Lib.rs

› Wasmtime › Features

Cargo Features

[dependencies]
wasmtime = { version = "32.0.0", default-features = false, features = ["cranelift", "winch", "pulley", "incremental-cache", "profiling", "parallel-compilation", "cache", "async", "pooling-allocator", "all-arch", "component-model", "wmemcheck", "trace-log", "demangle", "coredump", "debug-builtins", "runtime", "gc", "gc-drc", "gc-null", "threads", "addr2line", "std", "call-hook", "memory-protection-keys", "reexport-wasmparser", "wave", "custom-virtual-memory", "custom-native-signals", "profile-pulley", "component-model-async", "wat"] }

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Features for the Wasmtime crate.

This section contains the compile-time features of the wasmtime crate. These features can be used to add more functionality and APIs exposed from the crate's API. Most of them are enabled by default. Disabling features can be done to cut down on binary size by disabling features that are not required for a particular embedding.

default = addr2line, async, cache, component-model, coredump, cranelift, debug-builtins, demangle, gc, gc-drc, gc-null, parallel-compilation, pooling-allocator, profiling, runtime, std, threads, wat

These default features are set whenever wasmtime is added without default-features = false somewhere in the dependency tree.

cranelift default = std

An on-by-default feature enabling runtime compilation of WebAssembly modules with the Cranelift compiler. Cranelift is the default compilation backend of Wasmtime. If disabled then WebAssembly modules can only be created from precompiled WebAssembly modules.

Enables wasmtime-cranelift

Affects serialization::append_compiler_info…

winch = std

Enables support for Winch, the WebAssembly baseline compiler. The Winch compiler strategy in Config will be available. It is currently in active development and shouldn't be used in production applications.

Enables wasmtime-winch

Affects serialization::append_compiler_info…

pulley all-arch? profile-pulley?

Enables support for Pulley, the WebAssembly interpreter. When paired with the cranelift feature, the compiler backends for the pulley32 and pulley64 targets will be available. When paired with the runtime feature, the Pulley interpreter will be built into the runtime and you can interpret WebAssembly modules that have been compiled to Pulley bytecode.

Affects profiling_agent::ProfilingAgent.register_interpreter…

incremental-cache = std

Enables support for incremental compilation cache to be enabled in Config.

Enables incremental-cache of optional wasmtime-cranelift

profiling default profile-pulley? = std

Enables support for profiling guest modules.

Enables fxprof-processed-profile ^0.6.0 and ittapi, serde_json and wasmtime-jit-debug, thread of rustix

parallel-compilation default = std

Enables parallel compilation of WebAssembly code.

Enables rayon

cache default = std

Enables support for automatic cache configuration to be enabled in Config.

Enables wasmtime-cache

async default component-model-async? = runtime

Enables support for "async stores" as well as defining host functions as async fn and calling functions asynchronously.

Enables wasmtime-fiber, async-trait and trait-variant, async of optional wasmtime-component-macro

Affects limits::ResourceLimiterAsync, gc_runtime::collect_async, pooling::InstanceLimits.total_stacks, pooling::PoolingInstanceAllocatorConfig.async_stack_keep_resident, allocator::InstanceAllocatorImpl.allocate_fiber_stack, allocator::InstanceAllocatorImpl.deallocate_fiber_stack, disabled::current_mask, enabled::current_mask, disabled::allow, disabled::ProtectionMask…

pooling-allocator default memory-protection-keys? = runtime, std

Enables support for the pooling instance allocation strategy

Affects config::PoolingAllocationConfig, gc_runtime::GcHeap.reset, disabled::is_supported, disabled::keys, vm::commit_pages, vm::decommit_pages, vm::commit_pages, vm::commit_pages, vm::decommit_pages, vm::commit_pages, vm::decommit_pages, disabled::allow, disabled::ProtectionMask…

all-arch = pulley

Enables support for all architectures in Cranelift, allowing cross-compilation using the wasmtime crate's API, notably the Engine::precompile_module function.

Enables all-arch of optional wasmtime-cranelift and optional wasmtime-winch

component-model default component-model-async? wave?

Enables in-progress support for the component model. Note that this feature is in-progress, buggy, and incomplete. This is primarily here for internal testing purposes.

Enables encoding_rs, semver, wasmtime-component-macro, and wasmtime-component-util, component-model of wasmtime-environ, optional wasmtime-cranelift, and optional wasmtime-winch

Affects allocator::InstanceAllocatorImpl.validate_component_impl, allocator::InstanceAllocator.validate_component, vm::component, vm::VMStore.component_calls, runtime::component…

wmemcheck = std

Enables wasmtime-wmemcheck, wmemcheck of wasmtime-environ, optional wasmtime-cranelift, and optional wasmtime-winch

trace-log

Enables detailed internal compiler logging via WASMTIME_LOG

Enables trace-log of optional wasmtime-cranelift

demangle default = std

Enables support for demangling WebAssembly function names at runtime in errors such as backtraces.

Enables demangle of wasmtime-environ

coredump default = runtime, std

Enable support for generating core dumps on traps.

