On Fri, Dec 2, 2022 at 4:44 PM Rick Edgecombe
[off-list ref] wrote:

So since 32 bit is not easy to support, and there are likely not many
users. More cleanly don't support 32 bit signals in a 64 bit address
space by not allowing 32 bit ABI signal handlers when shadow stack is
enabled. Do this by clearing any 32 bit ABI signal handlers when shadow
stack is enabled, and disallow any further 32 bit ABI signal handlers.
Also, return an error code for the clone operations when in a 32 bit
syscall.

This seems unfortunate.  The result will be a highly incomprehensible
crash.  Maybe instead deny enabling shadow stack in the first place?
Or at least pr_warn_once if anything gets flushed.