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 
36 extern int
37 UNW_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 
45 extern int
46 UNW_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 
87 struct 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 
103 static 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 
163 static 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 struct table_entry {
189 	u32 start_ip_offset;
190 	u32 fde_offset;
191 };
192 
193 struct eh_frame_hdr {
194 	unsigned char version;
195 	unsigned char eh_frame_ptr_enc;
196 	unsigned char fde_count_enc;
197 	unsigned char table_enc;
198 
199 	/*
200 	 * The rest of the header is variable-length and consists of the
201 	 * following members:
202 	 *
203 	 *	encoded_t eh_frame_ptr;
204 	 *	encoded_t fde_count;
205 	 */
206 
207 	/* A single encoded pointer should not be more than 8 bytes. */
208 	u64 enc[2];
209 
210 	/*
211 	 * struct {
212 	 *    encoded_t start_ip;
213 	 *    encoded_t fde_addr;
214 	 * } binary_search_table[fde_count];
215 	 */
216 	char data[0];
217 } __packed;
218 
219 static int unwind_spec_ehframe(struct dso *dso, struct machine *machine,
220 			       u64 offset, u64 *table_data, u64 *segbase,
221 			       u64 *fde_count)
222 {
223 	struct eh_frame_hdr hdr;
224 	u8 *enc = (u8 *) &hdr.enc;
225 	u8 *end = (u8 *) &hdr.data;
226 	ssize_t r;
227 
228 	r = dso__data_read_offset(dso, machine, offset,
229 				  (u8 *) &hdr, sizeof(hdr));
230 	if (r != sizeof(hdr))
231 		return -EINVAL;
232 
233 	/* We dont need eh_frame_ptr, just skip it. */
234 	dw_read_encoded_value(enc, end, hdr.eh_frame_ptr_enc);
235 
236 	*fde_count  = dw_read_encoded_value(enc, end, hdr.fde_count_enc);
237 	*segbase    = offset;
238 	*table_data = (enc - (u8 *) &hdr) + offset;
239 	return 0;
240 }
241 
242 static int read_unwind_spec_eh_frame(struct dso *dso, struct machine *machine,
243 				     u64 *table_data, u64 *segbase,
244 				     u64 *fde_count)
245 {
246 	int ret = -EINVAL, fd;
247 	u64 offset;
248 
249 	fd = dso__data_fd(dso, machine);
250 	if (fd < 0)
251 		return -EINVAL;
252 
253 	/* Check the .eh_frame section for unwinding info */
254 	offset = elf_section_offset(fd, ".eh_frame_hdr");
255 
256 	if (offset)
257 		ret = unwind_spec_ehframe(dso, machine, offset,
258 					  table_data, segbase,
259 					  fde_count);
260 
261 	return ret;
262 }
263 
264 #ifndef NO_LIBUNWIND_DEBUG_FRAME
265 static int read_unwind_spec_debug_frame(struct dso *dso,
266 					struct machine *machine, u64 *offset)
267 {
268 	int fd = dso__data_fd(dso, machine);
269 
270 	if (fd < 0)
271 		return -EINVAL;
272 
273 	/* Check the .debug_frame section for unwinding info */
274 	*offset = elf_section_offset(fd, ".debug_frame");
275 
276 	if (*offset)
277 		return 0;
278 
279 	return -EINVAL;
280 }
281 #endif
282 
283 static struct map *find_map(unw_word_t ip, struct unwind_info *ui)
284 {
285 	struct addr_location al;
286 
287 	thread__find_addr_map(ui->thread, ui->machine, PERF_RECORD_MISC_USER,
