From: David Daney <ddaney.cavm@gmail.com>
To: "Maciej W. Rozycki" <macro@linux-mips.org>
Cc: Rich Felker <dalias@aerifal.cx>,
linux-mips@linux-mips.org, "Pinski,
Andrew" <Andrew.Pinski@caviumnetworks.com>
Subject: Re: 2GB userspace limitation in ABI N32
Date: Wed, 10 Oct 2012 10:34:21 -0700 [thread overview]
Message-ID: <5075B19D.4080701@gmail.com> (raw)
In-Reply-To: <alpine.LFD.2.02.1210101805410.21287@eddie.linux-mips.org>
On 10/10/2012 10:10 AM, Maciej W. Rozycki wrote:
> On Wed, 10 Oct 2012, David Daney wrote:
>
>> The only disadvantage of doing this is that the code will be slightly
>> larger/slower as it takes three instructions to load a zero extended 32-bit
>> pointer verses two for n32-2GB.
>
> And of course such code will only run on 64-bit processors that not only
> support 64-bit data, but 64-bit addressing as well.
That's right. All of this assumes a fully 64-bit operating system
kernel (Linux).
It is not really very interesting on 'small' systems that have less than
about 1GB of RAM. And obviously impossible if 64-bit addressing is not
supported.
So the interesting use cases are 'modern' systems with 4GB or more of
ram installed. And only then for the subset of applications that need
more than 2GB of virtual address space but will never need to consider
more than 4GB.
> That is implement the
> CP0.Status.UX bit rather than CP0.Status.PX only -- the latters are still
> compatible with the true n32 ABI. See also CP0.Config.AT.
>
> Maciej
>
>
next prev parent reply other threads:[~2012-10-10 17:34 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-10-10 6:32 2GB userspace limitation in ABI N32 Ronny Meeus
2012-10-10 8:07 ` Ralf Baechle
2012-10-10 12:57 ` Rich Felker
2012-10-10 16:56 ` David Daney
2012-10-10 17:10 ` Maciej W. Rozycki
2012-10-10 17:34 ` David Daney [this message]
2012-10-10 17:49 ` Ronny Meeus
2012-10-10 18:08 ` David Daney
2012-10-10 15:12 ` Ronny Meeus
2012-10-12 10:18 ` Ralf Baechle
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