rigless 0.1.0

// Copyright (c) 2026 Rigless Labs.
// SPDX-License-Identifier: MIT OR Apache-2.0
//! The target's memory: every region's bytes, which the runtime owns and the core maps.
//!
//! The core reaches a region's bytes directly once it has mapped them, at the region's own address
//! and at each address an alias gives it, so both are the same bytes. A region the guest can't
//! write is mapped read-only: the guest's store there reaches the access callback, which drops it,
//! and the runtime's own writes, an image placed or a snapshot put back, land all the same.
//!
//! The core keeps pointers into the bytes between calls, so this module never borrows them. Every
//! read and write here goes through the same pointer the core's do. It calls no C, so Miri checks it
//! with no core.
#![expect(
    unsafe_code,
    reason = "the core keeps pointers into the regions, so they're reached through raw pointers only"
)]

use std::ptr::NonNull;

use crate::emulator::Alias;
use crate::soc::{Endian, Region, Width};

/// One region and its bytes.
#[derive(Debug)]
struct Bytes {
    base: u64,
    /// Where the same bytes also answer.
    aliases: Vec<u64>,
    writable: bool,
    /// The region's bytes, which this owns as the box they came from.
    contents: NonNull<u8>,
    size: usize,
}

// SAFETY: `Bytes` owns its allocation as a `Box<[u8]>` would, and nothing else holds a pointer
// into it but the core on the thread the run moves it to.
unsafe impl Send for Bytes {}

impl Drop for Bytes {
    fn drop(&mut self) {
        if self.size > 0 {
            // SAFETY: the allocation `Bytes::zeroed` made, with the same layout, freed once.
            unsafe { std::alloc::dealloc(self.contents.as_ptr(), layout(self.size)) }
        }
    }
}

/// How a region's bytes are allocated: page-aligned, so the core maps whole host pages of them.
fn layout(size: usize) -> std::alloc::Layout {
    std::alloc::Layout::from_size_align(size, PAGE_ALIGNMENT).expect("a region fits in memory")
}

/// The alignment of every region's bytes, and so the largest page a processor may map them in.
pub(crate) const PAGE_ALIGNMENT: usize = 4096;

impl Bytes {
    fn zeroed(base: u64, aliases: Vec<u64>, writable: bool, size: usize) -> Self {
        let contents = if size == 0 {
            NonNull::dangling()
        } else {
            // SAFETY: a nonzero size.
            NonNull::new(unsafe { std::alloc::alloc_zeroed(layout(size)) })
                .unwrap_or_else(|| std::alloc::handle_alloc_error(layout(size)))
        };
        Self {
            base,
            aliases,
            writable,
            contents,
            size,
        }
    }

    /// The offset of `address` into this region, at its own address or an alias, when the whole
    /// `length` fits.
    fn offset(&self, address: u64, length: u64) -> Option<usize> {
        let size = self.size as u64;
        self.starts()
            .find(|&base| {
                address >= base
                    && address
                        .checked_add(length)
                        .zip(base.checked_add(size))
                        .is_some_and(|(end, limit)| end <= limit)
            })
            .map(|base| usize::try_from(address - base).expect("inside a region in memory"))
    }

    /// The region's own address, then each alias.
    fn starts(&self) -> impl Iterator<Item = u64> {
        std::iter::once(self.base).chain(self.aliases.iter().copied())
    }

    /// The byte at `offset`, which the caller has checked is inside.
    fn at(&self, offset: usize) -> *mut u8 {
        self.contents.as_ptr().wrapping_add(offset)
    }

    /// Fills `into` from `offset`.
    fn copy_out(&self, offset: usize, into: &mut [u8]) {
        assert!(offset + into.len() <= self.size, "inside the region");
        // SAFETY: inside the allocation, and `into` is the caller's own, so no overlap.
        unsafe { std::ptr::copy_nonoverlapping(self.at(offset), into.as_mut_ptr(), into.len()) }
    }

    /// Writes `bytes` at `offset`.
    fn copy_in(&mut self, offset: usize, bytes: &[u8]) {
        assert!(offset + bytes.len() <= self.size, "inside the region");
        // SAFETY: as `copy_out`.
        unsafe { std::ptr::copy_nonoverlapping(bytes.as_ptr(), self.at(offset), bytes.len()) }
    }
}

/// Every region of one target.
#[derive(Debug)]
pub(crate) struct Memory {
    regions: Vec<Bytes>,
    /// The order a value's bytes are in.
    endian: Endian,
}

/// Memory a processor holds pointers into, from the moment it's mapped into it until the processor
/// is dropped. Its bytes must never move or be freed while the processor lives, so this lends
/// `&Memory`, and writes into its bytes where they are, but never lends `&mut Memory`, which could
/// replace it or take it.
#[derive(Debug)]
pub(crate) struct Mapped(Memory);

impl Mapped {
    pub(crate) fn new(memory: Memory) -> Self {
        Self(memory)
    }

    /// [`Memory::place`], in place.
    pub(crate) fn place(&mut self, address: u64, bytes: &[u8]) -> bool {
        self.0.place(address, bytes)
    }

