1 /*
2  * arch/arm/kernel/unwind.c
3  *
4  * Copyright (C) 2008 ARM Limited
5  *
6  * This program is free software; you can redistribute it and/or modify
7  * it under the terms of the GNU General Public License version 2 as
8  * published by the Free Software Foundation.
9  *
10  * This program is distributed in the hope that it will be useful,
11  * but WITHOUT ANY WARRANTY; without even the implied warranty of
12  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
13  * GNU General Public License for more details.
14  *
15  * You should have received a copy of the GNU General Public License
16  * along with this program; if not, write to the Free Software
17  * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
18  *
19  *
20  * Stack unwinding support for ARM
21  *
22  * An ARM EABI version of gcc is required to generate the unwind
23  * tables. For information about the structure of the unwind tables,
24  * see "Exception Handling ABI for the ARM Architecture" at:
25  *
26  * http://infocenter.arm.com/help/topic/com.arm.doc.subset.swdev.abi/index.html
27  */
28 
29 #ifndef __CHECKER__
30 #if !defined (__ARM_EABI__)
31 #warning Your compiler does not have EABI support.
32 #warning    ARM unwind is known to compile only with EABI compilers.
33 #warning    Change compiler or disable ARM_UNWIND option.
34 #elif (__GNUC__ == 4 && __GNUC_MINOR__ <= 2)
35 #warning Your compiler is too buggy; it is known to not compile ARM unwind support.
36 #warning    Change compiler or disable ARM_UNWIND option.
37 #endif
38 #endif /* __CHECKER__ */
39 
40 #include <linux/kernel.h>
41 #include <linux/init.h>
42 #include <linux/export.h>
43 #include <linux/sched.h>
44 #include <linux/slab.h>
45 #include <linux/spinlock.h>
46 #include <linux/list.h>
47 
48 #include <asm/stacktrace.h>
49 #include <asm/traps.h>
50 #include <asm/unwind.h>
51 
52 /* Dummy functions to avoid linker complaints */
__aeabi_unwind_cpp_pr0(void)53 void __aeabi_unwind_cpp_pr0(void)
54 {
55 };
56 EXPORT_SYMBOL(__aeabi_unwind_cpp_pr0);
57 
__aeabi_unwind_cpp_pr1(void)58 void __aeabi_unwind_cpp_pr1(void)
59 {
60 };
61 EXPORT_SYMBOL(__aeabi_unwind_cpp_pr1);
62 
__aeabi_unwind_cpp_pr2(void)63 void __aeabi_unwind_cpp_pr2(void)
64 {
65 };
66 EXPORT_SYMBOL(__aeabi_unwind_cpp_pr2);
67 
68 struct unwind_ctrl_block {
69 	unsigned long vrs[16];		/* virtual register set */
70 	const unsigned long *insn;	/* pointer to the current instructions word */
71 	int entries;			/* number of entries left to interpret */
72 	int byte;			/* current byte number in the instructions word */
73 };
74 
75 enum regs {
76 #ifdef CONFIG_THUMB2_KERNEL
77 	FP = 7,
78 #else
79 	FP = 11,
80 #endif
81 	SP = 13,
82 	LR = 14,
83 	PC = 15
84 };
85 
86 extern const struct unwind_idx __start_unwind_idx[];
87 static const struct unwind_idx *__origin_unwind_idx;
88 extern const struct unwind_idx __stop_unwind_idx[];
89 
90 static DEFINE_SPINLOCK(unwind_lock);
91 static LIST_HEAD(unwind_tables);
92 
93 /* Convert a prel31 symbol to an absolute address */
94 #define prel31_to_addr(ptr)				\
95 ({							\
96 	/* sign-extend to 32 bits */			\
97 	long offset = (((long)*(ptr)) << 1) >> 1;	\
98 	(unsigned long)(ptr) + offset;			\
99 })
100 
101 /*
102  * Binary search in the unwind index. The entries are
103  * guaranteed to be sorted in ascending order by the linker.
