[Reason077]

> "This blog doesn’t explain why their JIT thread needs to make illegal memory accesses instead of an explicit check."

Because explicit checks on every memory access (pointer dereference) makes Java significantly slower, even with compiler optimisations to remove redundant checks[1]. Memory protection is a fundamental, very useful, hardware feature and it's perfectly reasonable for user space language runtimes to take advantage of it.

Or, to put it another way, SIGSEGV has been a part of Unix-family OSes for decades. It works perfectly fine on Linux and Windows and there's no reason it shouldn't work on macOS.

[1] (Many years ago I worked on a cross-platform implementation of the Java runtime and wrote much of the threads and signal handling code. We had an option to enable explicit memory checks, which got us up and running faster on new platforms where the SIGSEGV handlers hadn't been written yet. From memory this made everything something like 30-50% slower, so it was definitely worthwhile to implement SIGSEGV handling. In our case SIGSEGV handlers were used both as part of the garbage collector/memory management and to implement Java's NullPointerException)