[poky] about ${KERNEL_CC} and ${CC}

[Gary Thomas]

On 12/23/2010 02:44 AM, Richard Purdie wrote:
> On Thu, 2010-12-23 at 14:11 +0800, Tian, Kevin wrote:
>> I'm a bit confused why a specific ${KERNEL_CC} is introduced instead of
>> reusing ${CC}, especially when two are defined differently:
>>
>> <kernel.bbclass>
>> KERNEL_CC = "${CCACHE}${HOST_PREFIX}gcc${KERNEL_CCSUFFIX} ${HOST_CC_KERNEL_ARCH}"
>>
>> <bitbake.conf>
>> export CC = "${CCACHE}${HOST_PREFIX}gcc ${HOST_CC_ARCH}${TOOLCHAIN_OPTIONS}"
>> TOOLCHAIN_OPTIONS = " --sysroot=${STAGING_DIR_TARGET}"
>>
>> I'm not sure whether kernel build requires "--sysroot" option, but it looks that it works well
>> so far even without that option (why?)
>
> The kernel doesn't link against system libraries or use system header
> files so it really doesn't matter whether it sees the sysroot or not.
>
> We use a different CC for the kernel so the user has the option of using
> a different compiler version for this. Whilst its a lot less common now,
> there were once use cases where the kernel would be compiled with one
> version of gcc and the userspace with a different version.
>
>> However this causes one issue under sstate, if the whole toolchain is installed from sstate
>> packages which are built from another machine. In such case the default path (decided at
>> compilation time) of gcc also points to the path on another machine, which is missing in
>> current machine doing build. Perf compilation is:
>>
>> do_compile_perf() {
>>          oe_runmake -C ${S}/tools/perf CC="${KERNEL_CC}" LD="${KERNEL_LD}" prefix=${prefix}
>> }
>>
>> Without an explicit "--sysroot" options, perf compilation is broken due to failing to check some
>> header files like gnu/libc-version.h. I can workaround it by:
>>
>> do_compile_perf() {
>>          oe_runmake -C ${S}/tools/perf CC="${CC}" LD="${LD}" AR="${AR}" prefix=${prefix}
>> }
>
> Perf should be compiled with the userspace toolchain, not the kernel
> one. I'd say this fix is therefore correct.
>
> Adding TOOLCHAIN_OPTIONS to KERNEL_CC would also probably be a good idea
> too.

Perfect idea!  I added this and I'm now able to rebuild my
kernel package using a sstate-cache based toolchain.  This
should close bug #605

Patch attached for review.

-- 
------------------------------------------------------------
Gary Thomas                 |  Consulting for the
MLB Associates              |    Embedded world
------------------------------------------------------------
-------------- next part --------------
An embedded and charset-unspecified text was scrubbed...
Name: 0001-Include-sysroot-in-KERNEL_CC-allows-tools-to-move.patch
URL: <http://lists.yoctoproject.org/pipermail/poky/attachments/20101223/9481c76f/attachment.ksh>