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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" | |
be8b1ea6 | 33 | #include "gdb_wait.h" |
4d157a3d | 34 | #include "i386-cpuid.h" |
7c97f91e MM |
35 | |
36 | #if HAVE_LINUX_PERF_EVENT_H | |
37 | ||
38 | #include <errno.h> | |
39 | #include <string.h> | |
40 | #include <stdint.h> | |
41 | #include <unistd.h> | |
42 | #include <sys/syscall.h> | |
43 | #include <sys/mman.h> | |
44 | #include <sys/user.h> | |
a950d57c MM |
45 | #include <sys/ptrace.h> |
46 | #include <sys/types.h> | |
a950d57c | 47 | #include <signal.h> |
7c97f91e MM |
48 | |
49 | /* A branch trace record in perf_event. */ | |
50 | struct perf_event_bts | |
51 | { | |
52 | /* The linear address of the branch source. */ | |
53 | uint64_t from; | |
54 | ||
55 | /* The linear address of the branch destination. */ | |
56 | uint64_t to; | |
57 | }; | |
58 | ||
59 | /* A perf_event branch trace sample. */ | |
60 | struct perf_event_sample | |
61 | { | |
62 | /* The perf_event sample header. */ | |
63 | struct perf_event_header header; | |
64 | ||
65 | /* The perf_event branch tracing payload. */ | |
66 | struct perf_event_bts bts; | |
67 | }; | |
68 | ||
69 | /* Get the perf_event header. */ | |
70 | ||
71 | static inline volatile struct perf_event_mmap_page * | |
72 | perf_event_header (struct btrace_target_info* tinfo) | |
73 | { | |
74 | return tinfo->buffer; | |
75 | } | |
76 | ||
77 | /* Get the size of the perf_event mmap buffer. */ | |
78 | ||
79 | static inline size_t | |
80 | perf_event_mmap_size (const struct btrace_target_info *tinfo) | |
81 | { | |
82 | /* The branch trace buffer is preceded by a configuration page. */ | |
83 | return (tinfo->size + 1) * PAGE_SIZE; | |
84 | } | |
85 | ||
86 | /* Get the size of the perf_event buffer. */ | |
87 | ||
88 | static inline size_t | |
89 | perf_event_buffer_size (struct btrace_target_info* tinfo) | |
90 | { | |
91 | return tinfo->size * PAGE_SIZE; | |
92 | } | |
93 | ||
94 | /* Get the start address of the perf_event buffer. */ | |
95 | ||
96 | static inline const uint8_t * | |
97 | perf_event_buffer_begin (struct btrace_target_info* tinfo) | |
98 | { | |
99 | return ((const uint8_t *) tinfo->buffer) + PAGE_SIZE; | |
100 | } | |
101 | ||
102 | /* Get the end address of the perf_event buffer. */ | |
103 | ||
104 | static inline const uint8_t * | |
105 | perf_event_buffer_end (struct btrace_target_info* tinfo) | |
106 | { | |
107 | return perf_event_buffer_begin (tinfo) + perf_event_buffer_size (tinfo); | |
108 | } | |
109 | ||
110 | /* Check whether an address is in the kernel. */ | |
111 | ||
112 | static inline int | |
113 | perf_event_is_kernel_addr (const struct btrace_target_info *tinfo, | |
114 | uint64_t addr) | |
115 | { | |
116 | uint64_t mask; | |
117 | ||
118 | /* If we don't know the size of a pointer, we can't check. Let's assume it's | |
119 | not a kernel address in this case. */ | |
120 | if (tinfo->ptr_bits == 0) | |
121 | return 0; | |
122 | ||
123 | /* A bit mask for the most significant bit in an address. */ | |
124 | mask = (uint64_t) 1 << (tinfo->ptr_bits - 1); | |
125 | ||
126 | /* Check whether the most significant bit in the address is set. */ | |
127 | return (addr & mask) != 0; | |
128 | } | |
129 | ||
130 | /* Check whether a perf event record should be skipped. */ | |
131 | ||
132 | static inline int | |
133 | perf_event_skip_record (const struct btrace_target_info *tinfo, | |
134 | const struct perf_event_bts *bts) | |
135 | { | |
