This commit adds support for the `prctl(PR_SET_SYSCALL_USER_DISPATCH)`
function in the Linux userspace emulator.
It is implemented as a fully host-independent function, by forcing
a SIGSYS early during syscall handling, if the PC is outside the
allowed range.
Since disabled SUD is indistinguishable from enabled SUD with
always-allowed region length == ~0, this encoding is used
instead of introducing a new flag.
Tested on [uglendix][1], will probably also apply to software like
tiny-wine, rpcsx, limbo, lazypoline, vicar, sysfail and endokernel,
to name a few.
[1]: https://sr.ht/~arusekk/uglendix
Signed-off-by: Arusekk <floss@arusekk.pl>
Message-ID: <20250711225226.14652-1-floss@arusekk.pl>
[rth: Split out is_vdso_sigreturn region matching and other minor tweaks.]
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
c8e5aed246