Acquiring a mutex during the Magenta kernel exception handler can cause deadlocks and races. This patch adds a checker that ensures that no mutexes are acquired during an interrupt context.
This checker looks good to me! I don't see any obvious problems, and i think we can land it into non-alpha (enabled by default) once reviewers' comments are addressed.
optin is for checkers for which we cannot make a good guess if the user wants those or not.
Can we make a guess by looking at the target triple in this case? If we can, then it should not go into optin, but rather auto-enabled on specific platform, similarly to how it works for eg. osx.
Indent slightly off.
To see if we're in an interrupt, take current LocationContext and see if its stack frame or a parent stack frame is for x86_exception_handler. I think you don't need a program state trait for that check - it's already in your location context - and checkBeginFunction()/checkEndFunction() can be removed. Also, as far as i remember (i may be wrong), AnalysisDeclContext will bring you the current top-level function declaration under analysis directly, without ascending the stack frames, if that's in fact all you need.
For exit-functions you'd still need a flag in the program state that says that there was an exit.
Probably a bool was intended. Also, this may be moved inside the assert body if not used anywhere else.
I'd suggest to use operator== for such cases because it's easier to read.