From mboxrd@z Thu Jan 1 00:00:00 1970 From: Laurent Vivier Subject: Re: [PATCH/RFC] Let gcc to choose which registers to save Date: Mon, 22 Oct 2007 17:24:39 +0200 Message-ID: <471CC0B7.204@bull.net> References: <11930647183090-git-send-email-Laurent.Vivier@bull.net> <471CBD5D.9040506@qumranet.com> Mime-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Cc: kvm-devel To: Avi Kivity Return-path: In-Reply-To: <471CBD5D.9040506-atKUWr5tajBWk0Htik3J/w@public.gmane.org> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: kvm-devel-bounces-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org Errors-To: kvm-devel-bounces-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org List-Id: kvm.vger.kernel.org Avi Kivity a =E9crit : > Laurent Vivier wrote: >> As x86_64 ABI defines some registers saved by the calling function, it = >> is not >> needed to save all registers in the called function when switching to = >> VCPU. >> (see http://www.x86-64.org/documentation/abi.pdf, chapter 3.2.1) >> >> The best way to do that is to inform GCC which registers we use and let >> it to save only needed registers. >> >> = > = > Strange, yesterday I started to do the same thing but dropped it after I = > got discouraged by reload errors from gcc. In french, we say "Les beaux esprits se rencontrent" (Voltaire) ;-) ("Great minds think alike") >> diff --git a/drivers/kvm/vmx.c b/drivers/kvm/vmx.c >> index 2c6b64a..d6c91ac 100644 >> --- a/drivers/kvm/vmx.c >> +++ b/drivers/kvm/vmx.c >> @@ -2243,16 +2243,12 @@ static void vmx_vcpu_run(struct kvm_vcpu = >> *vcpu, struct kvm_run *kvm_run) >> asm( >> /* Store host registers */ >> #ifdef CONFIG_X86_64 >> - "push %%rax; push %%rbx; push %%rdx;" >> - "push %%rsi; push %%rdi; push %%rbp;" >> - "push %%r8; push %%r9; push %%r10; push %%r11;" >> - "push %%r12; push %%r13; push %%r14; push %%r15;" >> + "push %%rdx; push %%rbp;" >> "push %%rcx \n\t" >> - ASM_VMX_VMWRITE_RSP_RDX "\n\t" >> #else >> "pusha; push %%ecx \n\t" >> - ASM_VMX_VMWRITE_RSP_RDX "\n\t" >> #endif >> + ASM_VMX_VMWRITE_RSP_RDX "\n\t" >> /* Check if vmlaunch of vmresume is needed */ >> "cmp $0, %1 \n\t" >> /* Load guest registers. Don't clobber flags. */ >> @@ -2311,12 +2307,8 @@ static void vmx_vcpu_run(struct kvm_vcpu *vcpu, = >> struct kvm_run *kvm_run) >> "mov %%r15, %c[r15](%3) \n\t" >> "mov %%cr2, %%rax \n\t" >> "mov %%rax, %c[cr2](%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" >> + "pop %%rcx; pop %%rbp; pop %%rdx \n\t" >> #else >> "xchg %3, (%%esp) \n\t" >> "mov %%eax, %c[rax](%3) \n\t" >> @@ -2354,7 +2346,12 @@ static void vmx_vcpu_run(struct kvm_vcpu *vcpu, = >> struct kvm_run *kvm_run) >> [r15]"i"(offsetof(struct kvm_vcpu, regs[VCPU_REGS_R15])), >> #endif >> [cr2]"i"(offsetof(struct kvm_vcpu, cr2)) >> - : "cc", "memory"); >> + : "cc", "memory", >> +#ifdef CONFIG_X86_64 >> + "rbx", "rdi", "rsi", >> + "r8", "r9", "r10", "r11", "r12", "r13", "r14", "r15" >> +#endif >> + ); >> = > = > The comma after "memory" worries me. Can you compile-test on i386? You're right, I thought I've corrected this. I rework this and test on i386. > Other than that the patch is very welcome -- the excessive register = > saving is very annoying to me. I think we can do the same thing with svm.c, but I can't test it. Regards, Laurent -- = ---------------- Laurent.Vivier-6ktuUTfB/bM@public.gmane.org ----------------- "Given enough eyeballs, all bugs are shallow" E. S. Raymond ------------------------------------------------------------------------- This SF.net email is sponsored by: Splunk Inc. Still grepping through log files to find problems? Stop. Now Search log events and configuration files using AJAX and a browser. Download your FREE copy of Splunk now >> http://get.splunk.com/