		pr_err("unwind: Can't create unwind address space.\n");
583		return -ENOMEM;
584	}
585
586	unw_set_caching_policy(addr_space, UNW_CACHE_GLOBAL);
587	thread__set_priv(thread, addr_space);
588
589	return 0;
590}
591
592void unwind__flush_access(struct thread *thread)
593{
594	unw_addr_space_t addr_space;
595
596	if (callchain_param.record_mode != CALLCHAIN_DWARF)
597		return;
598
599	addr_space = thread__priv(thread);
600	unw_flush_cache(addr_space, 0, 0);
601}
602
603void unwind__finish_access(struct thread *thread)
604{
605	unw_addr_space_t addr_space;
606
607	if (callchain_param.record_mode != CALLCHAIN_DWARF)
608		return;
609
610	addr_space = thread__priv(thread);
611	unw_destroy_addr_space(addr_space);
612}
613
614static int get_entries(struct unwind_info *ui, unwind_entry_cb_t cb,
615		       void *arg, int max_stack)
616{
617	unw_addr_space_t addr_space;
618	unw_cursor_t c;
619	int ret;
620
621	addr_space = thread__priv(ui->thread);
622	if (addr_space == NULL)
623		return -1;
624
625	ret = unw_init_remote(&c, addr_space, ui);
626	if (ret)
627		display_error(ret);
628
629	while (!ret && (unw_step(&c) > 0) && max_stack--) {
630		unw_word_t ip;
631
632		unw_get_reg(&c, UNW_REG_IP, &ip);
633		ret = ip ? entry(ip, ui->thread, cb, arg) : 0;
634	}
635
636	return ret;
637}
638
639int unwind__get_entries(unwind_entry_cb_t cb, void *arg,
640			struct thread *thread,
641			struct perf_sample *data, int max_stack)
642{
643	u64 ip;
644	struct unwind_info ui = {
645		.sample       = data,
646		.thread       = thread,
647		.machine      = thread->mg->machine,
648	};
649	int ret;
650
651	if (!data->user_regs.regs)
652		return -EINVAL;
653
654	ret = perf_reg_value(&ip, &data->user_regs, PERF_REG_IP);
655	if (ret)
656		return ret;
657
658	ret = entry(ip, thread, cb, arg);
659	if (ret)
660		return -ENOMEM;
661
662	return --max_stack > 0 ? get_entries(&ui, cb, arg, max_stack) : 0;
663}
664