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Simplify the signalhandlers module (#854)

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* Remove the unused EnsureDarwinMachPorts function

When compiling the C++ shims for longjmp/setjmp/signal handling we don't
use the `USE_APPLE_MACH_PORTS` directive, so this function was entirely
unused anyway. This looks to be a holdover from when this was originally
copied from C++, but no need for keeping around this now-legacy
initialization.

* Remove the `wasmtime_init_finish` function

This looks like it's perhaps largely historical cruft at this point now
I think? The function, with the removal of the mach ports from the
previous commit, only reads the initializtion state of the signal
handlers. If the signal handlers failed to get installed, though, it
simply returns early rather than erroring out anyway. In any case a
follow-up commit will refactor `wasmtime_init_eager` to handle this as
well.

* Pare down `wasmtime_init_eager`

Similar to previous commits it looks like this function may have accrued
some debt over time, nowadays it doesn't really do much other than
capture a backtrace and install signal handlers. The `lazy_static` state
isn't really that necessary and we can rely on the `Once` primitive in
the standard library for one-time initialization.

This also updates the code to unconditionally panic if signal handlers
fail to get installed, which I think is the behavior that we'll want for
now and we can enhance it over time if necessary, but I don't think we
have a use case where it's currently necessary.
This commit is contained in:
Alex Crichton
2020-01-23 15:42:55 -06:00
committed by GitHub
parent 05d6c27142
commit 177af53578
5 changed files with 16 additions and 193 deletions
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56
crates/runtime/signalhandlers/SignalHandlers.cpp
View File

@@ -779,59 +779,3 @@ EnsureEagerSignalHandlers()
return true;
}
int
EnsureDarwinMachPorts()
{
#ifdef USE_APPLE_MACH_PORTS
pthread_attr_t handlerThreadAttr;
int r = pthread_attr_init(&handlerThreadAttr);
if (r != 0) {
return false;
}
// Create the port that all of our threads will redirect their traps to.
kern_return_t kret;
kret = mach_port_allocate(mach_task_self(), MACH_PORT_RIGHT_RECEIVE, &sMachDebugPort);
if (kret != KERN_SUCCESS) {
return false;
}
kret = mach_port_insert_right(mach_task_self(), sMachDebugPort, sMachDebugPort,
MACH_MSG_TYPE_MAKE_SEND);
if (kret != KERN_SUCCESS) {
return false;
}
// Create the thread that will wait on and service sMachDebugPort.
// It's not useful to destroy this thread on process shutdown so
// immediately detach on successful start.
pthread_t handlerThread;
r = pthread_create(&handlerThread, &handlerThreadAttr, MachExceptionHandlerThread, nullptr);
if (r != 0) {
return false;
}
r = pthread_detach(handlerThread);
assert(r == 0);
// In addition to the process-wide signal handler setup, OSX needs each
// thread configured to send its exceptions to sMachDebugPort. While there
// are also task-level (i.e. process-level) exception ports, those are
// "claimed" by breakpad and chaining Mach exceptions is dark magic that we
// avoid by instead intercepting exceptions at the thread level before they
// propagate to the process-level. This works because there are no other
// uses of thread-level exception ports.
assert(sMachDebugPort != MACH_PORT_NULL);
thread_port_t thisThread = mach_thread_self();
kret = thread_set_exception_ports(thisThread,
EXC_MASK_BAD_ACCESS | EXC_MASK_BAD_INSTRUCTION,
sMachDebugPort,
EXCEPTION_DEFAULT | MACH_EXCEPTION_CODES,
THREAD_STATE_NONE);
mach_port_deallocate(mach_task_self(), thisThread);
if (kret != KERN_SUCCESS) {
return false;
}
#endif
return true;
}