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