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1// SPDX-License-Identifier: GPL-2.0
2/*
3 * Post mortem Dwarf CFI based unwinding on top of regs and stack dumps.
4 *
5 * Lots of this code have been borrowed or heavily inspired from parts of
6 * the libunwind 0.99 code which are (amongst other contributors I may have
7 * forgotten):
8 *
9 * Copyright (C) 2002-2007 Hewlett-Packard Co
10 * Contributed by David Mosberger-Tang <davidm@hpl.hp.com>
11 *
12 * And the bugs have been added by:
13 *
14 * Copyright (C) 2010, Frederic Weisbecker <fweisbec@gmail.com>
15 * Copyright (C) 2012, Jiri Olsa <jolsa@redhat.com>
16 *
17 */
18
19#include <elf.h>
20#include <errno.h>
21#include <gelf.h>
22#include <fcntl.h>
23#include <inttypes.h>
24#include <string.h>
25#include <unistd.h>
26#include <sys/mman.h>
27#include <linux/list.h>
28#ifndef REMOTE_UNWIND_LIBUNWIND
29#include <libunwind.h>
30#include <libunwind-ptrace.h>
31#endif
32#include "callchain.h"
33#include "thread.h"
34#include "session.h"
35#include "perf_regs.h"
36#include "unwind.h"
37#include "symbol.h"
38#include "util.h"
39#include "debug.h"
40#include "asm/bug.h"
41#include "dso.h"
42
43extern int
44UNW_OBJ(dwarf_search_unwind_table) (unw_addr_space_t as,
45 unw_word_t ip,
46 unw_dyn_info_t *di,
47 unw_proc_info_t *pi,
48 int need_unwind_info, void *arg);
49
50#define dwarf_search_unwind_table UNW_OBJ(dwarf_search_unwind_table)
51
52extern int
53UNW_OBJ(dwarf_find_debug_frame) (int found, unw_dyn_info_t *di_debug,
54 unw_word_t ip,
55 unw_word_t segbase,
56 const char *obj_name, unw_word_t start,
57 unw_word_t end);
58
59#define dwarf_find_debug_frame UNW_OBJ(dwarf_find_debug_frame)
60
61#define DW_EH_PE_FORMAT_MASK 0x0f /* format of the encoded value */
62#define DW_EH_PE_APPL_MASK 0x70 /* how the value is to be applied */
63
64/* Pointer-encoding formats: */
65#define DW_EH_PE_omit 0xff
66#define DW_EH_PE_ptr 0x00 /* pointer-sized unsigned value */
67#define DW_EH_PE_udata4 0x03 /* unsigned 32-bit value */
68#define DW_EH_PE_udata8 0x04 /* unsigned 64-bit value */
69#define DW_EH_PE_sdata4 0x0b /* signed 32-bit value */
70#define DW_EH_PE_sdata8 0x0c /* signed 64-bit value */
71
72/* Pointer-encoding application: */
73#define DW_EH_PE_absptr 0x00 /* absolute value */
74#define DW_EH_PE_pcrel 0x10 /* rel. to addr. of encoded value */
75
76/*
77 * The following are not documented by LSB v1.3, yet they are used by
78 * GCC, presumably they aren't documented by LSB since they aren't
79 * used on Linux:
80 */
81#define DW_EH_PE_funcrel 0x40 /* start-of-procedure-relative */
82#define DW_EH_PE_aligned 0x50 /* aligned pointer */
83
84/* Flags intentionaly not handled, since they're not needed:
85 * #define DW_EH_PE_indirect 0x80
86 * #define DW_EH_PE_uleb128 0x01
87 * #define DW_EH_PE_udata2 0x02
88 * #define DW_EH_PE_sleb128 0x09
89 * #define DW_EH_PE_sdata2 0x0a
90 * #define DW_EH_PE_textrel 0x20
91 * #define DW_EH_PE_datarel 0x30
92 */
93
94struct unwind_info {
95 struct perf_sample *sample;
96 struct machine *machine;
97 struct thread *thread;
98};
99
100#define dw_read(ptr, type, end) ({ \
