arch/microblaze/kernel/unwind.c

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