136 | /* The hardware may report branches from kernel into user space. Branches | |
137 | from user into kernel space will be suppressed. We filter the former to | |
138 | provide a consistent branch trace excluding kernel. */ | |
139 | return perf_event_is_kernel_addr (tinfo, bts->from); | |
140 | } | |
141 | ||
142 | /* Perform a few consistency checks on a perf event sample record. This is | |
143 | meant to catch cases when we get out of sync with the perf event stream. */ | |
144 | ||
145 | static inline int | |
146 | perf_event_sample_ok (const struct perf_event_sample *sample) | |
147 | { | |
148 | if (sample->header.type != PERF_RECORD_SAMPLE) | |
149 | return 0; | |
150 | ||
151 | if (sample->header.size != sizeof (*sample)) | |
152 | return 0; | |
153 | ||
154 | return 1; | |
155 | } | |
156 | ||
157 | /* Branch trace is collected in a circular buffer [begin; end) as pairs of from | |
158 | and to addresses (plus a header). | |
159 | ||
160 | Start points into that buffer at the next sample position. | |
161 | We read the collected samples backwards from start. | |
162 | ||
163 | While reading the samples, we convert the information into a list of blocks. | |
164 | For two adjacent samples s1 and s2, we form a block b such that b.begin = | |
165 | s1.to and b.end = s2.from. | |
166 | ||
167 | In case the buffer overflows during sampling, one sample may have its lower | |
168 | part at the end and its upper part at the beginning of the buffer. */ | |
169 | ||
170 | static VEC (btrace_block_s) * | |
171 | perf_event_read_bts (struct btrace_target_info* tinfo, const uint8_t *begin, | |
172 | const uint8_t *end, const uint8_t *start) | |
173 | { | |
174 | VEC (btrace_block_s) *btrace = NULL; | |
175 | struct perf_event_sample sample; | |
176 | size_t read = 0, size = (end - begin); | |
177 | struct btrace_block block = { 0, 0 }; | |
178 | struct regcache *regcache; | |
179 | ||
180 | gdb_assert (begin <= start); | |
181 | gdb_assert (start <= end); | |
182 | ||
183 | /* The first block ends at the current pc. */ | |
184 | #ifdef GDBSERVER | |
185 | regcache = get_thread_regcache (find_thread_ptid (tinfo->ptid), 1); | |
186 | #else | |
187 | regcache = get_thread_regcache (tinfo->ptid); | |
188 | #endif | |
189 | block.end = regcache_read_pc (regcache); | |
190 | ||
191 | /* The buffer may contain a partial record as its last entry (i.e. when the | |
192 | buffer size is not a multiple of the sample size). */ | |
193 | read = sizeof (sample) - 1; | |
194 | ||
195 | for (; read < size; read += sizeof (sample)) | |
196 | { | |
197 | const struct perf_event_sample *psample; | |
198 | ||
199 | /* Find the next perf_event sample in a backwards traversal. */ | |
200 | start -= sizeof (sample); | |
201 | ||
202 | /* If we're still inside the buffer, we're done. */ | |
203 | if (begin <= start) | |
204 | psample = (const struct perf_event_sample *) start; | |
205 | else | |
206 | { | |
207 | int missing; | |
208 | ||
209 | /* We're to the left of the ring buffer, we will wrap around and | |
210 | reappear at the very right of the ring buffer. */ | |
211 | ||
212 | missing = (begin - start); | |
213 | start = (end - missing); | |
214 | ||
215 | /* If the entire sample is missing, we're done. */ | |
216 | if (missing == sizeof (sample)) | |
217 | psample = (const struct perf_event_sample *) start; | |
218 | else | |
219 | { | |
220 | uint8_t *stack; | |
221 | ||
222 | /* The sample wrapped around. The lower part is at the end and | |
223 | the upper part is at the beginning of the buffer. */ | |
