Re: 2GB userspace limitation in ABI N32
From: David Daney <hidden>
Date: 2012-10-10 18:09:04
On 10/10/2012 10:49 AM, Ronny Meeus wrote:
This is exactly the platform we are targeting: - a Cavium processor - running 64bit Linux - 4Gb of ram of which almost 3Gb will be used by 1 process (consisting of multiple threads) It would be really great that we could get help from you guys here.
As far as I know, we are not actively working on this. So, as I see it, your options are: A) Use n64. B) Do all the work yourself. C) Pay someone to do the work for you. David Daney
Many thanks for the effort you are putting into this. On Wed, Oct 10, 2012 at 7:34 PM, David Daney [off-list ref] wrote:quoted
On 10/10/2012 10:10 AM, Maciej W. Rozycki wrote:quoted
On Wed, 10 Oct 2012, David Daney wrote:quoted
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.quoted
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