101 type *__p = (type *) ptr; \
102 type __v; \
103 if ((__p + 1) > (type *) end) \
104 return -EINVAL; \
105 __v = *__p++; \
106 ptr = (typeof(ptr)) __p; \
107 __v; \
108 })
109
110static int __dw_read_encoded_value(u8 **p, u8 *end, u64 *val,
111 u8 encoding)
112{
113 u8 *cur = *p;
114 *val = 0;
115
116 switch (encoding) {
117 case DW_EH_PE_omit:
118 *val = 0;
119 goto out;
120 case DW_EH_PE_ptr:
121 *val = dw_read(cur, unsigned long, end);
122 goto out;
123 default:
124 break;
125 }
126
127 switch (encoding & DW_EH_PE_APPL_MASK) {
128 case DW_EH_PE_absptr:
129 break;
130 case DW_EH_PE_pcrel:
131 *val = (unsigned long) cur;
132 break;
133 default:
134 return -EINVAL;
135 }
136
137 if ((encoding & 0x07) == 0x00)
138 encoding |= DW_EH_PE_udata4;
139
140 switch (encoding & DW_EH_PE_FORMAT_MASK) {
141 case DW_EH_PE_sdata4:
142 *val += dw_read(cur, s32, end);
143 break;
144 case DW_EH_PE_udata4:
145 *val += dw_read(cur, u32, end);
146 break;
147 case DW_EH_PE_sdata8:
148 *val += dw_read(cur, s64, end);
149 break;
150 case DW_EH_PE_udata8:
151 *val += dw_read(cur, u64, end);
152 break;
153 default:
154 return -EINVAL;
155 }
156
157 out:
158 *p = cur;
159 return 0;
160}
161
162#define dw_read_encoded_value(ptr, end, enc) ({ \
163 u64 __v; \
164 if (__dw_read_encoded_value(&ptr, end, &__v, enc)) { \
165 return -EINVAL; \
166 } \
167 __v; \
168 })
169
170static u64 elf_section_offset(int fd, const char *name)
171{
172 Elf *elf;
173 GElf_Ehdr ehdr;
174 GElf_Shdr shdr;
175 u64 offset = 0;
176
177 elf = elf_begin(fd, PERF_ELF_C_READ_MMAP, NULL);
178 if (elf == NULL)
179 return 0;
180
181 do {
182 if (gelf_getehdr(elf, &ehdr) == NULL)
183 break;
184
185 if (!elf_section_by_name(elf, &ehdr, &shdr, name, NULL))
186 break;
187
188 offset = shdr.sh_offset;
189 } while (0);
190
191 elf_end(elf);
192 return offset;
193}
194
195#ifndef NO_LIBUNWIND_DEBUG_FRAME
196static int elf_is_exec(int fd, const char *name)
197{
198 Elf *elf;
199 GElf_Ehdr ehdr;
200 int retval = 0;
201
202 elf = elf_begin(fd, PERF_ELF_C_READ_MMAP, NULL);
203 if (elf == NULL)
204 return 0;
205 if (gelf_getehdr(elf, &ehdr) == NULL)
206 goto out;
207
208 retval = (ehdr.e_type == ET_EXEC);
209
210out:
211 elf_end(elf);
212 pr_debug("unwind: elf_is_exec(%s): %d\n", name, retval);
213 return retval;
214}
215#endif
216
217struct table_entry {
218 u32 start_ip_offset;
219 u32 fde_offset;
220};
221
222struct eh_frame_hdr {
223 unsigned char version;
224 unsigned char eh_frame_ptr_enc;
225 unsigned char fde_count_enc;
226 unsigned char table_enc;
227
228 /*
229 * The rest of the header is variable-length and consists of the
230 * following members:
231 *
232 * encoded_t eh_frame_ptr;
233 * encoded_t fde_count;
234 */
235
236 /* A single encoded pointer should not be more than 8 bytes. */
237 u64 enc[2];
238
239 /*
240 * struct {
241 * encoded_t start_ip;
242 * encoded_t fde_addr;
243 * } binary_search_table[fde_count];
244 */
245 char data[0];
246} __packed;
247
248static int unwind_spec_ehframe(struct dso *dso, struct machine *machine,
249 u64 offset, u64 *table_data, u64 *segbase,
