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_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	}
280
281	if (offset)
282		ret = unwind_spec_ehframe(dso, machine, offset,
283					  table_data, segbase,
284					  fde_count);
285
286	return ret;
287}
288
289#ifndef NO_LIBUNWIND_DEBUG_FRAME
290static int read_unwind_spec_debug_frame(struct dso *dso,
291					struct machine *machine, u64 *offset)
292{
293	int fd;
294	u64 ofs = dso->data.debug_frame_offset;
295
296	if (ofs == 0) {
297		fd = dso__data_fd(dso, machine);
298		if (fd < 0)
299			return -EINVAL;
300
301		/* Check the .debug_frame section for unwinding info */
302		ofs = elf_section_offset(fd, ".debug_frame");
303		dso->data.debug_frame_offset = ofs;
304	}
305
306	*offset = ofs;
307	if (*offset)
308		return 0;
309
310	return -EINVAL;
311}
312#endif
313
314static struct map *find_map(unw_word_t ip, struct unwind_info *ui)
315{
316	struct addr_location al;
317
318	thread__find_addr_map(ui->thread, PERF_RECORD_MISC_USER,
319			      MAP__FUNCTION, ip, &al);
320	return al.map;
321}
322
323static int
324find_proc_info(unw_addr_space_t as, unw_word_t ip, unw_proc_info_t *pi,
325	       int need_unwind_info, void *arg)
326{
327	struct unwind_info *ui = arg;
328	struct map *map;
329	unw_dyn_info_t di;
330	u64 table_data, segbase, fde_count;
331
332	map = find_map(ip, ui);
333	if (!map || !map->dso)
334		return -EINVAL;
335
336	pr_debug("unwind: find_proc_info dso %s\n", map->dso->name);
337
338	/* Check the .eh_frame section for unwinding info */
339	if (!read_unwind_spec_eh_frame(map->dso, ui->machine,
340				       &table_data, &segbase, &fde_count)) {
341		memset(&di, 0, sizeof(di));
342		di.format   = UNW_INFO_FORMAT_REMOTE_TABLE;
343		di.start_ip = map->start;
344		di.end_ip   = map->end;
345		di.u.rti.segbase    = map->start + segbase;
346		di.u.rti.table_data = map->start + table_data;
347		di.u.rti.table_len  = fde_count * sizeof(struct table_entry)
348				      / sizeof(unw_word_t);
349		return dwarf_search_unwind_table(as, ip, &di, pi,
350						 need_unwind_info, arg);
351	}
352
353#ifndef NO_LIBUNWIND_DEBUG_FRAME
354	/* Check the .debug_frame section for unwinding info */
355	if (!read_unwind_spec_debug_frame(map->dso, ui->machine, &segbase)) {
356		int fd = dso__data_fd(map->dso, ui->machine);
357		int is_exec = elf_is_exec(fd, map->dso->name);
358		unw_word_t base = is_exec ? 0 : map->start;
359
360		memset(&di, 0, sizeof(di));
361		if (dwarf_find_debug_frame(0, &di, ip, base, map->dso->name,
362					   map->start, map->end))
363			return dwarf_search_unwind_table(as, ip, &di, pi,
364							 need_unwind_info, arg);
365	}
366#endif
367
368	return -EINVAL;
369}
370
371static int access_fpreg(unw_addr_space_t __maybe_unused as,
372			unw_regnum_t __maybe_unused num,
373			unw_fpreg_t __maybe_unused *val,
374			int __maybe_unused __write,
375			void __maybe_unused *arg)
376{
377	pr_err("unwind: access_fpreg unsupported\n");
378	return -UNW_EINVAL;
379}
380
381static int get_dyn_info_list_addr(unw_addr_space_t __maybe_unused as,
382				  unw_word_t __maybe_unused *dil_addr,
383				  void __maybe_unused *arg)
384{
385	return -UNW_ENOINFO;
386}
387
388static int resume(unw_addr_space_t __maybe_unused as,
389		  unw_cursor_t __maybe_unused *cu,
390		  void __maybe_unused *arg)
