[PATCH 0/7] Streamline arithmetic instruction emulation

Avi Kivity
2012-12-22T12:32:38Z

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.

Avi Kivity (7):
KVM: x86 emulator: framework for streamlining arithmetic opcodes
KVM: x86 emulator: Support for declaring single operand fastops
KVM: x86 emulator: introduce NoWrite flag
KVM: x86 emulator: mark CMP, CMPS, SCAS, TEST as NoWrite
KVM: x86 emulator: convert NOT, NEG to fastop
KVM: x86 emulator: add macros for defining 2-operand fastop emulation
KVM: x86 emulator: convert basic ALU ops to fastop

arch/x86/kvm/emulate.c | 215 +++++++++++++++++++++++++++----------------------
1 file changed, 120 insertions(+), 95 deletions(-)

--
1.7.11.7