Simplify some trap handling in wasmtime runtime (#9673)

The `needs_backtrace` field on `TrapReason` is an old artifact of having
the `wasmtime` and `wasmtime-runtime` crates split and there's no longer
any need for that. This commit removes the field and directly queries it
from the error as necessary when capturing backtraces.

Author: alexcrichton

crates/wasmtime/src/runtime/component/func/host.rs

@@ -311,7 +311,7 @@ unsafe fn call_host_and_handle_result<T>(
 
     match res {
         Ok(()) => {}
-        Err(e) => crate::trap::raise(e),
+        Err(e) => crate::runtime::vm::raise_user_trap(e),
     }
 }
 

crates/wasmtime/src/runtime/func.rs

@@ -2371,7 +2371,7 @@ impl HostContext {
 
         match result {
             Ok(val) => val,
-            Err(err) => crate::trap::raise(err),
+            Err(err) => crate::runtime::vm::raise_user_trap(err),
         }
     }
 }

crates/wasmtime/src/runtime/trampoline/func.rs

@@ -61,7 +61,7 @@ unsafe extern "C" fn array_call_shim<F>(
         // call-site, which gets unwrapped in `Trap::from_runtime` later on as we
         // convert from the internal `Trap` type to our own `Trap` type in this
         // crate.
-        Err(trap) => crate::trap::raise(trap.into()),
+        Err(err) => crate::runtime::vm::raise_user_trap(err),
     }
 }
 

crates/wasmtime/src/runtime/trap.rs

@@ -68,13 +68,6 @@ use wasmtime_environ::{demangle_function_name, demangle_function_name_or_index,
 /// ```
 pub use wasmtime_environ::Trap;
 
-// Same safety requirements and caveats as
-// `crate::runtime::vm::raise_user_trap`.
-pub(crate) unsafe fn raise(error: anyhow::Error) -> ! {
-    let needs_backtrace = error.downcast_ref::<WasmBacktrace>().is_none();
-    crate::runtime::vm::raise_user_trap(error, needs_backtrace)
-}
-
 #[cold] // traps are exceptional, this helps move handling off the main path
 pub(crate) fn from_runtime_box(
     store: &mut StoreOpaque,
@@ -99,15 +92,7 @@ pub(crate) fn from_runtime_box(
         // provide useful information to debug with for the embedder/caller,
         // otherwise the information about what the wasm was doing when the
         // error was generated would be lost.
-        crate::runtime::vm::TrapReason::User {
-            error,
-            needs_backtrace,
-        } => {
-            debug_assert!(
-                needs_backtrace == backtrace.is_some() || !store.engine().config().wasm_backtrace
-            );
-            (error, None)
-        }
+        crate::runtime::vm::TrapReason::User(error) => (error, None),
         #[cfg(all(feature = "signals-based-traps", not(miri)))]
         crate::runtime::vm::TrapReason::Jit {
             pc,

crates/wasmtime/src/runtime/vm/component/libcalls.rs

@@ -132,10 +132,7 @@ mod trampolines {
                     match result {
                         Ok(ret) => shims!(@convert_ret ret $($pname: $param)*),
                         Err(err) => crate::runtime::vm::traphandlers::raise_trap(
-                            crate::runtime::vm::traphandlers::TrapReason::User {
-                                error: err,
-                                needs_backtrace: true,
-                            },
+                            crate::runtime::vm::traphandlers::TrapReason::User(err)
                         ),
                     }
                 }

crates/wasmtime/src/runtime/vm/libcalls.rs

@@ -199,12 +199,7 @@ fn memory32_grow(
     memory_index: u32,
 ) -> Result<*mut u8, TrapReason> {
     let memory_index = MemoryIndex::from_u32(memory_index);
-    let result = match instance
-        .memory_grow(store, memory_index, delta)
-        .map_err(|error| TrapReason::User {
-            error,
-            needs_backtrace: true,
-        })? {
+    let result = match instance.memory_grow(store, memory_index, delta)? {
         Some(size_in_bytes) => size_in_bytes / instance.memory_page_size(memory_index),
         None => usize::max_value(),
     };

crates/wasmtime/src/runtime/vm/traphandlers.rs

@@ -18,6 +18,7 @@ pub use self::signals::*;
 use crate::prelude::*;
 use crate::runtime::vm::sys::traphandlers;
 use crate::runtime::vm::{Instance, VMContext, VMRuntimeLimits};
+use crate::WasmBacktrace;
 use core::cell::{Cell, UnsafeCell};
 use core::mem::MaybeUninit;
 use core::ops::Range;
@@ -58,11 +59,8 @@ pub unsafe fn raise_trap(reason: TrapReason) -> ! {
 /// Only safe to call when wasm code is on the stack, aka `catch_traps` must
 /// have been previously called. Additionally no Rust destructors can be on the
 /// stack. They will be skipped and not executed.
-pub unsafe fn raise_user_trap(error: Error, needs_backtrace: bool) -> ! {
-    raise_trap(TrapReason::User {
-        error,
-        needs_backtrace,
-    })
+pub unsafe fn raise_user_trap(error: Error) -> ! {
+    raise_trap(TrapReason::User(error))
 }
 
 /// Invokes the closure `f` and returns the result.
@@ -113,12 +111,7 @@ pub struct Trap {
 #[derive(Debug)]
 pub enum TrapReason {
     /// A user-raised trap through `raise_user_trap`.
-    User {
-        /// The actual user trap error.
-        error: Error,
-        /// Whether we need to capture a backtrace for this error or not.
-        needs_backtrace: bool,
-    },
+    User(Error),
 
     /// A trap raised from Cranelift-generated code.
     #[cfg(all(feature = "signals-based-traps", not(miri)))]
@@ -150,17 +143,14 @@ pub enum TrapReason {
 
 impl TrapReason {
     /// Create a new `TrapReason::User` that does not have a backtrace yet.
-    pub fn user_without_backtrace(error: Error) -> Self {
-        TrapReason::User {
-            error,
-            needs_backtrace: true,
-        }
+    pub fn user(error: Error) -> Self {
+        TrapReason::User(error)
     }
 }
 
 impl From<Error> for TrapReason {
     fn from(err: Error) -> Self {
-        TrapReason::user_without_backtrace(err)
+        TrapReason::user(err)
     }
 }
 
@@ -359,7 +349,7 @@ impl CallThreadState {
     }
 
     fn unwind_with(&self, reason: UnwindReason) -> ! {
-        let (backtrace, coredump) = match reason {
+        let (backtrace, coredump) = match &reason {
             // Panics don't need backtraces. There is nowhere to attach the
             // hypothetical backtrace to and it doesn't really make sense to try
             // in the first place since this is a Rust problem rather than a
@@ -369,10 +359,11 @@ impl CallThreadState {
             // And if we are just propagating an existing trap that already has
             // a backtrace attached to it, then there is no need to capture a
             // new backtrace either.
-            UnwindReason::Trap(TrapReason::User {
-                needs_backtrace: false,
-                ..
-            }) => (None, None),
+            UnwindReason::Trap(TrapReason::User(err))
+                if err.downcast_ref::<WasmBacktrace>().is_some() =>
+            {
+                (None, None)
+            }
             UnwindReason::Trap(_) => (
                 self.capture_backtrace(self.limits, None),
                 self.capture_coredump(self.limits, None),