xref: /openbmc/linux/arch/arc/kernel/stacktrace.c (revision c819e2cf)
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 
42 static void seed_unwind_frame_info(struct task_struct *tsk,
43 				   struct pt_regs *regs,
44 				   struct unwind_frame_info *frame_info)
45 {
46 	if (tsk == NULL && regs == NULL) {
47 		unsigned long fp, sp, blink, ret;
48 		frame_info->task = current;
49 
50 		__asm__ __volatile__(
51 			"mov %0,r27\n\t"
52 			"mov %1,r28\n\t"
53 			"mov %2,r31\n\t"
54 			"mov %3,r63\n\t"
55 			: "=r"(fp), "=r"(sp), "=r"(blink), "=r"(ret)
56 		);
57 
58 		frame_info->regs.r27 = fp;
59 		frame_info->regs.r28 = sp;
60 		frame_info->regs.r31 = blink;
61 		frame_info->regs.r63 = ret;
62 		frame_info->call_frame = 0;
63 	} else if (regs == NULL) {
64 
65 		frame_info->task = tsk;
66 
67 		frame_info->regs.r27 = KSTK_FP(tsk);
68 		frame_info->regs.r28 = KSTK_ESP(tsk);
69 		frame_info->regs.r31 = KSTK_BLINK(tsk);
70 		frame_info->regs.r63 = (unsigned int)__switch_to;
71 
72 		/* In the prologue of __switch_to, first FP is saved on stack
73 		 * and then SP is copied to FP. Dwarf assumes cfa as FP based
74 		 * but we didn't save FP. The value retrieved above is FP's
75 		 * state in previous frame.
76 		 * As a work around for this, we unwind from __switch_to start
77 		 * and adjust SP accordingly. The other limitation is that
78 		 * __switch_to macro is dwarf rules are not generated for inline
79 		 * assembly code
80 		 */
81 		frame_info->regs.r27 = 0;
82 		frame_info->regs.r28 += 60;
83 		frame_info->call_frame = 0;
84 
85 	} else {
86 		frame_info->task = tsk;
87 
88 		frame_info->regs.r27 = regs->fp;
89 		frame_info->regs.r28 = regs->sp;
90 		frame_info->regs.r31 = regs->blink;
91 		frame_info->regs.r63 = regs->ret;
92 		frame_info->call_frame = 0;
93 	}
94 }
95 
96 #endif
97 
98 static noinline unsigned int
99 arc_unwind_core(struct task_struct *tsk, struct pt_regs *regs,
100 		int (*consumer_fn) (unsigned int, void *), void *arg)
101 {
102 #ifdef CONFIG_ARC_DW2_UNWIND
103 	int ret = 0;
104 	unsigned int address;
105 	struct unwind_frame_info frame_info;
106 
107 	seed_unwind_frame_info(tsk, regs, &frame_info);
108 
109 	while (1) {
110 		address = UNW_PC(&frame_info);
111 
112 		if (address && __kernel_text_address(address)) {
113 			if (consumer_fn(address, arg) == -1)
114 				break;
115 		}
116 
117 		ret = arc_unwind(&frame_info);
118 
119 		if (ret == 0) {
120 			frame_info.regs.r63 = frame_info.regs.r31;
121 			continue;
122 		} else {
123 			break;
124 		}
125 	}
126 
127 	return address;		/* return the last address it saw */
128 #else
129 	/* On ARC, only Dward based unwinder works. fp based backtracing is
130 	 * not possible (-fno-omit-frame-pointer) because of the way function
131 	 * prelogue is setup (callee regs saved and then fp set and not other
132 	 * way around
133 	 */
134 	pr_warn("CONFIG_ARC_DW2_UNWIND needs to be enabled\n");
135 	return 0;
136 
137 #endif
138 }
139 
140 /*-------------------------------------------------------------------------
141  * callbacks called by unwinder iterator to implement kernel APIs
142  *
143  * The callback can return -1 to force the iterator to stop, which by default
144  * keeps going till the bottom-most frame.
145  *-------------------------------------------------------------------------
146  */
147 
148 /* Call-back which plugs into unwinding core to dump the stack in
149  * case of panic/OOPs/BUG etc
150  */
151 static int __print_sym(unsigned int address, void *unused)
152 {
153 	__print_symbol("  %s\n", address);
154 	return 0;
155 }
156 
157 #ifdef CONFIG_STACKTRACE
158 
159 /* Call-back which plugs into unwinding core to capture the
160  * traces needed by kernel on /proc/<pid>/stack
161  */
162 static int __collect_all(unsigned int address, void *arg)
163 {
164 	struct stack_trace *trace = arg;
165 
166 	if (trace->skip > 0)
167 		trace->skip--;
168 	else
169 		trace->entries[trace->nr_entries++] = address;
170 
171 	if (trace->nr_entries >= trace->max_entries)
172 		return -1;
173 
174 	return 0;
175 }
176 
177 static int __collect_all_but_sched(unsigned int address, void *arg)
178 {
179 	struct stack_trace *trace = arg;
180 
181 	if (in_sched_functions(address))
182 		return 0;
183 
184 	if (trace->skip > 0)
185 		trace->skip--;
186 	else
187 		trace->entries[trace->nr_entries++] = address;
188 
189 	if (trace->nr_entries >= trace->max_entries)
190 		return -1;
191 
192 	return 0;
193 }
194 
195 #endif
196 
197 static int __get_first_nonsched(unsigned int address, void *unused)
198 {
199 	if (in_sched_functions(address))
200 		return 0;
201 
202 	return -1;
203 }
204 
205 /*-------------------------------------------------------------------------
206  *              APIs expected by various kernel sub-systems
207  *-------------------------------------------------------------------------
208  */
209 
210 noinline void show_stacktrace(struct task_struct *tsk, struct pt_regs *regs)
211 {
212 	pr_info("\nStack Trace:\n");
213 	arc_unwind_core(tsk, regs, __print_sym, NULL);
214 }
215 EXPORT_SYMBOL(show_stacktrace);
216 
217 /* Expected by sched Code */
218 void show_stack(struct task_struct *tsk, unsigned long *sp)
219 {
220 	show_stacktrace(tsk, NULL);
221 }
222 
223 /* Another API expected by schedular, shows up in "ps" as Wait Channel
224  * Ofcourse just returning schedule( ) would be pointless so unwind until
225  * the function is not in schedular code
226  */
227 unsigned int get_wchan(struct task_struct *tsk)
228 {
229 	return arc_unwind_core(tsk, NULL, __get_first_nonsched, NULL);
230 }
231 
232 #ifdef CONFIG_STACKTRACE
233 
234 /*
235  * API required by CONFIG_STACKTRACE, CONFIG_LATENCYTOP.
236  * A typical use is when /proc/<pid>/stack is queried by userland
237  */
238 void save_stack_trace_tsk(struct task_struct *tsk, struct stack_trace *trace)
239 {
240 	/* Assumes @tsk is sleeping so unwinds from __switch_to */
241 	arc_unwind_core(tsk, NULL, __collect_all_but_sched, trace);
242 }
243 
244 void save_stack_trace(struct stack_trace *trace)
245 {
246 	/* Pass NULL for task so it unwinds the current call frame */
247 	arc_unwind_core(NULL, NULL, __collect_all, trace);
248 }
249 EXPORT_SYMBOL_GPL(save_stack_trace);
250 #endif
251