Hello,

Avid Wasmtime users in our Nginx embedding, we are facing an assertion failure when running it with Wasmtime on macos (x86 and arm64):

thread '<unnamed>' panicked at 'assertion failed: `(left == right)`
  left: `268435466`,
 right: `0`: failed to set thread exception port', crates/runtime/src/traphandlers/macos.rs:474:9

This assertion systematically fails with Wasmtime 8.0.1 (and probably earlier) to 11.0.1 when Nginx is configured with daemon on (which ends here in Nginx forking into a background process). It seems it occurs in our call to wasmtime_linker_instantiate after having initialized an engine and a single store.

Not forking the master process (daemon off) seems to be working fine, even in forked worker processes (managed by the master process in foreground); instances are created and behave as expected in the Nginx worker processes.
The assertion failure specifically occurs once the master process has forked itself into a background process with daemon on.

In summary:

• Works with daemon off: master process (foreground) -> wasmtime_linker_instantiate (temporary instance) -> fork() -> worker processes -> wasmtime_linker_instantiate (worker instances processing requests).
• Fails with daemon on: master process (foreground) -> fork() (background daemon) -> wasmtime_linker_instantiate (temporary instance) -> assertion failure, no instance created, and no chance to fork() into worker processes.

In the past we used to have a CI/CD pipeline with macos targets and Wasmtime used to work fine; but this CI/CD pipeline was taken down, and this bit us in the last few days. It seems like older macos work on Wasmtime has something to do with it, but I know nothing of the macos system interface...

So far the root cause of this assertion failure has eluded us; probably state that aren't being carried over to the forked process or something like this. Could someone shed some light on what may be at cause here?

Thanks!