250 u64 *fde_count)
251{
252 struct eh_frame_hdr hdr;
253 u8 *enc = (u8 *) &hdr.enc;
254 u8 *end = (u8 *) &hdr.data;
255 ssize_t r;
256
257 r = dso__data_read_offset(dso, machine, offset,
258 (u8 *) &hdr, sizeof(hdr));
259 if (r != sizeof(hdr))
260 return -EINVAL;
261
262 /* We dont need eh_frame_ptr, just skip it. */
263 dw_read_encoded_value(enc, end, hdr.eh_frame_ptr_enc);
264
265 *fde_count = dw_read_encoded_value(enc, end, hdr.fde_count_enc);
266 *segbase = offset;
267 *table_data = (enc - (u8 *) &hdr) + offset;
268 return 0;
269}
270
271static int read_unwind_spec_eh_frame(struct dso *dso, struct machine *machine,
272 u64 *table_data, u64 *segbase,
273 u64 *fde_count)
274{
275 int ret = -EINVAL, fd;
276 u64 offset = dso->data.eh_frame_hdr_offset;
277
278 if (offset == 0) {
279 fd = dso__data_get_fd(dso, machine);
280 if (fd < 0)
281 return -EINVAL;
282
283 /* Check the .eh_frame section for unwinding info */
284 offset = elf_section_offset(fd, ".eh_frame_hdr");
285 dso->data.eh_frame_hdr_offset = offset;
286 dso__data_put_fd(dso);
287 }
288
289 if (offset)
290 ret = unwind_spec_ehframe(dso, machine, offset,
291 table_data, segbase,
292 fde_count);
293
294 return ret;
295}
296
297#ifndef NO_LIBUNWIND_DEBUG_FRAME
298static int read_unwind_spec_debug_frame(struct dso *dso,
299 struct machine *machine, u64 *offset)
300{
301 int fd;
302 u64 ofs = dso->data.debug_frame_offset;
303
304 /* debug_frame can reside in:
305 * - dso
306 * - debug pointed by symsrc_filename
307 * - gnu_debuglink, which doesn't necessary
308 * has to be pointed by symsrc_filename
309 */
310 if (ofs == 0) {
311 fd = dso__data_get_fd(dso, machine);
312 if (fd >= 0) {
313 ofs = elf_section_offset(fd, ".debug_frame");
314 dso__data_put_fd(dso);
315 }
316
317 if (ofs <= 0) {
318 fd = open(dso->symsrc_filename, O_RDONLY);
319 if (fd >= 0) {
320 ofs = elf_section_offset(fd, ".debug_frame");
321 close(fd);
322 }
323 }
324
325 if (ofs <= 0) {
326 char *debuglink = malloc(PATH_MAX);
327 int ret = 0;
328
329 ret = dso__read_binary_type_filename(
330 dso, DSO_BINARY_TYPE__DEBUGLINK,
331 machine->root_dir, debuglink, PATH_MAX);
332 if (!ret) {
333 fd = open(debuglink, O_RDONLY);
334 if (fd >= 0) {
335 ofs = elf_section_offset(fd,
336 ".debug_frame");
337 close(fd);
338 }
339 }
340 if (ofs > 0) {
341 if (dso->symsrc_filename != NULL) {
342 pr_warning(
343 "%s: overwrite symsrc(%s,%s)\n",
344 __func__,
345 dso->symsrc_filename,
346 debuglink);
347 free(dso->symsrc_filename);
348 }
349 dso->symsrc_filename = debuglink;
350 } else {
351 free(debuglink);
352 }
353 }
354
355 dso->data.debug_frame_offset = ofs;
356 }
357
358 *offset = ofs;
359 if (*offset)
360 return 0;
361
362 return -EINVAL;
363}
364#endif
365
366static struct map *find_map(unw_word_t ip, struct unwind_info *ui)
367{
368 struct addr_location al;
369
370 thread__find_addr_map(ui->thread, PERF_RECORD_MISC_USER,
371 MAP__FUNCTION, ip, &al);
372 if (!al.map) {
373 /*
374 * We've seen cases (softice) where DWARF unwinder went
375 * through non executable mmaps, which we need to lookup
376 * in MAP__VARIABLE tree.
