arch/arm/kernel/stacktrace.c

   1 #include <linux/export.h>
   2 #include <linux/sched.h>
   3 #include <linux/sched/debug.h>
   4 #include <linux/stacktrace.h>
   5
   6 #include <asm/stacktrace.h>
   7 #include <asm/traps.h>
   8
   9 #if defined(CONFIG_FRAME_POINTER) && !defined(CONFIG_ARM_UNWIND)
  10 /*
  11  * Unwind the current stack frame and store the new register values in the
  12  * structure passed as argument. Unwinding is equivalent to a function return,
  13  * hence the new PC value rather than LR should be used for backtrace.
  14  *
  15  * With framepointer enabled, a simple function prologue looks like this:
  16  *      mov     ip, sp
  17  *      stmdb   sp!, {fp, ip, lr, pc}
  18  *      sub     fp, ip, #4
  19  *
  20  * A simple function epilogue looks like this:
  21  *      ldm     sp, {fp, sp, pc}
  22  *
  23  * When compiled with clang, pc and sp are not pushed. A simple function
  24  * prologue looks like this when built with clang:
  25  *
  26  *      stmdb   {..., fp, lr}
  27  *      add     fp, sp, #x
  28  *      sub     sp, sp, #y
  29  *
  30  * A simple function epilogue looks like this when built with clang:
  31  *
  32  *      sub     sp, fp, #x
  33  *      ldm     {..., fp, pc}
  34  *
  35  *
  36  * Note that with framepointer enabled, even the leaf functions have the same
  37  * prologue and epilogue, therefore we can ignore the LR value in this case.
  38  */
  39 int notrace unwind_frame(struct stackframe *frame)
  40 {
  41         unsigned long high, low;
  42         unsigned long fp = frame->fp;
  43
  44         /* only go to a higher address on the stack */
  45         low = frame->sp;
  46         high = ALIGN(low, THREAD_SIZE);
  47
  48 #ifdef CONFIG_CC_IS_CLANG
  49         /* check current frame pointer is within bounds */
  50         if (fp < low + 4 || fp > high - 4)
  51                 return -EINVAL;
  52
  53         frame->sp = frame->fp;
  54         frame->fp = *(unsigned long *)(fp);
  55         frame->pc = frame->lr;
  56         frame->lr = *(unsigned long *)(fp + 4);
  57 #else
  58         /* check current frame pointer is within bounds */
  59         if (fp < low + 12 || fp > high - 4)
  60                 return -EINVAL;
  61
  62         /* restore the registers from the stack frame */
  63         frame->fp = *(unsigned long *)(fp - 12);
  64         frame->sp = *(unsigned long *)(fp - 8);
  65         frame->pc = *(unsigned long *)(fp - 4);
  66 #endif
  67
  68         return 0;
  69 }
  70 #endif
  71
  72 void notrace walk_stackframe(struct stackframe *frame,
  73                      int (*fn)(struct stackframe *, void *), void *data)
  74 {
  75         while (1) {
  76                 int ret;
  77
  78                 if (fn(frame, data))
  79                         break;
  80                 ret = unwind_frame(frame);
  81                 if (ret < 0)
  82                         break;
  83         }
  84 }
  85 EXPORT_SYMBOL(walk_stackframe);
  86
  87 #ifdef CONFIG_STACKTRACE
  88 struct stack_trace_data {
  89         struct stack_trace *trace;
  90         unsigned long last_pc;
  91         unsigned int no_sched_functions;
  92         unsigned int skip;
  93 };
  94
  95 static int save_trace(struct stackframe *frame, void *d)
  96 {
  97         struct stack_trace_data *data = d;
  98         struct stack_trace *trace = data->trace;
  99         struct pt_regs *regs;
 100         unsigned long addr = frame->pc;
 101
 102         if (data->no_sched_functions && in_sched_functions(addr))
 103                 return 0;
 104         if (data->skip) {
 105                 data->skip--;
 106                 return 0;
 107         }
 108
 109         trace->entries[trace->nr_entries++] = addr;
 110
 111         if (trace->nr_entries >= trace->max_entries)
 112                 return 1;
 113
 114         /*
 115          * in_exception_text() is designed to test if the PC is one of
 116          * the functions which has an exception stack above it, but
 117          * unfortunately what is in frame->pc is the return LR value,
 118          * not the saved PC value.  So, we need to track the previous
 119          * frame PC value when doing this.
