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Re: 2GB userspace limitation in ABI N32

To: Ralf Baechle <>
Subject: Re: 2GB userspace limitation in ABI N32
From: Ronny Meeus <>
Date: Wed, 10 Oct 2012 17:12:16 +0200
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Do you have any clue (rough) on the amount of effort this change would cost?

About the limited gain we can discuss: if you have a large application
that has been created assuming 32bit and it needs to be ported to a
64bit architecture, I think the effort can be huge and the risk for
forgetting things is high. It will be very hard to check whether the
system behaves well under all conditions.


On Wed, Oct 10, 2012 at 10:07 AM, Ralf Baechle <> wrote:
> 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 -
>> 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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