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 "thread.h"
28#include "session.h"
29#include "perf_regs.h"
30#include "unwind.h"
31#include "util.h"
32
33extern int
34UNW_OBJ(dwarf_search_unwind_table) (unw_addr_space_t as,
35				    unw_word_t ip,
36				    unw_dyn_info_t *di,
37				    unw_proc_info_t *pi,
38				    int need_unwind_info, void *arg);
39
40#define dwarf_search_unwind_table UNW_OBJ(dwarf_search_unwind_table)
41
42#define DW_EH_PE_FORMAT_MASK	0x0f	/* format of the encoded value */
43#define DW_EH_PE_APPL_MASK	0x70	/* how the value is to be applied */
44
45/* Pointer-encoding formats: */
46#define DW_EH_PE_omit		0xff
47#define DW_EH_PE_ptr		0x00	/* pointer-sized unsigned value */
48#define DW_EH_PE_udata4		0x03	/* unsigned 32-bit value */
49#define DW_EH_PE_udata8		0x04	/* unsigned 64-bit value */
50#define DW_EH_PE_sdata4		0x0b	/* signed 32-bit value */
51#define DW_EH_PE_sdata8		0x0c	/* signed 64-bit value */
52
53/* Pointer-encoding application: */
54#define DW_EH_PE_absptr		0x00	/* absolute value */
55#define DW_EH_PE_pcrel		0x10	/* rel. to addr. of encoded value */
56
57/*
58 * The following are not documented by LSB v1.3, yet they are used by
59 * GCC, presumably they aren't documented by LSB since they aren't
60 * used on Linux:
61 */
62#define DW_EH_PE_funcrel	0x40	/* start-of-procedure-relative */
63#define DW_EH_PE_aligned	0x50	/* aligned pointer */
64
65/* Flags intentionaly not handled, since they're not needed:
66 * #define DW_EH_PE_indirect      0x80
67 * #define DW_EH_PE_uleb128       0x01
68 * #define DW_EH_PE_udata2        0x02
69 * #define DW_EH_PE_sleb128       0x09
70 * #define DW_EH_PE_sdata2        0x0a
71 * #define DW_EH_PE_textrel       0x20
72 * #define DW_EH_PE_datarel       0x30
73 */
74
75struct unwind_info {
76	struct perf_sample	*sample;
77	struct machine		*machine;
78	struct thread		*thread;
79	u64			sample_uregs;
80};
81
82#define dw_read(ptr, type, end) ({	\
83	type *__p = (type *) ptr;	\
84	type  __v;			\
85	if ((__p + 1) > (type *) end)	\
86		return -EINVAL;		\
87	__v = *__p++;			\
88	ptr = (typeof(ptr)) __p;	\
89	__v;				\
90	})
91
92static int __dw_read_encoded_value(u8 **p, u8 *end, u64 *val,
93				   u8 encoding)
94{
95	u8 *cur = *p;
96	*val = 0;
97
98	switch (encoding) {
99	case DW_EH_PE_omit:
100		*val = 0;
101		goto out;
102	case DW_EH_PE_ptr:
103		*val = dw_read(cur, unsigned long, end);
104		goto out;
105	default:
106		break;
107	}
108
109	switch (encoding & DW_EH_PE_APPL_MASK) {
110	case DW_EH_PE_absptr:
111		break;
112	case DW_EH_PE_pcrel:
113		*val = (unsigned long) cur;
114		break;
115	default:
116		return -EINVAL;
117	}
118
119	if ((encoding & 0x07) == 0x00)
120		encoding |= DW_EH_PE_udata4;
121
122	switch (encoding & DW_EH_PE_FORMAT_MASK) {
123	case DW_EH_PE_sdata4:
124		*val += dw_read(cur, s32, end);
125		break;
126	case DW_EH_PE_udata4:
127		*val += dw_read(cur, u32, end);
128		break;
129	case DW_EH_PE_sdata8:
130		*val += dw_read(cur, s64, end);
131		break;
132	case DW_EH_PE_udata8:
133		*val += dw_read(cur, u64, end);
134		break;
135	default:
136		return -EINVAL;
137	}
138
139 out:
140	*p = cur;
141	return 0;
142}
143
144#define dw_read_encoded_value(ptr, end, enc) ({			\
145	u64 __v;						\
146	if (__dw_read_encoded_value(&ptr, end, &__v, enc)) {	\
147		return -EINVAL;                                 \
148	}                                                       \
149	__v;                                                    \
150	})
151
152static Elf_Scn *elf_section_by_name(Elf *elf, GElf_Ehdr *ep,
