[OE-core] [PATCH] kernel.bbclass: fix SOURCE_DATE_EPOCH for non-git kernel builds

[Alex Kiernan]

On Sat, Mar 7, 2020 at 8:04 PM <christopher.w.clark at gmail.com> wrote:
>
> From: Christopher Clark <christopher.w.clark at gmail.com>
>
> Only use git to set SOURCE_DATE_EPOCH if ${S} is the top level of a git
> repository.
>
> Fixes the following errors with the prior logic when building a kernel
> that is not obtained from a git repository:
>
> 1. With TMPDIR set to a directory outside any git repository on a
> mounted filesystem, reproducible builds fail in do_compile with this git
> error:
>
>   fatal: not a git repository (or any parent up to mount point <abspath>)
>   Stopping at filesystem boundary (GIT_DISCOVERY_ACROSS_FILESYSTEM not set).
>
> aborting before the error handling logic.
>
> 2. With TMPDIR located within a subdirectory of a git repository, the
> SOURCE_DATE_EPOCH timestamp would be that of said repository rather than
> that of the kernel.
>
> Signed-off-by: Christopher Clark <christopher.w.clark at gmail.com>
> ---
>  meta/classes/kernel.bbclass | 12 ++++++++----
>  1 file changed, 8 insertions(+), 4 deletions(-)
>
> diff --git a/meta/classes/kernel.bbclass b/meta/classes/kernel.bbclass
> index 0eadd3efb8..2603f24709 100644
> --- a/meta/classes/kernel.bbclass
> +++ b/meta/classes/kernel.bbclass
> @@ -296,10 +296,14 @@ kernel_do_compile() {
>                 if [ "${SOURCE_DATE_EPOCH}" = "" -o "${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}
> +                       # This kernel dir is not necessarily a git repo and we
> +                       # must ensure that git does not incorrectly query a
> +                       # repository in a parent directory.
> +                       GIT_TOP=`git rev-parse --show-toplevel 2>/dev/null || echo ""`
> +                       if [ "${S}" = "${GIT_TOP}" ]; then

Will that work if ${S} isn't a canonical path?

> +                               SOURCE_DATE_EPOCH=`git log  -1 --pretty=%ct`
> +                       else
> +                               SOURCE_DATE_EPOCH="${REPRODUCIBLE_TIMESTAMP_ROOTFS}"
>                         fi
>                         cd $olddir
>                 fi

Would something like this resolve the problem (untested):

diff --git a/meta/classes/kernel.bbclass b/meta/classes/kernel.bbclass
index 0eadd3efb8d9..a17ca7adccca 100644
--- a/meta/classes/kernel.bbclass
+++ b/meta/classes/kernel.bbclass
@@ -294,14 +294,11 @@ kernel_do_compile() {
                # kernel sources do not use do_unpack, so
SOURCE_DATE_EPOCH may not
                # be set....
                if [ "${SOURCE_DATE_EPOCH}" = "" -o
"${SOURCE_DATE_EPOCH}" = "0" ]; then
-                       olddir=`pwd`
-                       cd ${S}
-                       SOURCE_DATE_EPOCH=`git log  -1 --pretty=%ct`
+                       SOURCE_DATE_EPOCH=`git --git-dir="${S}/.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`

--
Alex Kiernan