1 /*
2 * Backtrace support for Microblaze
3 *
4 * Copyright (C) 2010 Digital Design Corporation
5 *
6 * Based on arch/sh/kernel/cpu/sh5/unwind.c code which is:
7 * Copyright (C) 2004 Paul Mundt
8 * Copyright (C) 2004 Richard Curnow
9 *
10 * This file is subject to the terms and conditions of the GNU General Public
11 * License. See the file "COPYING" in the main directory of this archive
12 * for more details.
13 */
14
15 /* #define DEBUG 1 */
16 #include <linux/export.h>
17 #include <linux/kallsyms.h>
18 #include <linux/kernel.h>
19 #include <linux/sched.h>
20 #include <linux/sched/task_stack.h>
21 #include <linux/stacktrace.h>
22 #include <linux/types.h>
23 #include <linux/errno.h>
24 #include <linux/io.h>
25 #include <asm/sections.h>
26 #include <asm/exceptions.h>
27 #include <asm/unwind.h>
28 #include <asm/switch_to.h>
29
30 struct stack_trace;
31
32 /*
33 * On Microblaze, finding the previous stack frame is a little tricky.
34 * At this writing (3/2010), Microblaze does not support CONFIG_FRAME_POINTERS,
35 * and even if it did, gcc (4.1.2) does not store the frame pointer at
36 * a consistent offset within each frame. To determine frame size, it is
37 * necessary to search for the assembly instruction that creates or reclaims
38 * the frame and extract the size from it.
39 *
40 * Microblaze stores the stack pointer in r1, and creates a frame via
41 *
42 * addik r1, r1, -FRAME_SIZE
43 *
44 * The frame is reclaimed via
45 *
46 * addik r1, r1, FRAME_SIZE
47 *
48 * Frame creation occurs at or near the top of a function.
49 * Depending on the compiler, reclaim may occur at the end, or before
50 * a mid-function return.
51 *
52 * A stack frame is usually not created in a leaf function.
53 *
54 */
55
56 /**
57 * get_frame_size - Extract the stack adjustment from an
58 * "addik r1, r1, adjust" instruction
59 * @instr : Microblaze instruction
60 *
61 * Return - Number of stack bytes the instruction reserves or reclaims
62 */
63 static inline long get_frame_size(unsigned long instr)
64 {
65 return abs((s16)(instr & 0xFFFF));
66 }
67
68 /**
69 * find_frame_creation - Search backward to find the instruction that creates
70 * the stack frame (hopefully, for the same function the
71 * initial PC is in).
72 * @pc : Program counter at which to begin the search
73 *
74 * Return - PC at which stack frame creation occurs
75 * NULL if this cannot be found, i.e. a leaf function
76 */
77 static unsigned long *find_frame_creation(unsigned long *pc)
78 {
79 int i;
80
81 /* NOTE: Distance to search is arbitrary
82 * 250 works well for most things,
83 * 750 picks up things like tcp_recvmsg(),
84 * 1000 needed for fat_fill_super()
85 */
86 for (i = 0; i < 1000; i++, pc--) {
87 unsigned long instr;
88 s16 frame_size;
89
90 if (!kernel_text_address((unsigned long) pc))
91 return NULL;
92
93 instr = *pc;
94
95 /* addik r1, r1, foo ? */
96 if ((instr & 0xFFFF0000) != 0x30210000)
97 continue; /* No */
98
99 frame_size = get_frame_size(instr);
100 if ((frame_size < 8) || (frame_size & 3)) {
101 pr_debug(" Invalid frame size %d at 0x%p\n",
102 frame_size, pc);
103 return NULL;
104 }
105
106 pr_debug(" Found frame creation at 0x%p, size %d\n", pc,
107 frame_size);
108 return pc;
109 }
110
111 return NULL;
112 }
113
114 /**
115 * lookup_prev_stack_frame - Find the stack frame of the previous function.
116 * @fp : Frame (stack) pointer for current function
117 * @pc : Program counter within current function
118 * @leaf_return : r15 value within current function. If the current function
119 * is a leaf, this is the caller's return address.
120 * @pprev_fp : On exit, set to frame (stack) pointer for previous function
121 * @pprev_pc : On exit, set to current function caller's return address
122 *
123 * Return - 0 on success, -EINVAL if the previous frame cannot be found
124 */
125 static int lookup_prev_stack_frame(unsigned long fp, unsigned long pc,
126 unsigned long leaf_return,
127 unsigned long *pprev_fp,
128 unsigned long *pprev_pc)
129 {
130 unsigned long *prologue = NULL;
131
132 /* _switch_to is a special leaf function */
133 if (pc != (unsigned long) &_switch_to)
134 prologue = find_frame_creation((unsigned long *)pc);
135
136 if (prologue) {
137 long frame_size = get_frame_size(*prologue);
138
139 *pprev_fp = fp + frame_size;
140 *pprev_pc = *(unsigned long *)fp;
141 } else {
142 if (!leaf_return)
143 return -EINVAL;
144 *pprev_pc = leaf_return;
145 *pprev_fp = fp;
146 }
147
148 /* NOTE: don't check kernel_text_address here, to allow display
149 * of userland return address
150 */
151 return (!*pprev_pc || (*pprev_pc & 3)) ? -EINVAL : 0;
152 }
153
154 static void microblaze_unwind_inner(struct task_struct *task,
155 unsigned long pc, unsigned long fp,
156 unsigned long leaf_return,
157 struct stack_trace *trace);
158
159 /**
160 * unwind_trap - Unwind through a system trap, that stored previous state
161 * on the stack.
