1/*
2 *	stacktrace.c : stacktracing APIs needed by rest of kernel
3 *			(wrappers over ARC dwarf based unwinder)
4 *
5 * Copyright (C) 2004, 2007-2010, 2011-2012 Synopsys, Inc. (www.synopsys.com)
6 *
7 * This program is free software; you can redistribute it and/or modify
8 * it under the terms of the GNU General Public License version 2 as
9 * published by the Free Software Foundation.
10 *
11 *  vineetg: aug 2009
12 *  -Implemented CONFIG_STACKTRACE APIs, primarily save_stack_trace_tsk( )
13 *   for displaying task's kernel mode call stack in /proc/<pid>/stack
14 *  -Iterator based approach to have single copy of unwinding core and APIs
15 *   needing unwinding, implement the logic in iterator regarding:
16 *      = which frame onwards to start capture
17 *      = which frame to stop capturing (wchan)
18 *      = specifics of data structs where trace is saved(CONFIG_STACKTRACE etc)
19 *
20 *  vineetg: March 2009
21 *  -Implemented correct versions of thread_saved_pc() and get_wchan()
22 *
23 *  rajeshwarr: 2008
24 *  -Initial implementation
25 */
26
27#include <linux/ptrace.h>
28#include <linux/export.h>
29#include <linux/stacktrace.h>
30#include <linux/kallsyms.h>
31#include <asm/arcregs.h>
32#include <asm/unwind.h>
33#include <asm/switch_to.h>
34
35/*-------------------------------------------------------------------------
36 *              Unwinder Iterator
37 *-------------------------------------------------------------------------
38 */
39
40#ifdef CONFIG_ARC_DW2_UNWIND
41
42static void seed_unwind_frame_info(struct task_struct *tsk,
43				   struct pt_regs *regs,
44				   struct unwind_frame_info *frame_info)
45{
46	/*
47	 * synchronous unwinding (e.g. dump_stack)
48	 *  - uses current values of SP and friends
49	 */
50	if (tsk == NULL && regs == NULL) {
51		unsigned long fp, sp, blink, ret;
52		frame_info->task = current;
53
54		__asm__ __volatile__(
55			"mov %0,r27\n\t"
56			"mov %1,r28\n\t"
57			"mov %2,r31\n\t"
58			"mov %3,r63\n\t"
59			: "=r"(fp), "=r"(sp), "=r"(blink), "=r"(ret)
60		);
61
62		frame_info->regs.r27 = fp;
63		frame_info->regs.r28 = sp;
64		frame_info->regs.r31 = blink;
65		frame_info->regs.r63 = ret;
66		frame_info->call_frame = 0;
67	} else if (regs == NULL) {
68		/*
69		 * Asynchronous unwinding of sleeping task
70		 *  - Gets SP etc from task's pt_regs (saved bottom of kernel
71		 *    mode stack of task)
72		 */
73
74		frame_info->task = tsk;
75
76		frame_info->regs.r27 = TSK_K_FP(tsk);
77		frame_info->regs.r28 = TSK_K_ESP(tsk);
78		frame_info->regs.r31 = TSK_K_BLINK(tsk);
79		frame_info->regs.r63 = (unsigned int)__switch_to;
80
81		/* In the prologue of __switch_to, first FP is saved on stack
82		 * and then SP is copied to FP. Dwarf assumes cfa as FP based
83		 * but we didn't save FP. The value retrieved above is FP's
84		 * state in previous frame.
85		 * As a work around for this, we unwind from __switch_to start
86		 * and adjust SP accordingly. The other limitation is that
87		 * __switch_to macro is dwarf rules are not generated for inline
88		 * assembly code
89		 */
90		frame_info->regs.r27 = 0;
91		frame_info->regs.r28 += 60;
92		frame_info->call_frame = 0;
93
94	} else {
95		/*
96		 * Asynchronous unwinding of intr/exception
97		 *  - Just uses the pt_regs passed
98		 */
99		frame_info->task = tsk;
100
101		frame_info->regs.r27 = regs->fp;
102		frame_info->regs.r28 = regs->sp;
103		frame_info->regs.r31 = regs->blink;
104		frame_info->regs.r63 = regs->ret;
105		frame_info->call_frame = 0;
106	}
107}
108
109#endif
110
111notrace noinline unsigned int
112arc_unwind_core(struct task_struct *tsk, struct pt_regs *regs,
113		int (*consumer_fn) (unsigned int, void *), void *arg)
114{
115#ifdef CONFIG_ARC_DW2_UNWIND
116	int ret = 0;
117	unsigned int address;
118	struct unwind_frame_info frame_info;
119
120	seed_unwind_frame_info(tsk, regs, &frame_info);
121
122	while (1) {
123		address = UNW_PC(&frame_info);
124
125		if (address && __kernel_text_address(address)) {
126			if (consumer_fn(address, arg) == -1)
127				break;
128		}
129
130		ret = arc_unwind(&frame_info);
131
132		if (ret == 0) {
133			frame_info.regs.r63 = frame_info.regs.r31;
134			continue;
135		} else {
136			break;
137		}
138	}
139
140	return address;		/* return the last address it saw */
141#else
142	/* On ARC, only Dward based unwinder works. fp based backtracing is
143	 * not possible (-fno-omit-frame-pointer) because of the way function
144	 * prelogue is setup (callee regs saved and then fp set and not other
145	 * way around
146	 */
147	pr_warn("CONFIG_ARC_DW2_UNWIND needs to be enabled\n");
148	return 0;
149
150#endif
151}
152
153/*-------------------------------------------------------------------------
154 * callbacks called by unwinder iterator to implement kernel APIs
155 *
156 * The callback can return -1 to force the iterator to stop, which by default
157 * keeps going till the bottom-most frame.
158 *-------------------------------------------------------------------------
159 */
160
161/* Call-back which plugs into unwinding core to dump the stack in
162 * case of panic/OOPs/BUG etc
163 */
164static int __print_sym(unsigned int address, void *unused)
165{
166	__print_symbol("  %s\n", address);
167	return 0;
168}
169
170#ifdef CONFIG_STACKTRACE
171
172/* Call-back which plugs into unwinding core to capture the
173 * traces needed by kernel on /proc/<pid>/stack
174 */
175static int __collect_all(unsigned int address, void *arg)
176{
177	struct stack_trace *trace = arg;
178
179	if (trace->skip > 0)
180		trace->skip--;
181	else
182		trace->entries[trace->nr_entries++] = address;
183
184	if (trace->nr_entries >= trace->max_entries)
185		return -1;
186
187	return 0;
188}
189
190static int __collect_all_but_sched(unsigned int address, void *arg)
191{
192	struct stack_trace *trace = arg;
193
194	if (in_sched_functions(address))
195		return 0;
196
197	if (trace->skip > 0)
198		trace->skip--;
199	else
200		trace->entries[trace->nr_entries++] = address;
201
202	if (trace->nr_entries >= trace->max_entries)
203		return -1;
204
205	return 0;
206}
207
208#endif
209
210static int __get_first_nonsched(unsigned int address, void *unused)
211{
212	if (in_sched_functions(address))
213		return 0;
214
215	return -1;
216}
217
218/*-------------------------------------------------------------------------
219 *              APIs expected by various kernel sub-systems
220 *-------------------------------------------------------------------------
221 */
222
223noinline void show_stacktrace(struct task_struct *tsk, struct pt_regs *regs)
224{
225	pr_info("\nStack Trace:\n");
226	arc_unwind_core(tsk, regs, __print_sym, NULL);
227}
228EXPORT_SYMBOL(show_stacktrace);
229
230/* Expected by sched Code */
231void show_stack(struct task_struct *tsk, unsigned long *sp)
232{
233	show_stacktrace(tsk, NULL);
234}
235
236/* Another API expected by schedular, shows up in "ps" as Wait Channel
237 * Ofcourse just returning schedule( ) would be pointless so unwind until
238 * the function is not in schedular code
239 */
240unsigned int get_wchan(struct task_struct *tsk)
241{
242	return arc_unwind_core(tsk, NULL, __get_first_nonsched, NULL);
243}
244
245#ifdef CONFIG_STACKTRACE
246
247/*
248 * API required by CONFIG_STACKTRACE, CONFIG_LATENCYTOP.
249 * A typical use is when /proc/<pid>/stack is queried by userland
250 */
251void save_stack_trace_tsk(struct task_struct *tsk, struct stack_trace *trace)
252{
253	/* Assumes @tsk is sleeping so unwinds from __switch_to */
254	arc_unwind_core(tsk, NULL, __collect_all_but_sched, trace);
255}
256
257void save_stack_trace(struct stack_trace *trace)
258{
259	/* Pass NULL for task so it unwinds the current call frame */
260	arc_unwind_core(NULL, NULL, __collect_all, trace);
261}
262EXPORT_SYMBOL_GPL(save_stack_trace);
263#endif
264