153				    GElf_Shdr *shp, const char *name)
154{
155	Elf_Scn *sec = NULL;
156
157	while ((sec = elf_nextscn(elf, sec)) != NULL) {
158		char *str;
159
160		gelf_getshdr(sec, shp);
161		str = elf_strptr(elf, ep->e_shstrndx, shp->sh_name);
162		if (!strcmp(name, str))
163			break;
164	}
165
166	return sec;
167}
168
169static u64 elf_section_offset(int fd, const char *name)
170{
171	Elf *elf;
172	GElf_Ehdr ehdr;
173	GElf_Shdr shdr;
174	u64 offset = 0;
175
176	elf = elf_begin(fd, PERF_ELF_C_READ_MMAP, NULL);
177	if (elf == NULL)
178		return 0;
179
180	do {
181		if (gelf_getehdr(elf, &ehdr) == NULL)
182			break;
183
184		if (!elf_section_by_name(elf, &ehdr, &shdr, name))
185			break;
186
187		offset = shdr.sh_offset;
188	} while (0);
189
190	elf_end(elf);
191	return offset;
192}
193
194struct table_entry {
195	u32 start_ip_offset;
196	u32 fde_offset;
197};
198
199struct eh_frame_hdr {
200	unsigned char version;
201	unsigned char eh_frame_ptr_enc;
202	unsigned char fde_count_enc;
203	unsigned char table_enc;
204
205	/*
206	 * The rest of the header is variable-length and consists of the
207	 * following members:
208	 *
209	 *	encoded_t eh_frame_ptr;
210	 *	encoded_t fde_count;
211	 */
212
213	/* A single encoded pointer should not be more than 8 bytes. */
214	u64 enc[2];
215
216	/*
217	 * struct {
218	 *    encoded_t start_ip;
219	 *    encoded_t fde_addr;
220	 * } binary_search_table[fde_count];
221	 */
222	char data[0];
223} __packed;
224
225static int unwind_spec_ehframe(struct dso *dso, struct machine *machine,
226			       u64 offset, u64 *table_data, u64 *segbase,
227			       u64 *fde_count)
228{
229	struct eh_frame_hdr hdr;
230	u8 *enc = (u8 *) &hdr.enc;
231	u8 *end = (u8 *) &hdr.data;
232	ssize_t r;
233
234	r = dso__data_read_offset(dso, machine, offset,
235				  (u8 *) &hdr, sizeof(hdr));
236	if (r != sizeof(hdr))
237		return -EINVAL;
238
239	/* We dont need eh_frame_ptr, just skip it. */
240	dw_read_encoded_value(enc, end, hdr.eh_frame_ptr_enc);
241
242	*fde_count  = dw_read_encoded_value(enc, end, hdr.fde_count_enc);
243	*segbase    = offset;
244	*table_data = (enc - (u8 *) &hdr) + offset;
245	return 0;
246}
247
248static int read_unwind_spec(struct dso *dso, struct machine *machine,
249			    u64 *table_data, u64 *segbase, u64 *fde_count)
250{
251	int ret = -EINVAL, fd;
252	u64 offset;
253
254	fd = dso__data_fd(dso, machine);
255	if (fd < 0)
256		return -EINVAL;
257
258	offset = elf_section_offset(fd, ".eh_frame_hdr");
259	close(fd);
260
261	if (offset)
262		ret = unwind_spec_ehframe(dso, machine, offset,
263					  table_data, segbase,
264					  fde_count);
265
266	/* TODO .debug_frame check if eh_frame_hdr fails */
267	return ret;
268}
269
270static struct map *find_map(unw_word_t ip, struct unwind_info *ui)
271{
272	struct addr_location al;
273
274	thread__find_addr_map(ui->thread, ui->machine, PERF_RECORD_MISC_USER,
275			      MAP__FUNCTION, ip, &al);
276	return al.map;
277}
278
279static int
280find_proc_info(unw_addr_space_t as, unw_word_t ip, unw_proc_info_t *pi,
281	       int need_unwind_info, void *arg)
282{
283	struct unwind_info *ui = arg;
284	struct map *map;
285	unw_dyn_info_t di;
286	u64 table_data, segbase, fde_count;
287
288	map = find_map(ip, ui);
289	if (!map || !map->dso)
290		return -EINVAL;
291
292	pr_debug("unwind: find_proc_info dso %s\n", map->dso->name);
293
294	if (read_unwind_spec(map->dso, ui->machine,
295			     &table_data, &segbase, &fde_count))
296		return -EINVAL;
297
298	memset(&di, 0, sizeof(di));
299	di.format   = UNW_INFO_FORMAT_REMOTE_TABLE;
