Crate wasmtime_internal_unwinder 

Wasmtime unwinder.

⚠️ Warning ⚠️: this crate is an internal-only crate for the Wasmtime project and is not intended for general use. APIs are not strictly reviewed for safety and usage outside of Wasmtime may have bugs. If you’re interested in using this feel free to file an issue on the Wasmtime repository to start a discussion about doing so, but otherwise be aware that your usage of this crate is not supported.

wasmtime-unwinder

This crate implements an unwind info format, stack walking, and unwinding for Wasmtime. It includes logic that:

• Can walk the Wasmstack and visit each frame;
• Can find exception handlers using an efficient format serialized from Cranelift compilation metadata that can be mapped and used in-place from disk;
• Provides a “throw” helper that, when called from host code that has been invoked from Wasmcode, can find a handler; and a “resume” stub that can be invoked to transfer control to the corresponding handler.

Structs

ExceptionTable

ExceptionTable deserialized from a serialized slice.

ExceptionTableBuilder

Collector struct for exception handlers per call site.

Frame

A stack frame within a Wasm stack trace.

UnwindHost

If we have the above host-specific implementations, we can implement Unwind.

Enums

ThrowAction

Throw action to perform.

Constants

NEXT_OLDER_FP_FROM_FP_OFFSET

The offset of the saved old-FP value in a frame, from the location pointed to by a given FP.

NEXT_OLDER_SP_FROM_FP_OFFSET

The offset of the next older SP value, from the value of a given FP.

Traits

Unwind

Implementation necessary to unwind the stack, used by Backtrace.

Functions

assert_fp_is_aligned

Assert that the given fp is aligned as expected by the host platform’s implementation of the Cranelift tail-call ABI. Frame pointers are aligned if they’re aligned to twice the size of a pointer.

compute_throw_action^⚠

Implementation of stack-walking to find a handler.

get_next_older_pc_from_fp^⚠

Get the return address in the function at the next-older frame from the given FP.

get_stack_pointer

Get the current stack pointer (at the time this function is executing). This may be used to check, e.g., approximate space remaining on a stack, but cannot be relied upon for anything exact because the stack pointer from within this function is read and the frame is later popped.

resume_to_exception_handler^⚠

Resume execution at the given PC, SP, and FP, with the given payload values, according to the tail-call ABI’s exception scheme. Note that this scheme does not restore any other registers, so the given state is all that we need.

visit_frames^⚠

Walk through a contiguous sequence of Wasm frames starting with the frame at the given PC and FP and ending at trampoline_fp. This FP should correspond to that of a trampoline that was used to enter the Wasm code.