stacktrace.c

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#include <linux/export.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);

    /* 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?  For now, ignore it as we
         * can't guarantee we won't explode.
         */
        if (trace->nr_entries < trace->max_entries)
            trace->entries[trace->nr_entries++] = ULONG_MAX;
        return;
#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