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Linux/tools/perf/util/unwind-libunwind.c

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

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