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unwind.c

/*
 * arch/sh/kernel/cpu/sh5/unwind.c
 *
 * Copyright (C) 2004  Paul Mundt
 * Copyright (C) 2004  Richard Curnow
 *
 * This file is subject to the terms and conditions of the GNU General Public
 * License.  See the file "COPYING" in the main directory of this archive
 * for more details.
 */
#include <linux/kallsyms.h>
#include <linux/kernel.h>
#include <linux/types.h>
#include <linux/errno.h>
#include <asm/page.h>
#include <asm/ptrace.h>
#include <asm/processor.h>
#include <asm/io.h>

static u8 regcache[63];

/*
 * Finding the previous stack frame isn't horribly straightforward as it is
 * on some other platforms. In the sh64 case, we don't have "linked" stack
 * frames, so we need to do a bit of work to determine the previous frame,
 * and in turn, the previous r14/r18 pair.
 *
 * There are generally a few cases which determine where we can find out
 * the r14/r18 values. In the general case, this can be determined by poking
 * around the prologue of the symbol PC is in (note that we absolutely must
 * have frame pointer support as well as the kernel symbol table mapped,
 * otherwise we can't even get this far).
 *
 * In other cases, such as the interrupt/exception path, we can poke around
 * the sp/fp.
 *
 * Notably, this entire approach is somewhat error prone, and in the event
 * that the previous frame cannot be determined, that's all we can do.
 * Either way, this still leaves us with a more correct backtrace then what
 * we would be able to come up with by walking the stack (which is garbage
 * for anything beyond the first frame).
 *                                  -- PFM.
 */
static int lookup_prev_stack_frame(unsigned long fp, unsigned long pc,
                  unsigned long *pprev_fp, unsigned long *pprev_pc,
                  struct pt_regs *regs)
{
      const char *sym;
      char namebuf[128];
      unsigned long offset;
      unsigned long prologue = 0;
      unsigned long fp_displacement = 0;
      unsigned long fp_prev = 0;
      unsigned long offset_r14 = 0, offset_r18 = 0;
      int i, found_prologue_end = 0;

      sym = kallsyms_lookup(pc, NULL, &offset, NULL, namebuf);
      if (!sym)
            return -EINVAL;

      prologue = pc - offset;
      if (!prologue)
            return -EINVAL;

      /* Validate fp, to avoid risk of dereferencing a bad pointer later.
         Assume 128Mb since that's the amount of RAM on a Cayman.  Modify
         when there is an SH-5 board with more. */
      if ((fp < (unsigned long) phys_to_virt(__MEMORY_START)) ||
          (fp >= (unsigned long)(phys_to_virt(__MEMORY_START)) + 128*1024*1024) ||
          ((fp & 7) != 0)) {
            return -EINVAL;
      }

      /*
       * Depth to walk, depth is completely arbitrary.
       */
      for (i = 0; i < 100; i++, prologue += sizeof(unsigned long)) {
            unsigned long op;
            u8 major, minor;
            u8 src, dest, disp;

            op = *(unsigned long *)prologue;

            major = (op >> 26) & 0x3f;
            src   = (op >> 20) & 0x3f;
            minor = (op >> 16) & 0xf;
            disp  = (op >> 10) & 0x3f;
            dest  = (op >>  4) & 0x3f;

            /*
             * Stack frame creation happens in a number of ways.. in the
             * general case when the stack frame is less than 511 bytes,
             * it's generally created by an addi or addi.l:
             *
             *    addi/addi.l r15, -FRAME_SIZE, r15
             *
             * in the event that the frame size is bigger than this, it's
             * typically created using a movi/sub pair as follows:
             *
             *    movi  FRAME_SIZE, rX
             *    sub   r15, rX, r15
             */

            switch (major) {
            case (0x00 >> 2):
                  switch (minor) {
                  case 0x8: /* add.l */
                  case 0x9: /* add */
                        /* Look for r15, r63, r14 */
                        if (src == 15 && disp == 63 && dest == 14)
                              found_prologue_end = 1;

                        break;
                  case 0xa: /* sub.l */
                  case 0xb: /* sub */
                        if (src != 15 || dest != 15)
                              continue;

                        fp_displacement -= regcache[disp];
                        fp_prev = fp - fp_displacement;
                        break;
                  }
                  break;
            case (0xa8 >> 2): /* st.l */
                  if (src != 15)
                        continue;

                  switch (dest) {
                  case 14:
                        if (offset_r14 || fp_displacement == 0)
                              continue;

                        offset_r14 = (u64)(((((s64)op >> 10) & 0x3ff) << 54) >> 54);
                        offset_r14 *= sizeof(unsigned long);
                        offset_r14 += fp_displacement;
                        break;
                  case 18:
                        if (offset_r18 || fp_displacement == 0)
                              continue;

                        offset_r18 = (u64)(((((s64)op >> 10) & 0x3ff) << 54) >> 54);
                        offset_r18 *= sizeof(unsigned long);
                        offset_r18 += fp_displacement;
                        break;
                  }

                  break;
            case (0xcc >> 2): /* movi */
                  if (dest >= 63) {
                        printk(KERN_NOTICE "%s: Invalid dest reg %d "
                               "specified in movi handler. Failed "
                               "opcode was 0x%lx: ", __func__,
                               dest, op);

