[gnome-continuous-yocto/gnomeostree-3.28-rocko: 7191/8267] kernel.bbclass: improve reproducibility

[Emmanuele Bassi <ebassi src gnome org>]

commit 55e9485735ae8393b410f30973c785236dc402d2
Author: Juro Bystricky <juro bystricky intel com>
Date:   Wed Aug 9 10:48:32 2017 -0700

    kernel.bbclass: improve reproducibility
    
    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>

 meta/classes/kernel.bbclass |   39 ++++++++++++++++++++++++++++++++++++---
 1 files changed, 36 insertions(+), 3 deletions(-)
---
diff --git a/meta/classes/kernel.bbclass b/meta/classes/kernel.bbclass
index ce2cab6..2a76554 100644
--- a/meta/classes/kernel.bbclass
+++ b/meta/classes/kernel.bbclass
@@ -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