Re: kernel: fix hv tools build for arm64 when cross-built

[Wei Liu <wei.liu@kernel.org>]

On Mon, Dec 09, 2024 at 12:30:35AM -0800, Saurabh Singh Sengar wrote:
> On Mon, Dec 09, 2024 at 12:44:22AM +0000, Wei Liu wrote:
> > On Wed, Oct 23, 2024 at 02:01:12PM +0000, Adrian Vladu wrote:
> > > Hello,
> > > 
> > > While trying to build the LIS daemons for Flatcar Container Linux for
> > > ARM64 (https://www.flatcar.org/), as we are doing Gentoo based
> > > cross-building from X64 boxes, there was an error while building those
> > > daemons, because the cross-compile scenario was not working, as ` ARCH
> > > := $(shell uname -m 2>/dev/null)` always returns `x86_64`.
> > > 
> > > I have a working patch for the Linux kernel here that was already
> > > applied in the Flatcar context and it works:
> > > https://github.com/flatcar/scripts/blob/94b1df1b19449eb5aa967fd48ba4c1f4a6d5f415/sdk_container/src/third_party/coreos-overlay/sys-kernel/coreos-sources/files/6.10/z0008-tools-hv-fix-cross-compilation-for-ARM64.patch
> > > 
> > > Raw patch link here:
> > > https://raw.githubusercontent.com/flatcar/scripts/94b1df1b19449eb5aa967fd48ba4c1f4a6d5f415/sdk_container/src/third_party/coreos-overlay/sys-kernel/coreos-sources/files/6.10/z0008-tools-hv-fix-cross-compilation-for-ARM64.patch
> > > 
> > > Sorry for the delivery method via github link, but I cannot send
> > > proper patches from my work email address currently, as the email
> > > server does not support it.
> > > 
> > > Please let me know if I need to send the patch via the recommended way
> > > or if the patch can be used directly.
> > > 
> > > Also, maybe there is a better way to address the cross-compilation
> > > issue, I just wanted to report the bug and also provide a possible
> > > fix.
> > 
> > Saurabh added the ARCH variable. He's CCed.
> > 
> > BTW I think your patch can be simplified by using
> >   ARCH ?= $(shell uname -m 2>/dev/null)
> > instead of the ifeq test in your patch.
> 
> Agree, this is better way to handle it.
> 
> > 
> > I don't think that's correct. ARCH will be set to the correct value by
> > Kbuild. 
> 
> If we build locally on ARM64, there is a chance that ARCH may not be set,
> leading to build failures for arm64. IMO we should provide a fallback
> option for local builds when ARCH is not set.

How do you build locally? Even if you build those tools in tools/hv, it
still uses the Kbuild system, which sets ARCH to the correct value,
right?

Thanks,
Wei.