linux-kernel - Re: RFD: x32 ABI system call numbers

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Date:	Wed, 31 Aug 2011 09:25:25 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Arnd Bergmann <arnd@...db.de>
CC:	Christoph Hellwig <hch@...radead.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>,
	"H.J. Lu" <hjl.tools@...il.com>, Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	Richard Kuo <rkuo@...eaurora.org>,
	Mark Salter <msalter@...hat.com>,
	Jonas Bonn <jonas@...thpole.se>,
	Tobias Klauser <tklauser@...tanz.ch>
Subject: Re: RFD: x32 ABI system call numbers

On 08/31/2011 09:14 AM, Arnd Bergmann wrote:
> 
> Ok, but I think we do need to consider the potential problems in this.
> I would expect a number of things to break if we just define it to
> 'long long' on new architectures, including:
> 
> * pre-c99 C compilers or programs that rely on --std=c89

This is a very long time ago by now.  Pre-C99 compilers without the long
long extension probably don't exist for these new architectures;
applications is a little bit messier, but still.

> * padding in struct timespec when you have a long long tv_sec and
>   32-bit long tv_nsec. This might cause kernel stack data leakage
>   in some kernel interfaces when they don't clear the padding.

Don't to that then.  For what it's worth, I think we currently use the
same size for both fields.

> * random broken applications assuming that timespec/timeval has
>   two 'long' members, instead of using the proper header files.
> 
> Obviously these are all fixable for any new ABI, but will cause
> some annoyance.
> 
> I've added a few people to Cc who are in various stages of the
> process to finalize their upstream kernel ports. It's clearly
> the right decision to have time_t 64-bit eventually, the question
> is how much work is everyone willing to spend in the short run,
> and who is going to test it. In particular, openrisc has just
> been merged, so we should not be changing it any more unless
> there is a serious problem, but if there is not much legacy user
> space with the current ABI yet, it may still be worth switching
> over.

Either way, all of this applies to x32 even more, sadly.

The other thing is that we probably need to do is to set a date when we
redefine legacy 32-bit time_t to be unsigned.  A good time might be some
time around (time_t)0x60000000 = Thu Jan 14 08:25:36 UTC 2021 if not sooner.

	-hpa
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