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7c97f91e MM |
1 | /* Linux-dependent part of branch trace support for GDB, and GDBserver. |
2 | ||
3 | Copyright (C) 2013 Free Software Foundation, Inc. | |
4 | ||
5 | Contributed by Intel Corp. <markus.t.metzger@intel.com> | |
6 | ||
7 | This file is part of GDB. | |
8 | ||
9 | This program is free software; you can redistribute it and/or modify | |
10 | it under the terms of the GNU General Public License as published by | |
11 | the Free Software Foundation; either version 3 of the License, or | |
12 | (at your option) any later version. | |
13 | ||
14 | This program is distributed in the hope that it will be useful, | |
15 | but WITHOUT ANY WARRANTY; without even the implied warranty of | |
16 | MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the | |
17 | GNU General Public License for more details. | |
18 | ||
19 | You should have received a copy of the GNU General Public License | |
20 | along with this program. If not, see <http://www.gnu.org/licenses/>. */ | |
21 | ||
22 | #ifdef GDBSERVER | |
23 | #include "server.h" | |
24 | #else | |
25 | #include "defs.h" | |
26 | #endif | |
27 | ||
28 | #include "linux-btrace.h" | |
29 | #include "common-utils.h" | |
30 | #include "gdb_assert.h" | |
31 | #include "regcache.h" | |
32 | #include "gdbthread.h" | |
33 | ||
34 | #if HAVE_LINUX_PERF_EVENT_H | |
35 | ||
36 | #include <errno.h> | |
37 | #include <string.h> | |
38 | #include <stdint.h> | |
39 | #include <unistd.h> | |
40 | #include <sys/syscall.h> | |
41 | #include <sys/mman.h> | |
42 | #include <sys/user.h> | |
a950d57c MM |
43 | #include <sys/ptrace.h> |
44 | #include <sys/types.h> | |
45 | #include <sys/wait.h> | |
46 | #include <signal.h> | |
7c97f91e MM |
47 | |
48 | /* A branch trace record in perf_event. */ | |
49 | struct perf_event_bts | |
50 | { | |
51 | /* The linear address of the branch source. */ | |
52 | uint64_t from; | |
53 | ||
54 | /* The linear address of the branch destination. */ | |
55 | uint64_t to; | |
56 | }; | |
57 | ||
58 | /* A perf_event branch trace sample. */ | |
59 | struct perf_event_sample | |
60 | { | |
61 | /* The perf_event sample header. */ | |
62 | struct perf_event_header header; | |
63 | ||
64 | /* The perf_event branch tracing payload. */ | |
65 | struct perf_event_bts bts; | |
66 | }; | |
67 | ||
68 | /* Get the perf_event header. */ | |
69 | ||
70 | static inline volatile struct perf_event_mmap_page * | |
71 | perf_event_header (struct btrace_target_info* tinfo) | |
72 | { | |
73 | return tinfo->buffer; | |
74 | } | |
75 | ||
76 | /* Get the size of the perf_event mmap buffer. */ | |
77 | ||
78 | static inline size_t | |
79 | perf_event_mmap_size (const struct btrace_target_info *tinfo) | |
80 | { | |
81 | /* The branch trace buffer is preceded by a configuration page. */ | |
82 | return (tinfo->size + 1) * PAGE_SIZE; | |
83 | } | |
84 | ||
85 | /* Get the size of the perf_event buffer. */ | |
86 | ||
87 | static inline size_t | |
88 | perf_event_buffer_size (struct btrace_target_info* tinfo) | |
89 | { | |
90 | return tinfo->size * PAGE_SIZE; | |
91 | } | |
92 | ||
93 | /* Get the start address of the perf_event buffer. */ | |
94 | ||
95 | static inline const uint8_t * | |
