arc/kernel/stacktrace.c

0001 // SPDX-License-Identifier: GPL-2.0-only
0002 /*
0003  *  stacktrace.c : stacktracing APIs needed by rest of kernel
0004  *          (wrappers over ARC dwarf based unwinder)
0005  *
0006  * Copyright (C) 2004, 2007-2010, 2011-2012 Synopsys, Inc. (www.synopsys.com)
0007  *
0008  *  vineetg: aug 2009
0009  *  -Implemented CONFIG_STACKTRACE APIs, primarily save_stack_trace_tsk( )
0010  *   for displaying task's kernel mode call stack in /proc/<pid>/stack
0011  *  -Iterator based approach to have single copy of unwinding core and APIs
0012  *   needing unwinding, implement the logic in iterator regarding:
0013  *      = which frame onwards to start capture
0014  *      = which frame to stop capturing (wchan)
0015  *      = specifics of data structs where trace is saved(CONFIG_STACKTRACE etc)
0016  *
0017  *  vineetg: March 2009
0018  *  -Implemented correct versions of thread_saved_pc() and __get_wchan()
0019  *
0020  *  rajeshwarr: 2008
0021  *  -Initial implementation
0022  */
0023
0024 #include <linux/ptrace.h>
0025 #include <linux/export.h>
0026 #include <linux/stacktrace.h>
0027 #include <linux/kallsyms.h>
0028 #include <linux/sched/debug.h>
0029
0030 #include <asm/arcregs.h>
0031 #include <asm/unwind.h>
0032 #include <asm/switch_to.h>
0033
0034 /*-------------------------------------------------------------------------
0035  *              Unwinder Iterator
0036  *-------------------------------------------------------------------------
0037  */
0038
0039 #ifdef CONFIG_ARC_DW2_UNWIND
0040
0041 static int
0042 seed_unwind_frame_info(struct task_struct *tsk, struct pt_regs *regs,
0043                struct unwind_frame_info *frame_info)
0044 {
0045     if (regs) {
0046         /*
0047          * Asynchronous unwinding of intr/exception
0048          *  - Just uses the pt_regs passed
0049          */
0050         frame_info->task = tsk;
0051
0052         frame_info->regs.r27 = regs->fp;
0053         frame_info->regs.r28 = regs->sp;
0054         frame_info->regs.r31 = regs->blink;
0055         frame_info->regs.r63 = regs->ret;
0056         frame_info->call_frame = 0;
0057     } else if (tsk == NULL || tsk == current) {
0058         /*
0059          * synchronous unwinding (e.g. dump_stack)
0060          *  - uses current values of SP and friends
0061          */
0062         unsigned long fp, sp, blink, ret;
0063         frame_info->task = current;
0064
0065         __asm__ __volatile__(
0066             "mov %0,r27\n\t"
0067             "mov %1,r28\n\t"
0068             "mov %2,r31\n\t"
0069             "mov %3,r63\n\t"
0070             : "=r"(fp), "=r"(sp), "=r"(blink), "=r"(ret)
0071         );
0072
0073         frame_info->regs.r27 = fp;
0074         frame_info->regs.r28 = sp;
0075         frame_info->regs.r31 = blink;
0076         frame_info->regs.r63 = ret;
0077         frame_info->call_frame = 0;
0078     } else {
0079         /*
0080          * Asynchronous unwinding of a likely sleeping task
0081          *  - first ensure it is actually sleeping
0082          *  - if so, it will be in __switch_to, kernel mode SP of task
0083          *    is safe-kept and BLINK at a well known location in there
0084          */
0085
0086         if (task_is_running(tsk))
0087             return -1;
0088
0089         frame_info->task = tsk;
0090
0091         frame_info->regs.r27 = TSK_K_FP(tsk);
0092         frame_info->regs.r28 = TSK_K_ESP(tsk);
0093         frame_info->regs.r31 = TSK_K_BLINK(tsk);
0094         frame_info->regs.r63 = (unsigned int)__switch_to;
0095
0096         /* In the prologue of __switch_to, first FP is saved on stack
0097          * and then SP is copied to FP. Dwarf assumes cfa as FP based
0098          * but we didn't save FP. The value retrieved above is FP's
0099          * state in previous frame.
