[yocto] x86_64 kernel with i586 userland plus SDK?

[Richard Weinberger]

Richard,

Am Montag, 17. Dezember 2018, 11:34:08 CET schrieb 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?

This was my hope, and this is also what I get when doing such builds manually.
Having a x86_64 gcc and building userspace with "-m32" appended.

Yocto seems to try a different approach.
When I use qemux86-64.conf with DEFAULTTUNE being "i586" it generates a 32bit
toolchain by default.

Build Configuration:
BB_VERSION           = "1.38.0"
BUILD_SYS            = "x86_64-linux"
NATIVELSBSTRING      = "universal"
TARGET_SYS           = "i686-poky-linux"
MACHINE              = "myqemux86-64"
DISTRO               = "poky"
DISTRO_VERSION       = "2.5.1"
TUNE_FEATURES        = "m32 i586"

What I need is a x86_64-poky-linux toolchain with -m32 set for everything except
kernel (and modules).

Thanks,
//richard

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