96 | perf_event_buffer_begin (struct btrace_target_info* tinfo) | |
97 | { | |
98 | return ((const uint8_t *) tinfo->buffer) + PAGE_SIZE; | |
99 | } | |
100 | ||
101 | /* Get the end address of the perf_event buffer. */ | |
102 | ||
103 | static inline const uint8_t * | |
104 | perf_event_buffer_end (struct btrace_target_info* tinfo) | |
105 | { | |
106 | return perf_event_buffer_begin (tinfo) + perf_event_buffer_size (tinfo); | |
107 | } | |
108 | ||
109 | /* Check whether an address is in the kernel. */ | |
110 | ||
111 | static inline int | |
112 | perf_event_is_kernel_addr (const struct btrace_target_info *tinfo, | |
113 | uint64_t addr) | |
114 | { | |
115 | uint64_t mask; | |
116 | ||
117 | /* If we don't know the size of a pointer, we can't check. Let's assume it's | |
118 | not a kernel address in this case. */ | |
119 | if (tinfo->ptr_bits == 0) | |
120 | return 0; | |
121 | ||
122 | /* A bit mask for the most significant bit in an address. */ | |
123 | mask = (uint64_t) 1 << (tinfo->ptr_bits - 1); | |
124 | ||
125 | /* Check whether the most significant bit in the address is set. */ | |
126 | return (addr & mask) != 0; | |
127 | } | |
128 | ||
129 | /* Check whether a perf event record should be skipped. */ | |
130 | ||
131 | static inline int | |
132 | perf_event_skip_record (const struct btrace_target_info *tinfo, | |
133 | const struct perf_event_bts *bts) | |
134 | { | |
135 | /* The hardware may report branches from kernel into user space. Branches | |
136 | from user into kernel space will be suppressed. We filter the former to | |
137 | provide a consistent branch trace excluding kernel. */ | |
138 | return perf_event_is_kernel_addr (tinfo, bts->from); | |
139 | } | |
140 | ||
141 | /* Perform a few consistency checks on a perf event sample record. This is | |
142 | meant to catch cases when we get out of sync with the perf event stream. */ | |
143 | ||
144 | static inline int | |
145 | perf_event_sample_ok (const struct perf_event_sample *sample) | |
146 | { | |
147 | if (sample->header.type != PERF_RECORD_SAMPLE) | |
148 | return 0; | |
149 | ||
150 | if (sample->header.size != sizeof (*sample)) | |
151 | return 0; | |
152 | ||
153 | return 1; | |
154 | } | |
155 | ||
156 | /* Branch trace is collected in a circular buffer [begin; end) as pairs of from | |
157 | and to addresses (plus a header). | |
158 | ||
159 | Start points into that buffer at the next sample position. | |
160 | We read the collected samples backwards from start. | |
161 | ||
162 | While reading the samples, we convert the information into a list of blocks. | |
163 | For two adjacent samples s1 and s2, we form a block b such that b.begin = | |
164 | s1.to and b.end = s2.from. | |
165 | ||
166 | In case the buffer overflows during sampling, one sample may have its lower | |
167 | part at the end and its upper part at the beginning of the buffer. */ | |
168 | ||
169 | static VEC (btrace_block_s) * | |
170 | perf_event_read_bts (struct btrace_target_info* tinfo, const uint8_t *begin, | |
171 | const uint8_t *end, const uint8_t *start) | |
172 | { | |
173 | VEC (btrace_block_s) *btrace = NULL; | |
174 | struct perf_event_sample sample; | |
175 | size_t read = 0, size = (end - begin); | |
