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}