1 // SPDX-License-Identifier: GPL-2.0-only
2 #include <linux/module.h>
3 #include <linux/sort.h>
4 #include <asm/ptrace.h>
5 #include <asm/stacktrace.h>
6 #include <asm/unwind.h>
7 #include <asm/orc_types.h>
8 #include <asm/orc_lookup.h>
9
10 #define orc_warn(fmt, ...) \
11 printk_deferred_once(KERN_WARNING pr_fmt("WARNING: " fmt), ##__VA_ARGS__)
12
13 extern int __start_orc_unwind_ip[];
14 extern int __stop_orc_unwind_ip[];
15 extern struct orc_entry __start_orc_unwind[];
16 extern struct orc_entry __stop_orc_unwind[];
17
18 static DEFINE_MUTEX(sort_mutex);
19 int *cur_orc_ip_table = __start_orc_unwind_ip;
20 struct orc_entry *cur_orc_table = __start_orc_unwind;
21
22 unsigned int lookup_num_blocks;
23 bool orc_init;
24
orc_ip(const int * ip)25 static inline unsigned long orc_ip(const int *ip)
26 {
27 return (unsigned long)ip + *ip;
28 }
29
__orc_find(int * ip_table,struct orc_entry * u_table,unsigned int num_entries,unsigned long ip)30 static struct orc_entry *__orc_find(int *ip_table, struct orc_entry *u_table,
31 unsigned int num_entries, unsigned long ip)
32 {
33 int *first = ip_table;
34 int *last = ip_table + num_entries - 1;
35 int *mid = first, *found = first;
36
37 if (!num_entries)
38 return NULL;
39
40 /*
41 * Do a binary range search to find the rightmost duplicate of a given
42 * starting address. Some entries are section terminators which are
43 * "weak" entries for ensuring there are no gaps. They should be
44 * ignored when they conflict with a real entry.
45 */
46 while (first <= last) {
47 mid = first + ((last - first) / 2);
48
49 if (orc_ip(mid) <= ip) {
50 found = mid;
51 first = mid + 1;
52 } else
53 last = mid - 1;
54 }
55
56 return u_table + (found - ip_table);
57 }
58
59 #ifdef CONFIG_MODULES
orc_module_find(unsigned long ip)60 static struct orc_entry *orc_module_find(unsigned long ip)
61 {
62 struct module *mod;
63
64 mod = __module_address(ip);
65 if (!mod || !mod->arch.orc_unwind || !mod->arch.orc_unwind_ip)
66 return NULL;
67 return __orc_find(mod->arch.orc_unwind_ip, mod->arch.orc_unwind,
68 mod->arch.num_orcs, ip);
69 }
70 #else
orc_module_find(unsigned long ip)71 static struct orc_entry *orc_module_find(unsigned long ip)
72 {
73 return NULL;
74 }
75 #endif
76
77 #ifdef CONFIG_DYNAMIC_FTRACE
78 static struct orc_entry *orc_find(unsigned long ip);
79
80 /*
81 * Ftrace dynamic trampolines do not have orc entries of their own.
82 * But they are copies of the ftrace entries that are static and
83 * defined in ftrace_*.S, which do have orc entries.
84 *
85 * If the unwinder comes across a ftrace trampoline, then find the
86 * ftrace function that was used to create it, and use that ftrace
87 * function's orc entry, as the placement of the return code in
88 * the stack will be identical.
89 */
orc_ftrace_find(unsigned long ip)90 static struct orc_entry *orc_ftrace_find(unsigned long ip)
91 {
92 struct ftrace_ops *ops;
93 unsigned long tramp_addr, offset;
94
95 ops = ftrace_ops_trampoline(ip);
96 if (!ops)
97 return NULL;
98
99 /* Set tramp_addr to the start of the code copied by the trampoline */
100 if (ops->flags & FTRACE_OPS_FL_SAVE_REGS)
101 tramp_addr = (unsigned long)ftrace_regs_caller;
102 else
103 tramp_addr = (unsigned long)ftrace_caller;
104
105 /* Now place tramp_addr to the location within the trampoline ip is at */
106 offset = ip - ops->trampoline;
107 tramp_addr += offset;
108
109 /* Prevent unlikely recursion */
110 if (ip == tramp_addr)
111 return NULL;
112
113 return orc_find(tramp_addr);
114 }
115 #else
orc_ftrace_find(unsigned long ip)116 static struct orc_entry *orc_ftrace_find(unsigned long ip)
117 {
118 return NULL;
119 }
120 #endif
121
122 /*
123 * If we crash with IP==0, the last successfully executed instruction
124 * was probably an indirect function call with a NULL function pointer,
125 * and we don't have unwind information for NULL.