176 | struct btrace_block block = { 0, 0 }; | |
177 | struct regcache *regcache; | |
178 | ||
179 | gdb_assert (begin <= start); | |
180 | gdb_assert (start <= end); | |
181 | ||
182 | /* The first block ends at the current pc. */ | |
183 | #ifdef GDBSERVER | |
184 | regcache = get_thread_regcache (find_thread_ptid (tinfo->ptid), 1); | |
185 | #else | |
186 | regcache = get_thread_regcache (tinfo->ptid); | |
187 | #endif | |
188 | block.end = regcache_read_pc (regcache); | |
189 | ||
190 | /* The buffer may contain a partial record as its last entry (i.e. when the | |
191 | buffer size is not a multiple of the sample size). */ | |
192 | read = sizeof (sample) - 1; | |
193 | ||
194 | for (; read < size; read += sizeof (sample)) | |
195 | { | |
196 | const struct perf_event_sample *psample; | |
197 | ||
198 | /* Find the next perf_event sample in a backwards traversal. */ | |
199 | start -= sizeof (sample); | |
200 | ||
201 | /* If we're still inside the buffer, we're done. */ | |
202 | if (begin <= start) | |
203 | psample = (const struct perf_event_sample *) start; | |
204 | else | |
205 | { | |
206 | int missing; | |
207 | ||
208 | /* We're to the left of the ring buffer, we will wrap around and | |
209 | reappear at the very right of the ring buffer. */ | |
210 | ||
211 | missing = (begin - start); | |
212 | start = (end - missing); | |
213 | ||
214 | /* If the entire sample is missing, we're done. */ | |
215 | if (missing == sizeof (sample)) | |
216 | psample = (const struct perf_event_sample *) start; | |
217 | else | |
218 | { | |
219 | uint8_t *stack; | |
220 | ||
221 | /* The sample wrapped around. The lower part is at the end and | |
222 | the upper part is at the beginning of the buffer. */ | |
223 | stack = (uint8_t *) &sample; | |
224 | ||
225 | /* Copy the two parts so we have a contiguous sample. */ | |
226 | memcpy (stack, start, missing); | |
227 | memcpy (stack + missing, begin, sizeof (sample) - missing); | |
228 | ||
229 | psample = &sample; | |
230 | } | |
231 | } | |
232 | ||
233 | if (!perf_event_sample_ok (psample)) | |
234 | { | |
235 | warning (_("Branch trace may be incomplete.")); | |
236 | break; | |
237 | } | |
238 | ||
239 | if (perf_event_skip_record (tinfo, &psample->bts)) | |
240 | continue; | |
241 | ||
242 | /* We found a valid sample, so we can complete the current block. */ | |
243 | block.begin = psample->bts.to; | |
244 | ||
245 | VEC_safe_push (btrace_block_s, btrace, &block); | |
246 | ||
247 | /* Start the next block. */ | |
248 | block.end = psample->bts.from; | |
249 | } | |
250 | ||
251 | return btrace; | |
252 | } | |
253 | ||
a950d57c MM |
254 | /* Check whether the kernel supports branch tracing. */ |
255 | ||
256 | static int | |
257 | kernel_supports_btrace (void) | |
258 | { | |
259 | struct perf_event_attr attr; | |
260 | pid_t child, pid; | |
261 | int status, file; | |
262 | ||
263 | errno = 0; | |
264 | child = fork (); | |
265 | switch (child) | |
266 | { | |
267 | case -1: | |
268 | warning (_("test branch tracing: cannot fork: %s."), strerror (errno)); | |
269 | return 0; | |
270 | ||
271 | case 0: | |
272 | status = ptrace (PTRACE_TRACEME, 0, NULL, NULL); | |
273 | if (status != 0) | |
274 | { | |