377 */
378 thread__find_addr_map(ui->thread, PERF_RECORD_MISC_USER,
379 MAP__VARIABLE, ip, &al);
380 }
381 return al.map;
382}
383
384static int
385find_proc_info(unw_addr_space_t as, unw_word_t ip, unw_proc_info_t *pi,
386 int need_unwind_info, void *arg)
387{
388 struct unwind_info *ui = arg;
389 struct map *map;
390 unw_dyn_info_t di;
391 u64 table_data, segbase, fde_count;
392 int ret = -EINVAL;
393
394 map = find_map(ip, ui);
395 if (!map || !map->dso)
396 return -EINVAL;
397
398 pr_debug("unwind: find_proc_info dso %s\n", map->dso->name);
399
400 /* Check the .eh_frame section for unwinding info */
401 if (!read_unwind_spec_eh_frame(map->dso, ui->machine,
402 &table_data, &segbase, &fde_count)) {
403 memset(&di, 0, sizeof(di));
404 di.format = UNW_INFO_FORMAT_REMOTE_TABLE;
405 di.start_ip = map->start;
406 di.end_ip = map->end;
407 di.u.rti.segbase = map->start + segbase - map->pgoff;
408 di.u.rti.table_data = map->start + table_data - map->pgoff;
409 di.u.rti.table_len = fde_count * sizeof(struct table_entry)
410 / sizeof(unw_word_t);
411 ret = dwarf_search_unwind_table(as, ip, &di, pi,
412 need_unwind_info, arg);
413 }
414
415#ifndef NO_LIBUNWIND_DEBUG_FRAME
416 /* Check the .debug_frame section for unwinding info */
417 if (ret < 0 &&
418 !read_unwind_spec_debug_frame(map->dso, ui->machine, &segbase)) {
419 int fd = dso__data_get_fd(map->dso, ui->machine);
420 int is_exec = elf_is_exec(fd, map->dso->name);
421 unw_word_t base = is_exec ? 0 : map->start;
422 const char *symfile;
423
424 if (fd >= 0)
425 dso__data_put_fd(map->dso);
426
427 symfile = map->dso->symsrc_filename ?: map->dso->name;
428
429 memset(&di, 0, sizeof(di));
430 if (dwarf_find_debug_frame(0, &di, ip, base, symfile,
431 map->start, map->end))
432 return dwarf_search_unwind_table(as, ip, &di, pi,
433 need_unwind_info, arg);
434 }
435#endif
436
437 return ret;
438}
439
440static int access_fpreg(unw_addr_space_t __maybe_unused as,
441 unw_regnum_t __maybe_unused num,
442 unw_fpreg_t __maybe_unused *val,
443 int __maybe_unused __write,
444 void __maybe_unused *arg)
445{
446 pr_err("unwind: access_fpreg unsupported\n");
447 return -UNW_EINVAL;
448}
449
450static int get_dyn_info_list_addr(unw_addr_space_t __maybe_unused as,
451 unw_word_t __maybe_unused *dil_addr,
452 void __maybe_unused *arg)
453{
454 return -UNW_ENOINFO;
455}
456
457static int resume(unw_addr_space_t __maybe_unused as,
458 unw_cursor_t __maybe_unused *cu,
459 void __maybe_unused *arg)
460{
461 pr_err("unwind: resume unsupported\n");
462 return -UNW_EINVAL;
463}
464
465static int
466get_proc_name(unw_addr_space_t __maybe_unused as,
467 unw_word_t __maybe_unused addr,
468 char __maybe_unused *bufp, size_t __maybe_unused buf_len,
469 unw_word_t __maybe_unused *offp, void __maybe_unused *arg)
470{
471 pr_err("unwind: get_proc_name unsupported\n");
472 return -UNW_EINVAL;
473}
474
475static int access_dso_mem(struct unwind_info *ui, unw_word_t addr,
476 unw_word_t *data)
477{
478 struct map *map;
479 ssize_t size;
480
481 map = find_map(addr, ui);
482 if (!map) {
483 pr_debug("unwind: no map for %lx\n", (unsigned long)addr);
484 return -1;
485 }
486
487 if (!map->dso)
488 return -1;
489
490 size = dso__data_read_addr(map->dso, map, ui->machine,
