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 }