wasmtime: Add a Config::native_unwind_info method

crates/fuzzing/src/generators/config.rs

@@ -172,7 +172,7 @@ impl Config {
  .wasm_simd(self.module_config.config.simd_enabled)
  .wasm_memory64(self.module_config.config.memory64_enabled)
  .wasm_threads(self.module_config.config.threads_enabled)
- .wasm_backtrace(self.wasmtime.wasm_backtraces)
+ .native_unwind_info(self.wasmtime.native_unwind_info)
  .cranelift_nan_canonicalization(self.wasmtime.canonicalize_nans)
  .cranelift_opt_level(self.wasmtime.opt_level.to_wasmtime())
  .consume_fuel(self.wasmtime.consume_fuel)
@@ -389,7 +389,7 @@ pub struct WasmtimeConfig {
  codegen: CodegenSettings,
  padding_between_functions: Option<u16>,
  generate_address_map: bool,
- wasm_backtraces: bool,
+ native_unwind_info: bool,
 }
 
 #[derive(Arbitrary, Clone, Debug, PartialEq, Eq, Hash)]

crates/wasmtime/src/config.rs

@@ -98,6 +98,7 @@ pub struct Config {
  pub(crate) features: WasmFeatures,
  pub(crate) wasm_backtrace: bool,
  pub(crate) wasm_backtrace_details_env_used: bool,
+ pub(crate) native_unwind_info: bool,
  #[cfg(feature = "async")]
  pub(crate) async_stack_size: usize,
  pub(crate) async_support: bool,
@@ -180,6 +181,7 @@ impl Config {
  max_wasm_stack: 512 * 1024,
  wasm_backtrace: true,
  wasm_backtrace_details_env_used: false,
+ native_unwind_info: true,
  features: WasmFeatures::default(),
  #[cfg(feature = "async")]
  async_stack_size: 2 << 20,
@@ -341,6 +343,8 @@ impl Config {
  ///
  /// When disabled, wasm backtrace details are ignored, and [`crate::Trap::trace()`]
  /// will always return `None`.
+ #[deprecated = "Backtraces will always be enabled in future Wasmtime releases; if this \
+ causes problems for you, please file an issue."]
  pub fn wasm_backtrace(&mut self, enable: bool) -> &mut Self {
  self.wasm_backtrace = enable;
  self
@@ -372,6 +376,24 @@ impl Config {
  self
  }
 
+ /// Configures whether to generate native unwind information
+ /// (e.g. `.eh_frame` on Linux).
+ ///
+ /// This configuration option only exists to help third-party stack
+ /// capturing mechanisms, such as the system's unwinder or the `backtrace`
+ /// crate, determine how to unwind through Wasm frames. It does not affect
+ /// whether Wasmtime can capture Wasm backtraces or not, or whether
+ /// [`Trap::trace`][crate::Trap::trace] returns `Some` or `None`.
+ ///
+ /// Note that native unwind information is always generated when targeting
+ /// Windows, since the Windows ABI requires it.
+ ///
+ /// This option defaults to `true`.
+ pub fn native_unwind_info(&mut self, enable: bool) -> &mut Self {
+ self.native_unwind_info = enable;
+ self
+ }
+
  /// Configures whether execution of WebAssembly will "consume fuel" to
  /// either halt or yield execution as desired.
  ///
@@ -1415,6 +1437,24 @@ impl Config {
  compiler.target(target.clone())?;
  }
 
+ if self.native_unwind_info ||
+ // Windows always needs unwind info, since it is part of the ABI.
+ self
+ .compiler_config
+ .target
+ .as_ref()
+ .map_or(cfg!(target_os = "windows"), |target| {
+ target.operating_system == target_lexicon::OperatingSystem::Windows
+ })
+ {
+ if !self
+ .compiler_config
+ .ensure_setting_unset_or_given("unwind_info", "true")
+ {
+ bail!("compiler option 'unwind_info' must be enabled profiling");
+ }
+ }
+
  // We require frame pointers for correct stack walking, which is safety
  // critical in the presence of reference types, and otherwise it is just
  // really bad developer experience to get wrong.
@@ -1423,18 +1463,6 @@ impl Config {
  .insert("preserve_frame_pointers".into(), "true".into());
 
  // check for incompatible compiler options and set required values
- if self.wasm_backtrace || self.features.reference_types {
- if !self
- .compiler_config
- .ensure_setting_unset_or_given("unwind_info", "true")
- {
- bail!("compiler option 'unwind_info' must be enabled when either 'backtraces' or 'reference types' are enabled");
- }
- } else {
- self.compiler_config
- .settings
- .insert("unwind_info".to_string(), "false".to_string());
- }
  if self.features.reference_types {
  if !self
  .compiler_config

crates/wasmtime/src/engine.rs

@@ -367,10 +367,9 @@ impl Engine {
  }
  }
 
- // If reference types or backtraces are enabled, we need unwind info. Otherwise, we
- // don't care.
+ // Windows requires unwind info as part of its ABI.
  "unwind_info" => {
- if self.config().wasm_backtrace || self.config().features.reference_types {
+ if self.target().operating_system == target_lexicon::OperatingSystem::Windows {
  *value == FlagValue::Bool(true)
  } else {
  return Ok(())
@@ -544,7 +543,6 @@ mod tests {
 
  use anyhow::Result;
  use tempfile::TempDir;
- use wasmtime_environ::FlagValue;
 
  #[test]
  fn cache_accounts_for_opt_level() -> Result<()> {
@@ -606,20 +604,4 @@ mod tests {
 
  Ok(())
  }
-
- #[test]
- #[cfg(compiler)]
- fn test_disable_backtraces() {
- let engine = Engine::new(
- Config::new()
- .wasm_backtrace(false)
- .wasm_reference_types(false),
- )
- .expect("failed to construct engine");
- assert_eq!(
- engine.compiler().flags().get("unwind_info"),
- Some(&FlagValue::Bool(false)),
- "unwind info should be disabled unless needed"
- );
- }
 }

tests/all/traps.rs

@@ -71,6 +71,7 @@ fn test_trap_trace() -> Result<()> {
 }
 
 #[test]
+#[allow(deprecated)]
 fn test_trap_backtrace_disabled() -> Result<()> {
  let mut config = Config::default();
  config.wasm_backtrace(false);