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