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	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
 98static noinline unsigned int
 99arc_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 */
151static 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 */
162static 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
177static 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
197static 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
210noinline 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}
215EXPORT_SYMBOL(show_stacktrace);
216
217/* Expected by sched Code */
218void 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 */
227unsigned 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 */
238void 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
244void 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}
249EXPORT_SYMBOL_GPL(save_stack_trace);
250#endif