491 addr, (u8 *) data, sizeof(*data));
492
493 return !(size == sizeof(*data));
494}
495
496static int access_mem(unw_addr_space_t __maybe_unused as,
497 unw_word_t addr, unw_word_t *valp,
498 int __write, void *arg)
499{
500 struct unwind_info *ui = arg;
501 struct stack_dump *stack = &ui->sample->user_stack;
502 u64 start, end;
503 int offset;
504 int ret;
505
506 /* Don't support write, probably not needed. */
507 if (__write || !stack || !ui->sample->user_regs.regs) {
508 *valp = 0;
509 return 0;
510 }
511
512 ret = perf_reg_value(&start, &ui->sample->user_regs,
513 LIBUNWIND__ARCH_REG_SP);
514 if (ret)
515 return ret;
516
517 end = start + stack->size;
518
519 /* Check overflow. */
520 if (addr + sizeof(unw_word_t) < addr)
521 return -EINVAL;
522
523 if (addr < start || addr + sizeof(unw_word_t) >= end) {
524 ret = access_dso_mem(ui, addr, valp);
525 if (ret) {
526 pr_debug("unwind: access_mem %p not inside range"
527 " 0x%" PRIx64 "-0x%" PRIx64 "\n",
528 (void *) (uintptr_t) addr, start, end);
529 *valp = 0;
530 return ret;
531 }
532 return 0;
533 }
534
535 offset = addr - start;
536 *valp = *(unw_word_t *)&stack->data[offset];
537 pr_debug("unwind: access_mem addr %p val %lx, offset %d\n",
538 (void *) (uintptr_t) addr, (unsigned long)*valp, offset);
539 return 0;
540}
541
542static int access_reg(unw_addr_space_t __maybe_unused as,
543 unw_regnum_t regnum, unw_word_t *valp,
544 int __write, void *arg)
545{
546 struct unwind_info *ui = arg;
547 int id, ret;
548 u64 val;
549
550 /* Don't support write, I suspect we don't need it. */
551 if (__write) {
552 pr_err("unwind: access_reg w %d\n", regnum);
553 return 0;
554 }
555
556 if (!ui->sample->user_regs.regs) {
557 *valp = 0;
558 return 0;
559 }
560
561 id = LIBUNWIND__ARCH_REG_ID(regnum);
562 if (id < 0)
563 return -EINVAL;
564
565 ret = perf_reg_value(&val, &ui->sample->user_regs, id);
566 if (ret) {
567 pr_err("unwind: can't read reg %d\n", regnum);
568 return ret;
569 }
570
571 *valp = (unw_word_t) val;
572 pr_debug("unwind: reg %d, val %lx\n", regnum, (unsigned long)*valp);
573 return 0;
574}
575
576static void put_unwind_info(unw_addr_space_t __maybe_unused as,
577 unw_proc_info_t *pi __maybe_unused,
578 void *arg __maybe_unused)
579{
580 pr_debug("unwind: put_unwind_info called\n");
581}
582
583static int entry(u64 ip, struct thread *thread,
584 unwind_entry_cb_t cb, void *arg)
585{
586 struct unwind_entry e;
587 struct addr_location al;
588
589 thread__find_addr_location(thread, PERF_RECORD_MISC_USER,
590 MAP__FUNCTION, ip, &al);
591
592 e.ip = al.addr;
593 e.map = al.map;
594 e.sym = al.sym;
595
596 pr_debug("unwind: %s:ip = 0x%" PRIx64 " (0x%" PRIx64 ")\n",
597 al.sym ? al.sym->name : "''",
598 ip,
599 al.map ? al.map->map_ip(al.map, ip) : (u64) 0);
600
601 return cb(&e, arg);
602}
603
604static void display_error(int err)
605{
606 switch (err) {
607 case UNW_EINVAL:
608 pr_err("unwind: Only supports local.\n");
609 break;
610 case UNW_EUNSPEC:
611 pr_err("unwind: Unspecified error.\n");
612 break;
613 case UNW_EBADREG:
614 pr_err("unwind: Register unavailable.\n");
615 break;
616 default:
617 break;
618 }
619}
620
621static unw_accessors_t accessors = {
622 .find_proc_info = find_proc_info,
623 .put_unwind_info = put_unwind_info,
