Re: [PATCH v3 0/7] Streamline arithmetic instruction emulation

Gleb Natapov
2013-01-08T11:38:40Z

On Fri, Jan 04, 2013 at 04:18:47PM +0200, Avi Kivity wrote:
> The current arithmetic instruction emulation is fairly clumsy: after
> decode, each instruction gets a switch (size), and for every size
> we fetch the operands, prepare flags, emulate the instruction, then store
> back the flags and operands.
>
> This patchset simplifies things by moving everything into common code
> except the instruction itself. All the pre- and post- processing is
> coded just once. The per-instrution code looks like:
>
> add %bl, %al
> ret
>
> add %bx, %ax
> ret
>
> add %ebx, %eax
> ret
>
> add %rbx, %rax
> ret
>
> The savings in size, for the ten instructions converted in this patchset,
> are fairly large:
>
> text data bss dec hex filename
> 63724 0 0 63724 f8ec arch/x86/kvm/emulate.o.before
> 61268 0 0 61268 ef54 arch/x86/kvm/emulate.o.after
>
> - around 2500 bytes.
>
> v3: fix reversed operand order in 2-operand macro
>
> v2: rebased
>
Acked-by: Gleb Natapov <gleb@redhat.com>

--
Gleb.