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