275 | warning (_("test branch tracing: cannot PTRACE_TRACEME: %s."), | |
276 | strerror (errno)); | |
277 | _exit (1); | |
278 | } | |
279 | ||
280 | status = raise (SIGTRAP); | |
281 | if (status != 0) | |
282 | { | |
283 | warning (_("test branch tracing: cannot raise SIGTRAP: %s."), | |
284 | strerror (errno)); | |
285 | _exit (1); | |
286 | } | |
287 | ||
288 | _exit (1); | |
289 | ||
290 | default: | |
291 | pid = waitpid (child, &status, 0); | |
292 | if (pid != child) | |
293 | { | |
294 | warning (_("test branch tracing: bad pid %ld, error: %s."), | |
295 | (long) pid, strerror (errno)); | |
296 | return 0; | |
297 | } | |
298 | ||
299 | if (!WIFSTOPPED (status)) | |
300 | { | |
301 | warning (_("test branch tracing: expected stop. status: %d."), | |
302 | status); | |
303 | return 0; | |
304 | } | |
305 | ||
306 | memset (&attr, 0, sizeof (attr)); | |
307 | ||
308 | attr.type = PERF_TYPE_HARDWARE; | |
309 | attr.config = PERF_COUNT_HW_BRANCH_INSTRUCTIONS; | |
310 | attr.sample_period = 1; | |
311 | attr.sample_type = PERF_SAMPLE_IP | PERF_SAMPLE_ADDR; | |
312 | attr.exclude_kernel = 1; | |
313 | attr.exclude_hv = 1; | |
314 | attr.exclude_idle = 1; | |
315 | ||
316 | file = syscall (SYS_perf_event_open, &attr, child, -1, -1, 0); | |
317 | if (file >= 0) | |
318 | close (file); | |
319 | ||
320 | kill (child, SIGKILL); | |
321 | ptrace (PTRACE_KILL, child, NULL, NULL); | |
322 | ||
323 | pid = waitpid (child, &status, 0); | |
324 | if (pid != child) | |
325 | { | |
326 | warning (_("test branch tracing: bad pid %ld, error: %s."), | |
327 | (long) pid, strerror (errno)); | |
328 | if (!WIFSIGNALED (status)) | |
329 | warning (_("test branch tracing: expected killed. status: %d."), | |
330 | status); | |
331 | } | |
332 | ||
333 | return (file >= 0); | |
334 | } | |
335 | } | |
336 | ||
337 | /* Check whether an Intel cpu supports branch tracing. */ | |
338 | ||
339 | static int | |
340 | intel_supports_btrace (void) | |
341 | { | |
342 | #if defined __i386__ || defined __x86_64__ | |
343 | unsigned int cpuid, model, family; | |
344 | ||
345 | __asm__ __volatile__ ("movl $1, %%eax;" | |
346 | "cpuid;" | |
347 | : "=a" (cpuid) | |
348 | :: "%ebx", "%ecx", "%edx"); | |
349 | ||
350 | family = (cpuid >> 8) & 0xf; | |
351 | model = (cpuid >> 4) & 0xf; | |
352 | ||
353 | switch (family) | |
354 | { | |
355 | case 0x6: | |
356 | model += (cpuid >> 12) & 0xf0; | |
357 | ||
358 | switch (model) | |
359 | { | |
360 | case 0x1a: /* Nehalem */ | |
361 | case 0x1f: | |
362 | case 0x1e: | |
363 | case 0x2e: | |
364 | case 0x25: /* Westmere */ | |
365 | case 0x2c: | |
366 | case 0x2f: | |
367 | case 0x2a: /* Sandy Bridge */ | |
368 | case 0x2d: | |
369 | case 0x3a: /* Ivy Bridge */ | |
370 | ||
371 | /* AAJ122: LBR, BTM, or BTS records may have incorrect branch | |
372 | "from" information afer an EIST transition, T-states, C1E, or | |
373 | Adaptive Thermal Throttling. */ | |
374 | return 0; | |
375 | } | |
376 | } | |
377 | ||
378 | return 1; | |
379 | ||
380 | #else /* !defined __i386__ && !defined __x86_64__ */ | |
381 | ||
382 | return 0; | |
383 | ||
384 | #endif /* !defined __i386__ && !defined __x86_64__ */ | |
385 | } | |
386 | ||
387 | /* Check whether the cpu supports branch tracing. */ | |
