[yocto] x86_64 kernel with i586 userland plus SDK?

[richard.purdie at linuxfoundation.org]

On Mon, 2018-12-17 at 11:26 +0100, Richard Weinberger wrote:
> On Wed, Nov 28, 2018 at 9:42 AM Richard Purdie
> <richard.purdie at linuxfoundation.org> wrote:
> > The system can definitely do it, its just not something we tend to
> > do
> > very often so its not entirely clear the best way to do it.
> > 
> > What may work is selecting the i586 tune from an x64-64 target
> > machine?
> > 
> > Copying qemux86-64.conf to qemux86-64-2.conf and changing it to
> > have
> > DEFAULTTUNE ?= "i586" did appear to start to build at least in a
> > quick
> > test here...
> 
> I went this approach for now.
> That way I get i586 userland and an SDK with both 32bit and 64bit
> toolchains.
> The SDK offers me multiple environment files to include.
> 
> What I don't understand right now is, how can i tell the kernel
> recipe
> that it has
> to use the 64bit toolchain to build the kernel?
> 
> Any hints?

I think (but am going from memory) that the x86 toolchains can generate
64 and 32 bit code with the right compiler option. The kernel just
passes in the right options if configured to build as 64 bit even if it
has the 32 bit toolchain?

Cheers,

Richard