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

use anyhow::{anyhow, bail, Result};
use serde_derive::{Deserialize, Serialize};
use target_lexicon::{PointerWidth, Triple};

/// Tunable parameters for WebAssembly compilation.
#[derive(Clone, Hash, Serialize, Deserialize, Debug)]
pub struct Tunables {
    /// For static heaps, the size in wasm pages of the heap protected by bounds
    /// checking.
    pub static_memory_bound: u64,

    /// The size in bytes of the offset guard for static heaps.
    pub static_memory_offset_guard_size: u64,

    /// The size in bytes of the offset guard for dynamic heaps.
    pub dynamic_memory_offset_guard_size: u64,

    /// The size, in bytes, of reserved memory at the end of a "dynamic" memory,
    /// before the guard page, that memory can grow into. This is intended to
    /// amortize the cost of `memory.grow` in the same manner that `Vec<T>` has
    /// space not in use to grow into.
    pub dynamic_memory_growth_reserve: 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 to treat the static memory bound as the maximum for
    /// unbounded heaps.
    pub static_memory_bound_is_maximum: 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,

    /// 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 can be tail-called or not.
    pub tail_callable: bool,

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

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 fn default_miri() -> Tunables {
        Tunables {
            // No virtual memory tricks are available on miri so make these
            // limits quite conservative.
            static_memory_bound: (1 << 20) / crate::WASM_PAGE_SIZE as u64,
            static_memory_offset_guard_size: 0,
            dynamic_memory_offset_guard_size: 0,
            dynamic_memory_growth_reserve: 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,
            static_memory_bound_is_maximum: false,
            guard_before_linear_memory: true,
            generate_address_map: true,
            debug_adapter_modules: false,
            relaxed_simd_deterministic: false,
            tail_callable: false,
            winch_callable: false,
        }
    }

    /// Returns the default set of tunables for running under a 32-bit host.
    pub 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.
            static_memory_bound: (10 * (1 << 20)) / crate::WASM_PAGE_SIZE as u64,
            static_memory_offset_guard_size: 0x1_0000,
            dynamic_memory_offset_guard_size: 0x1_0000,
            dynamic_memory_growth_reserve: 1 << 20, // 1MB

            ..Tunables::default_miri()
        }
    }

    /// Returns the default set of tunables for running under a 64-bit host.
    pub 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.
            //
            // Coupled with a 2 GiB address space guard it lets us translate
            // wasm offsets into x86 offsets as aggressively as we can.
            static_memory_bound: 0x1_0000,
            static_memory_offset_guard_size: 0x8000_0000,

            // Size in bytes of the offset guard for dynamic memories.
            //
            // Allocate a small guard to optimize common cases but without
            // wasting too much memory.
            dynamic_memory_offset_guard_size: 0x1_0000,

            // 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.
            dynamic_memory_growth_reserve: 2 << 30, // 2GB

            ..Tunables::default_miri()
        }
    }
}