224 | stack = (uint8_t *) &sample; | |
225 | ||
226 | /* Copy the two parts so we have a contiguous sample. */ | |
227 | memcpy (stack, start, missing); | |
228 | memcpy (stack + missing, begin, sizeof (sample) - missing); | |
229 | ||
230 | psample = &sample; | |
231 | } | |
232 | } | |
233 | ||
234 | if (!perf_event_sample_ok (psample)) | |
235 | { | |
236 | warning (_("Branch trace may be incomplete.")); | |
237 | break; | |
238 | } | |
239 | ||
240 | if (perf_event_skip_record (tinfo, &psample->bts)) | |
241 | continue; | |
242 | ||
243 | /* We found a valid sample, so we can complete the current block. */ | |
244 | block.begin = psample->bts.to; | |
245 | ||
246 | VEC_safe_push (btrace_block_s, btrace, &block); | |
247 | ||
248 | /* Start the next block. */ | |
249 | block.end = psample->bts.from; | |
250 | } | |
251 | ||
252 | return btrace; | |
253 | } | |
254 | ||
a950d57c MM |
255 | /* Check whether the kernel supports branch tracing. */ |
256 | ||
257 | static int | |
258 | kernel_supports_btrace (void) | |
259 | { | |
260 | struct perf_event_attr attr; | |
261 | pid_t child, pid; | |
262 | int status, file; | |
263 | ||
264 | errno = 0; | |
265 | child = fork (); | |
266 | switch (child) | |
267 | { | |
268 | case -1: | |
269 | warning (_("test branch tracing: cannot fork: %s."), strerror (errno)); | |
270 | return 0; | |
271 | ||
272 | case 0: | |
273 | status = ptrace (PTRACE_TRACEME, 0, NULL, NULL); | |
274 | if (status != 0) | |
275 | { | |
276 | warning (_("test branch tracing: cannot PTRACE_TRACEME: %s."), | |
277 | strerror (errno)); | |
278 | _exit (1); | |
279 | } | |
280 | ||
281 | status = raise (SIGTRAP); | |
282 | if (status != 0) | |
283 | { | |
284 | warning (_("test branch tracing: cannot raise SIGTRAP: %s."), | |
285 | strerror (errno)); | |
286 | _exit (1); | |
287 | } | |
288 | ||
289 | _exit (1); | |
290 | ||
291 | default: | |
292 | pid = waitpid (child, &status, 0); | |
293 | if (pid != child) | |
294 | { | |
295 | warning (_("test branch tracing: bad pid %ld, error: %s."), | |
296 | (long) pid, strerror (errno)); | |
297 | return 0; | |
298 | } | |
299 | ||
300 | if (!WIFSTOPPED (status)) | |
301 | { | |
302 | warning (_("test branch tracing: expected stop. status: %d."), | |
303 | status); | |
304 | return 0; | |
305 | } | |
306 | ||
307 | memset (&attr, 0, sizeof (attr)); | |
308 | ||
309 | attr.type = PERF_TYPE_HARDWARE; | |
310 | attr.config = PERF_COUNT_HW_BRANCH_INSTRUCTIONS; | |
311 | attr.sample_period = 1; | |
312 | attr.sample_type = PERF_SAMPLE_IP | PERF_SAMPLE_ADDR; | |
313 | attr.exclude_kernel = 1; | |
314 | attr.exclude_hv = 1; | |
315 | attr.exclude_idle = 1; | |
316 | ||
317 | file = syscall (SYS_perf_event_open, &attr, child, -1, -1, 0); | |
318 | if (file >= 0) | |
319 | close (file); | |
320 | ||
321 | kill (child, SIGKILL); | |
322 | ptrace (PTRACE_KILL, child, NULL, NULL); | |
323 | ||
324 | pid = waitpid (child, &status, 0); | |
325 | if (pid != child) | |
326 | { | |
327 | warning (_("test branch tracing: bad pid %ld, error: %s."), | |
328 | (long) pid, strerror (errno)); | |
329 | if (!WIFSIGNALED (status)) | |
330 | warning (_("test branch tracing: expected killed. status: %d."), | |
331 | status); | |
332 | } | |
333 | ||
334 | return (file >= 0); | |
335 | } | |
336 | } | |
337 | ||
338 | /* Check whether an Intel cpu supports branch tracing. */ | |
339 | ||
340 | static int | |
341 | intel_supports_btrace (void) | |
342 | { | |
5f8e0b8f MF |
343 | unsigned int cpuid, model, family; |