391{
392	pr_err("unwind: resume unsupported\n");
393	return -UNW_EINVAL;
394}
395
396static int
397get_proc_name(unw_addr_space_t __maybe_unused as,
398	      unw_word_t __maybe_unused addr,
399		char __maybe_unused *bufp, size_t __maybe_unused buf_len,
400		unw_word_t __maybe_unused *offp, void __maybe_unused *arg)
401{
402	pr_err("unwind: get_proc_name unsupported\n");
403	return -UNW_EINVAL;
404}
405
406static int access_dso_mem(struct unwind_info *ui, unw_word_t addr,
407			  unw_word_t *data)
408{
409	struct addr_location al;
410	ssize_t size;
411
412	thread__find_addr_map(ui->thread, PERF_RECORD_MISC_USER,
413			      MAP__FUNCTION, addr, &al);
414	if (!al.map) {
415		pr_debug("unwind: no map for %lx\n", (unsigned long)addr);
416		return -1;
417	}
418
419	if (!al.map->dso)
420		return -1;
421
422	size = dso__data_read_addr(al.map->dso, al.map, ui->machine,
423				   addr, (u8 *) data, sizeof(*data));
424
425	return !(size == sizeof(*data));
426}
427
428static int access_mem(unw_addr_space_t __maybe_unused as,
429		      unw_word_t addr, unw_word_t *valp,
430		      int __write, void *arg)
431{
432	struct unwind_info *ui = arg;
433	struct stack_dump *stack = &ui->sample->user_stack;
434	u64 start, end;
435	int offset;
436	int ret;
437
438	/* Don't support write, probably not needed. */
439	if (__write || !stack || !ui->sample->user_regs.regs) {
440		*valp = 0;
441		return 0;
442	}
443
444	ret = perf_reg_value(&start, &ui->sample->user_regs, PERF_REG_SP);
445	if (ret)
446		return ret;
447
448	end = start + stack->size;
449
450	/* Check overflow. */
451	if (addr + sizeof(unw_word_t) < addr)
452		return -EINVAL;
453
454	if (addr < start || addr + sizeof(unw_word_t) >= end) {
455		ret = access_dso_mem(ui, addr, valp);
456		if (ret) {
457			pr_debug("unwind: access_mem %p not inside range"
458				 " 0x%" PRIx64 "-0x%" PRIx64 "\n",
459				 (void *) addr, start, end);
460			*valp = 0;
461			return ret;
462		}
463		return 0;
464	}
465
466	offset = addr - start;
467	*valp  = *(unw_word_t *)&stack->data[offset];
468	pr_debug("unwind: access_mem addr %p val %lx, offset %d\n",
469		 (void *) addr, (unsigned long)*valp, offset);
470	return 0;
471}
472
473static int access_reg(unw_addr_space_t __maybe_unused as,
474		      unw_regnum_t regnum, unw_word_t *valp,
475		      int __write, void *arg)
476{
477	struct unwind_info *ui = arg;
478	int id, ret;
479	u64 val;
480
481	/* Don't support write, I suspect we don't need it. */
482	if (__write) {
483		pr_err("unwind: access_reg w %d\n", regnum);
484		return 0;
485	}
486
487	if (!ui->sample->user_regs.regs) {
488		*valp = 0;
489		return 0;
490	}
491
492	id = libunwind__arch_reg_id(regnum);
493	if (id < 0)
494		return -EINVAL;
495
496	ret = perf_reg_value(&val, &ui->sample->user_regs, id);
497	if (ret) {
498		pr_err("unwind: can't read reg %d\n", regnum);
499		return ret;
500	}
501
502	*valp = (unw_word_t) val;
503	pr_debug("unwind: reg %d, val %lx\n", regnum, (unsigned long)*valp);
504	return 0;
505}
506
507static void put_unwind_info(unw_addr_space_t __maybe_unused as,
508			    unw_proc_info_t *pi __maybe_unused,
509			    void *arg __maybe_unused)
510{
511	pr_debug("unwind: put_unwind_info called\n");
512}
513
514static int entry(u64 ip, struct thread *thread,
