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

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Date:	Wed, 10 Feb 2010 15:18:36 +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

static inline int user_regset_copyout(unsigned int *pos, unsigned int *count,
				      void **kbuf,
				      void __user **ubuf, const void *data,
				      const int start_pos, const int end_pos)
{
	if (*count == 0)
		return 0;
	BUG_ON(*pos < start_pos);
	if (end_pos < 0 || *pos < end_pos) {
		unsigned int copy = (end_pos < 0 ? *count
				     : min(*count, end_pos - *pos));
		data += *pos - start_pos;
                            ^^^
Is it correct? Shouldn't it be

		data += *pos + start_pos;

?

Currently this doesn't matter, start_pos == 0 always. In fact I don't
understand why do we need this arg. In unlikely case the caller wants
to copy the part of *data, it can adjust data/end_pos itself.

Oleg.

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