1
  2
  3
  4
  5
  6
  7
  8
  9
 10
 11
 12
 13
 14
 15
 16
 17
 18
 19
 20
 21
 22
 23
 24
 25
 26
 27
 28
 29
 30
 31
 32
 33
 34
 35
 36
 37
 38
 39
 40
 41
 42
 43
 44
 45
 46
 47
 48
 49
 50
 51
 52
 53
 54
 55
 56
 57
 58
 59
 60
 61
 62
 63
 64
 65
 66
 67
 68
 69
 70
 71
 72
 73
 74
 75
 76
 77
 78
 79
 80
 81
 82
 83
 84
 85
 86
 87
 88
 89
 90
 91
 92
 93
 94
 95
 96
 97
 98
 99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147

use crate::globals::Globals;
use crate::trap::{Result, Trap, TrapReason};
use crate::value::LittleEndian;
use std::any;
use std::mem::size_of;
use wain_ast as ast;

const PAGE_SIZE: usize = 65536; // 64Ki

// Memory instance
pub struct Memory {
    max: Option<u32>,
    data: Vec<u8>,
}

impl Memory {
    // https://webassembly.github.io/spec/core/exec/modules.html#alloc-mem
    pub fn allocate(memories: &[ast::Memory]) -> Result<Self> {
        // Note: Only one memory exists thanks to validation
        assert!(memories.len() <= 1);
        if let Some(memory) = memories.get(0) {
            if let Some(i) = &memory.import {
                Err(Trap::unknown_import(i, "memory", memory.start))
            } else {
                let (min, max) = match &memory.ty.limit {
                    ast::Limits::Range(min, max) => (*min, Some(*max)),
                    ast::Limits::From(min) => (*min, None),
                };
                let data = if min == 0 {
                    vec![]
                } else {
                    let len = (min as usize) * PAGE_SIZE;
                    vec![0; len]
                };
                Ok(Self { max, data })
            }
        } else {
            // When no table is set use dummy empty table
            Ok(Self {
                max: Some(0),
                data: vec![],
            })
        }
    }

    // 10. and 14. https://webassembly.github.io/spec/core/exec/modules.html#instantiation
    pub fn new_data(&mut self, segment: &ast::DataSegment, globals: &Globals) -> Result<()> {
        // By validation of constant expression, at least one instruction in the sequence is guaranteed
        // and type must be i32
        let offset = match &segment.offset[segment.offset.len() - 1].kind {
            ast::InsnKind::GlobalGet(idx) => globals.get(*idx),
            ast::InsnKind::I32Const(i) => *i,
            _ => unreachable!("unexpected instruction for element offset"),
        };
        let offset = offset as usize;
        let data = &segment.data;
        let end_addr = offset + data.len();

        if let Some(max) = self.max {
            let max = max as usize;
            if end_addr > max * PAGE_SIZE {
                return Err(Trap::new(
                    TrapReason::OutOfLimit {
                        max,
                        idx: end_addr,
                        kind: "data element",
                    },
                    segment.start,
                ));
            }
        }

        if self.data.len() <= end_addr {
            return Err(Trap::new(
                TrapReason::DataSegmentOutOfBuffer {
                    segment_end: end_addr,
                    buffer_size: self.data.len(),
                },
                segment.start,
            ));
        }

        self.data[offset..end_addr].copy_from_slice(&segment.data);

        Ok(())
    }

    pub fn size(&self) -> u32 {
        (self.data.len() / PAGE_SIZE) as u32
    }

    pub fn grow(&mut self, num_pages: u32) -> i32 {
        // https://webassembly.github.io/spec/core/exec/instructions.html#exec-memory-grow
        let prev = self.size();
        let next = prev + num_pages;
        if let Some(max) = self.max {
            if next > max {
                return -1;
            }
        }
        let next_len = (next as usize) * PAGE_SIZE;
        self.data.resize(next_len, 0);
        prev as i32
    }

    fn check_addr<V: LittleEndian>(
        &self,
        addr: usize,
        at: usize,
        operation: &'static str,
    ) -> Result<()> {
        if addr + size_of::<V>() > self.data.len() {
            Err(Trap::new(
                TrapReason::LoadMemoryOutOfRange {
                    max: self.data.len(),
                    addr,
                    operation,
                    ty: any::type_name::<V>(),
                },
                at,
            ))
        } else {
            Ok(())
        }
    }

    // https://webassembly.github.io/spec/core/exec/instructions.html#and
    pub fn load<V: LittleEndian>(&self, addr: usize, at: usize) -> Result<V> {
        self.check_addr::<V>(addr, at, "load")?;
        Ok(LittleEndian::read(&self.data, addr))
    }

    // https://webassembly.github.io/spec/core/exec/instructions.html#and
    pub fn store<V: LittleEndian>(&mut self, addr: usize, v: V, at: usize) -> Result<()> {
        self.check_addr::<V>(addr, at, "store")?;
        LittleEndian::write(&mut self.data, addr, v);
        Ok(())
    }

    pub fn data(&self) -> &'_ [u8] {
        &self.data
    }

    pub fn data_mut(&mut self) -> &mut [u8] {
        &mut self.data
    }
}