// exported symbols from asm/linker.
// They are always unsafe.
extern "C" {
	fn ___KERNEL_START__();
	fn ___KERNEL_END__();
	fn ___BSS_START__();
	fn ___BSS_END__();
}

pub fn pmap_kernel_start() -> u64 {
	return ___KERNEL_START__ as u64;
}

pub fn pmap_kernel_end() -> u64 {
	return ___KERNEL_END__ as u64;
}
pub fn pmap_bss_start() -> u64 {
	return ___BSS_START__ as u64;
}

pub fn pmap_bss_end() -> u64 {
	return ___BSS_END__ as u64;
}

pub fn roundup_4k(addr: u64) -> u64 {
	return (addr + 0xfff) & !0xfff;
}

pub fn rounddown_4k(addr: u64) -> u64 {
	return addr & !0xfff;
}

pub struct Mem;
impl Mem {
	// units
	pub const K: u64 = 1024;
	pub const M: u64 = 1024 * Mem::K;
	pub const G: u64 = 1024 * Mem::M;
	// physical memory layout: qemu defaults to 128 MiB phy Memory
	pub const PHY_TOP: u64 = 128 * Mem::M;
	// 4 lv 4K paging
	pub const PAGE_SIZE: u64 = 0x1000;
	pub const PAGE_SHIFT: u64 = 12;
	pub const PAGE_MASK: u64 = 0xfff;
	pub const L0_SHIFT: u8 = 39;
	pub const L0_MASK: u64 = 0x1ff << Mem::L0_SHIFT;
	pub const L1_SHIFT: u8 = 30;
	pub const L1_MASK: u64 = 0x1ff << Mem::L1_SHIFT;
	pub const L2_SHIFT: u8 = 21;
	pub const L2_MASK: u64 = 0x1ff << Mem::L2_SHIFT;
	pub const L3_SHIFT: u8 = 12;
	pub const L3_MASK: u64 = 0x1ff << Mem::L3_SHIFT;
	pub const PHY_PAGES: u64 = Mem::PHY_TOP >> Mem::PAGE_SHIFT;
	// size of frame allocator bitmap: number of physical frames / 8 for 128M
	// memory (37268) 4k pages, 37268 bits are needed, hence
	// 4096 bytes, exactly one page!
	pub const PHY_BM_SIZE: u64 = Mem::PHY_PAGES >> 3;
}

// PHY_TOP			128M
// ~				free frames
// PMA::bitmap		+ PHY_BM_SIZE
// ~				___KERNEL_END__
// KERNEL IMAGE
// KERNEL START		1 M