Re: AMD64: 64 bit kernel 32 bit userland - some pending questions

[Andi Kleen]

Thomas Glanzmann <sithglan@xxxxxxxxxxxxxxxxxxxx> writes:

> Hello everyone,
> I would like to use an AMD64 Opteron System with a 64 bit Linux Kernel,
> but a 32 bit userland (Debian Sarge). I have a few questions about this:

The main caveat is that iptables and ipsec need 64bit executables
to be set up. The rest should work.

> 
>         - Is it possible to give the userland 3Gbyte virtual address
>           space (default for 2.4 and 2.6).

The default is 4GB, but you can get 3GB by running it under linux32 --3gb

> But give the Kernel a 64 bit
>           virtual address space so that I get more than 1 Gbyte physical
>           Memory into LOWMEM - say I want 8 Gbyte - without using HIGHMEM

The 64bit kernel never uses highmem.

>         - What is the easiest way to build a 64 bit kernel on a 32 bit
>           Debian sarge. Are there crosscompiler packages available? Are
>           there any guides on this?

If all fails you can get a cross compiler from crosstool.
Then normal kernel compilation command with 

make ... ARCH=x86_64 CROSS_COMPILE=x86_64-linux-
 

-Andi
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