126 * This hardcoded ORC entry for IP==0 allows us to unwind from a NULL function
127 * pointer into its parent and then continue normally from there.
128 */
129 static struct orc_entry null_orc_entry = {
130 .sp_offset = sizeof(long),
131 .sp_reg = ORC_REG_SP,
132 .bp_reg = ORC_REG_UNDEFINED,
133 .type = ORC_TYPE_CALL
134 };
135
136 /* Fake frame pointer entry -- used as a fallback for generated code */
137 static struct orc_entry orc_fp_entry = {
138 .type = ORC_TYPE_CALL,
139 .sp_reg = ORC_REG_BP,
140 .sp_offset = 16,
141 .bp_reg = ORC_REG_PREV_SP,
142 .bp_offset = -16,
143 .end = 0,
144 };
145
orc_find(unsigned long ip)146 static struct orc_entry *orc_find(unsigned long ip)
147 {
148 static struct orc_entry *orc;
149
150 if (ip == 0)
151 return &null_orc_entry;
152
153 /* For non-init vmlinux addresses, use the fast lookup table: */
154 if (ip >= LOOKUP_START_IP && ip < LOOKUP_STOP_IP) {
155 unsigned int idx, start, stop;
156
157 idx = (ip - LOOKUP_START_IP) / LOOKUP_BLOCK_SIZE;
158
159 if (unlikely((idx >= lookup_num_blocks-1))) {
160 orc_warn("WARNING: bad lookup idx: idx=%u num=%u ip=%pB\n",
161 idx, lookup_num_blocks, (void *)ip);
162 return NULL;
163 }
164
165 start = orc_lookup[idx];
166 stop = orc_lookup[idx + 1] + 1;
167
168 if (unlikely((__start_orc_unwind + start >= __stop_orc_unwind) ||
169 (__start_orc_unwind + stop > __stop_orc_unwind))) {
170 orc_warn("WARNING: bad lookup value: idx=%u num=%u start=%u stop=%u ip=%pB\n",
171 idx, lookup_num_blocks, start, stop, (void *)ip);
172 return NULL;
173 }
174
175 return __orc_find(__start_orc_unwind_ip + start,
176 __start_orc_unwind + start, stop - start, ip);
177 }
178
179 /* vmlinux .init slow lookup: */
180 if (init_kernel_text(ip))
181 return __orc_find(__start_orc_unwind_ip, __start_orc_unwind,
182 __stop_orc_unwind_ip - __start_orc_unwind_ip, ip);
183
184 /* Module lookup: */
185 orc = orc_module_find(ip);
186 if (orc)
187 return orc;
188
189 return orc_ftrace_find(ip);
190 }
191
orc_sort_swap(void * _a,void * _b,int size)192 static void orc_sort_swap(void *_a, void *_b, int size)
193 {
194 struct orc_entry *orc_a, *orc_b;
195 struct orc_entry orc_tmp;
196 int *a = _a, *b = _b, tmp;
197 int delta = _b - _a;
198
199 /* Swap the .orc_unwind_ip entries: */
200 tmp = *a;
201 *a = *b + delta;
202 *b = tmp - delta;
203
204 /* Swap the corresponding .orc_unwind entries: */
205 orc_a = cur_orc_table + (a - cur_orc_ip_table);
206 orc_b = cur_orc_table + (b - cur_orc_ip_table);
207 orc_tmp = *orc_a;
208 *orc_a = *orc_b;
209 *orc_b = orc_tmp;
210 }
211
orc_sort_cmp(const void * _a,const void * _b)212 static int orc_sort_cmp(const void *_a, const void *_b)
213 {
214 struct orc_entry *orc_a;
215 const int *a = _a, *b = _b;
216 unsigned long a_val = orc_ip(a);
217 unsigned long b_val = orc_ip(b);
218
219 if (a_val > b_val)
220 return 1;
221 if (a_val < b_val)
222 return -1;
223
224 /*
225 * The "weak" section terminator entries need to always be on the left
226 * to ensure the lookup code skips them in favor of real entries.
