Commits
Uros Bizjak committed 4b1e54786e4
KVM/x86: Use assembly instruction mnemonics instead of .byte streams
Recently the minimum required version of binutils was changed to 2.20,
which supports all VMX instruction mnemonics. The patch removes
all .byte #defines and uses real instruction mnemonics instead.
The compiler is now able to pass memory operand to the instruction,
so there is no need for memory clobber anymore. Also, the compiler
adds CC register clobber automatically to all extended asm clauses,
so the patch also removes explicit CC clobber.
The immediate benefit of the patch is removal of many unnecesary
register moves, resulting in 1434 saved bytes in vmx.o:
text data bss dec hex filename
151257 18246 8500 178003 2b753 vmx.o
152691 18246 8500 179437 2bced vmx-old.o
Some examples of improvement include removal of unneeded moves
of %rsp to %rax in front of invept and invvpid instructions:
a57e: b9 01 00 00 00 mov $0x1,%ecx
a583: 48 89 04 24 mov %rax,(%rsp)
a587: 48 89 e0 mov %rsp,%rax
a58a: 48 c7 44 24 08 00 00 movq $0x0,0x8(%rsp)
a591: 00 00
a593: 66 0f 38 80 08 invept (%rax),%rcx
to:
a45c: 48 89 04 24 mov %rax,(%rsp)
a460: b8 01 00 00 00 mov $0x1,%eax
a465: 48 c7 44 24 08 00 00 movq $0x0,0x8(%rsp)
a46c: 00 00
a46e: 66 0f 38 80 04 24 invept (%rsp),%rax
and the ability to use more optimal registers and memory operands
in the instruction:
8faa: 48 8b 44 24 28 mov 0x28(%rsp),%rax
8faf: 4c 89 c2 mov %r8,%rdx
8fb2: 0f 79 d0 vmwrite %rax,%rdx
to:
8e7c: 44 0f 79 44 24 28 vmwrite 0x28(%rsp),%r8
Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>