 120          */
 121         addr = data->last_pc;
 122         data->last_pc = frame->pc;
 123         if (!in_exception_text(addr))
 124                 return 0;
 125
 126         regs = (struct pt_regs *)frame->sp;
 127
 128         trace->entries[trace->nr_entries++] = regs->ARM_pc;
 129
 130         return trace->nr_entries >= trace->max_entries;
 131 }
 132
 133 /* This must be noinline to so that our skip calculation works correctly */
 134 static noinline void __save_stack_trace(struct task_struct *tsk,
 135         struct stack_trace *trace, unsigned int nosched)
 136 {
 137         struct stack_trace_data data;
 138         struct stackframe frame;
 139
 140         data.trace = trace;
 141         data.last_pc = ULONG_MAX;
 142         data.skip = trace->skip;
 143         data.no_sched_functions = nosched;
 144
 145         if (tsk != current) {
 146 #ifdef CONFIG_SMP
 147                 /*
 148                  * What guarantees do we have here that 'tsk' is not
 149                  * running on another CPU?  For now, ignore it as we
 150                  * can't guarantee we won't explode.
 151                  */
 152                 if (trace->nr_entries < trace->max_entries)
 153                         trace->entries[trace->nr_entries++] = ULONG_MAX;
 154                 return;
 155 #else
 156                 frame.fp = thread_saved_fp(tsk);
 157                 frame.sp = thread_saved_sp(tsk);
 158                 frame.lr = 0;           /* recovered from the stack */
 159                 frame.pc = thread_saved_pc(tsk);
 160 #endif
 161         } else {
 162                 /* We don't want this function nor the caller */
 163                 data.skip += 2;
 164                 frame.fp = (unsigned long)__builtin_frame_address(0);
 165                 frame.sp = current_stack_pointer;
 166                 frame.lr = (unsigned long)__builtin_return_address(0);
 167                 frame.pc = (unsigned long)__save_stack_trace;
 168         }
 169
 170         walk_stackframe(&frame, save_trace, &data);
 171         if (trace->nr_entries < trace->max_entries)
 172                 trace->entries[trace->nr_entries++] = ULONG_MAX;
 173 }
 174
 175 void save_stack_trace_regs(struct pt_regs *regs, struct stack_trace *trace)
 176 {
 177         struct stack_trace_data data;
 178         struct stackframe frame;
 179
 180         data.trace = trace;
 181         data.skip = trace->skip;
 182         data.no_sched_functions = 0;
 183
 184         frame.fp = regs->ARM_fp;
 185         frame.sp = regs->ARM_sp;
 186         frame.lr = regs->ARM_lr;
 187         frame.pc = regs->ARM_pc;
 188
 189         walk_stackframe(&frame, save_trace, &data);
 190         if (trace->nr_entries < trace->max_entries)
 191                 trace->entries[trace->nr_entries++] = ULONG_MAX;
 192 }
 193
 194 void save_stack_trace_tsk(struct task_struct *tsk, struct stack_trace *trace)
 195 {
 196         __save_stack_trace(tsk, trace, 1);
 197 }
 198 EXPORT_SYMBOL(save_stack_trace_tsk);
 199
 200 void save_stack_trace(struct stack_trace *trace)
 201 {
 202         __save_stack_trace(current, trace, 0);
 203 }
 204 EXPORT_SYMBOL_GPL(save_stack_trace);
 205 #endif