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memory.go
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memory.go
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package mipsevm
import (
"encoding/binary"
"encoding/json"
"fmt"
"io"
"math/bits"
"sort"
"github.com/ethereum/go-ethereum/crypto"
)
// Note: 2**12 = 4 KiB, the min phys page size in the Go runtime.
const (
PageAddrSize = 12
PageKeySize = 32 - PageAddrSize
PageSize = 1 << PageAddrSize
PageAddrMask = PageSize - 1
MaxPageCount = 1 << PageKeySize
PageKeyMask = MaxPageCount - 1
)
func HashPair(left, right [32]byte) [32]byte {
out := crypto.Keccak256Hash(left[:], right[:])
//fmt.Printf("0x%x 0x%x -> 0x%x\n", left, right, out)
return out
}
var zeroHashes = func() [256][32]byte {
// empty parts of the tree are all zero. Precompute the hash of each full-zero range sub-tree level.
var out [256][32]byte
for i := 1; i < 256; i++ {
out[i] = HashPair(out[i-1], out[i-1])
}
return out
}()
type Memory struct {
// generalized index -> merkle root or nil if invalidated
nodes map[uint64]*[32]byte
// pageIndex -> cached page
pages map[uint32]*CachedPage
// Note: since we don't de-alloc pages, we don't do ref-counting.
// Once a page exists, it doesn't leave memory
// two caches: we often read instructions from one page, and do memory things with another page.
// this prevents map lookups each instruction
lastPageKeys [2]uint32
lastPage [2]*CachedPage
}
func NewMemory() *Memory {
return &Memory{
nodes: make(map[uint64]*[32]byte),
pages: make(map[uint32]*CachedPage),
lastPageKeys: [2]uint32{^uint32(0), ^uint32(0)}, // default to invalid keys, to not match any pages
}
}
func (m *Memory) PageCount() int {
return len(m.pages)
}
func (m *Memory) ForEachPage(fn func(pageIndex uint32, page *Page) error) error {
for pageIndex, cachedPage := range m.pages {
if err := fn(pageIndex, cachedPage.Data); err != nil {
return err
}
}
return nil
}
func (m *Memory) Invalidate(addr uint32) {
// addr must be aligned to 4 bytes
if addr&0x3 != 0 {
panic(fmt.Errorf("unaligned memory access: %x", addr))
}
// find page, and invalidate addr within it
if p, ok := m.pageLookup(addr >> PageAddrSize); ok {
prevValid := p.Ok[1]
p.Invalidate(addr & PageAddrMask)
if !prevValid { // if the page was already invalid before, then nodes to mem-root will also still be.
return
}
} else { // no page? nothing to invalidate
return
}
// find the gindex of the first page covering the address
gindex := ((uint64(1) << 32) | uint64(addr)) >> PageAddrSize
for gindex > 0 {
m.nodes[gindex] = nil
gindex >>= 1
}
}
func (m *Memory) MerkleizeSubtree(gindex uint64) [32]byte {
l := uint64(bits.Len64(gindex))
if l > 28 {
panic("gindex too deep")
}
if l > PageKeySize {
depthIntoPage := l - 1 - PageKeySize
pageIndex := (gindex >> depthIntoPage) & PageKeyMask
if p, ok := m.pages[uint32(pageIndex)]; ok {
pageGindex := (1 << depthIntoPage) | (gindex & ((1 << depthIntoPage) - 1))
return p.MerkleizeSubtree(pageGindex)
} else {
return zeroHashes[28-l] // page does not exist
}
}
if l > PageKeySize+1 {
panic("cannot jump into intermediate node of page")
}
n, ok := m.nodes[gindex]
if !ok {
// if the node doesn't exist, the whole sub-tree is zeroed
return zeroHashes[28-l]
}
if n != nil {
return *n
}
left := m.MerkleizeSubtree(gindex << 1)
right := m.MerkleizeSubtree((gindex << 1) | 1)
r := HashPair(left, right)
m.nodes[gindex] = &r
return r
}
func (m *Memory) MerkleProof(addr uint32) (out [28 * 32]byte) {
proof := m.traverseBranch(1, addr, 0)
// encode the proof
for i := 0; i < 28; i++ {
copy(out[i*32:(i+1)*32], proof[i][:])
}
return out
}
func (m *Memory) traverseBranch(parent uint64, addr uint32, depth uint8) (proof [][32]byte) {
if depth == 32-5 {
proof = make([][32]byte, 0, 32-5+1)
proof = append(proof, m.MerkleizeSubtree(parent))
return
}
if depth > 32-5 {
panic("traversed too deep")
}
self := parent << 1
sibling := self | 1
if addr&(1<<(31-depth)) != 0 {
self, sibling = sibling, self
}
proof = m.traverseBranch(self, addr, depth+1)
siblingNode := m.MerkleizeSubtree(sibling)
proof = append(proof, siblingNode)
return
}
func (m *Memory) MerkleRoot() [32]byte {
return m.MerkleizeSubtree(1)
}
func (m *Memory) pageLookup(pageIndex uint32) (*CachedPage, bool) {
// hit caches
if pageIndex == m.lastPageKeys[0] {
return m.lastPage[0], true
}
if pageIndex == m.lastPageKeys[1] {
return m.lastPage[1], true
}
p, ok := m.pages[pageIndex]
// only cache existing pages.