515		 unwind_entry_cb_t cb, void *arg)
516{
517	struct unwind_entry e;
518	struct addr_location al;
519
520	thread__find_addr_location(thread, PERF_RECORD_MISC_USER,
521				   MAP__FUNCTION, ip, &al);
522
523	e.ip = ip;
524	e.map = al.map;
525	e.sym = al.sym;
526
527	pr_debug("unwind: %s:ip = 0x%" PRIx64 " (0x%" PRIx64 ")\n",
528		 al.sym ? al.sym->name : "''",
529		 ip,
530		 al.map ? al.map->map_ip(al.map, ip) : (u64) 0);
531
532	return cb(&e, arg);
533}
534
535static void display_error(int err)
536{
537	switch (err) {
538	case UNW_EINVAL:
539		pr_err("unwind: Only supports local.\n");
540		break;
541	case UNW_EUNSPEC:
542		pr_err("unwind: Unspecified error.\n");
543		break;
544	case UNW_EBADREG:
545		pr_err("unwind: Register unavailable.\n");
546		break;
547	default:
548		break;
549	}
550}
551
552static unw_accessors_t accessors = {
553	.find_proc_info		= find_proc_info,
554	.put_unwind_info	= put_unwind_info,
555	.get_dyn_info_list_addr	= get_dyn_info_list_addr,
556	.access_mem		= access_mem,
557	.access_reg		= access_reg,
558	.access_fpreg		= access_fpreg,
559	.resume			= resume,
560	.get_proc_name		= get_proc_name,
561};
562
563int unwind__prepare_access(struct thread *thread)
564{
565	unw_addr_space_t addr_space;
566
567	if (callchain_param.record_mode != CALLCHAIN_DWARF)
568		return 0;
569
570	addr_space = unw_create_addr_space(&accessors, 0);
571	if (!addr_space) {
572		pr_err("unwind: Can't create unwind address space.\n");
573		return -ENOMEM;
574	}
575
576	unw_set_caching_policy(addr_space, UNW_CACHE_GLOBAL);
577	thread__set_priv(thread, addr_space);
578
579	return 0;
580}
581
582void unwind__flush_access(struct thread *thread)
583{
584	unw_addr_space_t addr_space;
585
586	if (callchain_param.record_mode != CALLCHAIN_DWARF)
587		return;
588
589	addr_space = thread__priv(thread);
590	unw_flush_cache(addr_space, 0, 0);
591}
592
593void unwind__finish_access(struct thread *thread)
594{
595	unw_addr_space_t addr_space;
596
597	if (callchain_param.record_mode != CALLCHAIN_DWARF)
598		return;
599
600	addr_space = thread__priv(thread);
601	unw_destroy_addr_space(addr_space);
602}
603
604static int get_entries(struct unwind_info *ui, unwind_entry_cb_t cb,
605		       void *arg, int max_stack)
606{
607	unw_addr_space_t addr_space;
608	unw_cursor_t c;
609	int ret;
610
611	addr_space = thread__priv(ui->thread);
612	if (addr_space == NULL)
613		return -1;
614
615	ret = unw_init_remote(&c, addr_space, ui);
616	if (ret)
617		display_error(ret);
618
619	while (!ret && (unw_step(&c) > 0) && max_stack--) {
620		unw_word_t ip;
621
622		unw_get_reg(&c, UNW_REG_IP, &ip);
623		ret = ip ? entry(ip, ui->thread, cb, arg) : 0;
624	}
625
626	return ret;
627}
628
629int unwind__get_entries(unwind_entry_cb_t cb, void *arg,
630			struct thread *thread,
631			struct perf_sample *data, int max_stack)
632{
633	u64 ip;
634	struct unwind_info ui = {
635		.sample       = data,
636		.thread       = thread,
637		.machine      = thread->mg->machine,
638	};
639	int ret;
640
641	if (!data->user_regs.regs)
642		return -EINVAL;
643
644	ret = perf_reg_value(&ip, &data->user_regs, PERF_REG_IP);
645	if (ret)
646		return ret;
647
648	ret = entry(ip, thread, cb, arg);
649	if (ret)
650		return -ENOMEM;
651
652	return --max_stack > 0 ? get_entries(&ui, cb, arg, max_stack) : 0;
653}
654