xref: /openbmc/linux/arch/arc/kernel/stacktrace.c (revision 4d369680)
1 // SPDX-License-Identifier: GPL-2.0-only
2 /*
3  *	stacktrace.c : stacktracing APIs needed by rest of kernel
4  *			(wrappers over ARC dwarf based unwinder)
5  *
6  * Copyright (C) 2004, 2007-2010, 2011-2012 Synopsys, Inc. (www.synopsys.com)
7  *
8  *  vineetg: aug 2009
9  *  -Implemented CONFIG_STACKTRACE APIs, primarily save_stack_trace_tsk( )
10  *   for displaying task's kernel mode call stack in /proc/<pid>/stack
11  *  -Iterator based approach to have single copy of unwinding core and APIs
12  *   needing unwinding, implement the logic in iterator regarding:
13  *      = which frame onwards to start capture
14  *      = which frame to stop capturing (wchan)
15  *      = specifics of data structs where trace is saved(CONFIG_STACKTRACE etc)
16  *
17  *  vineetg: March 2009
18  *  -Implemented correct versions of thread_saved_pc() and __get_wchan()
19  *
20  *  rajeshwarr: 2008
21  *  -Initial implementation
22  */
23 
24 #include <linux/ptrace.h>
25 #include <linux/export.h>
26 #include <linux/stacktrace.h>
27 #include <linux/kallsyms.h>
28 #include <linux/sched/debug.h>
29 
30 #include <asm/arcregs.h>
31 #include <asm/unwind.h>
32 #include <asm/stacktrace.h>
33 #include <asm/switch_to.h>
34 
35 /*-------------------------------------------------------------------------
36  *              Unwinder Iterator
37  *-------------------------------------------------------------------------
38  */
39 
40 #ifdef CONFIG_ARC_DW2_UNWIND
41 
42 static int
seed_unwind_frame_info(struct task_struct * tsk,struct pt_regs * regs,struct unwind_frame_info * frame_info)43 seed_unwind_frame_info(struct task_struct *tsk, struct pt_regs *regs,
44 		       struct unwind_frame_info *frame_info)
45 {
46 	if (regs) {
47 		/*
48 		 * Asynchronous unwinding of intr/exception
49 		 *  - Just uses the pt_regs passed
50 		 */
51 		frame_info->task = tsk;
52 
53 		frame_info->regs.r27 = regs->fp;
54 		frame_info->regs.r28 = regs->sp;
55 		frame_info->regs.r31 = regs->blink;
56 		frame_info->regs.r63 = regs->ret;
57 		frame_info->call_frame = 0;
58 	} else if (tsk == NULL || tsk == current) {
59 		/*
60 		 * synchronous unwinding (e.g. dump_stack)
61 		 *  - uses current values of SP and friends
62 		 */
63 		unsigned long fp, sp, blink, ret;
64 		frame_info->task = current;
65 
66 		__asm__ __volatile__(
67 			"mov %0,r27\n\t"
68 			"mov %1,r28\n\t"
69 			"mov %2,r31\n\t"
70 			"mov %3,r63\n\t"
71 			: "=r"(fp), "=r"(sp), "=r"(blink), "=r"(ret)
72 		);
73 
74 		frame_info->regs.r27 = fp;
75 		frame_info->regs.r28 = sp;
76 		frame_info->regs.r31 = blink;
77 		frame_info->regs.r63 = ret;
78 		frame_info->call_frame = 0;
79 	} else {
80 		/*
81 		 * Asynchronous unwinding of a likely sleeping task
82 		 *  - first ensure it is actually sleeping
83 		 *  - if so, it will be in __switch_to, kernel mode SP of task
84 		 *    is safe-kept and BLINK at a well known location in there
85 		 */
86 
87 		if (task_is_running(tsk))
88 			return -1;
89 
90 		frame_info->task = tsk;
91 
92 		frame_info->regs.r27 = TSK_K_FP(tsk);
93 		frame_info->regs.r28 = TSK_K_ESP(tsk);
94 		frame_info->regs.r31 = TSK_K_BLINK(tsk);
95 		frame_info->regs.r63 = (unsigned int)__switch_to;
96 
97 		/* In the prologue of __switch_to, first FP is saved on stack
98 		 * and then SP is copied to FP. Dwarf assumes cfa as FP based
99 		 * but we didn't save FP. The value retrieved above is FP's
100 		 * state in previous frame.
