Re: [PATCH L-C v3 6/7] buildchroot-host: install qemu-static to support hybrid cross-compiles

[Cedric Hombourger <Cedric_Hombourger@mentor.com>]

On 11/8/19 8:14 AM, Jan Kiszka wrote:
> On 08.11.19 08:07, Cedric Hombourger wrote:
>> The Linux kernel has great support for cross-compiling the kernel image
>> and modules. There is however no support/mechanism for 
>> cross-compiling the
>> build tools from its "scripts" directory. While HOSTCC may be set to use
>> our cross-compiler, the kernel build infrasture would then try to run
>> foreign-arch binaries such as fixdep. The easiest and least intrusive 
>> way
>> to support this is to enable execution of such binaries via binfmt/qemu
>> like we do in the buildchroot-target environment.
>>
>> Signed-off-by: Cedric Hombourger <Cedric_Hombourger@mentor.com>
>> ---
>>   meta/recipes-devtools/buildchroot/buildchroot-host.bb | 6 ++++++
>>   1 file changed, 6 insertions(+)
>>
>> diff --git a/meta/recipes-devtools/buildchroot/buildchroot-host.bb 
>> b/meta/recipes-devtools/buildchroot/buildchroot-host.bb
>> index 408ad39..2e76acb 100644
>> --- a/meta/recipes-devtools/buildchroot/buildchroot-host.bb
>> +++ b/meta/recipes-devtools/buildchroot/buildchroot-host.bb
>> @@ -15,3 +15,9 @@ BUILDCHROOT_PREINSTALL ?= " \
>>       ${BUILDCHROOT_PREINSTALL_COMMON} \
>>       libc6:${DISTRO_ARCH} \
>>       crossbuild-essential-${DISTRO_ARCH}"
>> +
>> +buildchroot_install_files_append() {
>> +    if [ -e '/usr/bin/qemu-${QEMU_ARCH}-static' ]; then
>> +       sudo cp '/usr/bin/qemu-${QEMU_ARCH}-static' 
>> '${BUILDCHROOT_DIR}/usr/bin/qemu-${QEMU_ARCH}-static'
>> +    fi
>> +}
>>
>
> You didn't address my comment on this one. I doubt it's the right 
> approach.

More specifically?

I do have something in the works but we *still* need to build a 
linux-kernel-headers package for the target. there are two approaches: 
(1) use the Makefiles from the kernel and "simply" override HOSTCC but 
you then need qemu-static since the kernel will need to run some of its 
tools from "scripts/" (fixdep in particular) when it builds the other 
tools (e.g modpost) or (2) do like upstream manually cross-compile the 
tools.

The downside of (2) is that you need to know what to compile (list of .c 
files) and how to compile them. That "knowledge" may vary from one 
kernel to another.

I have local patches to produce a linux-kernel-headers-cross-amd64 
package which will ship headers in /usr/${DEB_HOST_GNU_TYPE} (i.e. next 
to libc headers) as well as kernel build tools for the build machine 
(typically amd64). This will allow us to cross-compile out-of-tree 
kernel modules without running any tools with a foreign-arch (for the 
avoidance of doubt, we still need qemu-user-static in buildchroot-host 
while building the kernel)

So with all that said, you are more than welcome to suggest a better 
approach....

>
> Jan
>