if ok {
m.lastPageKeys[1] = m.lastPageKeys[0]
m.lastPage[1] = m.lastPage[0]
m.lastPageKeys[0] = pageIndex
m.lastPage[0] = p
}
return p, ok
}
func (m *Memory) SetMemory(addr uint32, v uint32) {
// addr must be aligned to 4 bytes
if addr&0x3 != 0 {
panic(fmt.Errorf("unaligned memory access: %x", addr))
}
pageIndex := addr >> PageAddrSize
pageAddr := addr & PageAddrMask
p, ok := m.pageLookup(pageIndex)
if !ok {
// allocate the page if we have not already.
// Go may mmap relatively large ranges, but we only allocate the pages just in time.
p = m.AllocPage(pageIndex)
} else {
m.Invalidate(addr) // invalidate this branch of memory, now that the value changed
}
binary.BigEndian.PutUint32(p.Data[pageAddr:pageAddr+4], v)
}
func (m *Memory) GetMemory(addr uint32) uint32 {
// addr must be aligned to 4 bytes
if addr&0x3 != 0 {
panic(fmt.Errorf("unaligned memory access: %x", addr))
}
p, ok := m.pageLookup(addr >> PageAddrSize)
if !ok {
return 0
}
pageAddr := addr & PageAddrMask
return binary.BigEndian.Uint32(p.Data[pageAddr : pageAddr+4])
}
func (m *Memory) AllocPage(pageIndex uint32) *CachedPage {
p := &CachedPage{Data: new(Page)}
m.pages[pageIndex] = p
// make nodes to root
k := (1 << PageKeySize) | uint64(pageIndex)
for k > 0 {
m.nodes[k] = nil
k >>= 1
}
return p
}
type pageEntry struct {
Index uint32 `json:"index"`
Data *Page `json:"data"`
}
func (m *Memory) MarshalJSON() ([]byte, error) { // nosemgrep
pages := make([]pageEntry, 0, len(m.pages))
for k, p := range m.pages {
pages = append(pages, pageEntry{
Index: k,
Data: p.Data,
})
}
sort.Slice(pages, func(i, j int) bool {
return pages[i].Index < pages[j].Index
})
return json.Marshal(pages)
}
func (m *Memory) UnmarshalJSON(data []byte) error {
var pages []pageEntry
if err := json.Unmarshal(data, &pages); err != nil {
return err
}
m.nodes = make(map[uint64]*[32]byte)
m.pages = make(map[uint32]*CachedPage)
m.lastPageKeys = [2]uint32{^uint32(0), ^uint32(0)}
m.lastPage = [2]*CachedPage{nil, nil}
for i, p := range pages {
if _, ok := m.pages[p.Index]; ok {
return fmt.Errorf("cannot load duplicate page, entry %d, page index %d", i, p.Index)
}
m.AllocPage(p.Index).Data = p.Data
}
return nil
}
func (m *Memory) SetMemoryRange(addr uint32, r io.Reader) error {
for {
pageIndex := addr >> PageAddrSize
pageAddr := addr & PageAddrMask
p, ok := m.pageLookup(pageIndex)
if !ok {
p = m.AllocPage(pageIndex)
}
p.InvalidateFull()
n, err := r.Read(p.Data[pageAddr:])
if err != nil {
if err == io.EOF {
return nil
}
return err
}
addr += uint32(n)
}
}
type memReader struct {
m *Memory
addr uint32
count uint32
}
func (r *memReader) Read(dest []byte) (n int, err error) {
if r.count == 0 {
return 0, io.EOF
}
// Keep iterating over memory until we have all our data.
// It may wrap around the address range, and may not be aligned
endAddr := r.addr + r.count
pageIndex := r.addr >> PageAddrSize
start := r.addr & PageAddrMask
end := uint32(PageSize)
if pageIndex == (endAddr >> PageAddrSize) {
end = endAddr & PageAddrMask
}
p, ok := r.m.pageLookup(pageIndex)
if ok {
n = copy(dest, p.Data[start:end])
} else {
n = copy(dest, make([]byte, end-start)) // default to zeroes
}
r.addr += uint32(n)
r.count -= uint32(n)
return n, nil
}
func (m *Memory) ReadMemoryRange(addr uint32, count uint32) io.Reader {
return &memReader{m: m, addr: addr, count: count}
}
func (m *Memory) Usage() string {
total := uint64(len(m.pages)) * PageSize
const unit = 1024
if total < unit {
return fmt.Sprintf("%d B", total)
}
div, exp := uint64(unit), 0
for n := total / unit; n >= unit; n /= unit {
div *= unit
exp++
}
// KiB, MiB, GiB, TiB, ...
return fmt.Sprintf("%.1f %ciB", float64(total)/float64(div), "KMGTPE"[exp])
}