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
148
149
150
151

//! Globals within a wasm module.
use crate::emit::{Emit, EmitContext, Section};
use crate::parse::IndicesToIds;
use crate::tombstone_arena::{Id, Tombstone, TombstoneArena};
use crate::{ImportId, InitExpr, Module, Result, ValType};

/// The id of a global.
pub type GlobalId = Id<Global>;

/// A wasm global.
#[derive(Debug)]
pub struct Global {
    // NB: Not public so that it can't get out of sync with the arena this is
    // contained within.
    id: GlobalId,

    /// This global's type.
    pub ty: ValType,

    /// Whether this global is mutable or not.
    pub mutable: bool,

    /// The kind of global this is
    pub kind: GlobalKind,
}

impl Tombstone for Global {}

/// The different kinds of globals a wasm module can have
#[derive(Debug)]
pub enum GlobalKind {
    /// An imported global without a known initializer
    Import(ImportId),
    /// A locally declare global with the specified identifier
    Local(InitExpr),
}

impl Global {
    /// Get this global's id.
    pub fn id(&self) -> GlobalId {
        self.id
    }
}

impl Emit for Global {
    fn emit(&self, cx: &mut EmitContext) {
        Emit::emit(&self.ty, cx);
        cx.encoder.byte(self.mutable as u8);
    }
}

/// The set of globals in each function in this module.
#[derive(Debug, Default)]
pub struct ModuleGlobals {
    /// The arena where the globals are stored.
    arena: TombstoneArena<Global>,
}

impl ModuleGlobals {
    /// Adds a new imported global to this list.
    pub fn add_import(&mut self, ty: ValType, mutable: bool, import_id: ImportId) -> GlobalId {
        self.arena.alloc_with_id(|id| Global {
            id,
            ty,
            mutable,
            kind: GlobalKind::Import(import_id),
        })
    }

    /// Construct a new global, that does not originate from any of the input
    /// wasm globals.
    pub fn add_local(&mut self, ty: ValType, mutable: bool, init: InitExpr) -> GlobalId {
        self.arena.alloc_with_id(|id| Global {
            id,
            ty,
            mutable,
            kind: GlobalKind::Local(init),
        })
    }

    /// Gets a reference to a memory given its id
    pub fn get(&self, id: GlobalId) -> &Global {
        &self.arena[id]
    }

    /// Gets a reference to a memory given its id
    pub fn get_mut(&mut self, id: GlobalId) -> &mut Global {
        &mut self.arena[id]
    }

    /// Removes a global from this module.
    ///
    /// It is up to you to ensure that any potential references to the deleted
    /// global are also removed, eg `get_global` expressions.
    pub fn delete(&mut self, id: GlobalId) {
        self.arena.delete(id);
    }

    /// Get a shared reference to this module's globals.
    pub fn iter(&self) -> impl Iterator<Item = &Global> {
        self.arena.iter().map(|(_, f)| f)
    }
}

impl Module {
    /// Construct a new, empty set of globals for a module.
    pub(crate) fn parse_globals(
        &mut self,
        section: wasmparser::GlobalSectionReader,
        ids: &mut IndicesToIds,
    ) -> Result<()> {
        log::debug!("parse global section");
        for g in section {
            let g = g?;
            let id = self.globals.add_local(
                ValType::parse(&g.ty.content_type)?,
                g.ty.mutable,
                InitExpr::eval(&g.init_expr, ids)?,
            );
            ids.push_global(id);
        }
        Ok(())
    }
}

impl Emit for ModuleGlobals {
    fn emit(&self, cx: &mut EmitContext) {
        log::debug!("emit global section");
        fn get_local(global: &Global) -> Option<(&Global, &InitExpr)> {
            match &global.kind {
                GlobalKind::Import(_) => None,
                GlobalKind::Local(local) => Some((global, local)),
            }
        }

        // All imported globals emitted earlier during the import section, so
        // filter those out.
        let globals = self.iter().filter_map(get_local).count();
        if globals == 0 {
            return;
        }

        let mut cx = cx.start_section(Section::Global);
        cx.encoder.usize(globals);
        for (global, local) in self.iter().filter_map(get_local) {
            cx.indices.push_global(global.id());
            global.emit(&mut cx);
            local.emit(&mut cx);
        }
    }
}