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Re: 2GB userspace limitation in ABI N32

To: Ronny Meeus <ronny.meeus@gmail.com>
Subject: Re: 2GB userspace limitation in ABI N32
From: Ralf Baechle <ralf@linux-mips.org>
Date: Wed, 10 Oct 2012 10:07:56 +0200
Cc: linux-mips@linux-mips.org
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On Wed, Oct 10, 2012 at 08:32:47AM +0200, Ronny Meeus wrote:

> I have a legacy application that we want to port to a MIPS (Cavium)
> architecture from a PPC based one.
> The board has 4GB memory of which we actually need almost 3GB in
> application space. On the PPC this is no issue since the split
> user/kernel is 3GB/1GB.
> We have to use the N32 ABI Initial tests on MIPS showed me the
> user-space limit of 2GB.
> We do not want to port the application to a 64bit
> 
> Now the question is: are there any workarounds, tricks existing to get
> around this limitation?
> I found some mailthreads on this subject (n32-big ABI -
> http://gcc.gnu.org/ml/gcc/2011-02/msg00278.html,
> http://elinux.org/images/1/1f/New-tricks-mips-linux.pdf) but is looks
> like this is not accepted by the community. Is there any process
> planned or made in this area?

I think limited time and gain killed the propoosed ABI rather than
theoretical issues raised.  Other architectures such as i386 - well,
IIRC any 32-bit ABI with more than 2GB userspace and a signed
ptrdiff_t - are suffering from them as well.

Also there's limited gain and even more limited time to implement things ...

  Ralf

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