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stacktrace.c

#include <linux/module.h>
#include <linux/sched.h>
#include <linux/stacktrace.h>

#include <asm/stacktrace.h>

#if defined(CONFIG_FRAME_POINTER) && !defined(CONFIG_ARM_UNWIND)
/*
 * Unwind the current stack frame and store the new register values in the
 * structure passed as argument. Unwinding is equivalent to a function return,
 * hence the new PC value rather than LR should be used for backtrace.
 *
 * With framepointer enabled, a simple function prologue looks like this:
 *    mov   ip, sp
 *    stmdb sp!, {fp, ip, lr, pc}
 *    sub   fp, ip, #4
 *
 * A simple function epilogue looks like this:
 *    ldm   sp, {fp, sp, pc}
 *
 * Note that with framepointer enabled, even the leaf functions have the same
 * prologue and epilogue, therefore we can ignore the LR value in this case.
 */
int notrace unwind_frame(struct stackframe *frame)
{
      unsigned long high, low;
      unsigned long fp = frame->fp;

      /* only go to a higher address on the stack */
      low = frame->sp;
      high = ALIGN(low, THREAD_SIZE) + THREAD_SIZE;

      /* check current frame pointer is within bounds */
      if (fp < (low + 12) || fp + 4 >= high)
            return -EINVAL;

      /* restore the registers from the stack frame */
      frame->fp = *(unsigned long *)(fp - 12);
      frame->sp = *(unsigned long *)(fp - 8);
      frame->pc = *(unsigned long *)(fp - 4);

      return 0;
}
#endif

void notrace walk_stackframe(struct stackframe *frame,
                 int (*fn)(struct stackframe *, void *), void *data)
{
      while (1) {
            int ret;

            if (fn(frame, data))
                  break;
            ret = unwind_frame(frame);
            if (ret < 0)
                  break;
      }
}
EXPORT_SYMBOL(walk_stackframe);

#ifdef CONFIG_STACKTRACE
struct stack_trace_data {
      struct stack_trace *trace;
      unsigned int no_sched_functions;
      unsigned int skip;
};

static int save_trace(struct stackframe *frame, void *d)
{
      struct stack_trace_data *data = d;
      struct stack_trace *trace = data->trace;
      unsigned long addr = frame->pc;

      if (data->no_sched_functions && in_sched_functions(addr))
            return 0;
      if (data->skip) {
            data->skip--;
            return 0;
      }

      trace->entries[trace->nr_entries++] = addr;

      return trace->nr_entries >= trace->max_entries;
}

void save_stack_trace_tsk(struct task_struct *tsk, struct stack_trace *trace)
{
      struct stack_trace_data data;
      struct stackframe frame;

      data.trace = trace;
      data.skip = trace->skip;

      if (tsk != current) {
#ifdef CONFIG_SMP
            /*
             * What guarantees do we have here that 'tsk'
             * is not running on another CPU?
             */
            BUG();
#else
            data.no_sched_functions = 1;
            frame.fp = thread_saved_fp(tsk);
            frame.sp = thread_saved_sp(tsk);
            frame.lr = 0;           /* recovered from the stack */
            frame.pc = thread_saved_pc(tsk);
#endif
      } else {
            register unsigned long current_sp asm ("sp");

            data.no_sched_functions = 0;
            frame.fp = (unsigned long)__builtin_frame_address(0);
            frame.sp = current_sp;
            frame.lr = (unsigned long)__builtin_return_address(0);
            frame.pc = (unsigned long)save_stack_trace_tsk;
      }

      walk_stackframe(&frame, save_trace, &data);
      if (trace->nr_entries < trace->max_entries)
            trace->entries[trace->nr_entries++] = ULONG_MAX;
}

void save_stack_trace(struct stack_trace *trace)
{
      save_stack_trace_tsk(current, trace);
}
EXPORT_SYMBOL_GPL(save_stack_trace);
#endif

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