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Re: MIPS64 status?

To: Matthew Dharm <mdharm@momenco.com>
Subject: Re: MIPS64 status?
From: Ralf Baechle <ralf@oss.sgi.com>
Date: Mon, 14 Jan 2002 15:05:54 -0800
Cc: linux-mips@oss.sgi.com
In-reply-to: <20020113211323.A7115@momenco.com>; from mdharm@momenco.com on Sun, Jan 13, 2002 at 09:13:23PM -0800
References: <20020113211323.A7115@momenco.com>
Sender: owner-linux-mips@oss.sgi.com
User-agent: Mutt/1.2.5i
On Sun, Jan 13, 2002 at 09:13:23PM -0800, Matthew Dharm wrote:

> As I understand it, 64-bit support is really two different things:  64-bit
> data path (i.e. unsigned long long) and 64-bit addressing (for more than 4G
> of RAM).

Right but due to the CPU architecture of pre-MIPS64 CPUs they always come
together unless the software does funny attempts at truncating OS support
to just 32-bit.  So the 32-bit kernel gives you none of the two, the mips64
kernel both.

> My understanding is that "MIPS64" generally refers to a kernel which
> supports a 64-bit data path, but we're still limited to 32-bit addressing.
> Is that correct?

MIPS64 is MIPS's MIPS64 processor architecture, mips64 is the 64-bit kernel.
That may sound like nitpicking but it's important to understand that both
are not the same.

> I suspect that this is very much a toolchain issue, as I don't think gcc
> will generate 64-bit addressing code.

Gcc is fine; the problem are binutils, that is as and ld.  As a result of
the gcc problems we don't have a 64-bit userspace either so all software
running on 64-bit kernels is currently old 32-bit software running in
compatibility mode.

  Ralf

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