wasmtime_environ/
tunables.rs

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
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
use anyhow::{anyhow, bail, Result};
use core::fmt;
use serde_derive::{Deserialize, Serialize};
use target_lexicon::{PointerWidth, Triple};

macro_rules! define_tunables {
    (
        $(#[$outer_attr:meta])*
        pub struct $tunables:ident {
            $(
                $(#[$field_attr:meta])*
                pub $field:ident : $field_ty:ty,
            )*
        }

        pub struct $config_tunables:ident {
            ...
        }
    ) => {
        $(#[$outer_attr])*
        pub struct $tunables {
            $(
                $(#[$field_attr])*
                pub $field: $field_ty,
            )*
        }

        /// Optional tunable configuration options used in `wasmtime::Config`
        #[derive(Default, Clone)]
        #[allow(missing_docs)]
        pub struct $config_tunables {
            $(pub $field: Option<$field_ty>,)*
        }

        impl $config_tunables {
            /// Formats configured fields into `f`.
            pub fn format(&self, f: &mut fmt::DebugStruct<'_,'_>) {
                $(
                    if let Some(val) = &self.$field {
                        f.field(stringify!($field), val);
                    }
                )*
            }

            /// Configure the `Tunables` provided.
            pub fn configure(&self, tunables: &mut Tunables) {
                $(
                    if let Some(val) = self.$field {
                        tunables.$field = val;
                    }
                )*
            }
        }
    };
}

define_tunables! {
    /// Tunable parameters for WebAssembly compilation.
    #[derive(Clone, Hash, Serialize, Deserialize, Debug)]
    pub struct Tunables {
        /// The garbage collector implementation to use, which implies the layout of
        /// GC objects and barriers that must be emitted in Wasm code.
        pub collector: Option<Collector>,

        /// Initial size, in bytes, to be allocated for linear memories.
        pub memory_reservation: u64,

        /// The size, in bytes, of the guard page region for linear memories.
        pub memory_guard_size: u64,

        /// The size, in bytes, to allocate at the end of a relocated linear
        /// memory for growth.
        pub memory_reservation_for_growth: u64,

        /// Whether or not to generate native DWARF debug information.
        pub generate_native_debuginfo: bool,

        /// Whether or not to retain DWARF sections in compiled modules.
        pub parse_wasm_debuginfo: bool,

        /// Whether or not fuel is enabled for generated code, meaning that fuel
        /// will be consumed every time a wasm instruction is executed.
        pub consume_fuel: bool,

        /// Whether or not we use epoch-based interruption.
        pub epoch_interruption: bool,

        /// Whether or not linear memories are allowed to be reallocated after
        /// initial allocation at runtime.
        pub memory_may_move: bool,

        /// Whether or not linear memory allocations will have a guard region at the
        /// beginning of the allocation in addition to the end.
        pub guard_before_linear_memory: bool,

        /// Whether to initialize tables lazily, so that instantiation is fast but
        /// indirect calls are a little slower. If false, tables are initialized
        /// eagerly from any active element segments that apply to them during
        /// instantiation.
        pub table_lazy_init: bool,

        /// Indicates whether an address map from compiled native code back to wasm
        /// offsets in the original file is generated.
        pub generate_address_map: bool,

        /// Flag for the component module whether adapter modules have debug
        /// assertions baked into them.
        pub debug_adapter_modules: bool,

        /// Whether or not lowerings for relaxed simd instructions are forced to
        /// be deterministic.
        pub relaxed_simd_deterministic: bool,

        /// Whether or not Wasm functions target the winch abi.
        pub winch_callable: bool,

        /// Whether or not the host will be using native signals (e.g. SIGILL,
        /// SIGSEGV, etc) to implement traps.
        pub signals_based_traps: bool,

        /// Whether CoW images might be used to initialize linear memories.
        pub memory_init_cow: bool,
    }

    pub struct ConfigTunables {
        ...
    }
}

impl Tunables {
    /// Returns a `Tunables` configuration assumed for running code on the host.
    pub fn default_host() -> Self {
        if cfg!(miri) {
            Tunables::default_miri()
        } else if cfg!(target_pointer_width = "32") {
            Tunables::default_u32()
        } else if cfg!(target_pointer_width = "64") {
            Tunables::default_u64()
        } else {
            panic!("unsupported target_pointer_width");
        }
    }

    /// Returns the default set of tunables for the given target triple.
    pub fn default_for_target(target: &Triple) -> Result<Self> {
        match target
            .pointer_width()
            .map_err(|_| anyhow!("failed to retrieve target pointer width"))?
        {
            PointerWidth::U32 => Ok(Tunables::default_u32()),
            PointerWidth::U64 => Ok(Tunables::default_u64()),
            _ => bail!("unsupported target pointer width"),
        }
    }

    /// Returns the default set of tunables for running under MIRI.
    pub const fn default_miri() -> Tunables {
        Tunables {
            collector: None,

            // No virtual memory tricks are available on miri so make these
            // limits quite conservative.
            memory_reservation: 1 << 20,
            memory_guard_size: 0,
            memory_reservation_for_growth: 0,

            // General options which have the same defaults regardless of
            // architecture.
            generate_native_debuginfo: false,
            parse_wasm_debuginfo: true,
            consume_fuel: false,
            epoch_interruption: false,
            memory_may_move: true,
            guard_before_linear_memory: true,
            table_lazy_init: true,
            generate_address_map: true,
            debug_adapter_modules: false,
            relaxed_simd_deterministic: false,
            winch_callable: false,
            signals_based_traps: true,
            memory_init_cow: true,
        }
    }

    /// Returns the default set of tunables for running under a 32-bit host.
    pub const fn default_u32() -> Tunables {
        Tunables {
            // For 32-bit we scale way down to 10MB of reserved memory. This
            // impacts performance severely but allows us to have more than a
            // few instances running around.
            memory_reservation: 10 * (1 << 20),
            memory_guard_size: 0x1_0000,
            memory_reservation_for_growth: 1 << 20, // 1MB

            ..Tunables::default_miri()
        }
    }

    /// Returns the default set of tunables for running under a 64-bit host.
    pub const fn default_u64() -> Tunables {
        Tunables {
            // 64-bit has tons of address space to static memories can have 4gb
            // address space reservations liberally by default, allowing us to
            // help eliminate bounds checks.
            //
            // A 32MiB default guard size is then allocated so we can remove
            // explicit bounds checks if any static offset is less than this
            // value. SpiderMonkey found, for example, that in a large corpus of
            // wasm modules 20MiB was the maximum offset so this is the
            // power-of-two-rounded up from that and matches SpiderMonkey.
            memory_reservation: 1 << 32,
            memory_guard_size: 32 << 20,

            // We've got lots of address space on 64-bit so use a larger
            // grow-into-this area, but on 32-bit we aren't as lucky. Miri is
            // not exactly fast so reduce memory consumption instead of trying
            // to avoid memory movement.
            memory_reservation_for_growth: 2 << 30, // 2GB

            ..Tunables::default_miri()
        }
    }
}

/// The garbage collector implementation to use.
#[derive(Clone, Copy, Hash, Serialize, Deserialize, Debug, PartialEq, Eq)]
pub enum Collector {
    /// The deferred reference-counting collector.
    DeferredReferenceCounting,
    /// The null collector.
    Null,
}

impl fmt::Display for Collector {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        match self {
            Collector::DeferredReferenceCounting => write!(f, "deferred reference-counting"),
            Collector::Null => write!(f, "null"),
        }
    }
}