    /// [`Memory::write`], in place.
    pub(crate) fn write(&mut self, address: u64, width: Width, value: u64) -> bool {
        self.0.write(address, width, value)
    }
}

impl std::ops::Deref for Mapped {
    type Target = Memory;

    fn deref(&self) -> &Memory {
        &self.0
    }
}

/// One mapping the core makes: where, how long, and whether the guest may write it.
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub(crate) struct Mapping {
    pub(crate) start: u64,
    pub(crate) length: u64,
    pub(crate) writable: bool,
}

/// The low `count` bytes of `value` as a target that's `endian` keeps them in memory, in the first
/// `count` of the answer.
pub(crate) fn to_target(value: u64, count: usize, endian: Endian) -> [u8; 8] {
    let mut bytes = [0; 8];
    match endian {
        Endian::Little => bytes[..count].copy_from_slice(&value.to_le_bytes()[..count]),
        Endian::Big => bytes[..count].copy_from_slice(&value.to_be_bytes()[8 - count..]),
    }
    bytes
}

/// The value of `bytes` as a target that's `endian` keeps them in memory.
pub(crate) fn from_target(bytes: &[u8], endian: Endian) -> u64 {
    let mut word = [0; 8];
    match endian {
        Endian::Little => {
            word[..bytes.len()].copy_from_slice(bytes);
            u64::from_le_bytes(word)
        }
        Endian::Big => {
            word[8 - bytes.len()..].copy_from_slice(bytes);
            u64::from_be_bytes(word)
        }
    }
}

impl Memory {
    /// The regions of `map`, zeroed, with each alias placed beside the region it names.
    pub(crate) fn new(map: &[Region], aliases: &[Alias], endian: Endian) -> Self {
        Self {
            regions: map
                .iter()
                .map(|region| {
                    Bytes::zeroed(
                        region.base,
                        aliases
                            .iter()
                            .filter(|alias| alias.region == region.name)
                            .map(|alias| alias.at)
                            .collect(),
                        region.kind.is_writable(),
                        usize::try_from(region.size).expect("a region fits in memory"),
                    )
                })
                .collect(),
            endian,
        }
    }

    /// The order a value's bytes are in.
    pub(crate) fn endian(&self) -> Endian {
        self.endian
    }

    /// Maps every region, at its own address and at its aliases, into `processor`, which reads and
    /// writes them from then on.
    ///
    /// # Safety
    ///
    /// This outlives `processor`, its `Drop` included. Nothing else borrows a region's bytes while
    /// a method of the processor runs, as [`Processor::map`](super::Processor::map) asks.
    #[cfg(not(emulator_absent))]
    pub(crate) unsafe fn map_into(&self, processor: &mut dyn super::Processor) {
        for region in &self.regions {
            for start in region.starts() {
                // SAFETY: the region's own bytes, all `size` of them, whole pages in an allocation
                // aligned to one that never moves and is freed only when this is dropped, and the
                // caller's promise for the rest. `Memory` reaches them only between the
                // processor's calls and from the bus during them.
                unsafe { processor.map(start, region.size as u64, region.at(0), region.writable) };
            }
        }
    }

    /// Every mapping the core makes, each region at its own address and at its aliases.
    pub(crate) fn mappings(&self) -> Vec<Mapping> {
        self.regions
            .iter()
            .flat_map(|region| {
                region.starts().map(|start| Mapping {
                    start,
                    length: region.size as u64,
                    writable: region.writable,
                })
            })
            .collect()
    }

    /// The first mapping that isn't whole pages of `page` bytes. The core maps memory a page at a
    /// time and reaches all of a page it maps, so a region that ends inside a page would let the
    /// guest past its end.
    pub(crate) fn partial_page(&self, page: u64) -> Option<Mapping> {
        self.mappings().into_iter().find(|mapping| {
            mapping.length == 0
                || !mapping.start.is_multiple_of(page)
                || !mapping.length.is_multiple_of(page)
        })
    }

    /// The host address of the byte at `address`, as the core keeps one.
    #[cfg(test)]
    fn host(&self, address: u64) -> Option<*mut u8> {
        self.regions.iter().find_map(|region| {
            let offset = region.offset(address, 1)?;
            Some(region.at(offset))
        })
    }

    /// Each region's base and bytes, the ones the guest can't write too with `read_only`.
    pub(crate) fn contents(&self, read_only: bool) -> Vec<(u64, Vec<u8>)> {
        self.regions
            .iter()
            .filter(|region| read_only || region.writable)
            .map(|region| {
                let mut bytes = vec![0; region.size];
                region.copy_out(0, &mut bytes);
                (region.base, bytes)
            })
            .collect()
    }

    /// Whether `address` is memory the guest can't write.
    pub(crate) fn read_only(&self, address: u64) -> bool {
        self.regions
            .iter()
            .any(|region| !region.writable && region.offset(address, 1).is_some())
    }