104  *
105  * start = first entry
106  * origin = first entry with positive offset (or stop if there is no such entry)
107  * stop - 1 = last entry
108  */
search_index(unsigned long addr,const struct unwind_idx * start,const struct unwind_idx * origin,const struct unwind_idx * stop)109 static const struct unwind_idx *search_index(unsigned long addr,
110 				       const struct unwind_idx *start,
111 				       const struct unwind_idx *origin,
112 				       const struct unwind_idx *stop)
113 {
114 	unsigned long addr_prel31;
115 
116 	pr_debug("%s(%08lx, %p, %p, %p)\n",
117 			__func__, addr, start, origin, stop);
118 
119 	/*
120 	 * only search in the section with the matching sign. This way the
121 	 * prel31 numbers can be compared as unsigned longs.
122 	 */
123 	if (addr < (unsigned long)start)
124 		/* negative offsets: [start; origin) */
125 		stop = origin;
126 	else
127 		/* positive offsets: [origin; stop) */
128 		start = origin;
129 
130 	/* prel31 for address relavive to start */
131 	addr_prel31 = (addr - (unsigned long)start) & 0x7fffffff;
132 
133 	while (start < stop - 1) {
134 		const struct unwind_idx *mid = start + ((stop - start) >> 1);
135 
136 		/*
137 		 * As addr_prel31 is relative to start an offset is needed to
138 		 * make it relative to mid.
139 		 */
140 		if (addr_prel31 - ((unsigned long)mid - (unsigned long)start) <
141 				mid->addr_offset)
142 			stop = mid;
143 		else {
144 			/* keep addr_prel31 relative to start */
145 			addr_prel31 -= ((unsigned long)mid -
146 					(unsigned long)start);
147 			start = mid;
148 		}
149 	}
150 
151 	if (likely(start->addr_offset <= addr_prel31))
152 		return start;
153 	else {
154 		pr_warning("unwind: Unknown symbol address %08lx\n", addr);
155 		return NULL;
156 	}
157 }
158 
unwind_find_origin(const struct unwind_idx * start,const struct unwind_idx * stop)159 static const struct unwind_idx *unwind_find_origin(
160 		const struct unwind_idx *start, const struct unwind_idx *stop)
161 {
162 	pr_debug("%s(%p, %p)\n", __func__, start, stop);
163 	while (start < stop) {
164 		const struct unwind_idx *mid = start + ((stop - start) >> 1);
165 
166 		if (mid->addr_offset >= 0x40000000)
167 			/* negative offset */
168 			start = mid + 1;
169 		else
170 			/* positive offset */
171 			stop = mid;
172 	}
173 	pr_debug("%s -> %p\n", __func__, stop);
174 	return stop;
175 }
176 
unwind_find_idx(unsigned long addr)177 static const struct unwind_idx *unwind_find_idx(unsigned long addr)
178 {
179 	const struct unwind_idx *idx = NULL;
180 	unsigned long flags;
181 
182 	pr_debug("%s(%08lx)\n", __func__, addr);
183 
184 	if (core_kernel_text(addr)) {
185 		if (unlikely(!__origin_unwind_idx))
186 			__origin_unwind_idx =
187 				unwind_find_origin(__start_unwind_idx,
188 						__stop_unwind_idx);
189 
190 		/* main unwind table */
191 		idx = search_index(addr, __start_unwind_idx,
192 				   __origin_unwind_idx,
193 				   __stop_unwind_idx);
194 	} else {
195 		/* module unwind tables */
196 		struct unwind_table *table;
197 
198 		spin_lock_irqsave(&unwind_lock, flags);
199 		list_for_each_entry(table, &unwind_tables, list) {
200 			if (addr >= table->begin_addr &&
201 			    addr < table->end_addr) {
202 				idx = search_index(addr, table->start,
203 						   table->origin,
204 						   table->stop);
205 				/* Move-to-front to exploit common traces */
206 				list_move(&table->list, &unwind_tables);
207 				break;
208 			}
209 		}
210 		spin_unlock_irqrestore(&unwind_lock, flags);
211 	}
212 
213 	pr_debug("%s: idx = %p\n", __func__, idx);
214 	return idx;
215 }
216 
unwind_get_byte(struct unwind_ctrl_block * ctrl)217 static unsigned long unwind_get_byte(struct unwind_ctrl_block *ctrl)
218 {
219 	unsigned long ret;
220 
221 	if (ctrl->entries <= 0) {
222 		pr_warning("unwind: Corrupt unwind table\n");
223 		return 0;
224 	}
225 
226 	ret = (*ctrl->insn >> (ctrl->byte * 8)) & 0xff;
227 
228 	if (ctrl->byte == 0) {
229 		ctrl->insn++;
230 		ctrl->entries--;
231 		ctrl->byte = 3;
232 	} else
233 		ctrl->byte--;
234 
235 	return ret;
236 }
237 
238 /*
239  * Execute the current unwind instruction.
