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backtrace.c

/**
 * @file backtrace.c
 *
 * @remark Copyright 2004 Silicon Graphics Inc.  All Rights Reserved.
 * @remark Read the file COPYING
 *
 * @author Greg Banks <gnb@melbourne.sgi.com>
 * @author Keith Owens <kaos@melbourne.sgi.com>
 * Based on work done for the ia64 port of the SGI kernprof patch, which is
 *    Copyright (c) 2003-2004 Silicon Graphics Inc.  All Rights Reserved.
 */

#include <linux/oprofile.h>
#include <linux/sched.h>
#include <linux/mm.h>
#include <asm/ptrace.h>
#include <asm/system.h>

/*
 * For IA64 we need to perform a complex little dance to get both
 * the struct pt_regs and a synthetic struct switch_stack in place
 * to allow the unwind code to work.  This dance requires our unwind
 * using code to be called from a function called from unw_init_running().
 * There we only get a single void* data pointer, so use this struct
 * to hold all the data we need during the unwind.
 */
00027 typedef struct
{
      unsigned int depth;
      struct pt_regs *regs;
      struct unw_frame_info frame;
      u64 *prev_pfs_loc;      /* state for WAR for old spinlock ool code */
} ia64_backtrace_t;

/* Returns non-zero if the PC is in the Interrupt Vector Table */
static __inline__ int in_ivt_code(unsigned long pc)
{
      extern char ia64_ivt[];
      return (pc >= (u_long)ia64_ivt && pc < (u_long)ia64_ivt+32768);
}

/*
 * Unwind to next stack frame.
 */
static __inline__ int next_frame(ia64_backtrace_t *bt)
{
      /*
       * Avoid unsightly console message from unw_unwind() when attempting
       * to unwind through the Interrupt Vector Table which has no unwind
       * information.
       */
      if (in_ivt_code(bt->frame.ip))
            return 0;

      /*
       * WAR for spinlock contention from leaf functions.  ia64_spinlock_contention_pre3_4
       * has ar.pfs == r0.  Leaf functions do not modify ar.pfs so ar.pfs remains
       * as 0, stopping the backtrace.  Record the previous ar.pfs when the current
       * IP is in ia64_spinlock_contention_pre3_4 then unwind, if pfs_loc has not changed
       * after unwind then use pt_regs.ar_pfs which is where the real ar.pfs is for
       * leaf functions.
       */
      if (bt->prev_pfs_loc && bt->regs && bt->frame.pfs_loc == bt->prev_pfs_loc)
            bt->frame.pfs_loc = &bt->regs->ar_pfs;
      bt->prev_pfs_loc = NULL;

      return unw_unwind(&bt->frame) == 0;
}


static void do_ia64_backtrace(struct unw_frame_info *info, void *vdata)
{
      ia64_backtrace_t *bt = vdata;
      struct switch_stack *sw;
      int count = 0;
      u_long pc, sp;

      sw = (struct switch_stack *)(info+1);
      /* padding from unw_init_running */
      sw = (struct switch_stack *)(((unsigned long)sw + 15) & ~15);

      unw_init_frame_info(&bt->frame, current, sw);

      /* skip over interrupt frame and oprofile calls */
      do {
            unw_get_sp(&bt->frame, &sp);
            if (sp >= (u_long)bt->regs)
                  break;
            if (!next_frame(bt))
                  return;
      } while (count++ < 200);

      /* finally, grab the actual sample */
      while (bt->depth-- && next_frame(bt)) {
            unw_get_ip(&bt->frame, &pc);
            oprofile_add_trace(pc);
            if (unw_is_intr_frame(&bt->frame)) {
                  /*
                   * Interrupt received on kernel stack; this can
                   * happen when timer interrupt fires while processing
                   * a softirq from the tail end of a hardware interrupt
                   * which interrupted a system call.  Don't laugh, it
                   * happens!  Splice the backtrace into two parts to
                   * avoid spurious cycles in the gprof output.
                   */
                  /* TODO: split rather than drop the 2nd half */
                  break;
            }
      }
}

void
ia64_backtrace(struct pt_regs * const regs, unsigned int depth)
{
      ia64_backtrace_t bt;
      unsigned long flags;

      /*
       * On IA64 there is little hope of getting backtraces from
       * user space programs -- the problems of getting the unwind
       * information from arbitrary user programs are extreme.
       */
      if (user_mode(regs))
            return;

      bt.depth = depth;
      bt.regs = regs;
      bt.prev_pfs_loc = NULL;
      local_irq_save(flags);
      unw_init_running(do_ia64_backtrace, &bt);
      local_irq_restore(flags);
}

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