288 			      MAP__FUNCTION, ip, &al);
289 	return al.map;
290 }
291 
292 static int
293 find_proc_info(unw_addr_space_t as, unw_word_t ip, unw_proc_info_t *pi,
294 	       int need_unwind_info, void *arg)
295 {
296 	struct unwind_info *ui = arg;
297 	struct map *map;
298 	unw_dyn_info_t di;
299 	u64 table_data, segbase, fde_count;
300 
301 	map = find_map(ip, ui);
302 	if (!map || !map->dso)
303 		return -EINVAL;
304 
305 	pr_debug("unwind: find_proc_info dso %s\n", map->dso->name);
306 
307 	/* Check the .eh_frame section for unwinding info */
308 	if (!read_unwind_spec_eh_frame(map->dso, ui->machine,
309 				       &table_data, &segbase, &fde_count)) {
310 		memset(&di, 0, sizeof(di));
311 		di.format   = UNW_INFO_FORMAT_REMOTE_TABLE;
312 		di.start_ip = map->start;
313 		di.end_ip   = map->end;
314 		di.u.rti.segbase    = map->start + segbase;
315 		di.u.rti.table_data = map->start + table_data;
316 		di.u.rti.table_len  = fde_count * sizeof(struct table_entry)
317 				      / sizeof(unw_word_t);
318 		return dwarf_search_unwind_table(as, ip, &di, pi,
319 						 need_unwind_info, arg);
320 	}
321 
322 #ifndef NO_LIBUNWIND_DEBUG_FRAME
323 	/* Check the .debug_frame section for unwinding info */
324 	if (!read_unwind_spec_debug_frame(map->dso, ui->machine, &segbase)) {
325 		memset(&di, 0, sizeof(di));
326 		if (dwarf_find_debug_frame(0, &di, ip, 0, map->dso->name,
327 					   map->start, map->end))
328 			return dwarf_search_unwind_table(as, ip, &di, pi,
329 							 need_unwind_info, arg);
330 	}
331 #endif
332 
333 	return -EINVAL;
334 }
335 
336 static int access_fpreg(unw_addr_space_t __maybe_unused as,
337 			unw_regnum_t __maybe_unused num,
338 			unw_fpreg_t __maybe_unused *val,
339 			int __maybe_unused __write,
340 			void __maybe_unused *arg)
341 {
342 	pr_err("unwind: access_fpreg unsupported\n");
343 	return -UNW_EINVAL;
344 }
345 
346 static int get_dyn_info_list_addr(unw_addr_space_t __maybe_unused as,
347 				  unw_word_t __maybe_unused *dil_addr,
348 				  void __maybe_unused *arg)
349 {
350 	return -UNW_ENOINFO;
351 }
352 
353 static int resume(unw_addr_space_t __maybe_unused as,
354 		  unw_cursor_t __maybe_unused *cu,
355 		  void __maybe_unused *arg)
356 {
357 	pr_err("unwind: resume unsupported\n");
358 	return -UNW_EINVAL;
359 }
360 
361 static int
362 get_proc_name(unw_addr_space_t __maybe_unused as,
363 	      unw_word_t __maybe_unused addr,
364 		char __maybe_unused *bufp, size_t __maybe_unused buf_len,
365 		unw_word_t __maybe_unused *offp, void __maybe_unused *arg)
366 {
367 	pr_err("unwind: get_proc_name unsupported\n");
368 	return -UNW_EINVAL;
369 }
370 
371 static int access_dso_mem(struct unwind_info *ui, unw_word_t addr,
372 			  unw_word_t *data)
373 {
374 	struct addr_location al;
375 	ssize_t size;
376 
377 	thread__find_addr_map(ui->thread, ui->machine, PERF_RECORD_MISC_USER,
378 			      MAP__FUNCTION, addr, &al);
379 	if (!al.map) {
380 		pr_debug("unwind: no map for %lx\n", (unsigned long)addr);
381 		return -1;
382 	}
383 
384 	if (!al.map->dso)
385 		return -1;
