aboutsummaryrefslogtreecommitdiffstats
path: root/arch/microblaze/kernel/unwind.c
blob: fefac5c3358672409446413ba69e9227af902d29 (plain) (blame)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
/*
 * Backtrace support for Microblaze
 *
 * Copyright (C) 2010  Digital Design Corporation
 *
 * Based on arch/sh/kernel/cpu/sh5/unwind.c code which is:
 * Copyright (C) 2004  Paul Mundt
 * Copyright (C) 2004  Richard Curnow
 *
 * This file is subject to the terms and conditions of the GNU General Public
 * License.  See the file "COPYING" in the main directory of this archive
 * for more details.
 */

/* #define DEBUG 1 */
#include <linux/kallsyms.h>
#include <linux/kernel.h>
#include <linux/sched.h>
#include <linux/stacktrace.h>
#include <linux/types.h>
#include <linux/errno.h>
#include <linux/module.h>
#include <linux/io.h>
#include <asm/sections.h>
#include <asm/exceptions.h>
#include <asm/unwind.h>

struct stack_trace;

/*
 * On Microblaze, finding the previous stack frame is a little tricky.
 * At this writing (3/2010), Microblaze does not support CONFIG_FRAME_POINTERS,
 * and even if it did, gcc (4.1.2) does not store the frame pointer at
 * a consistent offset within each frame. To determine frame size, it is
 * necessary to search for the assembly instruction that creates or reclaims
 * the frame and extract the size from it.
 *
 * Microblaze stores the stack pointer in r1, and creates a frame via
 *
 *     addik r1, r1, -FRAME_SIZE
 *
 * The frame is reclaimed via
 *
 *     addik r1, r1, FRAME_SIZE
 *
 * Frame creation occurs at or near the top of a function.
 * Depending on the compiler, reclaim may occur at the end, or before
 * a mid-function return.
 *
 * A stack frame is usually not created in a leaf function.
 *
 */

/**
 * get_frame_size - Extract the stack adjustment from an
 *                  "addik r1, r1, adjust" instruction
 * @instr : Microblaze instruction
 *
 * Return - Number of stack bytes the instruction reserves or reclaims
 */
inline long get_frame_size(unsigned long instr)
{
	return abs((s16)(instr & 0xFFFF));
}

/**
 * find_frame_creation - Search backward to find the instruction that creates
 *                       the stack frame (hopefully, for the same function the
 *                       initial PC is in).
 * @pc : Program counter at which to begin the search
 *
 * Return - PC at which stack frame creation occurs
 *          NULL if this cannot be found, i.e. a leaf function
 */
static unsigned long *find_frame_creation(unsigned long *pc)
{
	int i;

	/* NOTE: Distance to search is arbitrary
	 *	 250 works well for most things,
	 *	 750 picks up things like tcp_recvmsg(),
	 *	1000 needed for fat_fill_super()
	 */
	for (i = 0; i < 1000; i++, pc--) {
		unsigned long instr;
		s16 frame_size;

		if (!kernel_text_address((unsigned long) pc))
			return NULL;

		instr = *pc;

		/* addik r1, r1, foo ? */
		if ((instr & 0xFFFF0000) != 0x30210000)
			continue;	/* No */

		frame_size = get_frame_size(instr);
		if ((frame_size < 8) || (frame_size & 3)) {
			pr_debug("    Invalid frame size %d at 0x%p\n",
				 frame_size, pc);
			return NULL;
		}

		pr_debug("    Found frame creation at 0x%p, size %d\n", pc,
			 frame_size);
		return pc;
	}

	return NULL;
}

/**
 * lookup_prev_stack_frame - Find the stack frame of the previous function.
 * @fp          : Frame (stack) pointer for current function
 * @pc          : Program counter within current function
 * @leaf_return : r15 value within current function. If the current function
 *		  is a leaf, this is the caller's return address.
 * @pprev_fp    : On exit, set to frame (stack) pointer for previous function
 * @pprev_pc    : On exit, set to current function caller's return address
 *
 * Return - 0 on success, -EINVAL if the previous frame cannot be found
 */
static int lookup_prev_stack_frame(unsigned long fp, unsigned long pc,
				   unsigned long leaf_return,
				   unsigned long *pprev_fp,
				   unsigned long *pprev_pc)
{
	unsigned long *prologue = NULL;

	/* _switch_to is a special leaf function */
	if (pc != (unsigned long) &_switch_to)
		prologue = find_frame_creation((unsigned long *)pc);

	if (prologue) {
		long frame_size = get_frame_size(*prologue);

		*pprev_fp = fp + frame_size;
		*pprev_pc = *(unsigned long *)fp;
	} else {
		if (!leaf_return)
			return -EINVAL;
		*pprev_pc = leaf_return;
		*pprev_fp = fp;
	}

	/* NOTE: don't check kernel_text_address here, to allow display
	 *	 of userland return address
	 */
	return (!*pprev_pc || (*pprev_pc & 3)) ? -EINVAL : 0;
}

static void microblaze_unwind_inner(struct task_struct *task,
				    unsigned long pc, unsigned long fp,
				    unsigned long leaf_return,
				    struct stack_trace *trace);

