linux-kernel - Re: [patch v2 2/4] x86, ptrace: regset extensions to support xstate

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Date:	Wed, 10 Feb 2010 16:43:33 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Suresh Siddha <suresh.b.siddha@...el.com>
Cc:	Roland McGrath <roland@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	LKML <linux-kernel@...r.kernel.org>, hjl.tools@...il.com
Subject: Re: [patch v2 2/4] x86, ptrace: regset extensions to support xstate

On 02/10, Oleg Nesterov wrote:
>
> On 02/09, Suresh Siddha wrote:
> >
> > +int xstateregs_get(struct task_struct *target, const struct user_regset *regset,
> > +		unsigned int pos, unsigned int count,
> > +		void *kbuf, void __user *ubuf)
> > +{
> > +	int ret;
> > +	int size = regset->n * regset->size;
> > +	struct xsave_hdr_struct *xsave_hdr =
> > +				&target->thread.xstate->xsave.xsave_hdr;
> > +
> > +	if (!cpu_has_xsave)
> > +		return -ENODEV;
> > +
> > +	ret = init_fpu(target);
> > +	if (ret)
> > +		return ret;
> > +
> > +	/*
> > +	 * First copy the fxsave bytes 0..463
> > +	 */
> > +	ret = user_regset_copyout(&pos, &count, &kbuf, &ubuf,
> > +				  &target->thread.xstate->xsave, 0,
> > +				  offsetof(struct i387_fxsave_struct,
> > +					   sw_reserved));
> > +	if (!ret)
> > +		/*
> > +		 * Copy the 48bytes defined by software
> > +		 */
> > +		ret = user_regset_copyout(&pos, &count, &kbuf, &ubuf,
> > +					  xstate_fx_sw_bytes,
> > +					  offsetof(struct i387_fxsave_struct,
> > +						   sw_reserved),
> > +					  offsetof(struct xsave_struct,
> > +						   xsave_hdr));
>
> Hmm. Suresh, could you confirm these offsetof's are correct?
>
> We are copying xstate_fx_sw_bytes array which is u64[6], but
> start_pos == sizeof(i387_fxsave_struct) - padding ?

Sorry for noise. Now I see this should be correct, see another email I sent.

In fact, unless I missed something again, the 2nd and 3rd _copyout's could
use pos as start_pos instead of offsetof(what_we_already_copied).

Oleg.

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