linux-kernel - Re: [PATCH] x86/fpu/xstate: calculate the number by sizeof and offsetof

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Date:   Wed, 20 Jan 2021 11:22:38 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     Yejune Deng <yejune.deng@...il.com>
Cc:     tglx@...utronix.de, mingo@...hat.com, x86@...nel.org,
        hpa@...or.com, dave.hansen@...ux.intel.com, yu-cheng.yu@...el.com,
        tony.luck@...el.com, fenghua.yu@...el.com,
        kan.liang@...ux.intel.com, viro@...iv.linux.org.uk,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] x86/fpu/xstate: calculate the number by sizeof and
 offsetof

On Wed, Jan 20, 2021 at 02:44:15PM +0800, Yejune Deng wrote:
> In fpstate_sanitize_xstate(), use memset and offsetof instead of '= 0',
> and use sizeof instead of a constant.
> 
> Signed-off-by: Yejune Deng <yejune.deng@...il.com>
> ---
>  arch/x86/kernel/fpu/xstate.c | 10 +++-------
>  1 file changed, 3 insertions(+), 7 deletions(-)
> 
> diff --git a/arch/x86/kernel/fpu/xstate.c b/arch/x86/kernel/fpu/xstate.c
> index 5d8047441a0a..2e75630c86e9 100644
> --- a/arch/x86/kernel/fpu/xstate.c
> +++ b/arch/x86/kernel/fpu/xstate.c
> @@ -161,20 +161,16 @@ void fpstate_sanitize_xstate(struct fpu *fpu)
>  	 * FP is in init state
>  	 */
>  	if (!(xfeatures & XFEATURE_MASK_FP)) {
> +		memset(fx, 0, offsetof(struct fxregs_state, mxcsr));

I'd prefer the explicit zeroing instead of having to look at
fxregs_state and where the offset of mxcsr is.

> +		memset(fx->st_space, 0, sizeof(fx->st_space));

This is ok I guess.

>  		fx->cwd = 0x37f;
> -		fx->swd = 0;
> -		fx->twd = 0;
> -		fx->fop = 0;
> -		fx->rip = 0;
> -		fx->rdp = 0;
> -		memset(&fx->st_space[0], 0, 128);
>  	}
>  
>  	/*
>  	 * SSE is in init state
>  	 */
>  	if (!(xfeatures & XFEATURE_MASK_SSE))
> -		memset(&fx->xmm_space[0], 0, 256);
> +		memset(fx->xmm_space, 0, sizeof(fx->xmm_space));

This too.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette