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/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                                     const char *loglvl);
 159
 160 /**
 161  * unwind_trap - Unwind through a system trap, that stored previous state
 162  *               on the stack.
 163  */
 164 static 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  */
 182 static 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, pc);
 244                 }
 245
 246                 /* Stop when we reach anything not part of the kernel */
 247                 if (!kernel_text_address(pc))
 248                         break;
 249
 250                 if (lookup_prev_stack_frame(fp, pc, leaf_return, &next_fp,
 251                                             &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  */
 273 void 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, regs->pc, regs->r1,
 280                                                 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                                                 (unsigned long) &_switch_to,
 289                                                 cpu_context->r1,
 290                                                 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, 0, trace, loglvl);
 307         }
 308 }
 309