Found the solution: Boot into recovery mode Open Terminal csrutill disable That by itself is enough.

Even better solution, which doesn't involve disabling SIP: spctl developer-mode enable-terminal This is in a regular Terminal window, not in recovery mode. Next, go to System Preferences - Security & Privacy - Privacy, and scroll down till you see an entry for "Developer Tools". Authenticate, tick the checkbox next to Terminal, and done!

You can decode the nature of the FPU exception in the SIGILL handler by declaring the third argument of your sigaction handler as a struct ucontext*, and then decoding scp->uc_mcontext->__es.esr in your handler. This is the value of the ESR_ELx, Exception Syndrome Register (ELx) register. If its top 6 bits (EC) are 0b101100, then the signal was triggered by a trapping AArch64 FPU operation. If in that case bit 23 of that register (TFV) is also 1, then the register's lower 7 bits will match what the lower 7 bits of the fpsr register would have been in case trapping would have been disabled (i.e., the kind of FPU exception triggered by the instruction). See section D7.2.27 of the ARMv8 architecture manual for more information.