                        continue;
                  }

                  /* Sign extend */
                  regcache[dest] =
                        ((((s64)(u64)op >> 10) & 0xffff) << 54) >> 54;
                  break;
            case (0xd0 >> 2): /* addi */
            case (0xd4 >> 2): /* addi.l */
                  /* Look for r15, -FRAME_SIZE, r15 */
                  if (src != 15 || dest != 15)
                        continue;

                  /* Sign extended frame size.. */
                  fp_displacement +=
                        (u64)(((((s64)op >> 10) & 0x3ff) << 54) >> 54);
                  fp_prev = fp - fp_displacement;
                  break;
            }

            if (found_prologue_end && offset_r14 && (offset_r18 || *pprev_pc) && fp_prev)
                  break;
      }

      if (offset_r14 == 0 || fp_prev == 0) {
            if (!offset_r14)
                  pr_debug("Unable to find r14 offset\n");
            if (!fp_prev)
                  pr_debug("Unable to find previous fp\n");

            return -EINVAL;
      }

      /* For innermost leaf function, there might not be a offset_r18 */
      if (!*pprev_pc && (offset_r18 == 0))
            return -EINVAL;

      *pprev_fp = *(unsigned long *)(fp_prev + offset_r14);

      if (offset_r18)
            *pprev_pc = *(unsigned long *)(fp_prev + offset_r18);

      *pprev_pc &= ~1;

      return 0;
}

/* Don't put this on the stack since we'll want to call sh64_unwind
 * when we're close to underflowing the stack anyway. */
static struct pt_regs here_regs;

extern const char syscall_ret;
extern const char ret_from_syscall;
extern const char ret_from_exception;
extern const char ret_from_irq;

static void sh64_unwind_inner(struct pt_regs *regs);

static void unwind_nested (unsigned long pc, unsigned long fp)
{
      if ((fp >= __MEMORY_START) &&
          ((fp & 7) == 0)) {
            sh64_unwind_inner((struct pt_regs *) fp);
      }
}

static void sh64_unwind_inner(struct pt_regs *regs)
{
      unsigned long pc, fp;
      int ofs = 0;
      int first_pass;

      pc = regs->pc & ~1;
      fp = regs->regs[14];

      first_pass = 1;
      for (;;) {
            int cond;
            unsigned long next_fp, next_pc;

            if (pc == ((unsigned long) &syscall_ret & ~1)) {
                  printk("SYSCALL\n");
                  unwind_nested(pc,fp);
                  return;
            }

            if (pc == ((unsigned long) &ret_from_syscall & ~1)) {
                  printk("SYSCALL (PREEMPTED)\n");
                  unwind_nested(pc,fp);
                  return;
            }

            /* In this case, the PC is discovered by lookup_prev_stack_frame but
               it has 4 taken off it to look like the 'caller' */
            if (pc == ((unsigned long) &ret_from_exception & ~1)) {
                  printk("EXCEPTION\n");
                  unwind_nested(pc,fp);
                  return;
            }

            if (pc == ((unsigned long) &ret_from_irq & ~1)) {
                  printk("IRQ\n");
                  unwind_nested(pc,fp);
                  return;
            }

            cond = ((pc >= __MEMORY_START) && (fp >= __MEMORY_START) &&
                  ((pc & 3) == 0) && ((fp & 7) == 0));

            pc -= ofs;

            printk("[<%08lx>] ", pc);
            print_symbol("%s\n", pc);

            if (first_pass) {
                  /* If the innermost frame is a leaf function, it's
                   * possible that r18 is never saved out to the stack.
                   */
                  next_pc = regs->regs[18];
            } else {
                  next_pc = 0;
            }

            if (lookup_prev_stack_frame(fp, pc, &next_fp, &next_pc, regs) == 0) {
                  ofs = sizeof(unsigned long);
                  pc = next_pc & ~1;
                  fp = next_fp;
            } else {
                  printk("Unable to lookup previous stack frame\n");
                  break;
            }
            first_pass = 0;
      }

      printk("\n");

}

void sh64_unwind(struct pt_regs *regs)
{
      if (!regs) {
            /*
             * Fetch current regs if we have no other saved state to back
             * trace from.
             */
            regs = &here_regs;

            __asm__ __volatile__ ("ori r14, 0, %0" : "=r" (regs->regs[14]));
            __asm__ __volatile__ ("ori r15, 0, %0" : "=r" (regs->regs[15]));
            __asm__ __volatile__ ("ori r18, 0, %0" : "=r" (regs->regs[18]));

            __asm__ __volatile__ ("gettr tr0, %0" : "=r" (regs->tregs[0]));
            __asm__ __volatile__ ("gettr tr1, %0" : "=r" (regs->tregs[1]));
            __asm__ __volatile__ ("gettr tr2, %0" : "=r" (regs->tregs[2]));
            __asm__ __volatile__ ("gettr tr3, %0" : "=r" (regs->tregs[3]));
            __asm__ __volatile__ ("gettr tr4, %0" : "=r" (regs->tregs[4]));
            __asm__ __volatile__ ("gettr tr5, %0" : "=r" (regs->tregs[5]));
            __asm__ __volatile__ ("gettr tr6, %0" : "=r" (regs->tregs[6]));
            __asm__ __volatile__ ("gettr tr7, %0" : "=r" (regs->tregs[7]));

            __asm__ __volatile__ (
                  "pta 0f, tr0\n\t"
                  "blink tr0, %0\n\t"
                  "0: nop"
                  : "=r" (regs->pc)
            );
      }

      printk("\nCall Trace:\n");
      sh64_unwind_inner(regs);
}


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