624 .get_dyn_info_list_addr = get_dyn_info_list_addr,
625 .access_mem = access_mem,
626 .access_reg = access_reg,
627 .access_fpreg = access_fpreg,
628 .resume = resume,
629 .get_proc_name = get_proc_name,
630};
631
632static int _unwind__prepare_access(struct thread *thread)
633{
634 if (!dwarf_callchain_users)
635 return 0;
636 thread->addr_space = unw_create_addr_space(&accessors, 0);
637 if (!thread->addr_space) {
638 pr_err("unwind: Can't create unwind address space.\n");
639 return -ENOMEM;
640 }
641
642 unw_set_caching_policy(thread->addr_space, UNW_CACHE_GLOBAL);
643 return 0;
644}
645
646static void _unwind__flush_access(struct thread *thread)
647{
648 if (!dwarf_callchain_users)
649 return;
650 unw_flush_cache(thread->addr_space, 0, 0);
651}
652
653static void _unwind__finish_access(struct thread *thread)
654{
655 if (!dwarf_callchain_users)
656 return;
657 unw_destroy_addr_space(thread->addr_space);
658}
659
660static int get_entries(struct unwind_info *ui, unwind_entry_cb_t cb,
661 void *arg, int max_stack)
662{
663 u64 val;
664 unw_word_t ips[max_stack];
665 unw_addr_space_t addr_space;
666 unw_cursor_t c;
667 int ret, i = 0;
668
669 ret = perf_reg_value(&val, &ui->sample->user_regs,
670 LIBUNWIND__ARCH_REG_IP);
671 if (ret)
672 return ret;
673
674 ips[i++] = (unw_word_t) val;
675
676 /*
677 * If we need more than one entry, do the DWARF
678 * unwind itself.
679 */
680 if (max_stack - 1 > 0) {
681 WARN_ONCE(!ui->thread, "WARNING: ui->thread is NULL");
682 addr_space = ui->thread->addr_space;
683
684 if (addr_space == NULL)
685 return -1;
686
687 ret = unw_init_remote(&c, addr_space, ui);
688 if (ret)
689 display_error(ret);
690
691 while (!ret && (unw_step(&c) > 0) && i < max_stack) {
692 unw_get_reg(&c, UNW_REG_IP, &ips[i]);
693
694 /*
695 * Decrement the IP for any non-activation frames.
696 * this is required to properly find the srcline
697 * for caller frames.
698 * See also the documentation for dwfl_frame_pc(),
699 * which this code tries to replicate.
700 */
701 if (unw_is_signal_frame(&c) <= 0)
702 --ips[i];
703
704 ++i;
705 }
706
707 max_stack = i;
708 }
709
710 /*
711 * Display what we got based on the order setup.
712 */
713 for (i = 0; i < max_stack && !ret; i++) {
714 int j = i;
715
716 if (callchain_param.order == ORDER_CALLER)
717 j = max_stack - i - 1;
718 ret = ips[j] ? entry(ips[j], ui->thread, cb, arg) : 0;
719 }
720
721 return ret;
722}
723
724static int _unwind__get_entries(unwind_entry_cb_t cb, void *arg,
725 struct thread *thread,
726 struct perf_sample *data, int max_stack)
727{
728 struct unwind_info ui = {
729 .sample = data,
730 .thread = thread,
731 .machine = thread->mg->machine,
732 };
733
734 if (!data->user_regs.regs)
735 return -EINVAL;
736
737 if (max_stack <= 0)
738 return -EINVAL;
739
740 return get_entries(&ui, cb, arg, max_stack);
741}
742
743static struct unwind_libunwind_ops
744_unwind_libunwind_ops = {
745 .prepare_access = _unwind__prepare_access,
746 .flush_access = _unwind__flush_access,
747 .finish_access = _unwind__finish_access,
748 .get_entries = _unwind__get_entries,
749};
750
751#ifndef REMOTE_UNWIND_LIBUNWIND
752struct unwind_libunwind_ops *
753local_unwind_libunwind_ops = &_unwind_libunwind_ops;
754#endif