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			break;
127
128		if (consumer_fn(address, arg) == -1)
129			break;
130
131		ret = arc_unwind(&frame_info);
132		if (ret)
133			break;
134
135		frame_info.regs.r63 = frame_info.regs.r31;
136	}
137
138	return address;		/* return the last address it saw */
139#else
140	/* On ARC, only Dward based unwinder works. fp based backtracing is
141	 * not possible (-fno-omit-frame-pointer) because of the way function
142	 * prelogue is setup (callee regs saved and then fp set and not other
143	 * way around
144	 */
145	pr_warn("CONFIG_ARC_DW2_UNWIND needs to be enabled\n");
146	return 0;
147
148#endif
149}
150
151/*-------------------------------------------------------------------------
152 * callbacks called by unwinder iterator to implement kernel APIs
153 *
154 * The callback can return -1 to force the iterator to stop, which by default
155 * keeps going till the bottom-most frame.
156 *-------------------------------------------------------------------------
157 */
158
159/* Call-back which plugs into unwinding core to dump the stack in
160 * case of panic/OOPs/BUG etc
161 */
162static int __print_sym(unsigned int address, void *unused)
163{
164	__print_symbol("  %s\n", address);
165	return 0;
166}
167
168#ifdef CONFIG_STACKTRACE
169
170/* Call-back which plugs into unwinding core to capture the
171 * traces needed by kernel on /proc/<pid>/stack
172 */
173static int __collect_all(unsigned int address, void *arg)
174{
175	struct stack_trace *trace = arg;
176
177	if (trace->skip > 0)
178		trace->skip--;
179	else
180		trace->entries[trace->nr_entries++] = address;
181
182	if (trace->nr_entries >= trace->max_entries)
183		return -1;
184
185	return 0;
186}
187
188static int __collect_all_but_sched(unsigned int address, void *arg)
189{
190	struct stack_trace *trace = arg;
191
192	if (in_sched_functions(address))
193		return 0;
194
195	if (trace->skip > 0)
196		trace->skip--;
197	else
198		trace->entries[trace->nr_entries++] = address;
199
200	if (trace->nr_entries >= trace->max_entries)
201		return -1;
202
203	return 0;
204}
205
206#endif
207
208static int __get_first_nonsched(unsigned int address, void *unused)
209{
210	if (in_sched_functions(address))
211		return 0;
212
213	return -1;
214}
215
216/*-------------------------------------------------------------------------
217 *              APIs expected by various kernel sub-systems
218 *-------------------------------------------------------------------------
219 */
220
221noinline void show_stacktrace(struct task_struct *tsk, struct pt_regs *regs)
222{
223	pr_info("\nStack Trace:\n");
224	arc_unwind_core(tsk, regs, __print_sym, NULL);
225}
226EXPORT_SYMBOL(show_stacktrace);
227
228/* Expected by sched Code */
229void show_stack(struct task_struct *tsk, unsigned long *sp)
230{
231	show_stacktrace(tsk, NULL);
232}
233
234/* Another API expected by schedular, shows up in "ps" as Wait Channel
235 * Ofcourse just returning schedule( ) would be pointless so unwind until
236 * the function is not in schedular code
237 */
238unsigned int get_wchan(struct task_struct *tsk)
239{
240	return arc_unwind_core(tsk, NULL, __get_first_nonsched, NULL);
241}
242
243#ifdef CONFIG_STACKTRACE
244
245/*
246 * API required by CONFIG_STACKTRACE, CONFIG_LATENCYTOP.
247 * A typical use is when /proc/<pid>/stack is queried by userland
248 */
249void save_stack_trace_tsk(struct task_struct *tsk, struct stack_trace *trace)
250{
251	/* Assumes @tsk is sleeping so unwinds from __switch_to */
252	arc_unwind_core(tsk, NULL, __collect_all_but_sched, trace);
253}
254
255void save_stack_trace(struct stack_trace *trace)
256{
257	/* Pass NULL for task so it unwinds the current call frame */
258	arc_unwind_core(NULL, NULL, __collect_all, trace);
259}
260EXPORT_SYMBOL_GPL(save_stack_trace);
261#endif
262