344 | ||
4d157a3d MF |
345 | if (!i386_cpuid (1, &cpuid, NULL, NULL, NULL)) |
346 | return 0; | |
5f8e0b8f MF |
347 | |
348 | family = (cpuid >> 8) & 0xf; | |
349 | model = (cpuid >> 4) & 0xf; | |
350 | ||
351 | switch (family) | |
352 | { | |
353 | case 0x6: | |
354 | model += (cpuid >> 12) & 0xf0; | |
355 | ||
356 | switch (model) | |
357 | { | |
358 | case 0x1a: /* Nehalem */ | |
359 | case 0x1f: | |
360 | case 0x1e: | |
361 | case 0x2e: | |
362 | case 0x25: /* Westmere */ | |
363 | case 0x2c: | |
364 | case 0x2f: | |
365 | case 0x2a: /* Sandy Bridge */ | |
366 | case 0x2d: | |
367 | case 0x3a: /* Ivy Bridge */ | |
368 | ||
369 | /* AAJ122: LBR, BTM, or BTS records may have incorrect branch | |
370 | "from" information afer an EIST transition, T-states, C1E, or | |
371 | Adaptive Thermal Throttling. */ | |
372 | return 0; | |
373 | } | |
374 | } | |
a950d57c MM |
375 | |
376 | return 1; | |
a950d57c MM |
377 | } |
378 | ||
379 | /* Check whether the cpu supports branch tracing. */ | |
380 | ||
381 | static int | |
382 | cpu_supports_btrace (void) | |
383 | { | |
4d157a3d | 384 | unsigned int ebx, ecx, edx; |
a950d57c | 385 | |
4d157a3d MF |
386 | if (!i386_cpuid (0, NULL, &ebx, &ecx, &edx)) |
387 | return 0; | |
388 | ||
4353c9e6 JK |
389 | if (ebx == signature_INTEL_ebx && ecx == signature_INTEL_ecx |
390 | && edx == signature_INTEL_edx) | |
a950d57c MM |
391 | return intel_supports_btrace (); |
392 | ||
393 | /* Don't know about others. Let's assume they do. */ | |
394 | return 1; | |
a950d57c MM |
395 | } |
396 | ||
7c97f91e MM |
397 | /* See linux-btrace.h. */ |
398 | ||
399 | int | |
400 | linux_supports_btrace (void) | |
401 | { | |
a950d57c MM |
402 | static int cached; |
403 | ||
404 | if (cached == 0) | |
405 | { | |
406 | if (!kernel_supports_btrace ()) | |
407 | cached = -1; | |
408 | else if (!cpu_supports_btrace ()) | |
409 | cached = -1; | |
410 | else | |
411 | cached = 1; | |
412 | } | |
413 | ||
414 | return cached > 0; | |
7c97f91e MM |
415 | } |
416 | ||
417 | /* See linux-btrace.h. */ | |
418 | ||
419 | struct btrace_target_info * | |
420 | linux_enable_btrace (ptid_t ptid) | |
421 | { | |
422 | struct btrace_target_info *tinfo; | |
423 | int pid; | |
424 | ||
425 | tinfo = xzalloc (sizeof (*tinfo)); | |
426 | tinfo->ptid = ptid; | |
427 | ||
428 | tinfo->attr.size = sizeof (tinfo->attr); | |
429 | tinfo->attr.type = PERF_TYPE_HARDWARE; | |
430 | tinfo->attr.config = PERF_COUNT_HW_BRANCH_INSTRUCTIONS; | |
431 | tinfo->attr.sample_period = 1; | |
432 | ||
433 | /* We sample from and to address. */ | |
434 | tinfo->attr.sample_type = PERF_SAMPLE_IP | PERF_SAMPLE_ADDR; | |
435 | ||
436 | tinfo->attr.exclude_kernel = 1; | |
437 | tinfo->attr.exclude_hv = 1; | |
438 | tinfo->attr.exclude_idle = 1; | |
439 | ||
440 | tinfo->ptr_bits = 0; | |
441 | ||
442 | pid = ptid_get_lwp (ptid); | |
443 | if (pid == 0) | |
444 | pid = ptid_get_pid (ptid); | |
445 | ||
446 | errno = 0; | |
447 | tinfo->file = syscall (SYS_perf_event_open, &tinfo->attr, pid, -1, -1, 0); | |
448 | if (tinfo->file < 0) | |
449 | goto err; | |
450 | ||
451 | /* We hard-code the trace buffer size. | |
452 | At some later time, we should make this configurable. */ | |
453 | tinfo->size = 1; | |
454 | tinfo->buffer = mmap (NULL, perf_event_mmap_size (tinfo), | |
455 | PROT_READ, MAP_SHARED, tinfo->file, 0); | |
456 | if (tinfo->buffer == MAP_FAILED) | |
457 | goto err_file; | |
458 | ||
459 | return tinfo; | |
460 | ||
461 | err_file: | |
462 | close (tinfo->file); | |
463 | ||
