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1 // SPDX-License-Identifier: GPL-2.0
3 * Copyright (C) 2009 Matt Fleming
5 * Based, in part, on kernel/time/clocksource.c.
7 * This file provides arbitration code for stack unwinders.
9 * Multiple stack unwinders can be available on a system, usually with
10 * the most accurate unwinder being the currently active one.
12 #include <linux/errno.h>
13 #include <linux/list.h>
14 #include <linux/spinlock.h>
15 #include <linux/module.h>
16 #include <asm/unwinder.h>
17 #include <linux/atomic.h>
20 * This is the most basic stack unwinder an architecture can
21 * provide. For architectures without reliable frame pointers, e.g.
22 * RISC CPUs, it can be implemented by looking through the stack for
23 * addresses that lie within the kernel text section.
25 * Other CPUs, e.g. x86, can use their frame pointer register to
26 * construct more accurate stack traces.
28 static struct list_head unwinder_list
;
29 static struct unwinder stack_reader
= {
30 .name
= "stack-reader",
31 .dump
= stack_reader_dump
,
34 .next
= &unwinder_list
,
35 .prev
= &unwinder_list
,
40 * "curr_unwinder" points to the stack unwinder currently in use. This
41 * is the unwinder with the highest rating.
43 * "unwinder_list" is a linked-list of all available unwinders, sorted
46 * All modifications of "curr_unwinder" and "unwinder_list" must be
47 * performed whilst holding "unwinder_lock".
49 static struct unwinder
*curr_unwinder
= &stack_reader
;
51 static struct list_head unwinder_list
= {
52 .next
= &stack_reader
.list
,
53 .prev
= &stack_reader
.list
,
56 static DEFINE_SPINLOCK(unwinder_lock
);
59 * select_unwinder - Select the best registered stack unwinder.
61 * Private function. Must hold unwinder_lock when called.
63 * Select the stack unwinder with the best rating. This is useful for
64 * setting up curr_unwinder.
66 static struct unwinder
*select_unwinder(void)
68 struct unwinder
*best
;
70 if (list_empty(&unwinder_list
))
73 best
= list_entry(unwinder_list
.next
, struct unwinder
, list
);
74 if (best
== curr_unwinder
)
81 * Enqueue the stack unwinder sorted by rating.
83 static int unwinder_enqueue(struct unwinder
*ops
)
85 struct list_head
*tmp
, *entry
= &unwinder_list
;
87 list_for_each(tmp
, &unwinder_list
) {
90 o
= list_entry(tmp
, struct unwinder
, list
);
93 /* Keep track of the place, where to insert */
94 if (o
->rating
>= ops
->rating
)
97 list_add(&ops
->list
, entry
);
103 * unwinder_register - Used to install new stack unwinder
104 * @u: unwinder to be registered
106 * Install the new stack unwinder on the unwinder list, which is sorted
109 * Returns -EBUSY if registration fails, zero otherwise.
111 int unwinder_register(struct unwinder
*u
)
116 spin_lock_irqsave(&unwinder_lock
, flags
);
117 ret
= unwinder_enqueue(u
);
119 curr_unwinder
= select_unwinder();
120 spin_unlock_irqrestore(&unwinder_lock
, flags
);
125 int unwinder_faulted
= 0;
128 * Unwind the call stack and pass information to the stacktrace_ops
129 * functions. Also handle the case where we need to switch to a new
130 * stack dumper because the current one faulted unexpectedly.
132 void unwind_stack(struct task_struct
*task
, struct pt_regs
*regs
,
133 unsigned long *sp
, const struct stacktrace_ops
*ops
,
139 * The problem with unwinders with high ratings is that they are
140 * inherently more complicated than the simple ones with lower
141 * ratings. We are therefore more likely to fault in the
142 * complicated ones, e.g. hitting BUG()s. If we fault in the
143 * code for the current stack unwinder we try to downgrade to
144 * one with a lower rating.
146 * Hopefully this will give us a semi-reliable stacktrace so we
147 * can diagnose why curr_unwinder->dump() faulted.
149 if (unwinder_faulted
) {
150 spin_lock_irqsave(&unwinder_lock
, flags
);
152 /* Make sure no one beat us to changing the unwinder */
153 if (unwinder_faulted
&& !list_is_singular(&unwinder_list
)) {
154 list_del(&curr_unwinder
->list
);
155 curr_unwinder
= select_unwinder();
157 unwinder_faulted
= 0;
160 spin_unlock_irqrestore(&unwinder_lock
, flags
);
163 curr_unwinder
->dump(task
, regs
, sp
, ops
, data
);
165 EXPORT_SYMBOL_GPL(unwind_stack
);