162 */
163 #ifdef CONFIG_MMU
164 static inline void unwind_trap(struct task_struct *task, unsigned long pc,
165 unsigned long fp, struct stack_trace *trace)
166 {
167 /* To be implemented */
168 }
169 #else
170 static inline void unwind_trap(struct task_struct *task, unsigned long pc,
171 unsigned long fp, struct stack_trace *trace)
172 {
173 const struct pt_regs *regs = (const struct pt_regs *) fp;
174 microblaze_unwind_inner(task, regs->pc, regs->r1, regs->r15, trace);
175 }
176 #endif
177
178 /**
179 * microblaze_unwind_inner - Unwind the stack from the specified point
180 * @task : Task whose stack we are to unwind (may be NULL)
181 * @pc : Program counter from which we start unwinding
182 * @fp : Frame (stack) pointer from which we start unwinding
183 * @leaf_return : Value of r15 at pc. If the function is a leaf, this is
184 * the caller's return address.
185 * @trace : Where to store stack backtrace (PC values).
186 * NULL == print backtrace to kernel log
187 */
188 static void microblaze_unwind_inner(struct task_struct *task,
189 unsigned long pc, unsigned long fp,
190 unsigned long leaf_return,
191 struct stack_trace *trace)
192 {
193 int ofs = 0;
194
195 pr_debug(" Unwinding with PC=%p, FP=%p\n", (void *)pc, (void *)fp);
196 if (!pc || !fp || (pc & 3) || (fp & 3)) {
197 pr_debug(" Invalid state for unwind, aborting\n");
198 return;
199 }
200 for (; pc != 0;) {
201 unsigned long next_fp, next_pc = 0;
202 unsigned long return_to = pc + 2 * sizeof(unsigned long);
203 const struct trap_handler_info *handler =
204 µblaze_trap_handlers;
205
206 /* Is previous function the HW exception handler? */
207 if ((return_to >= (unsigned long)&_hw_exception_handler)
208 &&(return_to < (unsigned long)&ex_handler_unhandled)) {
209 /*
210 * HW exception handler doesn't save all registers,
211 * so we open-code a special case of unwind_trap()
212 */
213 #ifndef CONFIG_MMU
214 const struct pt_regs *regs =
215 (const struct pt_regs *) fp;
216 #endif
217 pr_info("HW EXCEPTION\n");
218 #ifndef CONFIG_MMU
219 microblaze_unwind_inner(task, regs->r17 - 4,
220 fp + EX_HANDLER_STACK_SIZ,
221 regs->r15, trace);
222 #endif
223 return;
224 }
225
226 /* Is previous function a trap handler? */
227 for (; handler->start_addr; ++handler) {
228 if ((return_to >= handler->start_addr)
229 && (return_to <= handler->end_addr)) {
230 if (!trace)
231 pr_info("%s\n", handler->trap_name);
232 unwind_trap(task, pc, fp, trace);
233 return;
234 }
235 }
236 pc -= ofs;
237
238 if (trace) {
239 #ifdef CONFIG_STACKTRACE
240 if (trace->skip > 0)
241 trace->skip--;
242 else
243 trace->entries[trace->nr_entries++] = pc;
244
245 if (trace->nr_entries >= trace->max_entries)
246 break;
247 #endif
248 } else {
249 /* Have we reached userland? */
250 if (unlikely(pc == task_pt_regs(task)->pc)) {
251 pr_info("[<%p>] PID %lu [%s]\n",
252 (void *) pc,
253 (unsigned long) task->pid,
254 task->comm);
255 break;
256 } else
257 print_ip_sym(pc);
258 }
259
260 /* Stop when we reach anything not part of the kernel */
261 if (!kernel_text_address(pc))
262 break;
263
264 if (lookup_prev_stack_frame(fp, pc, leaf_return, &next_fp,
265 &next_pc) == 0) {
266 ofs = sizeof(unsigned long);
267 pc = next_pc & ~3;
268 fp = next_fp;
269 leaf_return = 0;
270 } else {
271 pr_debug(" Failed to find previous stack frame\n");
272 break;
273 }
274
275 pr_debug(" Next PC=%p, next FP=%p\n",
276 (void *)next_pc, (void *)next_fp);
277 }
278 }
279
280 /**
281 * microblaze_unwind - Stack unwinder for Microblaze (external entry point)
282 * @task : Task whose stack we are to unwind (NULL == current)
283 * @trace : Where to store stack backtrace (PC values).
284 * NULL == print backtrace to kernel log
285 */
286 void microblaze_unwind(struct task_struct *task, struct stack_trace *trace)
287 {
288 if (task) {
289 if (task == current) {
290 const struct pt_regs *regs = task_pt_regs(task);
291 microblaze_unwind_inner(task, regs->pc, regs->r1,
292 regs->r15, trace);
293 } else {
294 struct thread_info *thread_info =
295 (struct thread_info *)(task->stack);
296 const struct cpu_context *cpu_context =
297 &thread_info->cpu_context;
298
299 microblaze_unwind_inner(task,
300 (unsigned long) &_switch_to,
301 cpu_context->r1,
302 cpu_context->r15, trace);
303 }
304 } else {
305 unsigned long pc, fp;
306
307 __asm__ __volatile__ ("or %0, r1, r0" : "=r" (fp));
308
309 __asm__ __volatile__ (
310 "brlid %0, 0f;"
311 "nop;"
312 "0:"
313 : "=r" (pc)
314 );
315
316 /* Since we are not a leaf function, use leaf_return = 0 */
317 microblaze_unwind_inner(current, pc, fp, 0, trace);
318 }
319 }
320