linux-kernel - [PATCH 14/55] KVM: SVM: Let gcc to choose which registers to save (i386)

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Message-Id: <1198667160-22953-15-git-send-email-avi@qumranet.com>
Date:	Wed, 26 Dec 2007 13:05:19 +0200
From:	Avi Kivity <avi@...ranet.com>
To:	linux-kernel@...r.kernel.org, kvm-devel@...ts.sourceforge.net
Cc:	Laurent Vivier <Laurent.Vivier@...l.net>
Subject: [PATCH 14/55] KVM: SVM: Let gcc to choose which registers to save (i386)

From: Laurent Vivier <Laurent.Vivier@...l.net>

This patch lets GCC to determine which registers to save when we
switch to/from a VCPU in the case of AMD i386

* Original code saves following registers:

    ebx, ecx, edx, esi, edi, ebp

* Patched code:

  - informs GCC that we modify following registers
    using the clobber description:

    ebx, ecx, edx, esi, edi

  - rbp is saved (pop/push) because GCC seems to ignore its use in the clobber
    description.

Signed-off-by: Laurent Vivier <Laurent.Vivier@...l.net>
Signed-off-by: Avi Kivity <avi@...ranet.com>
---
 drivers/kvm/svm.c |    8 ++++----
 1 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/drivers/kvm/svm.c b/drivers/kvm/svm.c
index 1298bde..cdd4fd2 100644
--- a/drivers/kvm/svm.c
+++ b/drivers/kvm/svm.c
@@ -1501,8 +1501,7 @@ static void svm_vcpu_run(struct kvm_vcpu *vcpu, struct kvm_run *kvm_run)
 #ifdef CONFIG_X86_64
 		"push %%rbp; \n\t"
 #else
-		"push %%ebx; push %%ecx; push %%edx;"
-		"push %%esi; push %%edi; push %%ebp;"
+		"push %%ebp; \n\t"
 #endif
 
 #ifdef CONFIG_X86_64
@@ -1573,8 +1572,7 @@ static void svm_vcpu_run(struct kvm_vcpu *vcpu, struct kvm_run *kvm_run)
 		"mov %%edi, %c[rdi](%[svm]) \n\t"
 		"mov %%ebp, %c[rbp](%[svm]) \n\t"
 
-		"pop  %%ebp; pop  %%edi; pop  %%esi;"
-		"pop  %%edx; pop  %%ecx; pop  %%ebx; \n\t"
+		"pop  %%ebp; \n\t"
 #endif
 		:
 		: [svm]"a"(svm),
@@ -1599,6 +1597,8 @@ static void svm_vcpu_run(struct kvm_vcpu *vcpu, struct kvm_run *kvm_run)
 #ifdef CONFIG_X86_64
 		, "rbx", "rcx", "rdx", "rsi", "rdi"
 		, "r8", "r9", "r10", "r11" , "r12", "r13", "r14", "r15"
+#else
+		, "ebx", "ecx", "edx" , "esi", "edi"
 #endif
 		);
 
-- 
1.5.3.7

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