kernel-devicetree: Fix intermittent build failures caused by DTB builds

Fix a build-time race condition that resulted in intermittent build
failures in the do_assemble_fitimage task. The race condition involved
the do_assemble_fitimage task reading the vmlinux file while the
do_compile_kernelmodules task was re-writing the vmlinux file.

This can be seen with an aarch64 image build that uses a 5.4 based
kernel and sets KERNEL_DEVICETREE. The problem is that the do_compile
snippet that the kernel-devicetree class appends did not specify the
full kernel build environment when building the DTB(s) from the kernel
tree. This resulted in CONFIG_CC_CAN_LINK=y being removed from the
kernel config file just before the do_compile task completed. The
CONFIG_CC_CAN_LINK=y line was then re-inserted into the kernel config
file as part of the do_compile_kernelmodules task.

In some cases, this resulted in the do_compile_kernelmodules task to
re-link vmlinux which sometimes occured at the same time that the
do_assemble_fitimage task was attempting to use vmlinux. The
do_assemble_fitimage task would fail with the following error message:

 aarch64-poky-linux-objcopy:vmlinux: file format not recognized

We can use the pine-a64-lts machine, from the meta-pine64 layer, to show
that the kernel config file was changed between do_compile and
do_compile_kernelmodules:

 $ C=tmp/work/pine_a64_lts-poky-linux/linux-pine64/5.7+gitAUTOINC+ae03bade3b-r0/linux-pine_a64_lts-standard-build/.config
 $ bitbake -c do_kernel_configcheck virtual/kernel
 ...
 $ md5sum $C; grep CC_CAN_LINK $C
 32b133cf8a749a91f698a7ca8616c84f  ...
 CONFIG_CC_CAN_LINK=y

 $ bitbake -c do_compile virtual/kernel
 ...
 $ md5sum $C; grep CC_CAN_LINK $C
 2fd2ec2a66eecc329dcb5afaf005eada  ...

 $ bitbake -c do_compile_kernelmodules virtual/kernel
 ...
 $ md5sum $C; grep CC_CAN_LINK $C
 32b133cf8a749a91f698a7ca8616c84f  ...
 CONFIG_CC_CAN_LINK=y

With this change, the do_compile snippet appended by the
kernel-devicetree class does not modify the kernel config. The kernel
config is unchanged across the do_compile and do_compile_kernelmodules
tasks and do_compile_kernelmodules will not attempt to re-link vmlinux.

(From OE-Core rev: 74619de0277471f446bf7a719f4c445359c823f6)

Signed-off-by: Tyler Hicks <tyhicks@linux.microsoft.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta/classes/kernel-devicetree.bbclass

@@ -52,7 +52,7 @@ do_configure_append() {
 do_compile_append() {
 	for dtbf in ${KERNEL_DEVICETREE}; do
 		dtb=`normalize_dtb "$dtbf"`
-		oe_runmake $dtb
+		oe_runmake $dtb CC="${KERNEL_CC} $cc_extra " LD="${KERNEL_LD}" ${KERNEL_EXTRA_ARGS}
 	done
 }