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use core::arch::asm;

use crate::MAX_BACKTRACE_ADRESSES;

/// Registers saved in trap handler
#[doc(hidden)]
#[allow(missing_docs)]
#[derive(Debug, Default, Clone, Copy)]
#[repr(C)]
pub(crate) struct TrapFrame {
    pub ra: usize,
    pub t0: usize,
    pub t1: usize,
    pub t2: usize,
    pub t3: usize,
    pub t4: usize,
    pub t5: usize,
    pub t6: usize,
    pub a0: usize,
    pub a1: usize,
    pub a2: usize,
    pub a3: usize,
    pub a4: usize,
    pub a5: usize,
    pub a6: usize,
    pub a7: usize,
    pub s0: usize,
    pub s1: usize,
    pub s2: usize,
    pub s3: usize,
    pub s4: usize,
    pub s5: usize,
    pub s6: usize,
    pub s7: usize,
    pub s8: usize,
    pub s9: usize,
    pub s10: usize,
    pub s11: usize,
    pub gp: usize,
    pub tp: usize,
    pub sp: usize,
    pub pc: usize,
    pub mstatus: usize,
    pub mcause: usize,
    pub mtval: usize,
}

/// Get an array of backtrace addresses.
///
/// This needs `force-frame-pointers` enabled.
pub fn backtrace() -> [Option<usize>; MAX_BACKTRACE_ADRESSES] {
    let fp = unsafe {
        let mut _tmp: u32;
        asm!("mv {0}, x8", out(reg) _tmp);
        _tmp
    };

    backtrace_internal(fp, 2)
}

pub(crate) fn backtrace_internal(
    fp: u32,
    suppress: i32,
) -> [Option<usize>; MAX_BACKTRACE_ADRESSES] {
    let mut result = [None; 10];
    let mut index = 0;

    let mut fp = fp;
    let mut suppress = suppress;
    let mut old_address = 0;
    loop {
        unsafe {
            let address = (fp as *const u32).offset(-1).read_volatile(); // RA/PC
            fp = (fp as *const u32).offset(-2).read_volatile(); // next FP

            if old_address == address {
                break;
            }

            old_address = address;

            if address == 0 {
                break;
            }

            if !crate::is_valid_ram_address(fp) {
                break;
            }

            if suppress == 0 {
                result[index] = Some(address as usize);
                index += 1;

                if index >= MAX_BACKTRACE_ADRESSES {
                    break;
                }
            } else {
                suppress -= 1;
            }
        }
    }

    result
}