/*
 * Stack tracing support
 *
 * Copyright (C) 2012 ARM Ltd.
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 2 as
 * published by the Free Software Foundation.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */
#include <linux/kernel.h>
#include <linux/export.h>
#include <linux/ftrace.h>
#include <linux/sched.h>
#include <linux/sched/debug.h>
#include <linux/sched/task_stack.h>
#include <linux/stacktrace.h>

#include <asm/irq.h>
#include <asm/stack_pointer.h>
#include <asm/stacktrace.h>

/*
 * AArch64 PCS assigns the frame pointer to x29.
 *
 * A simple function prologue looks like this:
 *      sub     sp, sp, #0x10
 *      stp     x29, x30, [sp]
 *      mov     x29, sp
 *
 * A simple function epilogue looks like this:
 *      mov     sp, x29
 *      ldp     x29, x30, [sp]
 *      add     sp, sp, #0x10
 */
int notrace unwind_frame(struct task_struct *tsk, struct stackframe *frame)
{
        unsigned long high, low;
        unsigned long fp = frame->fp;
        unsigned long irq_stack_ptr;

        if (!tsk)
                tsk = current;

        /*
         * Switching between stacks is valid when tracing current and in
         * non-preemptible context.
         */
        if (tsk == current && !preemptible())
                irq_stack_ptr = IRQ_STACK_PTR(smp_processor_id());
        else
                irq_stack_ptr = 0;

        low  = frame->sp;
        /* irq stacks are not THREAD_SIZE aligned */
        if (on_irq_stack(frame->sp, raw_smp_processor_id()))
                high = irq_stack_ptr;
        else
                high = ALIGN(low, THREAD_SIZE) - 0x20;

        if (fp < low || fp > high || fp & 0xf)
                return -EINVAL;

        frame->sp = fp + 0x10;
        frame->fp = READ_ONCE_NOCHECK(*(unsigned long *)(fp));
        frame->pc = READ_ONCE_NOCHECK(*(unsigned long *)(fp + 8));

#ifdef CONFIG_FUNCTION_GRAPH_TRACER
        if (tsk->ret_stack &&
                        (frame->pc == (unsigned long)return_to_handler)) {
                /*
                 * This is a case where function graph tracer has
                 * modified a return address (LR) in a stack frame
                 * to hook a function return.
                 * So replace it to an original value.
                 */
                frame->pc = tsk->ret_stack[frame->graph--].ret;
        }
#endif /* CONFIG_FUNCTION_GRAPH_TRACER */

        /*
         * Check whether we are going to walk through from interrupt stack
         * to task stack.
         * If we reach the end of the stack - and its an interrupt stack,
         * unpack the dummy frame to find the original elr.
         *
         * Check the frame->fp we read from the bottom of the irq_stack,
         * and the original task stack pointer are both in current->stack.
         */
        if (frame->sp == irq_stack_ptr) {
                struct pt_regs *irq_args;
                unsigned long orig_sp = IRQ_STACK_TO_TASK_STACK(irq_stack_ptr);

                if (object_is_on_stack((void *)orig_sp) &&
                   object_is_on_stack((void *)frame->fp)) {
                        frame->sp = orig_sp;

                        /* orig_sp is the saved pt_regs, find the elr */
                        irq_args = (struct pt_regs *)orig_sp;
                        frame->pc = irq_args->pc;
                } else {
                        /*
                         * This frame has a non-standard format, and we
                         * didn't fix it, because the data looked wrong.
                         * Refuse to output this frame.
                         */
                        return -EINVAL;
                }
        }

        return 0;
}

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

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

#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_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->regs[29];
        frame.sp = regs->sp;
        frame.pc = regs->pc;
#ifdef CONFIG_FUNCTION_GRAPH_TRACER
        frame.graph = current->curr_ret_stack;
#endif

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

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

        if (!try_get_task_stack(tsk))
                return;

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

        if (tsk != current) {
                data.no_sched_functions = 1;
                frame.fp = thread_saved_fp(tsk);
                frame.sp = thread_saved_sp(tsk);
                frame.pc = thread_saved_pc(tsk);
        } else {
                data.no_sched_functions = 0;
                frame.fp = (unsigned long)__builtin_frame_address(0);
                frame.sp = current_stack_pointer;
                frame.pc = (unsigned long)save_stack_trace_tsk;
        }
#ifdef CONFIG_FUNCTION_GRAPH_TRACER
        frame.graph = tsk->curr_ret_stack;
#endif

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

        put_task_stack(tsk);
}
EXPORT_SYMBOL_GPL(save_stack_trace_tsk);

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