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 */
 27typedef 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 */
 36static __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 */
 45static __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
 71static 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
112void
113ia64_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}