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         u64 *prev_pfs_loc;      /* state for WAR for old spinlock ool code */
  33 } ia64_backtrace_t;
  34
  35 #if __GNUC__ < 3 || (__GNUC__ == 3 && __GNUC_MINOR__ < 3)
  36 /*
  37  * Returns non-zero if the PC is in the spinlock contention out-of-line code
  38  * with non-standard calling sequence (on older compilers).
  39  */
  40 static __inline__ int in_old_ool_spinlock_code(unsigned long pc)
  41 {
  42         extern const char ia64_spinlock_contention_pre3_4[] __attribute__ ((weak));
  43         extern const char ia64_spinlock_contention_pre3_4_end[] __attribute__ ((weak));
  44         unsigned long sc_start = (unsigned long)ia64_spinlock_contention_pre3_4;
  45         unsigned long sc_end = (unsigned long)ia64_spinlock_contention_pre3_4_end;
  46         return (sc_start && sc_end && pc >= sc_start && pc < sc_end);
  47 }
  48 #else
  49 /* Newer spinlock code does a proper br.call and works fine with the unwinder */
  50 #define in_old_ool_spinlock_code(pc)    0
  51 #endif
  52
  53 /* Returns non-zero if the PC is in the Interrupt Vector Table */
  54 static __inline__ int in_ivt_code(unsigned long pc)
  55 {
  56         extern char ia64_ivt[];
  57         return (pc >= (u_long)ia64_ivt && pc < (u_long)ia64_ivt+32768);
  58 }
  59
  60 /*
  61  * Unwind to next stack frame.
  62  */
  63 static __inline__ int next_frame(ia64_backtrace_t *bt)
  64 {
  65         /*
  66          * Avoid unsightly console message from unw_unwind() when attempting
  67          * to unwind through the Interrupt Vector Table which has no unwind
  68          * information.
  69          */
  70         if (in_ivt_code(bt->frame.ip))
  71                 return 0;
  72
  73         /*
  74          * WAR for spinlock contention from leaf functions.  ia64_spinlock_contention_pre3_4
  75          * has ar.pfs == r0.  Leaf functions do not modify ar.pfs so ar.pfs remains
  76          * as 0, stopping the backtrace.  Record the previous ar.pfs when the current
  77          * IP is in ia64_spinlock_contention_pre3_4 then unwind, if pfs_loc has not changed
  78          * after unwind then use pt_regs.ar_pfs which is where the real ar.pfs is for
  79          * leaf functions.
  80          */
  81         if (bt->prev_pfs_loc && bt->regs && bt->frame.pfs_loc == bt->prev_pfs_loc)
  82                 bt->frame.pfs_loc = &bt->regs->ar_pfs;
  83         bt->prev_pfs_loc = (in_old_ool_spinlock_code(bt->frame.ip) ? bt->frame.pfs_loc : NULL);
  84
  85         return unw_unwind(&bt->frame) == 0;
  86 }
  87
  88
  89 static void do_ia64_backtrace(struct unw_frame_info *info, void *vdata)
  90 {
  91         ia64_backtrace_t *bt = vdata;
  92         struct switch_stack *sw;
  93         int count = 0;
  94         u_long pc, sp;
  95
  96         sw = (struct switch_stack *)(info+1);
  97         /* padding from unw_init_running */
  98         sw = (struct switch_stack *)(((unsigned long)sw + 15) & ~15);
  99
 100         unw_init_frame_info(&bt->frame, current, sw);
 101
 102         /* skip over interrupt frame and oprofile calls */
 103         do {
 104                 unw_get_sp(&bt->frame, &sp);
 105                 if (sp >= (u_long)bt->regs)
 106                         break;
 107                 if (!next_frame(bt))
 108                         return;
 109         } while (count++ < 200);
 110
 111         /* finally, grab the actual sample */
 112         while (bt->depth-- && next_frame(bt)) {
 113                 unw_get_ip(&bt->frame, &pc);
 114                 oprofile_add_trace(pc);
 115                 if (unw_is_intr_frame(&bt->frame)) {
 116                         /*
 117                          * Interrupt received on kernel stack; this can
 118                          * happen when timer interrupt fires while processing
 119                          * a softirq from the tail end of a hardware interrupt
 120                          * which interrupted a system call.  Don't laugh, it
 121                          * happens!  Splice the backtrace into two parts to
 122                          * avoid spurious cycles in the gprof output.
 123                          */
 124                         /* TODO: split rather than drop the 2nd half */
 125                         break;
 126                 }
 127         }
 128 }
 129
 130 void
 131 ia64_backtrace(struct pt_regs * const regs, unsigned int depth)
 132 {
 133         ia64_backtrace_t bt;
 134         unsigned long flags;
 135
 136         /*
 137          * On IA64 there is little hope of getting backtraces from
 138          * user space programs -- the problems of getting the unwind
 139          * information from arbitrary user programs are extreme.
 140          */
 141         if (user_mode(regs))
 142                 return;
 143
 144         bt.depth = depth;
 145         bt.regs = regs;
 146         bt.prev_pfs_loc = NULL;
 147         local_irq_save(flags);
 148         unw_init_running(do_ia64_backtrace, &bt);
 149         local_irq_restore(flags);
 150 }