240  */
unwind_exec_insn(struct unwind_ctrl_block * ctrl)241 static int unwind_exec_insn(struct unwind_ctrl_block *ctrl)
242 {
243 	unsigned long insn = unwind_get_byte(ctrl);
244 
245 	pr_debug("%s: insn = %08lx\n", __func__, insn);
246 
247 	if ((insn & 0xc0) == 0x00)
248 		ctrl->vrs[SP] += ((insn & 0x3f) << 2) + 4;
249 	else if ((insn & 0xc0) == 0x40)
250 		ctrl->vrs[SP] -= ((insn & 0x3f) << 2) + 4;
251 	else if ((insn & 0xf0) == 0x80) {
252 		unsigned long mask;
253 		unsigned long *vsp = (unsigned long *)ctrl->vrs[SP];
254 		int load_sp, reg = 4;
255 
256 		insn = (insn << 8) | unwind_get_byte(ctrl);
257 		mask = insn & 0x0fff;
258 		if (mask == 0) {
259 			pr_warning("unwind: 'Refuse to unwind' instruction %04lx\n",
260 				   insn);
261 			return -URC_FAILURE;
262 		}
263 
264 		/* pop R4-R15 according to mask */
265 		load_sp = mask & (1 << (13 - 4));
266 		while (mask) {
267 			if (mask & 1)
268 				ctrl->vrs[reg] = *vsp++;
269 			mask >>= 1;
270 			reg++;
271 		}
272 		if (!load_sp)
273 			ctrl->vrs[SP] = (unsigned long)vsp;
274 	} else if ((insn & 0xf0) == 0x90 &&
275 		   (insn & 0x0d) != 0x0d)
276 		ctrl->vrs[SP] = ctrl->vrs[insn & 0x0f];
277 	else if ((insn & 0xf0) == 0xa0) {
278 		unsigned long *vsp = (unsigned long *)ctrl->vrs[SP];
279 		int reg;
280 
281 		/* pop R4-R[4+bbb] */
282 		for (reg = 4; reg <= 4 + (insn & 7); reg++)
283 			ctrl->vrs[reg] = *vsp++;
284 		if (insn & 0x80)
285 			ctrl->vrs[14] = *vsp++;
286 		ctrl->vrs[SP] = (unsigned long)vsp;
287 	} else if (insn == 0xb0) {
288 		if (ctrl->vrs[PC] == 0)
289 			ctrl->vrs[PC] = ctrl->vrs[LR];
290 		/* no further processing */
291 		ctrl->entries = 0;
292 	} else if (insn == 0xb1) {
293 		unsigned long mask = unwind_get_byte(ctrl);
294 		unsigned long *vsp = (unsigned long *)ctrl->vrs[SP];
295 		int reg = 0;
296 
297 		if (mask == 0 || mask & 0xf0) {
298 			pr_warning("unwind: Spare encoding %04lx\n",
299 			       (insn << 8) | mask);
300 			return -URC_FAILURE;
301 		}
302 
303 		/* pop R0-R3 according to mask */
304 		while (mask) {
305 			if (mask & 1)
306 				ctrl->vrs[reg] = *vsp++;
307 			mask >>= 1;
308 			reg++;
309 		}
310 		ctrl->vrs[SP] = (unsigned long)vsp;
311 	} else if (insn == 0xb2) {
312 		unsigned long uleb128 = unwind_get_byte(ctrl);
313 
314 		ctrl->vrs[SP] += 0x204 + (uleb128 << 2);
315 	} else {
316 		pr_warning("unwind: Unhandled instruction %02lx\n", insn);
317 		return -URC_FAILURE;
318 	}
319 
320 	pr_debug("%s: fp = %08lx sp = %08lx lr = %08lx pc = %08lx\n", __func__,
321 		 ctrl->vrs[FP], ctrl->vrs[SP], ctrl->vrs[LR], ctrl->vrs[PC]);