388 | ||
389 | static int | |
390 | cpu_supports_btrace (void) | |
391 | { | |
392 | #if defined __i386__ || defined __x86_64__ | |
393 | char vendor[13]; | |
394 | ||
395 | __asm__ __volatile__ ("xorl %%ebx, %%ebx;" | |
396 | "xorl %%ecx, %%ecx;" | |
397 | "xorl %%edx, %%edx;" | |
398 | "movl $0, %%eax;" | |
399 | "cpuid;" | |
400 | "movl %%ebx, %0;" | |
401 | "movl %%edx, %1;" | |
402 | "movl %%ecx, %2;" | |
403 | : "=m" (vendor[0]), | |
404 | "=m" (vendor[4]), | |
405 | "=m" (vendor[8]) | |
406 | : | |
407 | : "%eax", "%ebx", "%ecx", "%edx"); | |
408 | vendor[12] = '\0'; | |
409 | ||
410 | if (strcmp (vendor, "GenuineIntel") == 0) | |
411 | return intel_supports_btrace (); | |
412 | ||
413 | /* Don't know about others. Let's assume they do. */ | |
414 | return 1; | |
415 | ||
416 | #else /* !defined __i386__ && !defined __x86_64__ */ | |
417 | ||
418 | return 0; | |
419 | ||
420 | #endif /* !defined __i386__ && !defined __x86_64__ */ | |
421 | } | |
422 | ||
7c97f91e MM |
423 | /* See linux-btrace.h. */ |
424 | ||
425 | int | |
426 | linux_supports_btrace (void) | |
427 | { | |
a950d57c MM |
428 | static int cached; |
429 | ||
430 | if (cached == 0) | |
431 | { | |
432 | if (!kernel_supports_btrace ()) | |
433 | cached = -1; | |
434 | else if (!cpu_supports_btrace ()) | |
435 | cached = -1; | |
436 | else | |
437 | cached = 1; | |
438 | } | |
439 | ||
440 | return cached > 0; | |
7c97f91e MM |
441 | } |
442 | ||
443 | /* See linux-btrace.h. */ | |
444 | ||
445 | struct btrace_target_info * | |
446 | linux_enable_btrace (ptid_t ptid) | |
447 | { | |
448 | struct btrace_target_info *tinfo; | |
449 | int pid; | |
450 | ||
451 | tinfo = xzalloc (sizeof (*tinfo)); | |
452 | tinfo->ptid = ptid; | |
453 | ||
454 | tinfo->attr.size = sizeof (tinfo->attr); | |
455 | tinfo->attr.type = PERF_TYPE_HARDWARE; | |
456 | tinfo->attr.config = PERF_COUNT_HW_BRANCH_INSTRUCTIONS; | |
457 | tinfo->attr.sample_period = 1; | |
458 | ||
459 | /* We sample from and to address. */ | |
460 | tinfo->attr.sample_type = PERF_SAMPLE_IP | PERF_SAMPLE_ADDR; | |
461 | ||
462 | tinfo->attr.exclude_kernel = 1; | |
463 | tinfo->attr.exclude_hv = 1; | |
464 | tinfo->attr.exclude_idle = 1; | |
465 | ||
466 | tinfo->ptr_bits = 0; | |
467 | ||
468 | pid = ptid_get_lwp (ptid); | |
469 | if (pid == 0) | |
470 | pid = ptid_get_pid (ptid); | |
471 | ||
472 | errno = 0; | |
473 | tinfo->file = syscall (SYS_perf_event_open, &tinfo->attr, pid, -1, -1, 0); | |
474 | if (tinfo->file < 0) | |
475 | goto err; | |
476 | ||
477 | /* We hard-code the trace buffer size. | |
478 | At some later time, we should make this configurable. */ | |
479 | tinfo->size = 1; | |
480 | tinfo->buffer = mmap (NULL, perf_event_mmap_size (tinfo), | |
481 | PROT_READ, MAP_SHARED, tinfo->file, 0); | |
482 | if (tinfo->buffer == MAP_FAILED) | |
483 | goto err_file; | |
484 | ||
485 | return tinfo; | |
486 | ||
487 | err_file: | |
488 | close (tinfo->file); | |
489 | ||
490 | err: | |
491 | xfree (tinfo); | |
492 | return NULL; | |
493 | } | |
494 | ||
495 | /* See linux-btrace.h. */ | |
496 | ||
497 | int | |
498 | linux_disable_btrace (struct btrace_target_info *tinfo) | |
499 | { | |
500 | int errcode; | |
501 | ||
502 | errno = 0; | |