300	di.start_ip = map->start;
301	di.end_ip   = map->end;
302	di.u.rti.segbase    = map->start + segbase;
303	di.u.rti.table_data = map->start + table_data;
304	di.u.rti.table_len  = fde_count * sizeof(struct table_entry)
305			      / sizeof(unw_word_t);
306	return dwarf_search_unwind_table(as, ip, &di, pi,
307					 need_unwind_info, arg);
308}
309
310static int access_fpreg(unw_addr_space_t __maybe_unused as,
311			unw_regnum_t __maybe_unused num,
312			unw_fpreg_t __maybe_unused *val,
313			int __maybe_unused __write,
314			void __maybe_unused *arg)
315{
316	pr_err("unwind: access_fpreg unsupported\n");
317	return -UNW_EINVAL;
318}
319
320static int get_dyn_info_list_addr(unw_addr_space_t __maybe_unused as,
321				  unw_word_t __maybe_unused *dil_addr,
322				  void __maybe_unused *arg)
323{
324	return -UNW_ENOINFO;
325}
326
327static int resume(unw_addr_space_t __maybe_unused as,
328		  unw_cursor_t __maybe_unused *cu,
329		  void __maybe_unused *arg)
330{
331	pr_err("unwind: resume unsupported\n");
332	return -UNW_EINVAL;
333}
334
335static int
336get_proc_name(unw_addr_space_t __maybe_unused as,
337	      unw_word_t __maybe_unused addr,
338		char __maybe_unused *bufp, size_t __maybe_unused buf_len,
339		unw_word_t __maybe_unused *offp, void __maybe_unused *arg)
340{
341	pr_err("unwind: get_proc_name unsupported\n");
342	return -UNW_EINVAL;
343}
344
345static int access_dso_mem(struct unwind_info *ui, unw_word_t addr,
346			  unw_word_t *data)
347{
348	struct addr_location al;
349	ssize_t size;
350
351	thread__find_addr_map(ui->thread, ui->machine, PERF_RECORD_MISC_USER,
352			      MAP__FUNCTION, addr, &al);
353	if (!al.map) {
354		pr_debug("unwind: no map for %lx\n", (unsigned long)addr);
355		return -1;
356	}
357
358	if (!al.map->dso)
359		return -1;
360
361	size = dso__data_read_addr(al.map->dso, al.map, ui->machine,
362				   addr, (u8 *) data, sizeof(*data));
363
364	return !(size == sizeof(*data));
365}
366
367static int reg_value(unw_word_t *valp, struct regs_dump *regs, int id,
368		     u64 sample_regs)
369{
370	int i, idx = 0;
371
372	if (!(sample_regs & (1 << id)))
373		return -EINVAL;
374
375	for (i = 0; i < id; i++) {
376		if (sample_regs & (1 << i))
377			idx++;
378	}
379
380	*valp = regs->regs[idx];
381	return 0;
382}
383
384static int access_mem(unw_addr_space_t __maybe_unused as,
385		      unw_word_t addr, unw_word_t *valp,
386		      int __write, void *arg)
387{
388	struct unwind_info *ui = arg;
389	struct stack_dump *stack = &ui->sample->user_stack;
390	unw_word_t start, end;
391	int offset;
392	int ret;
393
394	/* Don't support write, probably not needed. */
395	if (__write || !stack || !ui->sample->user_regs.regs) {
396		*valp = 0;
397		return 0;
398	}
399
400	ret = reg_value(&start, &ui->sample->user_regs, PERF_REG_SP,
401			ui->sample_uregs);
402	if (ret)
403		return ret;
404
405	end = start + stack->size;
406
407	/* Check overflow. */
408	if (addr + sizeof(unw_word_t) < addr)
409		return -EINVAL;
410
411	if (addr < start || addr + sizeof(unw_word_t) >= end) {
412		ret = access_dso_mem(ui, addr, valp);
413		if (ret) {
414			pr_debug("unwind: access_mem %p not inside range %p-%p\n",
415				(void *)addr, (void *)start, (void *)end);
416			*valp = 0;
417			return ret;
418		}
419		return 0;
420	}
421
422	offset = addr - start;
423	*valp  = *(unw_word_t *)&stack->data[offset];
424	pr_debug("unwind: access_mem addr %p, val %lx, offset %d\n",
425		 (void *)addr, (unsigned long)*valp, offset);
426	return 0;
427}
428
