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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 bytes of virtual memory reservation for
/// the heap.
pub static_memory_reservation: 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,
/// 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,
}
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_reservation: 1 << 20,
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,
table_lazy_init: true,
generate_address_map: true,
debug_adapter_modules: false,
relaxed_simd_deterministic: 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_reservation: 10 * (1 << 20),
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_reservation: 1 << 32,
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()
}
}
}