227 * These terminator entries exist to handle any gaps created by
228 * whitelisted .o files which didn't get objtool generation.
229 */
230 orc_a = cur_orc_table + (a - cur_orc_ip_table);
231 return orc_a->sp_reg == ORC_REG_UNDEFINED && !orc_a->end ? -1 : 1;
232 }
233
234 #ifdef CONFIG_MODULES
unwind_module_init(struct module * mod,void * _orc_ip,size_t orc_ip_size,void * _orc,size_t orc_size)235 void unwind_module_init(struct module *mod, void *_orc_ip, size_t orc_ip_size,
236 void *_orc, size_t orc_size)
237 {
238 int *orc_ip = _orc_ip;
239 struct orc_entry *orc = _orc;
240 unsigned int num_entries = orc_ip_size / sizeof(int);
241
242 WARN_ON_ONCE(orc_ip_size % sizeof(int) != 0 ||
243 orc_size % sizeof(*orc) != 0 ||
244 num_entries != orc_size / sizeof(*orc));
245
246 /*
247 * The 'cur_orc_*' globals allow the orc_sort_swap() callback to
248 * associate an .orc_unwind_ip table entry with its corresponding
249 * .orc_unwind entry so they can both be swapped.
250 */
251 mutex_lock(&sort_mutex);
252 cur_orc_ip_table = orc_ip;
253 cur_orc_table = orc;
254 sort(orc_ip, num_entries, sizeof(int), orc_sort_cmp, orc_sort_swap);
255 mutex_unlock(&sort_mutex);
256
257 mod->arch.orc_unwind_ip = orc_ip;
258 mod->arch.orc_unwind = orc;
259 mod->arch.num_orcs = num_entries;
260 }
261 #endif
262
unwind_init(void)263 void __init unwind_init(void)
264 {
265 size_t orc_ip_size = (void *)__stop_orc_unwind_ip - (void *)__start_orc_unwind_ip;
266 size_t orc_size = (void *)__stop_orc_unwind - (void *)__start_orc_unwind;
267 size_t num_entries = orc_ip_size / sizeof(int);
268 struct orc_entry *orc;
269 int i;
270
271 if (!num_entries || orc_ip_size % sizeof(int) != 0 ||
272 orc_size % sizeof(struct orc_entry) != 0 ||
273 num_entries != orc_size / sizeof(struct orc_entry)) {
274 orc_warn("WARNING: Bad or missing .orc_unwind table. Disabling unwinder.\n");
275 return;
276 }
277
278 /* Sort the .orc_unwind and .orc_unwind_ip tables: */
279 sort(__start_orc_unwind_ip, num_entries, sizeof(int), orc_sort_cmp,
280 orc_sort_swap);
281
282 /* Initialize the fast lookup table: */
283 lookup_num_blocks = orc_lookup_end - orc_lookup;
284 for (i = 0; i < lookup_num_blocks-1; i++) {
285 orc = __orc_find(__start_orc_unwind_ip, __start_orc_unwind,
286 num_entries,
287 LOOKUP_START_IP + (LOOKUP_BLOCK_SIZE * i));
288 if (!orc) {
289 orc_warn("WARNING: Corrupt .orc_unwind table. Disabling unwinder.\n");
290 return;
291 }
292
293 orc_lookup[i] = orc - __start_orc_unwind;
294 }
295
296 /* Initialize the ending block: */
297 orc = __orc_find(__start_orc_unwind_ip, __start_orc_unwind, num_entries,
298 LOOKUP_STOP_IP);
299 if (!orc) {
300 orc_warn("WARNING: Corrupt .orc_unwind table. Disabling unwinder.\n");
301 return;
302 }
303 orc_lookup[lookup_num_blocks-1] = orc - __start_orc_unwind;
304
305 orc_init = true;
306 }
307
unwind_get_return_address(struct unwind_state * state)308 unsigned long unwind_get_return_address(struct unwind_state *state)
309 {
310 if (unwind_done(state))
311 return 0;
312
313 return __kernel_text_address(state->ip) ? state->ip : 0;
314 }
315 EXPORT_SYMBOL_GPL(unwind_get_return_address);
316
unwind_get_return_address_ptr(struct unwind_state * state)317 unsigned long *unwind_get_return_address_ptr(struct unwind_state *state)
318 {
319 if (unwind_done(state))
320 return NULL;
321
322 if (state->regs)
323 return &state->regs->ip;
324
325 if (state->sp)
326 return (unsigned long *)state->sp - 1;
327
328 return NULL;
329 }
330
stack_access_ok(struct unwind_state * state,unsigned long _addr,size_t len)331 static bool stack_access_ok(struct unwind_state *state, unsigned long _addr,
