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
30struct 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 */
63static 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 */
77static 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(addr: (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 */
125static 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(pc: (unsigned long *)pc);
135
136 if (prologue) {
137 long frame_size = get_frame_size(instr: *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
154static 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 const char *loglvl);
159
160/**
161 * unwind_trap - Unwind through a system trap, that stored previous state
162 * on the stack.
163 */
164static inline void unwind_trap(struct task_struct *task, unsigned long pc,
165 unsigned long fp, struct stack_trace *trace,
166 const char *loglvl)
167{
168 /* To be implemented */
169}
170
171/**
172 * microblaze_unwind_inner - Unwind the stack from the specified point
173 * @task : Task whose stack we are to unwind (may be NULL)
174 * @pc : Program counter from which we start unwinding
175 * @fp : Frame (stack) pointer from which we start unwinding
176 * @leaf_return : Value of r15 at pc. If the function is a leaf, this is
177 * the caller's return address.
178 * @trace : Where to store stack backtrace (PC values).
179 * NULL == print backtrace to kernel log
180 * @loglvl : Used for printk log level if (trace == NULL).
181 */
182static void microblaze_unwind_inner(struct task_struct *task,
183 unsigned long pc, unsigned long fp,
184 unsigned long leaf_return,
185 struct stack_trace *trace,
186 const char *loglvl)
187{
188 int ofs = 0;
189
190 pr_debug(" Unwinding with PC=%p, FP=%p\n", (void *)pc, (void *)fp);
191 if (!pc || !fp || (pc & 3) || (fp & 3)) {
192 pr_debug(" Invalid state for unwind, aborting\n");
193 return;
194 }
195 for (; pc != 0;) {
196 unsigned long next_fp, next_pc = 0;
197 unsigned long return_to = pc + 2 * sizeof(unsigned long);
198 const struct trap_handler_info *handler =
199 &microblaze_trap_handlers;
200
201 /* Is previous function the HW exception handler? */
202 if ((return_to >= (unsigned long)&_hw_exception_handler)
203 &&(return_to < (unsigned long)&ex_handler_unhandled)) {
204 /*
205 * HW exception handler doesn't save all registers,
206 * so we open-code a special case of unwind_trap()
207 */
208 printk("%sHW EXCEPTION\n", loglvl);
209 return;
210 }
211
212 /* Is previous function a trap handler? */
213 for (; handler->start_addr; ++handler) {
214 if ((return_to >= handler->start_addr)
215 && (return_to <= handler->end_addr)) {
216 if (!trace)
217 printk("%s%s\n", loglvl, handler->trap_name);
218 unwind_trap(task, pc, fp, trace, loglvl);
219 return;
220 }
221 }
222 pc -= ofs;
223
224 if (trace) {
225#ifdef CONFIG_STACKTRACE
226 if (trace->skip > 0)
227 trace->skip--;
228 else
229 trace->entries[trace->nr_entries++] = pc;
230
231 if (trace->nr_entries >= trace->max_entries)
232 break;
233#endif
234 } else {
235 /* Have we reached userland? */
236 if (unlikely(pc == task_pt_regs(task)->pc)) {
237 printk("%s[<%p>] PID %lu [%s]\n",
238 loglvl, (void *) pc,
239 (unsigned long) task->pid,
240 task->comm);
241 break;
242 } else
243 print_ip_sym(loglvl, ip: pc);
244 }
245
246 /* Stop when we reach anything not part of the kernel */
247 if (!kernel_text_address(addr: pc))
248 break;
249
250 if (lookup_prev_stack_frame(fp, pc, leaf_return, pprev_fp: &next_fp,
251 pprev_pc: &next_pc) == 0) {
252 ofs = sizeof(unsigned long);
253 pc = next_pc & ~3;
254 fp = next_fp;
255 leaf_return = 0;
256 } else {
257 pr_debug(" Failed to find previous stack frame\n");
258 break;
259 }
260
261 pr_debug(" Next PC=%p, next FP=%p\n",
262 (void *)next_pc, (void *)next_fp);
263 }
264}
265
266/**
267 * microblaze_unwind - Stack unwinder for Microblaze (external entry point)
268 * @task : Task whose stack we are to unwind (NULL == current)
269 * @trace : Where to store stack backtrace (PC values).
270 * NULL == print backtrace to kernel log
271 * @loglvl : Used for printk log level if (trace == NULL).
272 */
273void microblaze_unwind(struct task_struct *task, struct stack_trace *trace,
274 const char *loglvl)
275{
276 if (task) {
277 if (task == current) {
278 const struct pt_regs *regs = task_pt_regs(task);
279 microblaze_unwind_inner(task, pc: regs->pc, fp: regs->r1,
280 leaf_return: regs->r15, trace, loglvl);
281 } else {
282 struct thread_info *thread_info =
283 (struct thread_info *)(task->stack);
284 const struct cpu_context *cpu_context =
285 &thread_info->cpu_context;
286
287 microblaze_unwind_inner(task,
288 pc: (unsigned long) &_switch_to,
289 fp: cpu_context->r1,
290 leaf_return: cpu_context->r15,
291 trace, loglvl);
292 }
293 } else {
294 unsigned long pc, fp;
295
296 __asm__ __volatile__ ("or %0, r1, r0" : "=r" (fp));
297
298 __asm__ __volatile__ (
299 "brlid %0, 0f;"
300 "nop;"
301 "0:"
302 : "=r" (pc)
303 );
304
305 /* Since we are not a leaf function, use leaf_return = 0 */
306 microblaze_unwind_inner(current, pc, fp, leaf_return: 0, trace, loglvl);
307 }
308}
309
310

source code of linux/arch/microblaze/kernel/unwind.c