For linux, page 0 is mapped as an execute-only gateway.  A gateway
page is a special bit in the page table that allows a B,GATE insn
within that page to raise processor permissions.  This is how system
calls are implemented for HPPA.

Rather than actually map anything here, or handle permissions at all,
implement the semantics of the actual linux syscall entry points.
Signed-off-by: NRichard Henderson <rth@twiddle.net>

Signed-off-by: NRichard Henderson <rth@twiddle.net>

Signed-off-by: NRichard Henderson <rth@twiddle.net>

The HPPA cpu has a unique form of predicated execution in which
almost any instruction can set the PSW[N] (or "nullify") bit,
which suppresses execution (and even decoding) of the following
instruction.  Execution of a nullified insn clears the PSW[N] bit.

This adds a generic framework for branching over nullified insns,
or for sufficiently simple insns, transforming the writeback of
the result to a conditional move.  In the process, we want to be
able to represent PSW[N] as a TCG condition, which implies management
of the related tcg temps.
Signed-off-by: NRichard Henderson <rth@twiddle.net>

This is just about the minimum required to enable compilation
without actually executing any instructions.  This contains the
HPPACPU structure and the required callbacks, the gdbstub, the
basic translation loop, and a translate_one function that always
results in an illegal instruction.
Signed-off-by: NRichard Henderson <rth@twiddle.net>