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kernel.bbclass: improve reproducibility

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Several tweaks to improve reproducibility:

1. If BUILD_REPRODUCIBLE_BINARIES == 1, set KBUILD_BUILD_TIMESTAMP
to a reproducible value. This is either a non-zero SOURCE_DATE_EPOCH, or the
value obtained from top entry of GIT repo, or (if there is no GIT repo)
fallback to REPRODUCIBLE_TIMESTAMP_ROOTFS as the last resort.
Also export KCONFIG_NOTIMESTAMP=1.

2. When compressing vmlinux.gz, use gzip "-n" option

3. Kernel and kernel modules contain hard coded paths referencing the host
build system. This is usually because the source code contains __FILE__
at some place. This prevents binary reproducibility. However, some compilers
allow remapping of the __FILE__ value. If we detect the compiler is capable
of doing this, we replace the source path $(S) part of __FILE__ by a string "/kernel-source".
For example:

​/data/master/build/tmp/work-shared/qemux86/kernel-source/drivers/media/v4l2-core/videobuf2-core.​c

will be replaced by a reproducible value:

/kernel-source/drivers/media/v4l2-core/videobuf2-core.c.

(From OE-Core rev: 012a70da7ae0617740cd0cf807d01c3cd912c823)

Signed-off-by: Juro Bystricky <juro.bystricky@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
This commit is contained in:
Juro Bystricky
2017-08-09 10:48:32 -07:00
committed by Richard Purdie
parent f3da1613c4
commit 55e9485735
1 changed files with 36 additions and 3 deletions
Download Patch File Download Diff File Expand all files Collapse all files

39
meta/classes/kernel.bbclass
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@@ -255,8 +255,39 @@ python do_devshell_prepend () {
addtask bundle_initramfs after do_install before do_deploy
get_cc_option () {
# Check if KERNEL_CC supports the option "file-prefix-map".
# This option allows us to build images with __FILE__ values that do not
# contain the host build path.
cc_option_supported=`${KERNEL_CC} -Q --help=joined | grep ffile-prefix-map`
cc_extra=""
if [ $cc_option_supported = "-ffile-prefix-map=<old=new>" ]; then
cc_extra=-ffile-prefix-map=${S}=/kernel-source/
fi
echo $cc_extra
}
kernel_do_compile() {
unset CFLAGS CPPFLAGS CXXFLAGS LDFLAGS MACHINE
if [ "$BUILD_REPRODUCIBLE_BINARIES" = "1" ]; then
# kernel sources do not use do_unpack, so SOURCE_DATE_EPOCH may not
# be set....
if [ "$SOURCE_DATE_EPOCH" = "0" ]; then
olddir=`pwd`
cd ${S}
SOURCE_DATE_EPOCH=`git log -1 --pretty=%ct`
# git repo not guaranteed, so fall back to REPRODUCIBLE_TIMESTAMP_ROOTFS
if [ $? -ne 0 ]; then
SOURCE_DATE_EPOCH=${REPRODUCIBLE_TIMESTAMP_ROOTFS}
fi
cd $olddir
fi
ts=`LC_ALL=C date -d @$SOURCE_DATE_EPOCH`
export KBUILD_BUILD_TIMESTAMP="$ts"
export KCONFIG_NOTIMESTAMP=1
bbnote "KBUILD_BUILD_TIMESTAMP: $ts"
fi
# The $use_alternate_initrd is only set from
# do_bundle_initramfs() This variable is specifically for the
# case where we are making a second pass at the kernel
@@ -270,20 +301,22 @@ kernel_do_compile() {
copy_initramfs
use_alternate_initrd=CONFIG_INITRAMFS_SOURCE=${B}/usr/${INITRAMFS_IMAGE_NAME}.cpio
fi
cc_extra=$(get_cc_option)
for typeformake in ${KERNEL_IMAGETYPE_FOR_MAKE} ; do
oe_runmake ${typeformake} CC="${KERNEL_CC}" LD="${KERNEL_LD}" ${KERNEL_EXTRA_ARGS} $use_alternate_initrd
oe_runmake ${typeformake} CC="${KERNEL_CC} $cc_extra " LD="${KERNEL_LD}" ${KERNEL_EXTRA_ARGS} $use_alternate_initrd
done
# vmlinux.gz is not built by kernel
if (echo "${KERNEL_IMAGETYPES}" | grep -wq "vmlinux\.gz"); then
mkdir -p "${KERNEL_OUTPUT_DIR}"
gzip -9c < ${B}/vmlinux > "${KERNEL_OUTPUT_DIR}/vmlinux.gz"
gzip -9cn < ${B}/vmlinux > "${KERNEL_OUTPUT_DIR}/vmlinux.gz"
fi
}
do_compile_kernelmodules() {
unset CFLAGS CPPFLAGS CXXFLAGS LDFLAGS MACHINE
if (grep -q -i -e '^CONFIG_MODULES=y$' ${B}/.config); then
oe_runmake -C ${B} ${PARALLEL_MAKE} modules CC="${KERNEL_CC}" LD="${KERNEL_LD}" ${KERNEL_EXTRA_ARGS}
cc_extra=$(get_cc_option)
oe_runmake -C ${B} ${PARALLEL_MAKE} modules CC="${KERNEL_CC} $cc_extra " LD="${KERNEL_LD}" ${KERNEL_EXTRA_ARGS}
# Module.symvers gets updated during the
# building of the kernel modules. We need to