386 
387 	size = dso__data_read_addr(al.map->dso, al.map, ui->machine,
388 				   addr, (u8 *) data, sizeof(*data));
389 
390 	return !(size == sizeof(*data));
391 }
392 
393 static int access_mem(unw_addr_space_t __maybe_unused as,
394 		      unw_word_t addr, unw_word_t *valp,
395 		      int __write, void *arg)
396 {
397 	struct unwind_info *ui = arg;
398 	struct stack_dump *stack = &ui->sample->user_stack;
399 	u64 start, end;
400 	int offset;
401 	int ret;
402 
403 	/* Don't support write, probably not needed. */
404 	if (__write || !stack || !ui->sample->user_regs.regs) {
405 		*valp = 0;
406 		return 0;
407 	}
408 
409 	ret = perf_reg_value(&start, &ui->sample->user_regs, PERF_REG_SP);
410 	if (ret)
411 		return ret;
412 
413 	end = start + stack->size;
414 
415 	/* Check overflow. */
416 	if (addr + sizeof(unw_word_t) < addr)
417 		return -EINVAL;
418 
419 	if (addr < start || addr + sizeof(unw_word_t) >= end) {
420 		ret = access_dso_mem(ui, addr, valp);
421 		if (ret) {
422 			pr_debug("unwind: access_mem %p not inside range"
423 				 " 0x%" PRIx64 "-0x%" PRIx64 "\n",
424 				 (void *) addr, start, end);
425 			*valp = 0;
426 			return ret;
427 		}
428 		return 0;
429 	}
430 
431 	offset = addr - start;
432 	*valp  = *(unw_word_t *)&stack->data[offset];
433 	pr_debug("unwind: access_mem addr %p val %lx, offset %d\n",
434 		 (void *) addr, (unsigned long)*valp, offset);
435 	return 0;
436 }
437 
438 static int access_reg(unw_addr_space_t __maybe_unused as,
439 		      unw_regnum_t regnum, unw_word_t *valp,
440 		      int __write, void *arg)
441 {
442 	struct unwind_info *ui = arg;
443 	int id, ret;
444 	u64 val;
445 
446 	/* Don't support write, I suspect we don't need it. */
447 	if (__write) {
448 		pr_err("unwind: access_reg w %d\n", regnum);
449 		return 0;
450 	}
451 
452 	if (!ui->sample->user_regs.regs) {
453 		*valp = 0;
454 		return 0;
455 	}
456 
457 	id = libunwind__arch_reg_id(regnum);
458 	if (id < 0)
459 		return -EINVAL;
460 
461 	ret = perf_reg_value(&val, &ui->sample->user_regs, id);
462 	if (ret) {
463 		pr_err("unwind: can't read reg %d\n", regnum);
464 		return ret;
465 	}
466 
467 	*valp = (unw_word_t) val;
468 	pr_debug("unwind: reg %d, val %lx\n", regnum, (unsigned long)*valp);
469 	return 0;
470 }
471 
472 static void put_unwind_info(unw_addr_space_t __maybe_unused as,
473 			    unw_proc_info_t *pi __maybe_unused,
474 			    void *arg __maybe_unused)
475 {
476 	pr_debug("unwind: put_unwind_info called\n");
477 }
478 
479 static int entry(u64 ip, struct thread *thread, struct machine *machine,
480 		 unwind_entry_cb_t cb, void *arg)
481 {
482 	struct unwind_entry e;
483 	struct addr_location al;
484 
485 	thread__find_addr_location(thread, machine,
486 				   PERF_RECORD_MISC_USER,
487 				   MAP__FUNCTION, ip, &al);
488 
489 	e.ip = ip;
490 	e.map = al.map;
491 	e.sym = al.sym;
492 
493 	pr_debug("unwind: %s:ip = 0x%" PRIx64 " (0x%" PRIx64 ")\n",
494 		 al.sym ? al.sym->name : "''",
495 		 ip,
496 		 al.map ? al.map->map_ip(al.map, ip) : (u64) 0);
