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

[Cedric Hombourger <cedric_hombourger@mentor.com>]

On 11/5/2019 3:52 PM, Jan Kiszka wrote:
> On 05.11.19 14:57, 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.
> What's the use case? Or why didn't we hit this issue so far?

when building with the kernel builddeb script, the linux-headers package 
will include scripts/basic/fixdep compiled for amd64 even though your 
target architecture is e.g. armhf

this went unnoticed because the kernel does not use debhelper and 
therefore does not benefit from the extra checks/stuff that it does

while migrating to custom build/packaging scripts using debhelper, that 
packaging mistake caused dpkg-buildpackage to fail

so things worked before by luck and also because nobody is actually 
doing on target development/builds (on non x86 machines that is). it is 
however desirable to have our linux-headers package for arch x (e.g. 
arm64) include arm64 binaries and not amd64

hope that makes more sense now

> Jan
>
>> 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
>> +}
>>