Finished First Pass

Mike McCarty Mike.McCarty at sbcglobal.net
Tue Feb 2 20:12:27 PST 2010


brown wrap wrote:

Congrats on completing the first pass!

[...]

> This is the paragraph I read that confused me about 32 and 64 bit machines

[...]

> This version of the book builds a 32-bit Linux system and requires an existing 32-bit version of of the
> kernel on the Intel/AMD x86 architecture. Adding capabilty for x86_64 systems is a major objective
> of a future version of LFS. Support for 64-bit systems and additional architectures can be found in the
> Cross-Compiled Linux From Scratch (CLFS) project at http://cross-lfs.org/view/svn/.

A machine which is both 32bit and 64bit capable is really
two different machines. It's analagous to a machine which
can run Intel instructions, and PPC instructions. One could
not hope to run that machine in PPC mode, using the PPC
tools, and build the object that it would boot and run in
Intel mode. One needs cross compile tools, that is, tools
intended to run on one architecture, and create objects to
run on another, different, architecture.

To put it another way, you have a machine which can execute
two distinct machine languages. You need tools written in
one machine language, and which produce programs written in
another machine language. The fact that the same silicon
can execute it is irrelevant, unless it can execute both
manchine languages at the same time. Since 32/64 bit
capable machines can't do that without horrible kludges
(like the 286 32 bit capable code which rebooted to execute
the BIOS calls, then rebooted back to 32 bit mode), you
need cross development tools.

Mike
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