464 | err: | |
465 | xfree (tinfo); | |
466 | return NULL; | |
467 | } | |
468 | ||
469 | /* See linux-btrace.h. */ | |
470 | ||
471 | int | |
472 | linux_disable_btrace (struct btrace_target_info *tinfo) | |
473 | { | |
474 | int errcode; | |
475 | ||
476 | errno = 0; | |
477 | errcode = munmap (tinfo->buffer, perf_event_mmap_size (tinfo)); | |
478 | if (errcode != 0) | |
479 | return errno; | |
480 | ||
481 | close (tinfo->file); | |
482 | xfree (tinfo); | |
483 | ||
484 | return 0; | |
485 | } | |
486 | ||
487 | /* Check whether the branch trace has changed. */ | |
488 | ||
489 | static int | |
490 | linux_btrace_has_changed (struct btrace_target_info *tinfo) | |
491 | { | |
492 | volatile struct perf_event_mmap_page *header = perf_event_header (tinfo); | |
493 | ||
494 | return header->data_head != tinfo->data_head; | |
495 | } | |
496 | ||
497 | /* See linux-btrace.h. */ | |
498 | ||
499 | VEC (btrace_block_s) * | |
500 | linux_read_btrace (struct btrace_target_info *tinfo, | |
501 | enum btrace_read_type type) | |
502 | { | |
503 | VEC (btrace_block_s) *btrace = NULL; | |
504 | volatile struct perf_event_mmap_page *header; | |
505 | const uint8_t *begin, *end, *start; | |
506 | unsigned long data_head, retries = 5; | |
507 | size_t buffer_size; | |
508 | ||
509 | if (type == btrace_read_new && !linux_btrace_has_changed (tinfo)) | |
510 | return NULL; | |
511 | ||
512 | header = perf_event_header (tinfo); | |
513 | buffer_size = perf_event_buffer_size (tinfo); | |
514 | ||
515 | /* We may need to retry reading the trace. See below. */ | |
516 | while (retries--) | |
517 | { | |
518 | data_head = header->data_head; | |
519 | ||
520 | /* If there's new trace, let's read it. */ | |
521 | if (data_head != tinfo->data_head) | |
522 | { | |
523 | /* Data_head keeps growing; the buffer itself is circular. */ | |
524 | begin = perf_event_buffer_begin (tinfo); | |
525 | start = begin + data_head % buffer_size; | |
526 | ||
527 | if (data_head <= buffer_size) | |
528 | end = start; | |
529 | else | |
530 | end = perf_event_buffer_end (tinfo); | |
531 | ||
532 | btrace = perf_event_read_bts (tinfo, begin, end, start); | |
533 | } | |
534 | ||
535 | /* The stopping thread notifies its ptracer before it is scheduled out. | |
536 | On multi-core systems, the debugger might therefore run while the | |
537 | kernel might be writing the last branch trace records. | |
538 | ||
539 | Let's check whether the data head moved while we read the trace. */ | |
540 | if (data_head == header->data_head) | |
541 | break; | |
542 | } | |
543 | ||
544 | tinfo->data_head = data_head; | |
545 | ||
546 | return btrace; | |
547 | } | |
548 | ||
549 | #else /* !HAVE_LINUX_PERF_EVENT_H */ | |
550 | ||
551 | /* See linux-btrace.h. */ | |
552 | ||
553 | int | |
554 | linux_supports_btrace (void) | |
555 | { | |
556 | return 0; | |
557 | } | |
558 | ||
559 | /* See linux-btrace.h. */ | |
560 | ||
561 | struct btrace_target_info * | |
562 | linux_enable_btrace (ptid_t ptid) | |
563 | { | |
564 | return NULL; | |
565 | } | |
566 | ||
567 | /* See linux-btrace.h. */ | |
568 | ||
569 | int | |
570 | linux_disable_btrace (struct btrace_target_info *tinfo) | |
571 | { | |
572 | return ENOSYS; | |
573 | } | |
574 | ||
575 | /* See linux-btrace.h. */ | |
576 | ||
577 | VEC (btrace_block_s) * | |
578 | linux_read_btrace (struct btrace_target_info *tinfo, | |
579 | enum btrace_read_type type) | |
580 | { | |
581 | return NULL; | |
582 | } | |
583 | ||
584 | #endif /* !HAVE_LINUX_PERF_EVENT_H */ |