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 #ifndef NO_LIBUNWIND_DEBUG_FRAME
189 static 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 
203 out:
204 	elf_end(elf);
205 	pr_debug("unwind: elf_is_exec(%s): %d\n", name, retval);
206 	return retval;
207 }
208 #endif
209 
210 struct table_entry {
211 	u32 start_ip_offset;
212 	u32 fde_offset;
213 };
214 
215 struct 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 
241 static 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 
264 static 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.frame_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.frame_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
290 static int read_unwind_spec_debug_frame(struct dso *dso,
291 					struct machine *machine, u64 *offset)
292 {
293 	int fd;
294 	u64 ofs = dso->data.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.frame_offset = ofs;
304 	}
305 
306 	*offset = ofs;
307 	if (*offset)
308 		return 0;
309 
310 	return -EINVAL;
311 }
312 #endif
313 
314 static 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 
323 static int
324 find_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 
371 static 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 
381 static 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 
388 static 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 
396 static int
397 get_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 
406 static 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 
428 static 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 
473 static 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 
507 static 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 
514 static 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 
535 static 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 
552 static 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 
563 int 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 
582 void 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 
593 void 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 
604 static 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 
629 int 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