KVM: VMX: Let gcc to choose which registers to save (i386)
This patch lets GCC to determine which registers to save when we
switch to/from a VCPU in the case of intel i386.
* Original code saves following registers:
eax, ebx, ecx, edx, edi, esi, ebp (using popa)
* Patched code:
- informs GCC that we modify following registers
using the clobber description:
ebx, edi, rsi
- doesn't save eax because it is an output operand (vmx->fail)
- cannot put ecx 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)
- ebp is saved (pop/push) because GCC seems to ignore its use the clobber
description.
- edx is saved (pop/push) because it is reserved by GCC (REGPARM) and
cannot be put in the clobber description.
- line "mov (%%esp), %3 \n\t" has been removed because %3
is ecx and ecx is restored just after.
Signed-off-by: Laurent Vivier <Laurent.Vivier@bull.net>
Signed-off-by: Avi Kivity <avi@qumranet.com>
diff --git a/drivers/kvm/vmx.c b/drivers/kvm/vmx.c
index 56c9bcc..2d7d638 100644
--- a/drivers/kvm/vmx.c
+++ b/drivers/kvm/vmx.c
@@ -2268,7 +2268,8 @@
"push %%rdx; push %%rbp;"
"push %%rcx \n\t"
#else
- "pusha; push %%ecx \n\t"
+ "push %%edx; push %%ebp;"
+ "push %%ecx \n\t"
#endif
ASM_VMX_VMWRITE_RSP_RDX "\n\t"
/* Check if vmlaunch of vmresume is needed */
@@ -2342,9 +2343,8 @@
"mov %%ebp, %c[rbp](%3) \n\t"
"mov %%cr2, %%eax \n\t"
"mov %%eax, %c[cr2](%3) \n\t"
- "mov (%%esp), %3 \n\t"
- "pop %%ecx; popa \n\t"
+ "pop %%ecx; pop %%ebp; pop %%edx \n\t"
#endif
"setbe %0 \n\t"
: "=q" (vmx->fail)
@@ -2372,6 +2372,8 @@
#ifdef CONFIG_X86_64
, "rbx", "rdi", "rsi"
, "r8", "r9", "r10", "r11", "r12", "r13", "r14", "r15"
+#else
+ , "ebx", "edi", "rsi"
#endif
);