Enables wasm-encoder ^0.228.0

debug-builtins default = std

Export some symbols from the final binary to assist in debugging Cranelift-generated code with native debuggers like GDB and LLDB.

Enables wasmtime-jit-debug

Affects vm::debug_builtins…

runtime default async coredump pooling-allocator

Enable support for executing compiled Wasm modules.

Enables mach2, memfd, psm, and cc, smallvec, wasmtime-asm-macros, wasmtime-jit-icache-coherence, wasmtime-slab, wasmtime-versioned-export-macros, and windows-sys, interp of pulley-interpreter, mm of rustix

Affects profiling_agent::ProfilingAgent.register_interpreter…

gc default gc-drc gc-null

Enable support for garbage collection-related things.

This Cargo feature is required to compile or run Wasm that uses any of the following Wasm proposals:

When a compiler Cargo feature (cranelift or winch) is enabled, this feature gates the ability to compile Wasm that uses those proposals.

When the runtime Cargo feature is enabled, this feature gates the ability to load and run Wasm that uses those proposals.

You can additionally configure which GC implementations are enabled via the gc-drc and gc-null features.

Enables gc of optional wasmtime-cranelift, wasmtime-environ, and optional wasmtime-winch

Affects gc_runtime::GcRuntime.new_gc_heap, pooling::InstanceLimits.total_gc_heaps, allocator::InstanceAllocatorImpl.allocate_gc_heap, allocator::InstanceAllocatorImpl.deallocate_gc_heap…

gc-drc default = gc

Enable the deferred reference counting garbage collector.

Enables gc-drc of optional wasmtime-cranelift, wasmtime-environ, and optional wasmtime-winch

gc-null default = gc

Enable the null garbage collector.

Enables gc-null of optional wasmtime-cranelift, wasmtime-environ, and optional wasmtime-winch

threads default = std

Enable runtime support for the WebAssembly threads proposal.

Enables threads of optional wasmtime-cranelift and optional wasmtime-winch

Affects memory::validate_atomic_addr…

addr2line default = std

Controls whether backtraces will attempt to parse DWARF information in WebAssembly modules and components to provide filenames and line numbers in stack traces.

Enables addr2line and gimli

Affects instantiate::SymbolizeContext…

std default addr2line cache component-model-async? coredump cranelift debug-builtins demangle incremental-cache? parallel-compilation pooling-allocator profiling threads winch? wmemcheck? = once_cell

Enables support for the Rust standard library, enabling APIs that require types and traits from Rust's std such as Path and Error.

Many features of the Wasmtime crate implicitly require this std feature. This will be automatically enabled if necessary.

Enables use-std of postcard, std of object and optional addr2line, std of pulley-interpreter, wasmtime-environ, wasmtime-math, and optional wasmtime-fiber

Affects serialization::detect_precompiled_file, mmap::open_file_for_mmap, mmap::open_file_for_mmap…

call-hook

Enables support for the Store::call_hook API which enables injecting custom logic around all entries/exits from WebAssembly. This has a slight performance cost for all host functions.

Affects async_::CallHookHandler…

memory-protection-keys = pooling-allocator

Enables support for "memory protection keys" which can be used in conjunction with the pooling allocator on x64 to compact linear memory allocations.

reexport-wasmparser

Enables a re-export of wasmparser, so that an embedder of Wasmtime can use exactly the version of the parser library that Wasmtime does. Sometimes this is necessary, e.g. to guarantee that there will not be any mismatches in which modules are accepted due to Wasm feature configuration or support levels.

Note that when this feature is enabled, the version of wasmparser that is re-exported is *not subject to semver*: we reserve the right to make patch releases of Wasmtime that bump the version of wasmparser used, and hence the version re-exported, in semver-incompatible ways. This is the tradeoff that the embedder needs to opt into: in order to stay exactly in sync with an internal detail of Wasmtime, the cost is visibility into potential internal version changes. This is why the re-export is guarded by a feature flag which is off by default.

wave = component-model

Enables instances of the traits defined in the wasm-wave crate, which provides a human-readable text format for component values.

Enables wasm-wave ^0.228.0

custom-virtual-memory

For platforms that Wasmtime does not have support for Wasmtime will disable the use of virtual memory by default, for example allocating linear memories with malloc instead. This feature can be used, for these platforms, to instead use a C API defined in wasmtime-platform.h instead.

For some more information see https://docs.wasmtime.dev/stability-platform-support.html#support-for-no_std

This feature is not necessary for supported platforms like Unix and Windows as virtual memory is always enabled there.

custom-native-signals

Same as custom-virtual-memory above, but for custom signal-handling APIs.

profile-pulley = profiling, pulley

Off-by-default support to profile the Pulley interpreter. This has a performance hit, even when not profiling, so it's disabled by default at compile time.

Enables profile of pulley-interpreter

component-model-async = async, component-model, std

Enables support for the Component Model Async ABI, along with future, stream, and error-context types.

Enables futures, component-model-async of optional wasmtime-component-macro

Affects vm::VMStore.component_async_store…

Features from optional dependencies

In crates that don't use the dep: syntax, optional dependencies automatically become Cargo features. These features may have been created by mistake, and this functionality may be removed in the future.

wat default
once_cell std