503 | errcode = munmap (tinfo->buffer, perf_event_mmap_size (tinfo)); | |
504 | if (errcode != 0) | |
505 | return errno; | |
506 | ||
507 | close (tinfo->file); | |
508 | xfree (tinfo); | |
509 | ||
510 | return 0; | |
511 | } | |
512 | ||
513 | /* Check whether the branch trace has changed. */ | |
514 | ||
515 | static int | |
516 | linux_btrace_has_changed (struct btrace_target_info *tinfo) | |
517 | { | |
518 | volatile struct perf_event_mmap_page *header = perf_event_header (tinfo); | |
519 | ||
520 | return header->data_head != tinfo->data_head; | |
521 | } | |
522 | ||
523 | /* See linux-btrace.h. */ | |
524 | ||
525 | VEC (btrace_block_s) * | |
526 | linux_read_btrace (struct btrace_target_info *tinfo, | |
527 | enum btrace_read_type type) | |
528 | { | |
529 | VEC (btrace_block_s) *btrace = NULL; | |
530 | volatile struct perf_event_mmap_page *header; | |
531 | const uint8_t *begin, *end, *start; | |
532 | unsigned long data_head, retries = 5; | |
533 | size_t buffer_size; | |
534 | ||
535 | if (type == btrace_read_new && !linux_btrace_has_changed (tinfo)) | |
536 | return NULL; | |
537 | ||
538 | header = perf_event_header (tinfo); | |
539 | buffer_size = perf_event_buffer_size (tinfo); | |
540 | ||
541 | /* We may need to retry reading the trace. See below. */ | |
542 | while (retries--) | |
543 | { | |
544 | data_head = header->data_head; | |
545 | ||
546 | /* If there's new trace, let's read it. */ | |
547 | if (data_head != tinfo->data_head) | |
548 | { | |
549 | /* Data_head keeps growing; the buffer itself is circular. */ | |
550 | begin = perf_event_buffer_begin (tinfo); | |
551 | start = begin + data_head % buffer_size; | |
552 | ||
553 | if (data_head <= buffer_size) | |
554 | end = start; | |
555 | else | |
556 | end = perf_event_buffer_end (tinfo); | |
557 | ||
558 | btrace = perf_event_read_bts (tinfo, begin, end, start); | |
559 | } | |
560 | ||
561 | /* The stopping thread notifies its ptracer before it is scheduled out. | |
562 | On multi-core systems, the debugger might therefore run while the | |
563 | kernel might be writing the last branch trace records. | |
564 | ||
565 | Let's check whether the data head moved while we read the trace. */ | |
566 | if (data_head == header->data_head) | |
567 | break; | |
568 | } | |
569 | ||
570 | tinfo->data_head = data_head; | |
571 | ||
572 | return btrace; | |
573 | } | |
574 | ||
575 | #else /* !HAVE_LINUX_PERF_EVENT_H */ | |
576 | ||
577 | /* See linux-btrace.h. */ | |
578 | ||
579 | int | |
580 | linux_supports_btrace (void) | |
581 | { | |
582 | return 0; | |
583 | } | |
584 | ||
585 | /* See linux-btrace.h. */ | |
586 | ||
587 | struct btrace_target_info * | |
588 | linux_enable_btrace (ptid_t ptid) | |
589 | { | |
590 | return NULL; | |
591 | } | |
592 | ||
593 | /* See linux-btrace.h. */ | |
594 | ||
595 | int | |
596 | linux_disable_btrace (struct btrace_target_info *tinfo) | |
597 | { | |
598 | return ENOSYS; | |
599 | } | |
600 | ||
601 | /* See linux-btrace.h. */ | |
602 | ||
603 | VEC (btrace_block_s) * | |
604 | linux_read_btrace (struct btrace_target_info *tinfo, | |
605 | enum btrace_read_type type) | |
606 | { | |
607 | return NULL; | |
608 | } | |
609 | ||
610 | #endif /* !HAVE_LINUX_PERF_EVENT_H */ |