0100          * As a work around for this, we unwind from __switch_to start
0101          * and adjust SP accordingly. The other limitation is that
0102          * __switch_to macro is dwarf rules are not generated for inline
0103          * assembly code
0104          */
0105         frame_info->regs.r27 = 0;
0106         frame_info->regs.r28 += 60;
0107         frame_info->call_frame = 0;
0108
0109     }
0110     return 0;
0111 }
0112
0113 #endif
0114
0115 notrace noinline unsigned int
0116 arc_unwind_core(struct task_struct *tsk, struct pt_regs *regs,
0117         int (*consumer_fn) (unsigned int, void *), void *arg)
0118 {
0119 #ifdef CONFIG_ARC_DW2_UNWIND
0120     int ret = 0, cnt = 0;
0121     unsigned int address;
0122     struct unwind_frame_info frame_info;
0123
0124     if (seed_unwind_frame_info(tsk, regs, &frame_info))
0125         return 0;
0126
0127     while (1) {
0128         address = UNW_PC(&frame_info);
0129
0130         if (!address || !__kernel_text_address(address))
0131             break;
0132
0133         if (consumer_fn(address, arg) == -1)
0134             break;
0135
0136         ret = arc_unwind(&frame_info);
0137         if (ret)
0138             break;
0139
0140         frame_info.regs.r63 = frame_info.regs.r31;
0141
0142         if (cnt++ > 128) {
0143             printk("unwinder looping too long, aborting !\n");
0144             return 0;
0145         }
0146     }
0147
0148     return address;     /* return the last address it saw */
0149 #else
0150     /* On ARC, only Dward based unwinder works. fp based backtracing is
0151      * not possible (-fno-omit-frame-pointer) because of the way function
0152      * prologue is setup (callee regs saved and then fp set and not other
0153      * way around
0154      */
0155     pr_warn_once("CONFIG_ARC_DW2_UNWIND needs to be enabled\n");
0156     return 0;
0157
0158 #endif
0159 }
0160
0161 /*-------------------------------------------------------------------------
0162  * callbacks called by unwinder iterator to implement kernel APIs
0163  *
0164  * The callback can return -1 to force the iterator to stop, which by default
0165  * keeps going till the bottom-most frame.
0166  *-------------------------------------------------------------------------
0167  */
0168
0169 /* Call-back which plugs into unwinding core to dump the stack in
0170  * case of panic/OOPs/BUG etc
0171  */
0172 static int __print_sym(unsigned int address, void *arg)
0173 {
0174     const char *loglvl = arg;
0175
0176     printk("%s  %pS\n", loglvl, (void *)address);
0177     return 0;
0178 }
0179
0180 #ifdef CONFIG_STACKTRACE
0181
0182 /* Call-back which plugs into unwinding core to capture the
0183  * traces needed by kernel on /proc/<pid>/stack
0184  */
0185 static int __collect_all(unsigned int address, void *arg)
0186 {
0187     struct stack_trace *trace = arg;
0188
0189     if (trace->skip > 0)
0190         trace->skip--;
0191     else
0192         trace->entries[trace->nr_entries++] = address;
0193
0194     if (trace->nr_entries >= trace->max_entries)
0195         return -1;
0196
0197     return 0;
0198 }
0199
0200 static int __collect_all_but_sched(unsigned int address, void *arg)
0201 {
0202     struct stack_trace *trace = arg;
0203
0204     if (in_sched_functions(address))
0205         return 0;
0206
0207     if (trace->skip > 0)
0208         trace->skip--;
0209     else
0210         trace->entries[trace->nr_entries++] = address;
0211
0212     if (trace->nr_entries >= trace->max_entries)
0213         return -1;
0214
0215     return 0;
0216 }
0217
0218 #endif
0219
0220 static int __get_first_nonsched(unsigned int address, void *unused)
0221 {
0222     if (in_sched_functions(address))
0223         return 0;
0224
0225     return -1;
0226 }
0227
0228 /*-------------------------------------------------------------------------
0229  *              APIs expected by various kernel sub-systems
0230  *-------------------------------------------------------------------------
0231  */
0232
0233 noinline void show_stacktrace(struct task_struct *tsk, struct pt_regs *regs,
0234                   const char *loglvl)
0235 {
0236     printk("%s\nStack Trace:\n", loglvl);
0237     arc_unwind_core(tsk, regs, __print_sym, (void *)loglvl);
0238 }
0239 EXPORT_SYMBOL(show_stacktrace);
0240
0241 /* Expected by sched Code */
0242 void show_stack(struct task_struct *tsk, unsigned long *sp, const char *loglvl)
0243 {
0244     show_stacktrace(tsk, NULL, loglvl);
0245 }
0246
0247 /* Another API expected by schedular, shows up in "ps" as Wait Channel
0248  * Of course just returning schedule( ) would be pointless so unwind until
0249  * the function is not in schedular code
0250  */
0251 unsigned int __get_wchan(struct task_struct *tsk)
0252 {
0253     return arc_unwind_core(tsk, NULL, __get_first_nonsched, NULL);
0254 }
0255
0256 #ifdef CONFIG_STACKTRACE
0257
0258 /*
0259  * API required by CONFIG_STACKTRACE, CONFIG_LATENCYTOP.
0260  * A typical use is when /proc/<pid>/stack is queried by userland
0261  */
0262 void save_stack_trace_tsk(struct task_struct *tsk, struct stack_trace *trace)
0263 {
0264     /* Assumes @tsk is sleeping so unwinds from __switch_to */
0265     arc_unwind_core(tsk, NULL, __collect_all_but_sched, trace);
0266 }
0267
0268 void save_stack_trace(struct stack_trace *trace)
0269 {
0270     /* Pass NULL for task so it unwinds the current call frame */
0271     arc_unwind_core(NULL, NULL, __collect_all, trace);
0272 }
0273 EXPORT_SYMBOL_GPL(save_stack_trace);
0274 #endif