1/*
  2 * Stack tracing support
  3 *
  4 * Copyright (C) 2012 ARM Ltd.
  5 *
  6 * This program is free software; you can redistribute it and/or modify
  7 * it under the terms of the GNU General Public License version 2 as
  8 * published by the Free Software Foundation.
  9 *
 10 * This program is distributed in the hope that it will be useful,
 11 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 12 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 13 * GNU General Public License for more details.
 14 *
 15 * You should have received a copy of the GNU General Public License
 16 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 17 */
 18#include <linux/kernel.h>
 19#include <linux/export.h>
 20#include <linux/ftrace.h>
 21#include <linux/sched.h>
 22#include <linux/sched/debug.h>
 23#include <linux/sched/task_stack.h>
 24#include <linux/stacktrace.h>
 25
 26#include <asm/irq.h>
 27#include <asm/stack_pointer.h>
 28#include <asm/stacktrace.h>
 29
 30/*
 31 * AArch64 PCS assigns the frame pointer to x29.
 32 *
 33 * A simple function prologue looks like this:
 34 * 	sub	sp, sp, #0x10
 35 *   	stp	x29, x30, [sp]
 36 *	mov	x29, sp
 37 *
 38 * A simple function epilogue looks like this:
 39 *	mov	sp, x29
 40 *	ldp	x29, x30, [sp]
 41 *	add	sp, sp, #0x10
 42 */
 43int notrace unwind_frame(struct task_struct *tsk, struct stackframe *frame)
 44{
 45	unsigned long fp = frame->fp;
 46
 47	if (fp & 0xf)
 48		return -EINVAL;
 49
 50	if (!tsk)
 51		tsk = current;
 52
 53	if (!on_accessible_stack(tsk, fp))
 54		return -EINVAL;
 55
 56	frame->fp = READ_ONCE_NOCHECK(*(unsigned long *)(fp));
 57	frame->pc = READ_ONCE_NOCHECK(*(unsigned long *)(fp + 8));
 58
 59#ifdef CONFIG_FUNCTION_GRAPH_TRACER
 60	if (tsk->ret_stack &&
 61			(frame->pc == (unsigned long)return_to_handler)) {
 62		if (WARN_ON_ONCE(frame->graph == -1))
 63			return -EINVAL;
 64		if (frame->graph < -1)
 65			frame->graph += FTRACE_NOTRACE_DEPTH;
 66
 67		/*
 68		 * This is a case where function graph tracer has
 69		 * modified a return address (LR) in a stack frame
 70		 * to hook a function return.
 71		 * So replace it to an original value.
 72		 */
 73		frame->pc = tsk->ret_stack[frame->graph--].ret;
 74	}
 75#endif /* CONFIG_FUNCTION_GRAPH_TRACER */
 76
 77	/*
 78	 * Frames created upon entry from EL0 have NULL FP and PC values, so
 79	 * don't bother reporting these. Frames created by __noreturn functions
 80	 * might have a valid FP even if PC is bogus, so only terminate where
 81	 * both are NULL.
 82	 */
 83	if (!frame->fp && !frame->pc)
 84		return -EINVAL;
 85
 86	return 0;
 87}
 88
 89void notrace walk_stackframe(struct task_struct *tsk, struct stackframe *frame,
 90		     int (*fn)(struct stackframe *, void *), void *data)
 91{
 92	while (1) {
 93		int ret;
 94
 95		if (fn(frame, data))
 96			break;
 97		ret = unwind_frame(tsk, frame);
 98		if (ret < 0)
 99			break;
100	}
101}
102
103#ifdef CONFIG_STACKTRACE
104struct stack_trace_data {
105	struct stack_trace *trace;
106	unsigned int no_sched_functions;
107	unsigned int skip;
108};
109
110static int save_trace(struct stackframe *frame, void *d)
111{
112	struct stack_trace_data *data = d;
113	struct stack_trace *trace = data->trace;
114	unsigned long addr = frame->pc;
115
116	if (data->no_sched_functions && in_sched_functions(addr))
117		return 0;
118	if (data->skip) {
119		data->skip--;
120		return 0;
121	}
122
123	trace->entries[trace->nr_entries++] = addr;
124
125	return trace->nr_entries >= trace->max_entries;
126}
127
128void save_stack_trace_regs(struct pt_regs *regs, struct stack_trace *trace)
129{
130	struct stack_trace_data data;
131	struct stackframe frame;
132
133	data.trace = trace;
134	data.skip = trace->skip;
135	data.no_sched_functions = 0;
136
137	frame.fp = regs->regs[29];
138	frame.pc = regs->pc;
139#ifdef CONFIG_FUNCTION_GRAPH_TRACER
140	frame.graph = current->curr_ret_stack;
141#endif
142
143	walk_stackframe(current, &frame, save_trace, &data);
144	if (trace->nr_entries < trace->max_entries)
145		trace->entries[trace->nr_entries++] = ULONG_MAX;
146}
147
148static noinline void __save_stack_trace(struct task_struct *tsk,
149	struct stack_trace *trace, unsigned int nosched)
150{
151	struct stack_trace_data data;
152	struct stackframe frame;
153
154	if (!try_get_task_stack(tsk))
155		return;
156
157	data.trace = trace;
158	data.skip = trace->skip;
159	data.no_sched_functions = nosched;
160
161	if (tsk != current) {
162		frame.fp = thread_saved_fp(tsk);
163		frame.pc = thread_saved_pc(tsk);
164	} else {
165		/* We don't want this function nor the caller */
166		data.skip += 2;
167		frame.fp = (unsigned long)__builtin_frame_address(0);
168		frame.pc = (unsigned long)__save_stack_trace;
169	}
170#ifdef CONFIG_FUNCTION_GRAPH_TRACER
171	frame.graph = tsk->curr_ret_stack;
172#endif
173
174	walk_stackframe(tsk, &frame, save_trace, &data);
175	if (trace->nr_entries < trace->max_entries)
176		trace->entries[trace->nr_entries++] = ULONG_MAX;
177
178	put_task_stack(tsk);
179}
180EXPORT_SYMBOL_GPL(save_stack_trace_tsk);
181
182void save_stack_trace_tsk(struct task_struct *tsk, struct stack_trace *trace)
183{
184	__save_stack_trace(tsk, trace, 1);
185}
186
187void save_stack_trace(struct stack_trace *trace)
188{
189	__save_stack_trace(current, trace, 0);
190}
191
192EXPORT_SYMBOL_GPL(save_stack_trace);
193#endif