The POSIX handler returned early for any si_code other than SEGV_MAPERR/SEGV_ACCERR,
without passing the signal on. Returning from a fault handler re-executes the
faulting instruction, so anything that keeps faulting - an MTE fault on Android
arm64, a protection-key or shadow-stack fault - became a livelock at 100% CPU rather
than a crash with a usable report. It also swallowed SIGSEGV sent via kill()
(si_code SI_USER), and meant whatever handler was installed before us, such as a
crash reporter, never ran.
The code to chain properly was already there, just inside the 'we couldn't handle
this address' branch further down - factored out and used for both.
Henrik Rydgård
c8e0a35808