    /// `width` from `address`, in the target's byte order, or `None` where no region has every
    /// byte.
    pub(crate) fn read(&self, address: u64, width: Width) -> Option<u64> {
        let bytes = usize::try_from(width.bytes()).expect("a width fits");
        self.regions.iter().find_map(|region| {
            let offset = region.offset(address, bytes as u64)?;
            let mut word = [0; 8];
            region.copy_out(offset, &mut word[..bytes]);
            Some(from_target(&word[..bytes], self.endian))
        })
    }

    /// Writes `width` of `value` at `address`, in the target's byte order, whether or not the guest
    /// may write there. Answers whether a region had every byte.
    pub(crate) fn write(&mut self, address: u64, width: Width, value: u64) -> bool {
        let bytes = usize::try_from(width.bytes()).expect("a width fits");
        self.place(address, &to_target(value, bytes, self.endian)[..bytes])
    }

    /// Writes `bytes` at `address`, whether or not the guest may write there. Answers whether one
    /// region had every byte.
    pub(crate) fn place(&mut self, address: u64, bytes: &[u8]) -> bool {
        self.regions.iter_mut().any(|region| {
            let Some(offset) = region.offset(address, bytes.len() as u64) else {
                return false;
            };
            region.copy_in(offset, bytes);
            true
        })
    }

    /// Whether `address` is in a region the guest can write, where its writes are kept.
    pub(crate) fn writable(&self, address: u64) -> bool {
        self.regions
            .iter()
            .any(|region| region.writable && region.offset(address, 1).is_some())
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    fn memory() -> Memory {
        Memory::new(
            &[
                Region::flash("flash", 0x0800_0000, 0x1000),
                Region::ram("sram", 0x2000_0000, 0x100),
            ],
            &[Alias {
                region: "flash",
                at: 0,
            }],
            Endian::Little,
        )
    }

    /// `contents` copies out each region whole, by its base, and the ones the guest can't write
    /// only when asked for.
    #[test]
    fn contents_copies_out_each_region_whole() {
        let mut memory = memory();
        assert!(memory.place(0x0800_0004, &[1, 2]));
        assert!(memory.place(0x2000_00FE, &[3, 4]));
        let writable = memory.contents(false);
        assert_eq!(writable.len(), 1);
        let (base, ram) = &writable[0];
        assert_eq!((*base, ram.len()), (0x2000_0000, 0x100));
        assert_eq!(&ram[0xFE..], [3, 4]);
        let every = memory.contents(true);
        assert_eq!(
            every
                .iter()
                .map(|(base, bytes)| (*base, bytes.len()))
                .collect::<Vec<_>>(),
            [(0x0800_0000, 0x1000), (0x2000_0000, 0x100)]
        );
        assert_eq!(&every[0].1[4..6], [1, 2]);
    }

    #[test]
    fn an_alias_is_the_same_bytes() {
        let mut memory = memory();
        assert!(memory.write(0x0800_0010, Width::W32, 0xDEAD_BEEF));
        assert_eq!(memory.read(0x10, Width::W32), Some(0xDEAD_BEEF));
        assert_eq!(memory.host(0x10), memory.host(0x0800_0010));
    }

    #[test]
    fn every_region_is_mapped_at_its_address_and_its_aliases() {
        let mappings = memory().mappings();
        assert_eq!(
            mappings,
            [
                Mapping {
                    start: 0x0800_0000,
                    length: 0x1000,
                    writable: false
                },
                Mapping {
                    start: 0,
                    length: 0x1000,
                    writable: false
                },
                Mapping {
                    start: 0x2000_0000,
                    length: 0x100,
                    writable: true
                },
            ]
        );
    }

    #[test]
    fn a_region_that_ends_inside_a_page_is_found() {
        assert_eq!(memory().partial_page(0x100), None);
        assert_eq!(
            memory().partial_page(0x400).map(|mapping| mapping.start),
            Some(0x2000_0000)
        );
    }

    /// The core keeps a pointer into a region and writes through it between the runtime's own reads
    /// and writes, and both see the other's, which is what Miri holds this module to.
    #[test]
    fn a_pointer_the_core_keeps_and_the_runtimes_own_access_share_the_bytes() {
        let mut memory = memory();
        let kept = memory.host(0x2000_0010).unwrap();
        assert!(memory.place(0x2000_0010, &[1, 2]));
        // SAFETY: inside the region, which outlives the pointer.
        assert_eq!(unsafe { kept.read() }, 1);
        // SAFETY: as above.
        unsafe { kept.write(9) };
        assert_eq!(memory.read(0x2000_0010, Width::W8), Some(9));
        assert!(memory.write(0x2000_0010, Width::W8, 7));
        // SAFETY: as above.
        assert_eq!(unsafe { kept.read() }, 7);
    }

    #[test]
    fn an_access_that_runs_off_a_region_is_nothing() {
        let memory = memory();
        assert_eq!(memory.read(0x2000_00FE, Width::W32), None);
        assert_eq!(memory.read(0x3000_0000, Width::W8), None);
        assert!(memory.read_only(0x10));
        assert!(!memory.read_only(0x2000_0000));
        assert!(memory.writable(0x2000_0000));
    }
}