Re: how to enable -m64 on x86-linux for building ATLAS

[Brian Dessent <brian@dessent.net>]

Dennis Wassel wrote:

> I've been trying to compile the ATLAS library on an 32-bit Linux
> system with my self-compiled gcc 4.3.0, but this fails.
> It boils down to the ATLAS config utility noticing that I have a
> 64-bit processor and trying to compile some low-level stuff with -m64,
> which doesn't work because I have not compiled in 64-bit support. [I
> could force 32-bit mode, but I feel that 64-bit mode surely improves
> performance, which is what ATLAS is for in the first place]

You could build a cross compiler, but what would be the point?  You're
running a 32 bit operating system which means you can't run 64 bit
binaries, even if you have a processor capable of doing so.  The
resulting output would be totally useless.  As Andrew said it only works
in the other direction.

It is also possible to build a native gcc that supports -m64 on a 32 bit
host.  To do so requires first installing the 64 bit libc headers and
libraries in the appropriate places (normally done through your distro's
package manager) as well as an x86_64 binutils in the same prefix and
then using --enable-targets=all when configuring.  If you're not root
this will likely be impossible since you can't write to /usr/lib64 or
whatever, so you'll have to go with the cross-compiler method.  But
again, simply switching to a 64 bit operating system is what is actually
required here since then gcc will generate 64 bit binaries by default,
and you'll actually be able to run the resulting binary.

Brian