KVM: VMX: Let gcc to choose which registers to save (x86_64)
This patch lets GCC to determine which registers to save when we switch to/from a VCPU in the case of intel x86_64. * Original code saves following registers: rax, rbx, rcx, rdx, rsi, rdi, rbp, r8, r9, r10, r11, r12, r13, r14, r15 * Patched code: - informs GCC that we modify following registers using the clobber description: rbx, rdi, rsi, r8, r9, r10, r11, r12, r13, r14, r15 - doesn't save rax because it is an output operand (vmx->fail) - cannot put rcx in clobber description because it is an input operand, but as we modify it and we want to keep its value (vcpu), we must save it (pop/push) - rbp is saved (pop/push) because GCC seems to ignore its use in the clobber description. - rdx is saved (pop/push) because it is reserved by GCC (REGPARM) and cannot be put in the clobber description. - line "mov (%%rsp), %3 \n\t" has been removed because %3 is rcx and rcx is restored just after. - line ASM_VMX_VMWRITE_RSP_RDX() is moved out of the ifdef/else/endif Signed-off-by: NLaurent Vivier <Laurent.Vivier@bull.net> Signed-off-by: NAvi Kivity <avi@qumranet.com>
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