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  */
  26 typedef 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 */
  35 static __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  */
  44 static __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
  70 static 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
 111 void
 112 ia64_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 }