linux-kernel - Re: [PATCH v3 4/4] x86, mpx: extend siginfo structure to include bound violation information

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Message-ID: <52E5BC03.3080207@zytor.com>
Date:	Sun, 26 Jan 2014 17:53:07 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Ren Qiaowei <qiaowei.ren@...el.com>,
	David Rientjes <rientjes@...gle.com>
CC:	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>, x86@...nel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 4/4] x86, mpx: extend siginfo structure to include
 bound violation information

On 01/26/2014 05:34 PM, Ren Qiaowei wrote:
>>
> I agree with you and we should suppress all the warnings as possible. If
> I use (unsgined long) to cast like the following code, what do you think
> about it? sizeof(long) will be 4 for 32-bit.
> 
>     info->si_lower = (void __user *)(unsigned long)
>         (xsave_buf->bndregs.bndregs[2*bndregno]);
>     info->si_upper = (void __user *)(unsigned long)
>     (~xsave_buf->bndregs.bndregs[2*bndregno+1]);
> 

That is the way it is usually done, yes.  Add a comment saying something
like:

	/* Note: the upper 32 bits are ignored in 32-bit mode. */

It is worth watching out a bit here, though, because you could be
running a 32-bit process on top of a 64-bit kernel.

	-hpa


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