101 		 * As a work around for this, we unwind from __switch_to start
102 		 * and adjust SP accordingly. The other limitation is that
103 		 * __switch_to macro is dwarf rules are not generated for inline
104 		 * assembly code
105 		 */
106 		frame_info->regs.r27 = 0;
107 		frame_info->regs.r28 += 60;
108 		frame_info->call_frame = 0;
109 
110 	}
111 	return 0;
112 }
113 
114 #endif
115 
116 notrace noinline unsigned int
arc_unwind_core(struct task_struct * tsk,struct pt_regs * regs,int (* consumer_fn)(unsigned int,void *),void * arg)117 arc_unwind_core(struct task_struct *tsk, struct pt_regs *regs,
118 		int (*consumer_fn) (unsigned int, void *), void *arg)
119 {
120 #ifdef CONFIG_ARC_DW2_UNWIND
121 	int ret = 0, cnt = 0;
122 	unsigned int address;
123 	struct unwind_frame_info frame_info;
124 
125 	if (seed_unwind_frame_info(tsk, regs, &frame_info))
126 		return 0;
127 
128 	while (1) {
129 		address = UNW_PC(&frame_info);
130 
131 		if (!address || !__kernel_text_address(address))
132 			break;
133 
134 		if (consumer_fn(address, arg) == -1)
135 			break;
136 
137 		ret = arc_unwind(&frame_info);
138 		if (ret)
139 			break;
140 
141 		frame_info.regs.r63 = frame_info.regs.r31;
142 
143 		if (cnt++ > 128) {
144 			printk("unwinder looping too long, aborting !\n");
145 			return 0;
146 		}
147 	}
148 
149 	return address;		/* return the last address it saw */
150 #else
151 	/* On ARC, only Dward based unwinder works. fp based backtracing is
152 	 * not possible (-fno-omit-frame-pointer) because of the way function
153 	 * prologue is setup (callee regs saved and then fp set and not other
154 	 * way around
155 	 */
156 	pr_warn_once("CONFIG_ARC_DW2_UNWIND needs to be enabled\n");
157 	return 0;
158 
159 #endif
160 }
161 
162 /*-------------------------------------------------------------------------
163  * callbacks called by unwinder iterator to implement kernel APIs
164  *
165  * The callback can return -1 to force the iterator to stop, which by default
166  * keeps going till the bottom-most frame.
167  *-------------------------------------------------------------------------
168  */
169 
170 /* Call-back which plugs into unwinding core to dump the stack in
171  * case of panic/OOPs/BUG etc
172  */
__print_sym(unsigned int address,void * arg)173 static int __print_sym(unsigned int address, void *arg)
174 {
175 	const char *loglvl = arg;
176 
177 	printk("%s  %pS\n", loglvl, (void *)address);
178 	return 0;
179 }
180 
181 #ifdef CONFIG_STACKTRACE
182 
183 /* Call-back which plugs into unwinding core to capture the
184  * traces needed by kernel on /proc/<pid>/stack
185  */
__collect_all(unsigned int address,void * arg)186 static int __collect_all(unsigned int address, void *arg)
187 {
188 	struct stack_trace *trace = arg;
189 
190 	if (trace->skip > 0)
191 		trace->skip--;
192 	else
193 		trace->entries[trace->nr_entries++] = address;
194 
195 	if (trace->nr_entries >= trace->max_entries)
196 		return -1;
197 
198 	return 0;
199 }
200 
__collect_all_but_sched(unsigned int address,void * arg)201 static int __collect_all_but_sched(unsigned int address, void *arg)
202 {
203 	struct stack_trace *trace = arg;
204 
205 	if (in_sched_functions(address))
206 		return 0;
207 
208 	if (trace->skip > 0)
209 		trace->skip--;
210 	else
211 		trace->entries[trace->nr_entries++] = address;
212 
213 	if (trace->nr_entries >= trace->max_entries)
214 		return -1;
215 
216 	return 0;
217 }
218 
219 #endif
220 
__get_first_nonsched(unsigned int address,void * unused)221 static int __get_first_nonsched(unsigned int address, void *unused)
222 {
223 	if (in_sched_functions(address))
224 		return 0;
225 
226 	return -1;
227 }
228 
229 /*-------------------------------------------------------------------------
230  *              APIs expected by various kernel sub-systems
231  *-------------------------------------------------------------------------
232  */
233 
show_stacktrace(struct task_struct * tsk,struct pt_regs * regs,const char * loglvl)234 noinline void show_stacktrace(struct task_struct *tsk, struct pt_regs *regs,
235 			      const char *loglvl)
236 {
237 	printk("%s\nStack Trace:\n", loglvl);
238 	arc_unwind_core(tsk, regs, __print_sym, (void *)loglvl);
239 }
240 EXPORT_SYMBOL(show_stacktrace);
241 
242 /* Expected by sched Code */
show_stack(struct task_struct * tsk,unsigned long * sp,const char * loglvl)243 void show_stack(struct task_struct *tsk, unsigned long *sp, const char *loglvl)
244 {
245 	show_stacktrace(tsk, NULL, loglvl);
246 }
247 
248 /* Another API expected by schedular, shows up in "ps" as Wait Channel
249  * Of course just returning schedule( ) would be pointless so unwind until
250  * the function is not in schedular code
251  */
__get_wchan(struct task_struct * tsk)252 unsigned int __get_wchan(struct task_struct *tsk)
253 {
254 	return arc_unwind_core(tsk, NULL, __get_first_nonsched, NULL);
255 }
256 
257 #ifdef CONFIG_STACKTRACE
258 
259 /*
260  * API required by CONFIG_STACKTRACE, CONFIG_LATENCYTOP.
261  * A typical use is when /proc/<pid>/stack is queried by userland
262  */
save_stack_trace_tsk(struct task_struct * tsk,struct stack_trace * trace)263 void save_stack_trace_tsk(struct task_struct *tsk, struct stack_trace *trace)
264 {
265 	/* Assumes @tsk is sleeping so unwinds from __switch_to */
266 	arc_unwind_core(tsk, NULL, __collect_all_but_sched, trace);
267 }
268 
save_stack_trace(struct stack_trace * trace)269 void save_stack_trace(struct stack_trace *trace)
270 {
271 	/* Pass NULL for task so it unwinds the current call frame */
272 	arc_unwind_core(NULL, NULL, __collect_all, trace);
273 }
274 EXPORT_SYMBOL_GPL(save_stack_trace);
275 #endif
276