[PATCH 1/11] KVM: optimize inline assembly

Avi Kivity
2007-01-30T14:37:00Z

From: Ingo Molnar <mingo-X9Un+BFzKDI@public.gmane.org>

forms like "0(%rsp)" generate an instruction with an unnecessary one byte
displacement under certain circumstances. replace with the equivalent
"(%rsp)".

Signed-off-by: Avi Kivity <avi-atKUWr5tajBWk0Htik3J/w@public.gmane.org>

Index: linux-2.6/drivers/kvm/vmx.c
===================================================================
--- linux-2.6.orig/drivers/kvm/vmx.c
+++ linux-2.6/drivers/kvm/vmx.c
@@ -1784,10 +1784,10 @@ again:
"kvm_vmx_return: "
/* Save guest registers, load host registers, keep flags */
#ifdef CONFIG_X86_64
- "xchg %3, 0(%%rsp) \n\t"
+ "xchg %3, (%%rsp) \n\t"
"mov %%rax, %c[rax](%3) \n\t"
"mov %%rbx, %c[rbx](%3) \n\t"
- "pushq 0(%%rsp); popq %c[rcx](%3) \n\t"
+ "pushq (%%rsp); popq %c[rcx](%3) \n\t"
"mov %%rdx, %c[rdx](%3) \n\t"
"mov %%rsi, %c[rsi](%3) \n\t"
"mov %%rdi, %c[rdi](%3) \n\t"
@@ -1802,24 +1802,24 @@ again:
"mov %%r15, %c[r15](%3) \n\t"
"mov %%cr2, %%rax \n\t"
"mov %%rax, %c[cr2](%3) \n\t"
- "mov 0(%%rsp), %3 \n\t"
+ "mov (%%rsp), %3 \n\t"

"pop %%rcx; pop %%r15; pop %%r14; pop %%r13; pop %%r12;"
"pop %%r11; pop %%r10; pop %%r9; pop %%r8;"
"pop %%rbp; pop %%rdi; pop %%rsi;"
"pop %%rdx; pop %%rbx; pop %%rax \n\t"
#else
- "xchg %3, 0(%%esp) \n\t"
+ "xchg %3, (%%esp) \n\t"
"mov %%eax, %c[rax](%3) \n\t"
"mov %%ebx, %c[rbx](%3) \n\t"
- "pushl 0(%%esp); popl %c[rcx](%3) \n\t"
+ "pushl (%%esp); popl %c[rcx](%3) \n\t"
"mov %%edx, %c[rdx](%3) \n\t"
"mov %%esi, %c[rsi](%3) \n\t"
"mov %%edi, %c[rdi](%3) \n\t"
"mov %%ebp, %c[rbp](%3) \n\t"
"mov %%cr2, %%eax \n\t"
"mov %%eax, %c[cr2](%3) \n\t"
- "mov 0(%%esp), %3 \n\t"
+ "mov (%%esp), %3 \n\t"

"pop %%ecx; popa \n\t"
#endif