/**
 * unwind_trap - Unwind through a system trap, that stored previous state
 *		 on the stack.
 */
#ifdef CONFIG_MMU
static inline void unwind_trap(struct task_struct *task, unsigned long pc,
				unsigned long fp, struct stack_trace *trace)
{
	/* To be implemented */
}
#else
static inline void unwind_trap(struct task_struct *task, unsigned long pc,
				unsigned long fp, struct stack_trace *trace)
{
	const struct pt_regs *regs = (const struct pt_regs *) fp;
	microblaze_unwind_inner(task, regs->pc, regs->r1, regs->r15, trace);
}
#endif

/**
 * microblaze_unwind_inner - Unwind the stack from the specified point
 * @task  : Task whose stack we are to unwind (may be NULL)
 * @pc    : Program counter from which we start unwinding
 * @fp    : Frame (stack) pointer from which we start unwinding
 * @leaf_return : Value of r15 at pc. If the function is a leaf, this is
 *				  the caller's return address.
 * @trace : Where to store stack backtrace (PC values).
 *	    NULL == print backtrace to kernel log
 */
void microblaze_unwind_inner(struct task_struct *task,
			     unsigned long pc, unsigned long fp,
			     unsigned long leaf_return,
			     struct stack_trace *trace)
{
	int ofs = 0;

	pr_debug("    Unwinding with PC=%p, FP=%p\n", (void *)pc, (void *)fp);
	if (!pc || !fp || (pc & 3) || (fp & 3)) {
		pr_debug("    Invalid state for unwind, aborting\n");
		return;
	}
	for (; pc != 0;) {
		unsigned long next_fp, next_pc = 0;
		unsigned long return_to = pc +  2 * sizeof(unsigned long);
		const struct trap_handler_info *handler =
			&microblaze_trap_handlers;

		/* Is previous function the HW exception handler? */
		if ((return_to >= (unsigned long)&_hw_exception_handler)
		    &&(return_to < (unsigned long)&ex_handler_unhandled)) {
			/*
			 * HW exception handler doesn't save all registers,
			 * so we open-code a special case of unwind_trap()
			 */
#ifndef CONFIG_MMU
			const struct pt_regs *regs =
				(const struct pt_regs *) fp;
#endif
			pr_info("HW EXCEPTION\n");
#ifndef CONFIG_MMU
			microblaze_unwind_inner(task, regs->r17 - 4,
						fp + EX_HANDLER_STACK_SIZ,
						regs->r15, trace);
#endif
			return;
		}

		/* Is previous function a trap handler? */
		for (; handler->start_addr; ++handler) {
			if ((return_to >= handler->start_addr)
			    && (return_to <= handler->end_addr)) {
				if (!trace)
					pr_info("%s\n", handler->trap_name);
				unwind_trap(task, pc, fp, trace);
				return;
			}
		}
		pc -= ofs;

		if (trace) {
#ifdef CONFIG_STACKTRACE
			if (trace->skip > 0)
				trace->skip--;
			else
				trace->entries[trace->nr_entries++] = pc;

			if (trace->nr_entries >= trace->max_entries)
				break;
#endif
		} else {
			/* Have we reached userland? */
			if (unlikely(pc == task_pt_regs(task)->pc)) {
				pr_info("[<%p>] PID %lu [%s]\n",
					(void *) pc,
					(unsigned long) task->pid,
					task->comm);
				break;
			} else
				print_ip_sym(pc);
		}

		/* Stop when we reach anything not part of the kernel */
		if (!kernel_text_address(pc))
			break;

		if (lookup_prev_stack_frame(fp, pc, leaf_return, &next_fp,
					    &next_pc) == 0) {
			ofs = sizeof(unsigned long);
			pc = next_pc & ~3;
			fp = next_fp;
			leaf_return = 0;
		} else {
			pr_debug("    Failed to find previous stack frame\n");
			break;
		}

		pr_debug("    Next PC=%p, next FP=%p\n",
			 (void *)next_pc, (void *)next_fp);
	}
}

/**
 * microblaze_unwind - Stack unwinder for Microblaze (external entry point)
 * @task  : Task whose stack we are to unwind (NULL == current)
 * @trace : Where to store stack backtrace (PC values).
 *	    NULL == print backtrace to kernel log
 */
void microblaze_unwind(struct task_struct *task, struct stack_trace *trace)
{
	if (task) {
		if (task == current) {
			const struct pt_regs *regs = task_pt_regs(task);
			microblaze_unwind_inner(task, regs->pc, regs->r1,
						regs->r15, trace);
		} else {
			struct thread_info *thread_info =
				(struct thread_info *)(task->stack);
			const struct cpu_context *cpu_context =
				&thread_info->cpu_context;

			microblaze_unwind_inner(task,
						(unsigned long) &_switch_to,
						cpu_context->r1,
						cpu_context->r15, trace);
		}
	} else {
		unsigned long pc, fp;

		__asm__ __volatile__ ("or %0, r1, r0" : "=r" (fp));

		__asm__ __volatile__ (
			"brlid %0, 0f;"
			"nop;"
			"0:"
			: "=r" (pc)
		);

		/* Since we are not a leaf function, use leaf_return = 0 */
		microblaze_unwind_inner(current, pc, fp, 0, trace);
	}
}