429static int access_reg(unw_addr_space_t __maybe_unused as,
430		      unw_regnum_t regnum, unw_word_t *valp,
431		      int __write, void *arg)
432{
433	struct unwind_info *ui = arg;
434	int id, ret;
435
436	/* Don't support write, I suspect we don't need it. */
437	if (__write) {
438		pr_err("unwind: access_reg w %d\n", regnum);
439		return 0;
440	}
441
442	if (!ui->sample->user_regs.regs) {
443		*valp = 0;
444		return 0;
445	}
446
447	id = unwind__arch_reg_id(regnum);
448	if (id < 0)
449		return -EINVAL;
450
451	ret = reg_value(valp, &ui->sample->user_regs, id, ui->sample_uregs);
452	if (ret) {
453		pr_err("unwind: can't read reg %d\n", regnum);
454		return ret;
455	}
456
457	pr_debug("unwind: reg %d, val %lx\n", regnum, (unsigned long)*valp);
458	return 0;
459}
460
461static void put_unwind_info(unw_addr_space_t __maybe_unused as,
462			    unw_proc_info_t *pi __maybe_unused,
463			    void *arg __maybe_unused)
464{
465	pr_debug("unwind: put_unwind_info called\n");
466}
467
468static int entry(u64 ip, struct thread *thread, struct machine *machine,
469		 unwind_entry_cb_t cb, void *arg)
470{
471	struct unwind_entry e;
472	struct addr_location al;
473
474	thread__find_addr_location(thread, machine,
475				   PERF_RECORD_MISC_USER,
476				   MAP__FUNCTION, ip, &al);
477
478	e.ip = ip;
479	e.map = al.map;
480	e.sym = al.sym;
481
482	pr_debug("unwind: %s:ip = 0x%" PRIx64 " (0x%" PRIx64 ")\n",
483		 al.sym ? al.sym->name : "''",
484		 ip,
485		 al.map ? al.map->map_ip(al.map, ip) : (u64) 0);
486
487	return cb(&e, arg);
488}
489
490static void display_error(int err)
491{
492	switch (err) {
493	case UNW_EINVAL:
494		pr_err("unwind: Only supports local.\n");
495		break;
496	case UNW_EUNSPEC:
497		pr_err("unwind: Unspecified error.\n");
498		break;
499	case UNW_EBADREG:
500		pr_err("unwind: Register unavailable.\n");
501		break;
502	default:
503		break;
504	}
505}
506
507static unw_accessors_t accessors = {
508	.find_proc_info		= find_proc_info,
509	.put_unwind_info	= put_unwind_info,
510	.get_dyn_info_list_addr	= get_dyn_info_list_addr,
511	.access_mem		= access_mem,
512	.access_reg		= access_reg,
513	.access_fpreg		= access_fpreg,
514	.resume			= resume,
515	.get_proc_name		= get_proc_name,
516};
517
518static int get_entries(struct unwind_info *ui, unwind_entry_cb_t cb,
519		       void *arg)
520{
521	unw_addr_space_t addr_space;
522	unw_cursor_t c;
523	int ret;
524
525	addr_space = unw_create_addr_space(&accessors, 0);
526	if (!addr_space) {
527		pr_err("unwind: Can't create unwind address space.\n");
528		return -ENOMEM;
529	}
530
531	ret = unw_init_remote(&c, addr_space, ui);
532	if (ret)
533		display_error(ret);
534
535	while (!ret && (unw_step(&c) > 0)) {
536		unw_word_t ip;
537
538		unw_get_reg(&c, UNW_REG_IP, &ip);
539		ret = entry(ip, ui->thread, ui->machine, cb, arg);
540	}
541
542	unw_destroy_addr_space(addr_space);
543	return ret;
544}
545
546int unwind__get_entries(unwind_entry_cb_t cb, void *arg,
547			struct machine *machine, struct thread *thread,
548			u64 sample_uregs, struct perf_sample *data)
549{
550	unw_word_t ip;
551	struct unwind_info ui = {
552		.sample       = data,
553		.sample_uregs = sample_uregs,
554		.thread       = thread,
555		.machine      = machine,
556	};
557	int ret;
558
559	if (!data->user_regs.regs)
560		return -EINVAL;
561
562	ret = reg_value(&ip, &data->user_regs, PERF_REG_IP, sample_uregs);
563	if (ret)
564		return ret;
565
566	ret = entry(ip, thread, machine, cb, arg);
567	if (ret)
568		return -ENOMEM;
569
570	return get_entries(&ui, cb, arg);
571}
572