LXR linux/arch/ia64/oprofile/backtrace.c

   1/**
   2 * @file backtrace.c
   3 *
   4 * @remark Copyright 2004 Silicon Graphics Inc.  All Rights Reserved.
   5 * @remark Read the file COPYING
   6 *
   7 * @author Greg Banks <gnb@melbourne.sgi.com>
   8 * @author Keith Owens <kaos@melbourne.sgi.com>
   9 * Based on work done for the ia64 port of the SGI kernprof patch, which is
  10 *    Copyright (c) 2003-2004 Silicon Graphics Inc.  All Rights Reserved.
  11 */
  12
  13#include <linux/oprofile.h>
  14#include <linux/sched.h>
  15#include <linux/mm.h>
  16#include <asm/ptrace.h>
  17
  18/*
  19 * For IA64 we need to perform a complex little dance to get both
  20 * the struct pt_regs and a synthetic struct switch_stack in place
  21 * to allow the unwind code to work.  This dance requires our unwind
  22 * using code to be called from a function called from unw_init_running().
  23 * There we only get a single void* data pointer, so use this struct
  24 * to hold all the data we need during the unwind.
  25 */
  26typedef struct
  27{
  28        unsigned int depth;
  29        struct pt_regs *regs;
  30        struct unw_frame_info frame;
  31        unsigned long *prev_pfs_loc;    /* state for WAR for old spinlock ool code */
  32} ia64_backtrace_t;
  33
  34/* Returns non-zero if the PC is in the Interrupt Vector Table */
  35static __inline__ int in_ivt_code(unsigned long pc)
  36{
  37        extern char ia64_ivt[];
  38        return (pc >= (u_long)ia64_ivt && pc < (u_long)ia64_ivt+32768);
  39}
  40
  41/*
  42 * Unwind to next stack frame.
  43 */
  44static __inline__ int next_frame(ia64_backtrace_t *bt)
  45{
  46        /*
  47         * Avoid unsightly console message from unw_unwind() when attempting
  48         * to unwind through the Interrupt Vector Table which has no unwind
  49         * information.
  50         */
  51        if (in_ivt_code(bt->frame.ip))
  52                return 0;
  53
  54        /*
  55         * WAR for spinlock contention from leaf functions.  ia64_spinlock_contention_pre3_4
  56         * has ar.pfs == r0.  Leaf functions do not modify ar.pfs so ar.pfs remains
  57         * as 0, stopping the backtrace.  Record the previous ar.pfs when the current
  58         * IP is in ia64_spinlock_contention_pre3_4 then unwind, if pfs_loc has not changed
  59         * after unwind then use pt_regs.ar_pfs which is where the real ar.pfs is for
  60         * leaf functions.
  61         */
  62        if (bt->prev_pfs_loc && bt->regs && bt->frame.pfs_loc == bt->prev_pfs_loc)
  63                bt->frame.pfs_loc = &bt->regs->ar_pfs;
  64        bt->prev_pfs_loc = NULL;
  65
  66        return unw_unwind(&bt->frame) == 0;
  67}
  68
  69
  70static void do_ia64_backtrace(struct unw_frame_info *info, void *vdata)
  71{
  72        ia64_backtrace_t *bt = vdata;
  73        struct switch_stack *sw;
  74        int count = 0;
  75        u_long pc, sp;
  76
  77        sw = (struct switch_stack *)(info+1);
  78        /* padding from unw_init_running */
  79        sw = (struct switch_stack *)(((unsigned long)sw + 15) & ~15);
  80
  81        unw_init_frame_info(&bt->frame, current, sw);
  82
  83        /* skip over interrupt frame and oprofile calls */
  84        do {
  85                unw_get_sp(&bt->frame, &sp);
  86                if (sp >= (u_long)bt->regs)
  87                        break;
  88                if (!next_frame(bt))
  89                        return;
  90        } while (count++ < 200);
  91
  92        /* finally, grab the actual sample */
  93        while (bt->depth-- && next_frame(bt)) {
  94                unw_get_ip(&bt->frame, &pc);
  95                oprofile_add_trace(pc);
  96                if (unw_is_intr_frame(&bt->frame)) {
  97                        /*
  98                         * Interrupt received on kernel stack; this can
  99                         * happen when timer interrupt fires while processing
 100                         * a softirq from the tail end of a hardware interrupt
 101                         * which interrupted a system call.  Don't laugh, it
 102                         * happens!  Splice the backtrace into two parts to
 103                         * avoid spurious cycles in the gprof output.
 104                         */
 105                        /* TODO: split rather than drop the 2nd half */
 106                        break;
 107                }
 108        }
 109}
 110
 111void
 112ia64_backtrace(struct pt_regs * const regs, unsigned int depth)
 113{
 114        ia64_backtrace_t bt;
 115        unsigned long flags;
 116
 117        /*
 118         * On IA64 there is little hope of getting backtraces from
 119         * user space programs -- the problems of getting the unwind
 120         * information from arbitrary user programs are extreme.
 121         */
 122        if (user_mode(regs))
 123                return;
 124
 125        bt.depth = depth;
 126        bt.regs = regs;
 127        bt.prev_pfs_loc = NULL;
 128        local_irq_save(flags);
 129        unw_init_running(do_ia64_backtrace, &bt);
 130        local_irq_restore(flags);
 131}
 132