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SubjectRe: 64bit port
   Date: Sat, 01 May 1999 03:05:51 -0700
From: "H. Peter Anvin" <hpa@transmeta.com>

I don't know what you mean with "medium-low code model"; I guess if
it was up to me I'd say to heck with it, and waste 1/4294967296 of
the address space as a 4 GB "null pointer check region"...

I presume the only reason you want that is to run 32-bit
code/64-bit data or something like that (shades of DOS.)

It's an important code model which will satisfy the needs of %99 of
all applications, it puts all code and data of the executable in the
low 32-bits of the address space. It allows all function calls done
within the executable to be a single instruction, and all address
formation to be done in 2 instructions for all objects within the
executable... the 64-bit types are the same etc.

We compile the sparc64 Linux kernel itself using this code model for
those advantages. We used to use the medium-med code model (low
44-bit address space) and the difference in the generated code is
phenominal.

Later,
David S. Miller
davem@redhat.com

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