linux-kernel - Re: [PATCH 2/2] x86/kvm: Add output operand in vmx_handle_external

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Date:	Mon, 25 Jan 2016 09:05:04 -0600
From:	Josh Poimboeuf <jpoimboe@...hat.com>
To:	Chris J Arges <chris.j.arges@...onical.com>
Cc:	live-patching@...r.kernel.org, x86@...nel.org, pbonzini@...hat.com,
	gleb@...nel.org, tglx@...utronix.de, mingo@...hat.com,
	hpa@...or.com, kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] x86/kvm: Add output operand in
 vmx_handle_external_intr inline asm

On Fri, Jan 22, 2016 at 03:44:38PM -0600, Chris J Arges wrote:
> Stacktool generates the following warning:
>   stacktool: arch/x86/kvm/vmx.o: vmx_handle_external_intr()+0x67: call without frame pointer save/setup
> 
> By adding the stackpointer as an output operand, this patch ensures that a
> stack frame is created when CONFIG_FRAME_POINTER is enabled for the inline
> assmebly statement.
> 
> Signed-off-by: Chris J Arges <chris.j.arges@...onical.com>

Reviewed-by: Josh Poimboeuf <jpoimboe@...hat.com>

> ---
>  arch/x86/kvm/vmx.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
> index e2951b6..e153522 100644
> --- a/arch/x86/kvm/vmx.c
> +++ b/arch/x86/kvm/vmx.c
> @@ -8356,6 +8356,7 @@ static void vmx_complete_atomic_exit(struct vcpu_vmx *vmx)
>  static void vmx_handle_external_intr(struct kvm_vcpu *vcpu)
>  {
>  	u32 exit_intr_info = vmcs_read32(VM_EXIT_INTR_INFO);
> +	register void *__sp asm(_ASM_SP);
>  
>  	/*
>  	 * If external interrupt exists, IF bit is set in rflags/eflags on the
> @@ -8388,8 +8389,9 @@ static void vmx_handle_external_intr(struct kvm_vcpu *vcpu)
>  			"call *%[entry]\n\t"
>  			:
>  #ifdef CONFIG_X86_64
> -			[sp]"=&r"(tmp)
> +			[sp]"=&r"(tmp),
>  #endif
> +			"+r"(__sp)
>  			:
>  			[entry]"r"(entry),
>  			[ss]"i"(__KERNEL_DS),
> -- 
> 2.5.0
>