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use alloc::boxed::FnBox;
use arch::cpu::{self,Regs};
use core::mem;
use ksyscall;
use libc::jmp_buf;
use once::{self,Once};
use prelude::*;
use ptr::Align;
use syscall::PackedArgs;

extern {
    static thread_entry_asm: u8;
    static syscall_entry_asm: u8;
}

pub type RegsHandler = Fn(&Regs) -> usize;

#[no_mangle]
pub unsafe fn syscall_entry(regs: &Regs) -> isize {
    let args = PackedArgs::from_tuple((regs.rdi as usize, regs.rsi as usize, regs.rdx as usize, regs.r8 as usize, regs.r9 as usize, regs.r10 as usize));
    ksyscall::dispatch(regs.rax as usize, args)
}

#[no_mangle]
pub fn thread_entry(p: *mut u8) -> ! {
    let start : Box<Box<FnBox()>>;
    unsafe {
        start = Box::from_raw(p as *mut _);
    }

    start();
    unreachable!()
}

pub fn new_jmp_buf<'a>(p: Box<FnBox() + 'a>, stack_ptr: *mut u8) -> jmp_buf {
    assert!(Align::is_aligned(stack_ptr, 16));

    let pp = Box::new(p);
    let rsp : *mut u8 = stack_ptr;
    let rip : *const u8 = &thread_entry_asm;
    let rbx : *const u8 = &*pp as *const _ as *const _;
    mem::forget(pp);

    jmp_buf {
        rbp: 0, r12: 0, r13: 0, r14: 0, r15: 0,
        rsp: rsp as i64 - 8, // compensate for setjmp misaligning rsp
        rip: rip as i64,
        rbx: rbx as i64
    }
}

pub unsafe fn jmp_user_mode(rip: *const u8, rsp: *mut u8) -> ! {
    assert!(Align::is_aligned(rsp, 16));
    let rsp = (rsp as *mut usize).offset(-1); // fake return address
    *rsp = 0;

    static INIT: Once = once::ONCE_INIT;
    INIT.call_once(|| {
        const KERNEL_CS: u16 = 0x08;  // KERNEL_SS = 0x10 (+8)
        const USER_CS_32: u16 = 0x23; // USER_SS = 0x2B (+8); USER_CS_64 = 0x33 (+16)
        const RFLAGS_IF: u64 = 1 << 9;
        cpu::wrmsr(cpu::IA32_STAR, (USER_CS_32 as u64) << 48 | (KERNEL_CS as u64) << 32);
        cpu::wrmsr(cpu::IA32_LSTAR, &syscall_entry_asm as *const u8 as u64);
        cpu::wrmsr(cpu::IA32_SFMASK, RFLAGS_IF);
    });

    log!("jmp_user_mode({:p}, {:p})", rip, rsp);
    cpu::sysret(rip, rsp, 1 << 9)
}