332 size_t len)
333 {
334 struct stack_info *info = &state->stack_info;
335 void *addr = (void *)_addr;
336
337 if (!on_stack(info, addr, len) &&
338 (get_stack_info(addr, state->task, info, &state->stack_mask)))
339 return false;
340
341 return true;
342 }
343
deref_stack_reg(struct unwind_state * state,unsigned long addr,unsigned long * val)344 static bool deref_stack_reg(struct unwind_state *state, unsigned long addr,
345 unsigned long *val)
346 {
347 if (!stack_access_ok(state, addr, sizeof(long)))
348 return false;
349
350 *val = READ_ONCE_NOCHECK(*(unsigned long *)addr);
351 return true;
352 }
353
deref_stack_regs(struct unwind_state * state,unsigned long addr,unsigned long * ip,unsigned long * sp)354 static bool deref_stack_regs(struct unwind_state *state, unsigned long addr,
355 unsigned long *ip, unsigned long *sp)
356 {
357 struct pt_regs *regs = (struct pt_regs *)addr;
358
359 /* x86-32 support will be more complicated due to the ®s->sp hack */
360 BUILD_BUG_ON(IS_ENABLED(CONFIG_X86_32));
361
362 if (!stack_access_ok(state, addr, sizeof(struct pt_regs)))
363 return false;
364
365 *ip = READ_ONCE_NOCHECK(regs->ip);
366 *sp = READ_ONCE_NOCHECK(regs->sp);
367 return true;
368 }
369
deref_stack_iret_regs(struct unwind_state * state,unsigned long addr,unsigned long * ip,unsigned long * sp)370 static bool deref_stack_iret_regs(struct unwind_state *state, unsigned long addr,
371 unsigned long *ip, unsigned long *sp)
372 {
373 struct pt_regs *regs = (void *)addr - IRET_FRAME_OFFSET;
374
375 if (!stack_access_ok(state, addr, IRET_FRAME_SIZE))
376 return false;
377
378 *ip = READ_ONCE_NOCHECK(regs->ip);
379 *sp = READ_ONCE_NOCHECK(regs->sp);
380 return true;
381 }
382
383 /*
384 * If state->regs is non-NULL, and points to a full pt_regs, just get the reg
385 * value from state->regs.
386 *
387 * Otherwise, if state->regs just points to IRET regs, and the previous frame
388 * had full regs, it's safe to get the value from the previous regs. This can
389 * happen when early/late IRQ entry code gets interrupted by an NMI.
390 */
get_reg(struct unwind_state * state,unsigned int reg_off,unsigned long * val)391 static bool get_reg(struct unwind_state *state, unsigned int reg_off,
392 unsigned long *val)
393 {
394 unsigned int reg = reg_off/8;
395
396 if (!state->regs)
397 return false;
398
399 if (state->full_regs) {
400 *val = READ_ONCE_NOCHECK(((unsigned long *)state->regs)[reg]);
401 return true;
402 }
403
404 if (state->prev_regs) {
405 *val = READ_ONCE_NOCHECK(((unsigned long *)state->prev_regs)[reg]);
406 return true;
407 }
408
409 return false;
410 }
411
unwind_next_frame(struct unwind_state * state)412 bool unwind_next_frame(struct unwind_state *state)
413 {
414 unsigned long ip_p, sp, tmp, orig_ip = state->ip, prev_sp = state->sp;
415 enum stack_type prev_type = state->stack_info.type;
416 struct orc_entry *orc;
417 bool indirect = false;
418
419 if (unwind_done(state))
420 return false;
421
422 /* Don't let modules unload while we're reading their ORC data. */
423 preempt_disable();
424
425 /* End-of-stack check for user tasks: */
426 if (state->regs && user_mode(state->regs))
427 goto the_end;
428
429 /*
430 * Find the orc_entry associated with the text address.
431 *
432 * For a call frame (as opposed to a signal frame), state->ip points to
433 * the instruction after the call. That instruction's stack layout
434 * could be different from the call instruction's layout, for example
435 * if the call was to a noreturn function. So get the ORC data for the
436 * call instruction itself.
