2 * Backtrace support for Microblaze
4 * Copyright (C) 2010 Digital Design Corporation
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
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
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>
25 #include <asm/sections.h>
26 #include <asm/exceptions.h>
27 #include <asm/unwind.h>
28 #include <asm/switch_to.h>
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.
40 * Microblaze stores the stack pointer in r1, and creates a frame via
42 * addik r1, r1, -FRAME_SIZE
44 * The frame is reclaimed via
46 * addik r1, r1, FRAME_SIZE
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.
52 * A stack frame is usually not created in a leaf function.
57 * get_frame_size - Extract the stack adjustment from an
58 * "addik r1, r1, adjust" instruction
59 * @instr : Microblaze instruction
61 * Return - Number of stack bytes the instruction reserves or reclaims
63 static inline long get_frame_size(unsigned long instr)
65 return abs((s16)(instr & 0xFFFF));
69 * find_frame_creation - Search backward to find the instruction that creates
70 * the stack frame (hopefully, for the same function the
72 * @pc : Program counter at which to begin the search
74 * Return - PC at which stack frame creation occurs
75 * NULL if this cannot be found, i.e. a leaf function
77 static unsigned long *find_frame_creation(unsigned long *pc)
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()
86 for (i = 0; i < 1000; i++, pc--) {
90 if (!kernel_text_address((unsigned long) pc))
95 /* addik r1, r1, foo ? */
96 if ((instr & 0xFFFF0000) != 0x30210000)
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",
106 pr_debug(" Found frame creation at 0x%p, size %d\n", pc,
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
123 * Return - 0 on success, -EINVAL if the previous frame cannot be found
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)
130 unsigned long *prologue = NULL;
132 /* _switch_to is a special leaf function */
133 if (pc != (unsigned long) &_switch_to)
134 prologue = find_frame_creation((unsigned long *)pc);
137 long frame_size = get_frame_size(*prologue);
139 *pprev_fp = fp + frame_size;
140 *pprev_pc = *(unsigned long *)fp;
144 *pprev_pc = leaf_return;
148 /* NOTE: don't check kernel_text_address here, to allow display
149 * of userland return address
151 return (!*pprev_pc || (*pprev_pc & 3)) ? -EINVAL : 0;
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,
161 * unwind_trap - Unwind through a system trap, that stored previous state
165 static inline void unwind_trap(struct task_struct *task, unsigned long pc,
166 unsigned long fp, struct stack_trace *trace,
169 /* To be implemented */
172 static inline void unwind_trap(struct task_struct *task, unsigned long pc,
173 unsigned long fp, struct stack_trace *trace,
176 const struct pt_regs *regs = (const struct pt_regs *) fp;
177 microblaze_unwind_inner(task, regs->pc, regs->r1, regs->r15, trace, loglvl);
182 * microblaze_unwind_inner - Unwind the stack from the specified point
183 * @task : Task whose stack we are to unwind (may be NULL)
184 * @pc : Program counter from which we start unwinding
185 * @fp : Frame (stack) pointer from which we start unwinding
186 * @leaf_return : Value of r15 at pc. If the function is a leaf, this is
187 * the caller's return address.
188 * @trace : Where to store stack backtrace (PC values).
189 * NULL == print backtrace to kernel log
190 * @loglvl : Used for printk log level if (trace == NULL).
192 static void microblaze_unwind_inner(struct task_struct *task,
193 unsigned long pc, unsigned long fp,
194 unsigned long leaf_return,
195 struct stack_trace *trace,
200 pr_debug(" Unwinding with PC=%p, FP=%p\n", (void *)pc, (void *)fp);
201 if (!pc || !fp || (pc & 3) || (fp & 3)) {
202 pr_debug(" Invalid state for unwind, aborting\n");
206 unsigned long next_fp, next_pc = 0;
207 unsigned long return_to = pc + 2 * sizeof(unsigned long);
208 const struct trap_handler_info *handler =
209 µblaze_trap_handlers;
211 /* Is previous function the HW exception handler? */
212 if ((return_to >= (unsigned long)&_hw_exception_handler)
213 &&(return_to < (unsigned long)&ex_handler_unhandled)) {
215 * HW exception handler doesn't save all registers,
216 * so we open-code a special case of unwind_trap()
219 const struct pt_regs *regs =
220 (const struct pt_regs *) fp;
222 printk("%sHW EXCEPTION\n", loglvl);
224 microblaze_unwind_inner(task, regs->r17 - 4,
225 fp + EX_HANDLER_STACK_SIZ,
226 regs->r15, trace, loglvl);
231 /* Is previous function a trap handler? */
232 for (; handler->start_addr; ++handler) {
233 if ((return_to >= handler->start_addr)
234 && (return_to <= handler->end_addr)) {
236 printk("%s%s\n", loglvl, handler->trap_name);
237 unwind_trap(task, pc, fp, trace, loglvl);
244 #ifdef CONFIG_STACKTRACE
248 trace->entries[trace->nr_entries++] = pc;
250 if (trace->nr_entries >= trace->max_entries)
254 /* Have we reached userland? */
255 if (unlikely(pc == task_pt_regs(task)->pc)) {
256 printk("%s[<%p>] PID %lu [%s]\n",
258 (unsigned long) task->pid,
262 print_ip_sym(loglvl, pc);
265 /* Stop when we reach anything not part of the kernel */
266 if (!kernel_text_address(pc))
269 if (lookup_prev_stack_frame(fp, pc, leaf_return, &next_fp,
271 ofs = sizeof(unsigned long);
276 pr_debug(" Failed to find previous stack frame\n");
280 pr_debug(" Next PC=%p, next FP=%p\n",
281 (void *)next_pc, (void *)next_fp);
286 * microblaze_unwind - Stack unwinder for Microblaze (external entry point)
287 * @task : Task whose stack we are to unwind (NULL == current)
288 * @trace : Where to store stack backtrace (PC values).
289 * NULL == print backtrace to kernel log
290 * @loglvl : Used for printk log level if (trace == NULL).
292 void microblaze_unwind(struct task_struct *task, struct stack_trace *trace,
296 if (task == current) {
297 const struct pt_regs *regs = task_pt_regs(task);
298 microblaze_unwind_inner(task, regs->pc, regs->r1,
299 regs->r15, trace, loglvl);
301 struct thread_info *thread_info =
302 (struct thread_info *)(task->stack);
303 const struct cpu_context *cpu_context =
304 &thread_info->cpu_context;
306 microblaze_unwind_inner(task,
307 (unsigned long) &_switch_to,
313 unsigned long pc, fp;
315 __asm__ __volatile__ ("or %0, r1, r0" : "=r" (fp));
317 __asm__ __volatile__ (
324 /* Since we are not a leaf function, use leaf_return = 0 */
325 microblaze_unwind_inner(current, pc, fp, 0, trace, loglvl);