I am trying to build 64 bit kernel in 32 bit environment (RH EL5.1) I update .config to
Is this possible? I tried the following:


thanks,

Piotr

Yes, it's possible, but you must also set the compiler flag -m64.

As long as you understand that you cannot switch to 64bit RHEL this way.

I am not trying to switch to 64 bit RHEL. I am just trying to compile a kernel for another machine.

I have tried to add "-m64" to CFLAGS
in the top Makefile but it produced the same result.

In any case even without adding it I see it being added in some places:

But I guess it should be added to every gcc line. Not only in arch/x86_64

Anybody?

Piotr

tytus;

You are doing a cross compile, you have to run the make config, xconfig or menuconfig which ever
is your preference, and set it up for the arch you are going to build for.

then do make CROSS_COMPILE=X86_64-vmlinuz

this is from the Makefile in the top of the kernel src tree:

snip---

# Cross compiling and selecting different set of gcc/bin-utils
# ---------------------------------------------------------------------------
#
# When performing cross compilation for other architectures ARCH shall be set
# to the target architecture. (See arch/* for the possibilities).
# ARCH can be set during invocation of make:
# make ARCH=ia64
# Another way is to have ARCH set in the environment.
# The default ARCH is the host where make is executed.

# CROSS_COMPILE specify the prefix used for all executables used
# during compilation. Only gcc and related bin-utils executables
# are prefixed with $(CROSS_COMPILE).
# CROSS_COMPILE can be set on the command line
# make CROSS_COMPILE=ia64-linux-
# Alternatively CROSS_COMPILE can be set in the environment.
# Default value for CROSS_COMPILE is not to prefix executables
# Note: Some architectures assign CROSS_COMPILE in their arch/*/Makefile

snap ---

You also have to have the multi-lib gcc & g++ installed.

best of luck

rcb

Can you elaborate what do you mean by multi-lib gcc and how to get it/build it. Are you talking about building a new instance of gcc for target=x86_64-linux?

Appreciate your help


Piotr

Piotr

The multilib libraries are required in order to cross compile various arches
they include the neccesary lib's to compile a 64 bit app in a 32 bit environment
and 32 bit apps in a 64 bit environment.

In your case, assuming you are using gentoo distro

do "emerge --search multilib"

get the flavor's that match the versions of your native gcc and g++ stdc and stdc++

If you are going to upgrade your installed gcc & g++, you should
definitely read the Gentoo howto's on doing this it's a little more involved than
most other distro's, IMHO gentoo is not very developer friendly.
But that just me.
For development work I use Slackware 12.0 stripped to the bones, ie no cruft no
office no bells & whistles just Xfce4 and Eclipse and gedit.
For normal everyday stuff I use Ubuntu 8.041

Gentoo Manual http://www.gentoo.org/doc/en/handbook/index.xml

Gentoo programmers forum http://forums.gentoo.org/viewforum-f-8.html

good luck
Happy Hacking

rcb

Thanks rcb,

This solves the question on my Ubuntu box. Ubuntu provides gcc-multilib packages. Here is what I installed on this box (most of them pulled in because of dependencies):
g++-4.2-multilib (4.2.4-1ubuntu3)
gcc-4.2-multilib (4.2.4-1ubuntu3)
lib64gcc1 (1:4.2.4-1ubuntu3)
lib64gomp1 (4.2.4-1ubuntu3)
lib64stdc++6 (4.2.4-1ubuntu3)
libc6-amd64 (2.7-10ubuntu4)
libc6-dev-amd64 (2.7-10ubuntu4)

I was able to compile stock 2.6.18 kernel with this setup with the following command:
I did not need to anything to CROSS_COMPILE variable in the top Makefile.
Before compiling I run:
and changing processor type to "Generic X86_64"

However, RedHat does not seem to provide gcc multilib packages and RHEL5 is our official build environment. I wonder if anybody knows how to do this trick on RHEL5.

Any help greatly appreciated.

Piotr