437 */
438 orc = orc_find(state->signal ? state->ip : state->ip - 1);
439 if (!orc) {
440 /*
441 * As a fallback, try to assume this code uses a frame pointer.
442 * This is useful for generated code, like BPF, which ORC
443 * doesn't know about. This is just a guess, so the rest of
444 * the unwind is no longer considered reliable.
445 */
446 orc = &orc_fp_entry;
447 state->error = true;
448 }
449
450 /* End-of-stack check for kernel threads: */
451 if (orc->sp_reg == ORC_REG_UNDEFINED) {
452 if (!orc->end)
453 goto err;
454
455 goto the_end;
456 }
457
458 /* Find the previous frame's stack: */
459 switch (orc->sp_reg) {
460 case ORC_REG_SP:
461 sp = state->sp + orc->sp_offset;
462 break;
463
464 case ORC_REG_BP:
465 sp = state->bp + orc->sp_offset;
466 break;
467
468 case ORC_REG_SP_INDIRECT:
469 sp = state->sp + orc->sp_offset;
470 indirect = true;
471 break;
472
473 case ORC_REG_BP_INDIRECT:
474 sp = state->bp + orc->sp_offset;
475 indirect = true;
476 break;
477
478 case ORC_REG_R10:
479 if (!get_reg(state, offsetof(struct pt_regs, r10), &sp)) {
480 orc_warn("missing regs for base reg R10 at ip %pB\n",
481 (void *)state->ip);
482 goto err;
483 }
484 break;
485
486 case ORC_REG_R13:
487 if (!get_reg(state, offsetof(struct pt_regs, r13), &sp)) {
488 orc_warn("missing regs for base reg R13 at ip %pB\n",
489 (void *)state->ip);
490 goto err;
491 }
492 break;
493
494 case ORC_REG_DI:
495 if (!get_reg(state, offsetof(struct pt_regs, di), &sp)) {
496 orc_warn("missing regs for base reg DI at ip %pB\n",
497 (void *)state->ip);
498 goto err;
499 }
500 break;
501
502 case ORC_REG_DX:
503 if (!get_reg(state, offsetof(struct pt_regs, dx), &sp)) {
504 orc_warn("missing regs for base reg DX at ip %pB\n",
505 (void *)state->ip);
506 goto err;
507 }
508 break;
509
510 default:
511 orc_warn("unknown SP base reg %d for ip %pB\n",
512 orc->sp_reg, (void *)state->ip);
513 goto err;
514 }
515
516 if (indirect) {
517 if (!deref_stack_reg(state, sp, &sp))
518 goto err;
519 }
520
521 /* Find IP, SP and possibly regs: */
522 switch (orc->type) {
523 case ORC_TYPE_CALL:
524 ip_p = sp - sizeof(long);
525
526 if (!deref_stack_reg(state, ip_p, &state->ip))
527 goto err;
528
529 state->ip = ftrace_graph_ret_addr(state->task, &state->graph_idx,
530 state->ip, (void *)ip_p);
531
532 state->sp = sp;
533 state->regs = NULL;
534 state->prev_regs = NULL;
535 state->signal = false;
536 break;
537
538 case ORC_TYPE_REGS:
539 if (!deref_stack_regs(state, sp, &state->ip, &state->sp)) {
540 orc_warn("can't dereference registers at %p for ip %pB\n",
541 (void *)sp, (void *)orig_ip);
542 goto err;
543 }
544
545 state->regs = (struct pt_regs *)sp;
546 state->prev_regs = NULL;
547 state->full_regs = true;
548 state->signal = true;
549 break;
550
551 case ORC_TYPE_REGS_IRET:
552 if (!deref_stack_iret_regs(state, sp, &state->ip, &state->sp)) {
553 orc_warn("can't dereference iret registers at %p for ip %pB\n",
554 (void *)sp, (void *)orig_ip);
555 goto err;
556 }
557
558 if (state->full_regs)
559 state->prev_regs = state->regs;
560 state->regs = (void *)sp - IRET_FRAME_OFFSET;
561 state->full_regs = false;
562 state->signal = true;
563 break;
564
565 default:
566 orc_warn("unknown .orc_unwind entry type %d for ip %pB\n",
567 orc->type, (void *)orig_ip);
568 goto err;
569 }
570
571 /* Find BP: */
572 switch (orc->bp_reg) {
573 case ORC_REG_UNDEFINED:
574 if (get_reg(state, offsetof(struct pt_regs, bp), &tmp))
575 state->bp = tmp;
576 break;
577
578 case ORC_REG_PREV_SP:
579 if (!deref_stack_reg(state, sp + orc->bp_offset, &state->bp))
580 goto err;
581 break;
582
583 case ORC_REG_BP:
584 if (!deref_stack_reg(state, state->bp + orc->bp_offset, &state->bp))
585 goto err;
586 break;
587
588 default:
589 orc_warn("unknown BP base reg %d for ip %pB\n",
590 orc->bp_reg, (void *)orig_ip);
591 goto err;
592 }
593
594 /* Prevent a recursive loop due to bad ORC data: */
595 if (state->stack_info.type == prev_type &&
596 on_stack(&state->stack_info, (void *)state->sp, sizeof(long)) &&
597 state->sp <= prev_sp) {
598 orc_warn("stack going in the wrong direction? ip=%pB\n",
599 (void *)orig_ip);
600 goto err;
601 }
602
603 preempt_enable();
604 return true;
605
606 err:
607 state->error = true;
608
609 the_end:
610 preempt_enable();
611 state->stack_info.type = STACK_TYPE_UNKNOWN;
612 return false;
613 }
614 EXPORT_SYMBOL_GPL(unwind_next_frame);
615
__unwind_start(struct unwind_state * state,struct task_struct * task,struct pt_regs * regs,unsigned long * first_frame)616 void __unwind_start(struct unwind_state *state, struct task_struct *task,
617 struct pt_regs *regs, unsigned long *first_frame)
618 {
619 memset(state, 0, sizeof(*state));
620 state->task = task;
621
622 if (!orc_init)
623 goto err;
624
625 /*
626 * Refuse to unwind the stack of a task while it's executing on another
627 * CPU. This check is racy, but that's ok: the unwinder has other
628 * checks to prevent it from going off the rails.
629 */
630 if (task_on_another_cpu(task))
631 goto err;
632
633 if (regs) {
634 if (user_mode(regs))
635 goto the_end;
636
637 state->ip = regs->ip;
638 state->sp = regs->sp;
639 state->bp = regs->bp;
640 state->regs = regs;
641 state->full_regs = true;
642 state->signal = true;
643
644 } else if (task == current) {
645 asm volatile("lea (%%rip), %0\n\t"
646 "mov %%rsp, %1\n\t"
647 "mov %%rbp, %2\n\t"
648 : "=r" (state->ip), "=r" (state->sp),
649 "=r" (state->bp));
650
651 } else {
652 struct inactive_task_frame *frame = (void *)task->thread.sp;
653
654 state->sp = task->thread.sp + sizeof(*frame);
655 state->bp = READ_ONCE_NOCHECK(frame->bp);
656 state->ip = READ_ONCE_NOCHECK(frame->ret_addr);
657 state->signal = (void *)state->ip == ret_from_fork;
658 }
659
660 if (get_stack_info((unsigned long *)state->sp, state->task,
661 &state->stack_info, &state->stack_mask)) {
662 /*
663 * We weren't on a valid stack. It's possible that
664 * we overflowed a valid stack into a guard page.
665 * See if the next page up is valid so that we can
666 * generate some kind of backtrace if this happens.
667 */
668 void *next_page = (void *)PAGE_ALIGN((unsigned long)state->sp);
669 state->error = true;
670 if (get_stack_info(next_page, state->task, &state->stack_info,
671 &state->stack_mask))
672 return;
673 }
674
675 /*
676 * The caller can provide the address of the first frame directly
677 * (first_frame) or indirectly (regs->sp) to indicate which stack frame
678 * to start unwinding at. Skip ahead until we reach it.
679 */
680
681 /* When starting from regs, skip the regs frame: */
682 if (regs) {
683 unwind_next_frame(state);
684 return;
685 }
686
687 /* Otherwise, skip ahead to the user-specified starting frame: */
688 while (!unwind_done(state) &&
689 (!on_stack(&state->stack_info, first_frame, sizeof(long)) ||
690 state->sp <= (unsigned long)first_frame))
691 unwind_next_frame(state);
692
693 return;
694
695 err:
696 state->error = true;
697 the_end:
698 state->stack_info.type = STACK_TYPE_UNKNOWN;
699 }
700 EXPORT_SYMBOL_GPL(__unwind_start);
701