// SPDX-License-Identifier: GPL-2.0-only
#include <linux/export.h>
#include <linux/kprobes.h>
#include <linux/sched.h>
#include <linux/sched/debug.h>
#include <linux/stacktrace.h>

#include <asm/sections.h>
#include <asm/stacktrace.h>
#include <asm/traps.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}
 *
 * When compiled with clang, pc and sp are not pushed. A simple function
 * prologue looks like this when built with clang:
 *
 *      stmdb   {..., fp, lr}
 *      add     fp, sp, #x
 *      sub     sp, sp, #y
 *
 * A simple function epilogue looks like this when built with clang:
 *
 *      sub     sp, fp, #x
 *      ldm     {..., fp, 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);

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

        frame->sp = frame->fp;
        frame->fp = READ_ONCE_NOCHECK(*(unsigned long *)(fp));
        frame->pc = READ_ONCE_NOCHECK(*(unsigned long *)(fp + 4));
#else
        /* check current frame pointer is within bounds */
        if (fp < low + 12 || fp > high - 4)
                return -EINVAL;

        /* restore the registers from the stack frame */
        frame->fp = READ_ONCE_NOCHECK(*(unsigned long *)(fp - 12));
        frame->sp = READ_ONCE_NOCHECK(*(unsigned long *)(fp - 8));
        frame->pc = READ_ONCE_NOCHECK(*(unsigned long *)(fp - 4));
#endif
#ifdef CONFIG_KRETPROBES
        if (is_kretprobe_trampoline(frame->pc))
                frame->pc = kretprobe_find_ret_addr(frame->tsk,
                                        (void *)frame->fp, &frame->kr_cur);
#endif

        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;
        struct pt_regs *regs;
        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;

        if (trace->nr_entries >= trace->max_entries)
                return 1;

        if (!in_entry_text(frame->pc))
                return 0;

        regs = (struct pt_regs *)frame->sp;
        if ((unsigned long)&regs[1] > ALIGN(frame->sp, THREAD_SIZE))
                return 0;

        trace->entries[trace->nr_entries++] = regs->ARM_pc;

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

/* This must be noinline to so that our skip calculation works correctly */
static noinline void __save_stack_trace(struct task_struct *tsk,
        struct stack_trace *trace, unsigned int nosched)
{
        struct stack_trace_data data;
        struct stackframe frame;

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

        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.
                 */
                return;
#else
                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 {
                /* We don't want this function nor the caller */
                data.skip += 2;
                frame.fp = (unsigned long)__builtin_frame_address(0);
                frame.sp = current_stack_pointer;
                frame.lr = (unsigned long)__builtin_return_address(0);
here:
                frame.pc = (unsigned long)&&here;
        }
#ifdef CONFIG_KRETPROBES
        frame.kr_cur = NULL;
        frame.tsk = tsk;
#endif

        walk_stackframe(&frame, save_trace, &data);
}

void save_stack_trace_regs(struct pt_regs *regs, struct stack_trace *trace)
{
        struct stack_trace_data data;
        struct stackframe frame;

        data.trace = trace;
        data.skip = trace->skip;
        data.no_sched_functions = 0;

        frame.fp = regs->ARM_fp;
        frame.sp = regs->ARM_sp;
        frame.lr = regs->ARM_lr;
        frame.pc = regs->ARM_pc;
#ifdef CONFIG_KRETPROBES
        frame.kr_cur = NULL;
        frame.tsk = current;
#endif

        walk_stackframe(&frame, save_trace, &data);
}

void save_stack_trace_tsk(struct task_struct *tsk, struct stack_trace *trace)
{
        __save_stack_trace(tsk, trace, 1);
}
EXPORT_SYMBOL(save_stack_trace_tsk);

void save_stack_trace(struct stack_trace *trace)
{
        __save_stack_trace(current, trace, 0);
}
EXPORT_SYMBOL_GPL(save_stack_trace);
#endif