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// os/src/mm/memory_set.rs
impl MemorySet {
    pub fn new_bare() -> Self {
        Self {
            page_table: PageTable::new(),
            areas: Vec::new(),
        }
    }
    fn push(&mut self, mut map_area: MapArea, data: Option<&[u8]>) {
        map_area.map(&mut self.page_table);
        if let Some(data) = data {
            map_area.copy_data(&mut self.page_table, data);
        }
        self.areas.push(map_area);
    }
    /// Assume that no conflicts.
    pub fn insert_framed_area(
        &mut self,
        start_va: VirtAddr, end_va: VirtAddr, permission: MapPermission
    ) {
        self.push(MapArea::new(
            start_va,
            end_va,
            MapType::Framed,
            permission,
        ), None);
    }
    pub fn new_kernel() -> Self;
    /// Include sections in elf and trampoline and TrapContext and user stack,
    /// also returns user_sp and entry point.
    pub fn from_elf(elf_data: &[u8]) -> (Self, usize, usize);
}

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// os/src/mm/memory_set.rs
impl MapArea {
    pub fn new(
        start_va: VirtAddr,
        end_va: VirtAddr,
        map_type: MapType,
        map_perm: MapPermission
    ) -> Self {
        let start_vpn: VirtPageNum = start_va.floor();
        let end_vpn: VirtPageNum = end_va.ceil();
        Self {
            vpn_range: VPNRange::new(start_vpn, end_vpn),
            data_frames: BTreeMap::new(),
            map_type,
            map_perm,
        }
    }
    pub fn map(&mut self, page_table: &mut PageTable) {
        for vpn in self.vpn_range {
            self.map_one(page_table, vpn);
        }
    }
    pub fn unmap(&mut self, page_table: &mut PageTable) {
        for vpn in self.vpn_range {
            self.unmap_one(page_table, vpn);
        }
    }
    /// data: start-aligned but maybe with shorter length
    /// assume that all frames were cleared before
    pub fn copy_data(&mut self, page_table: &mut PageTable, data: &[u8]) {
        assert_eq!(self.map_type, MapType::Framed);
        let mut start: usize = 0;
        let mut current_vpn = self.vpn_range.get_start();
        let len = data.len();
        loop {
            let src = &data[start..len.min(start + PAGE_SIZE)];
            let dst = &mut page_table
                .translate(current_vpn)
                .unwrap()
                .ppn()
                .get_bytes_array()[..src.len()];
            dst.copy_from_slice(src);
            start += PAGE_SIZE;
            if start >= len {
                break;
            }
            current_vpn.step();
        }
    }
}

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// os/src/mm/memoryset.rs
impl MemoryArea {
    pub fn map_one(&mut self, page_table: &mut PageTable, vpn: VirtPageNum) {
        let ppn: PhysPageNum;
        match self.map_type {
            MapType::Identical => {
                ppn = PhysPageNum(vpn.0);
            }
            MapType::Framed => {
                let frame = frame_alloc().unwrap();
                ppn = frame.ppn;
                self.data_frames.insert(vpn, frame);
            }
        }
        let pte_flags = PTEFlags::from_bits(self.map_perm.bits).unwrap();
        page_table.map(vpn, ppn, pte_flags);
    }
    pub fn unmap_one(&mut self, page_table: &mut PageTable, vpn: VirtPageNum) {
        match self.map_type {
            MapType::Framed => {
                self.data_frames.remove(&vpn);
            }
             => {}
        }
        page_table.unmap(vpn);
    }
}

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// os/src/mm/memory_set.rs
extern “C” {
    fn stext();
    fn etext();
    fn srodata();
    fn erodata();
    fn sdata();
    fn edata();
    fn sbss_with_stack();
    fn ebss();
    fn ekernel();
    fn strampoline();
}
impl MemorySet {
    /// Without kernel stacks.
    pub fn new_kernel() -> Self {
        let mut memory_set = Self::new_bare();
        // map trampoline
        memory_set.map_trampoline();
        // map kernel sections
        println!(“.text [{:#x}, {:#x})”, stext as usize, etext as usize);
        println!(“.rodata [{:#x}, {:#x})”, srodata as usize, erodata as usize);
        println!(“.data [{:#x}, {:#x})”, sdata as usize, edata as usize);
        println!(“.bss [{:#x}, {:#x})”, sbss_with_stack as usize, ebss as usize);
        println!(“mapping .text section”);
        memory_set.push(MapArea::new(
            (stext as usize).into(),
            (etext as usize).into(),
            MapType::Identical,
            MapPermission::R | MapPermission::X,
        ), None);
        println!(“mapping .rodata section”);
        memory_set.push(MapArea::new(
            (srodata as usize).into(),
            (erodata as usize).into(),
            MapType::Identical,
            MapPermission::R,
        ), None);
        println!(“mapping .data section”);
        memory_set.push(MapArea::new(
            (sdata as usize).into(),
            (edata as usize).into(),
            MapType::Identical,
            MapPermission::R | MapPermission::W,
        ), None);
        println!(“mapping .bss section”);
        memory_set.push(MapArea::new(
            (sbss_with_stack as usize).into(),
            (ebss as usize).into(),
            MapType::Identical,
            MapPermission::R | MapPermission::W,
        ), None);
        println!(“mapping physical memory”);
        memory_set.push(MapArea::new(
            (ekernel as usize).into(),
            MEMORY_END.into(),
            MapType::Identical,
            MapPermission::R | MapPermission::W,
        ), None);
        memory_set
    }
}

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/ user/src/linker.ld /
OUTPUT_ARCH(riscv)
ENTRY(_start)
BASE_ADDRESS = 0x0;
SECTIONS
{
    . = BASE_ADDRESS;
    .text : {
        (.text.entry)
        (.text .text.)
    }
    . = ALIGN(4K);
    .rodata : {
        (.rodata .rodata.)
    }
    . = ALIGN(4K);
    .data : {
        (.data .data.)
    }
    .bss : {
        (.bss .bss.)
    }
    /DISCARD/ : {
        (.eh_frame)
        (.debug)
    }
}

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// os/src/mm/memory_set.rs
impl MemorySet {
    /// Include sections in elf and trampoline and TrapContext and user stack,
    /// also returns user_sp and entry point.
    pub fn from_elf(elf_data: &[u8]) -> (Self, usize, usize) {
        let mut memory_set = Self::new_bare();
        // map trampoline
        memory_set.map_trampoline();
        // map program headers of elf, with U flag
        let elf = xmas_elf::ElfFile::new(elf_data).unwrap();
        let elf_header = elf.header;
        let magic = elf_header.pt1.magic;
        assert_eq!(magic, [0x7f, 0x45, 0x4c, 0x46], “invalid elf!”);
        let ph_count = elf_header.pt2.ph_count();
        let mut max_end_vpn = VirtPageNum(0);
        for i in 0..ph_count {
            let ph = elf.program_header(i).unwrap();
            if ph.get_type().unwrap() == xmas_elf::program::Type::Load {
                let start_va: VirtAddr = (ph.virtual_addr() as usize).into();
                let end_va: VirtAddr = ((ph.virtual_addr() + ph.mem_size()) as usize).into();
                let mut map_perm = MapPermission::U;
                let ph_flags = ph.flags();
                if ph_flags.is_read() { map_perm |= MapPermission::R; }
                if ph_flags.is_write() { map_perm |= MapPermission::W; }
                if ph_flags.is_execute() { map_perm |= MapPermission::X; }
                let map_area = MapArea::new(
                    start_va,
                    end_va,
                    MapType::Framed,
                    map_perm,
                );
                max_end_vpn = map_area.vpn_range.get_end();
                memory_set.push(
                    map_area,
                    Some(&elf.input[ph.offset() as usize..(ph.offset() + ph.file_size()) as usize])
                );
            }
        }
        // map user stack with U flags
        let max_end_va: VirtAddr = max_end_vpn.into();
        let mut user_stack_bottom: usize = max_end_va.into();
        // guard page
        user_stack_bottom += PAGE_SIZE;
        let user_stack_top = user_stack_bottom + USER_STACK_SIZE;
        memory_set.push(MapArea::new(
            user_stack_bottom.into(),
            user_stack_top.into(),
            MapType::Framed,
            MapPermission::R | MapPermission::W | MapPermission::U,
        ), None);
        // map TrapContext
        memory_set.push(MapArea::new(
            TRAP_CONTEXT.into(),
            TRAMPOLINE.into(),
            MapType::Framed,
            MapPermission::R | MapPermission::W,
        ), None);
        (memory_set, user_stack_top, elf.header.pt2.entry_point() as usize)
    }
}