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

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Date:   Fri, 22 Jan 2021 09:27:48 +0800
From:   Yejune Deng <yejune.deng@...il.com>
To:     Borislav Petkov <bp@...en8.de>
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 Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] x86/fpu/xstate: calculate the number by sizeof and offsetof

Thank you for your suggestion！

On Wed, Jan 20, 2021 at 6:22 PM Borislav Petkov <bp@...en8.de> wrote:
>
> 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