322 
323 	return URC_OK;
324 }
325 
326 /*
327  * Unwind a single frame starting with *sp for the symbol at *pc. It
328  * updates the *pc and *sp with the new values.
329  */
unwind_frame(struct stackframe * frame)330 int unwind_frame(struct stackframe *frame)
331 {
332 	unsigned long high, low;
333 	const struct unwind_idx *idx;
334 	struct unwind_ctrl_block ctrl;
335 
336 	/* only go to a higher address on the stack */
337 	low = frame->sp;
338 	high = ALIGN(low, THREAD_SIZE);
339 
340 	pr_debug("%s(pc = %08lx lr = %08lx sp = %08lx)\n", __func__,
341 		 frame->pc, frame->lr, frame->sp);
342 
343 	if (!kernel_text_address(frame->pc))
344 		return -URC_FAILURE;
345 
346 	idx = unwind_find_idx(frame->pc);
347 	if (!idx) {
348 		pr_warning("unwind: Index not found %08lx\n", frame->pc);
349 		return -URC_FAILURE;
350 	}
351 
352 	ctrl.vrs[FP] = frame->fp;
353 	ctrl.vrs[SP] = frame->sp;
354 	ctrl.vrs[LR] = frame->lr;
355 	ctrl.vrs[PC] = 0;
356 
357 	if (idx->insn == 1)
358 		/* can't unwind */
359 		return -URC_FAILURE;
360 	else if ((idx->insn & 0x80000000) == 0)
361 		/* prel31 to the unwind table */
362 		ctrl.insn = (unsigned long *)prel31_to_addr(&idx->insn);
363 	else if ((idx->insn & 0xff000000) == 0x80000000)
364 		/* only personality routine 0 supported in the index */
365 		ctrl.insn = &idx->insn;
366 	else {
367 		pr_warning("unwind: Unsupported personality routine %08lx in the index at %p\n",
368 			   idx->insn, idx);
369 		return -URC_FAILURE;
370 	}
371 
372 	/* check the personality routine */
373 	if ((*ctrl.insn & 0xff000000) == 0x80000000) {
374 		ctrl.byte = 2;
375 		ctrl.entries = 1;
376 	} else if ((*ctrl.insn & 0xff000000) == 0x81000000) {
377 		ctrl.byte = 1;
378 		ctrl.entries = 1 + ((*ctrl.insn & 0x00ff0000) >> 16);
379 	} else {
380 		pr_warning("unwind: Unsupported personality routine %08lx at %p\n",
381 			   *ctrl.insn, ctrl.insn);
382 		return -URC_FAILURE;
383 	}
384 
385 	while (ctrl.entries > 0) {
386 		int urc = unwind_exec_insn(&ctrl);
387 		if (urc < 0)
388 			return urc;
389 		if (ctrl.vrs[SP] < low || ctrl.vrs[SP] >= high)
390 			return -URC_FAILURE;
391 	}
392 
393 	if (ctrl.vrs[PC] == 0)
394 		ctrl.vrs[PC] = ctrl.vrs[LR];
395 
396 	/* check for infinite loop */
397 	if (frame->pc == ctrl.vrs[PC])
398 		return -URC_FAILURE;
399 
400 	frame->fp = ctrl.vrs[FP];
401 	frame->sp = ctrl.vrs[SP];
402 	frame->lr = ctrl.vrs[LR];
403 	frame->pc = ctrl.vrs[PC];
404 
405 	return URC_OK;
406 }
407 
unwind_backtrace(struct pt_regs * regs,struct task_struct * tsk)408 void unwind_backtrace(struct pt_regs *regs, struct task_struct *tsk)
409 {
410 	struct stackframe frame;
411 	register unsigned long current_sp asm ("sp");
412 
413 	pr_debug("%s(regs = %p tsk = %p)\n", __func__, regs, tsk);
414 
415 	if (!tsk)
416 		tsk = current;
417 
418 	if (regs) {
419 		frame.fp = regs->ARM_fp;
420 		frame.sp = regs->ARM_sp;
421 		frame.lr = regs->ARM_lr;
422 		/* PC might be corrupted, use LR in that case. */
423 		frame.pc = kernel_text_address(regs->ARM_pc)
424 			 ? regs->ARM_pc : regs->ARM_lr;
425 	} else if (tsk == current) {
426 		frame.fp = (unsigned long)__builtin_frame_address(0);
427 		frame.sp = current_sp;
428 		frame.lr = (unsigned long)__builtin_return_address(0);
429 		frame.pc = (unsigned long)unwind_backtrace;
430 	} else {
431 		/* task blocked in __switch_to */
432 		frame.fp = thread_saved_fp(tsk);
433 		frame.sp = thread_saved_sp(tsk);
434 		/*
435 		 * The function calling __switch_to cannot be a leaf function
436 		 * so LR is recovered from the stack.
437 		 */
438 		frame.lr = 0;
439 		frame.pc = thread_saved_pc(tsk);
440 	}
441 
442 	while (1) {
443 		int urc;
444 		unsigned long where = frame.pc;
445 
446 		urc = unwind_frame(&frame);
447 		if (urc < 0)
448 			break;
449 		dump_backtrace_entry(where, frame.pc, frame.sp - 4);
450 	}
451 }
452 
unwind_table_add(unsigned long start,unsigned long size,unsigned long text_addr,unsigned long text_size)453 struct unwind_table *unwind_table_add(unsigned long start, unsigned long size,
454 				      unsigned long text_addr,
455 				      unsigned long text_size)
456 {
457 	unsigned long flags;
458 	struct unwind_table *tab = kmalloc(sizeof(*tab), GFP_KERNEL);
459 
460 	pr_debug("%s(%08lx, %08lx, %08lx, %08lx)\n", __func__, start, size,
461 		 text_addr, text_size);
462 
463 	if (!tab)
464 		return tab;
465 
466 	tab->start = (const struct unwind_idx *)start;
467 	tab->stop = (const struct unwind_idx *)(start + size);
468 	tab->origin = unwind_find_origin(tab->start, tab->stop);
469 	tab->begin_addr = text_addr;
470 	tab->end_addr = text_addr + text_size;
471 
472 	spin_lock_irqsave(&unwind_lock, flags);
473 	list_add_tail(&tab->list, &unwind_tables);
474 	spin_unlock_irqrestore(&unwind_lock, flags);
475 
476 	return tab;
477 }
478 
unwind_table_del(struct unwind_table * tab)479 void unwind_table_del(struct unwind_table *tab)
480 {
481 	unsigned long flags;
482 
483 	if (!tab)
484 		return;
485 
486 	spin_lock_irqsave(&unwind_lock, flags);
487 	list_del(&tab->list);
488 	spin_unlock_irqrestore(&unwind_lock, flags);
489 
490 	kfree(tab);
491 }
492