497 
498 	return cb(&e, arg);
499 }
500 
501 static void display_error(int err)
502 {
503 	switch (err) {
504 	case UNW_EINVAL:
505 		pr_err("unwind: Only supports local.\n");
506 		break;
507 	case UNW_EUNSPEC:
508 		pr_err("unwind: Unspecified error.\n");
509 		break;
510 	case UNW_EBADREG:
511 		pr_err("unwind: Register unavailable.\n");
512 		break;
513 	default:
514 		break;
515 	}
516 }
517 
518 static unw_accessors_t accessors = {
519 	.find_proc_info		= find_proc_info,
520 	.put_unwind_info	= put_unwind_info,
521 	.get_dyn_info_list_addr	= get_dyn_info_list_addr,
522 	.access_mem		= access_mem,
523 	.access_reg		= access_reg,
524 	.access_fpreg		= access_fpreg,
525 	.resume			= resume,
526 	.get_proc_name		= get_proc_name,
527 };
528 
529 int unwind__prepare_access(struct thread *thread)
530 {
531 	unw_addr_space_t addr_space;
532 
533 	if (callchain_param.record_mode != CALLCHAIN_DWARF)
534 		return 0;
535 
536 	addr_space = unw_create_addr_space(&accessors, 0);
537 	if (!addr_space) {
538 		pr_err("unwind: Can't create unwind address space.\n");
539 		return -ENOMEM;
540 	}
541 
542 	unw_set_caching_policy(addr_space, UNW_CACHE_GLOBAL);
543 	thread__set_priv(thread, addr_space);
544 
545 	return 0;
546 }
547 
548 void unwind__flush_access(struct thread *thread)
549 {
550 	unw_addr_space_t addr_space;
551 
552 	if (callchain_param.record_mode != CALLCHAIN_DWARF)
553 		return;
554 
555 	addr_space = thread__priv(thread);
556 	unw_flush_cache(addr_space, 0, 0);
557 }
558 
559 void unwind__finish_access(struct thread *thread)
560 {
561 	unw_addr_space_t addr_space;
562 
563 	if (callchain_param.record_mode != CALLCHAIN_DWARF)
564 		return;
565 
566 	addr_space = thread__priv(thread);
567 	unw_destroy_addr_space(addr_space);
568 }
569 
570 static int get_entries(struct unwind_info *ui, unwind_entry_cb_t cb,
571 		       void *arg, int max_stack)
572 {
573 	unw_addr_space_t addr_space;
574 	unw_cursor_t c;
575 	int ret;
576 
577 	addr_space = thread__priv(ui->thread);
578 	if (addr_space == NULL)
579 		return -1;
580 
581 	ret = unw_init_remote(&c, addr_space, ui);
582 	if (ret)
583 		display_error(ret);
584 
585 	while (!ret && (unw_step(&c) > 0) && max_stack--) {
586 		unw_word_t ip;
587 
588 		unw_get_reg(&c, UNW_REG_IP, &ip);
589 		ret = ip ? entry(ip, ui->thread, ui->machine, cb, arg) : 0;
590 	}
591 
592 	return ret;
593 }
594 
595 int unwind__get_entries(unwind_entry_cb_t cb, void *arg,
596 			struct machine *machine, struct thread *thread,
597 			struct perf_sample *data, int max_stack)
598 {
599 	u64 ip;
600 	struct unwind_info ui = {
601 		.sample       = data,
602 		.thread       = thread,
603 		.machine      = machine,
604 	};
605 	int ret;
606 
607 	if (!data->user_regs.regs)
608 		return -EINVAL;
609 
610 	ret = perf_reg_value(&ip, &data->user_regs, PERF_REG_IP);
611 	if (ret)
612 		return ret;
613 
614 	ret = entry(ip, thread, machine, cb, arg);
615 	if (ret)
616 		return -ENOMEM;
617 
618 	return --max_stack > 0 ? get_entries(&ui, cb, arg, max_stack) : 0;
619 }
620