On Mon, Feb 05, 2018 at 09:37:10AM -0600, William Harrington wrote:
> On Mon, February 5, 2018 03:26, Thomas Seeling wrote:
> > Hallo,
> >
> >
> > I am unsure if it's possible to create a reliable 32-bit kernel with a
> > 64-bit LFS. I have a running LFS svn with the latest gcc but I have
> > other machines where I'm reluctant to upgrade everything so I
> > contemplated simply compiling the kernel on the LFS svn system and the
> > copy it over to feel good (although on a server machine for DNS I don't
> > expect a real threat from Meltdown or Spectre ...).
> >
> > Can I simply take my 32 bit .config, make and copy the resulting kernel
> > and modules? Or is there still a risk of 64-bit CPU instructions to slip
> > in which might break the older machine?
> >
> > Tschau...Thomas
>
> Hello Thomas,
>
> The kernel will be fine if building for a different target. It requires a
> Binutils and GCC that can build for the target. If multilib isn't disabled
> during Binutils and GCC with LFS, then it will be no problem and you can
> build a 32-bit kernel without issue. You can be confident it will run
> fine. I've built 32-bit kernels from 64-bit hosts and vice versa. The
> kernel build system will use the correct options for Binutils and GCC to
> build for 32-bit/64-bit.
>
In LFS we disable multilib. For the kernel, the easiest approach
used to be: build pass-1 binutils and gcc for the target, installing
them somewhere not on the normal path. Then cross compile, putting
the cross tools first on the PATH.
My memory is becoming hazy this year, I was going to mention
elfutils as a possible problem, but I believe the objtool changes
that require that are x86_64 only.
And I vaguely remember that make modules install used to use a
variant of the DESTDIR approach (a different variable name).
ĸen
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