dev

Config knobs and validation for record-replay (#12375)

v41.0.1: Release Wasmtime 41.0.1 (#12434)

41.0.1

Released 2026-01-26.

Fixed

• Fixed a bug in lowering of f64.copysign on x86-64 whereby when combined
  with an f64.load, the resulting machine code could read 16 bytes rather
  than 8 bytes. This could result in a segfault when Wasmtime is configured
  without signals-based traps.

v40.0.3: Release Wasmtime 40.0.3 (#12433)

40.0.3

Released 2026-01-26.

Fixed

• Fixed a bug in lowering of f64.copysign on x86-64 whereby when combined
  with an f64.load, the resulting machine code could read 16 bytes rather
  than 8 bytes. This could result in a segfault when Wasmtime is configured
  without signals-based traps.

v36.0.5: Release Wasmtime 36.0.5 (#12432)

36.0.5

Released 2026-01-26.

Fixed

• Fixed a bug in lowering of f64.copysign on x86-64 whereby when combined
  with an f64.load, the resulting machine code could read 16 bytes rather
  than 8 bytes. This could result in a segfault when Wasmtime is configured
  without signals-based traps.

v41.0.0: Release Wasmtime 41.0.0 (#12373)

41.0.0

Released 2026-01-20.

Added

• Support for {Future,Stream}Any in the component model has improved.
  #12142

• Wasmtime has initial support for breakpoints and single-stepping with the
  debug feature for guest programs.
  #12133

• Wasmtime has begun adding a new Error type which is similar to
  anyhow::Error but supports gracefully handling OOM. Wasmtime still uses
  anyhow::Error but this will change in the future to wasmtime::Error which
  will be a distinct type.
  #12163

• An initial top-level crate for async-debugging guest programs has been added.
  #12183

Changed

• Cranelift now optimizes redundant select + icmp instructions.
  #12135

• Synchronous component model functions can no longer block before returning.
  This implements a change in the upstream specification to the upcoming async
  support in the component model which places stricter restrictions on
  non-async functions and their ability to perform blocking operations.
  #12043

• Frame iteration in debug mode now visits all activations which enables
  seeing all frames from recursive wasm calls.
  #12176

• Wasmtime now requires Rust 1.90.0 or later.
  #12167

• Intra-component stream/future reads/writes are now allowed for simple data
  types.
  #12181

• The POLL callback code has been removed from the canonical ABI for async
  functions and the waitable-set.poll function no longer yields.
  #12182

• Guest-to-guest adapters injected by Wasmtime now have improved trapping error
  messages.
  #12215

Fixed

• #[derive(Lift)] for enums with exactly 256 cases has been fixed.
  #12140

• With component-model-async support recursively calling a guest from a host
  function has now been fixed.
  #12152

v40.0.2: Release Wasmtime 40.0.2 (#12346)

40.0.2

Released 2026-01-14.

Fixed

• A possible stack overflow in the x64 backend with cmp emission has been
  fixed.
  #12333

• Some ISLE optimization rules which created erroneous IR for vector inputs have
  been fixed.
  #12179
  #12335

• The x64 lowering of shld has been fixed for some edge caxes.
  #12321

v39.0.2: Release Wasmtime 39.0.2 (#12347)

39.0.2

Released 2026-01-14.

Fixed

• A possible stack overflow in the x64 backend with cmp emission has been
  fixed.
  #12333

v36.0.4: Release Wasmtime 36.0.4 (#12348)

36.0.4

Released 2026-01-14.

Fixed

• A possible stack overflow in the x64 backend with cmp emission has been
  fixed.
  #12333

v40.0.1: Release Wasmtime 40.0.1 (#12271)

40.0.1

Released 2026-01-07.

Changed

• This release is a test of Wasmtime's CI-based crate publishing infrastructure.
  Wasmtime is switching to crates.io-based trusted publishing for this release
  and is testing that everything works.
  #12257

v40.0.0: Release Wasmtime 40.0.0 (#12192)

40.0.0

Released 2025-12-20.

Added

• WASIp3 support for wasi:http now implements Response::from_http to convert
  from standard Rust types to WASI types.
  #12063

• Cranelift now supports a "patchable" ABI which has a maximum number of
  arguments and clobbers no registers. This is paired as well with a new
  patchable_call instruction which supports being turned into NOPs at runtime.
  #12061
  #12101

Changed

• Support for the WebAssembly threads proposal is now classified as tier 2 by
  default. Additionally creation of SharedMemory is disabled by deafult behind
  a new config knob/CLI flag.
  #12036

• A variety of peephole-style optimizations have been added to Cranelift's
  optimization passes.
  #11994
  #11995
  #11996
  #11997
  #11998
  #11999
  #12000
  #12006
  #12008

• Component host functions have been slightly optimized to remove an Arc clone
  and reduce contention.
  #11987

• Support for component-model-async has been updated to account for the
  changes specified in WebAssembly/component-model#578.
  This means that historical binaries using WASIp3, for example, are no longer
  valid. Recompilation of historical components will be required and
  source-level changes may also be required in some circumstances.
  #12031
  #12043

• The UnsyncBoxBody type is now used everywhere in wasmtime-wasi-http instead
  of just in the wasip3 support.
  #12060

• Initial groundwork for gracefully handling OOM (e.g. returning an error
  instead of aborting) has been added.
  #12070
  #12089

• Wasmtime will create a private copy of code memory when guest debugging is
  enabled to assist with modifying code when adding/removing breakpoints.
  #12051

• The ResourceTable type will no longer use Tombstone when compiled in debug
  mode.
  #12114

• Intra-component future/stream reads/writes will now trap instead of
  accidentally being allowed.
  #12117

• Cranelift optimization rules have been tweaked after it was discovered that
  they could pessimize code containing long chains of computations.
  #12116

Fixed

• Compilation of i8x16.popcnt has been fixed in Winch for some potential
  inputs.
  #12010

• A panic in Instance::prepare_call for some component-model-async situations
  has been fixed.
  #12054

• An off-by-one error for lifting/lowering enums/variants with 255 cases has
  been fixed.
  #12066

• Restarting the read of a host future after cancellation has been fixed.
  #12093

• Compilation for OpenBSD on x86_64 has been fixed.
  #12097

• Components containing a module type which exoprts a tag are now supported.
  #12125