Currently version.o is explicitly ignored as the file would change as a result
of the orignal and the patched build having possibly different dates, times or
changeset strings (by the patched build appending -dirty).

Fix such difference by exporting the date and time from the build script, so
that both builds share the same build time.  The changeset string gets set in
.scmversion, and is cleaned on script exit if it wasn't present initially. This
allows checking for changes in version.c, since the rest of fields need to be
manually changed in order to produce different output.

Setting XEN_BUILD_{DATE,TIME} as an environment variable and .scmversion has
been supported since before livepatch support was added to Xen, so it's safe to
export those variables unconditionally.

Reported-by: Andrew Cooper <andrew.cooper3@citrix.com>
Signed-off-by: Roger Pau Monné <roger.pau@citrix.com>
---
Changes since v1:
 - Also ensure consistent changeset version.
---
 livepatch-build | 14 ++++++++++++++
 livepatch-gcc   |  2 --
 2 files changed, 14 insertions(+), 2 deletions(-)

diff --git a/livepatch-build b/livepatch-build
index e2ccce4f7fd7..332d26f5c6b6 100755
--- a/livepatch-build
+++ b/livepatch-build
@@ -392,6 +392,10 @@ echo "Output directory: $outputarg"
 echo "================================================"
 echo
 
+cleanup_version() {
+    rm -rf "${SRCDIR}/xen/.scmversion"
+}
+
 if [ "${SKIP}" != "build" ]; then
     # Make sure output directory doesn't exist, and create it.
     [ -e "$outputarg" ] && die "Output directory exists"
@@ -417,6 +421,16 @@ if [ "${SKIP}" != "build" ]; then
 
     export CROSS_COMPILE="${TOOLSDIR}/livepatch-gcc "
 
+    # Force same date and time to prevent unwanted changes in version.c
+    export XEN_BUILD_DATE=`LC_ALL=C date`
+    export XEN_BUILD_TIME=`LC_ALL=C date +%T`
+
+    # Ensure uniform changeset between builds
+    if [ ! -e "${SRCDIR}/xen/.scmversion" ]; then
+        trap cleanup_version EXIT
+        echo "unavailable" > "${SRCDIR}/xen/.scmversion"
+    fi
+
     echo "Perform full initial build with ${CPUS} CPU(s)..."
     build_full
 
diff --git a/livepatch-gcc b/livepatch-gcc
index fcad80551aa0..e4cb6fb59029 100755
--- a/livepatch-gcc
+++ b/livepatch-gcc
@@ -33,7 +33,6 @@ if [[ "$TOOLCHAINCMD" =~ $GCC_RE ]] ; then
             obj=$2
             [[ $2 = */.tmp_*.o ]] && obj=${2/.tmp_/}
             case "$(basename $obj)" in
-            version.o|\
             debug.o|\
             check.o|\
             *.xen-syms.*.o|\
@@ -63,7 +62,6 @@ done
 elif [[ "$TOOLCHAINCMD" =~ $OBJCOPY_RE ]] ; then
     obj="${!#}"
     case "$(basename $obj)" in
-        version.o|\
         debug.o|\
         check.o|\
         boot.o|\

base-commit: 0ed8ef88dc300750696a64e89efa3b82502f6dc7
-- 
2.43.0

On Thu, Dec 14, 2023 at 8:54 AM Roger Pau Monne <roger.pau@citrix.com> wrote:
>
> Currently version.o is explicitly ignored as the file would change as a result
> of the orignal and the patched build having possibly different dates, times or
> changeset strings (by the patched build appending -dirty).
>
> Fix such difference by exporting the date and time from the build script, so
> that both builds share the same build time.  The changeset string gets set in
> .scmversion, and is cleaned on script exit if it wasn't present initially. This
> allows checking for changes in version.c, since the rest of fields need to be
> manually changed in order to produce different output.
>
> Setting XEN_BUILD_{DATE,TIME} as an environment variable and .scmversion has
> been supported since before livepatch support was added to Xen, so it's safe to
> export those variables unconditionally.
>
> Reported-by: Andrew Cooper <andrew.cooper3@citrix.com>
> Signed-off-by: Roger Pau Monné <roger.pau@citrix.com>
> ---
> Changes since v1:
>  - Also ensure consistent changeset version.
> ---
>  livepatch-build | 14 ++++++++++++++
>  livepatch-gcc   |  2 --
>  2 files changed, 14 insertions(+), 2 deletions(-)
>
> diff --git a/livepatch-build b/livepatch-build
> index e2ccce4f7fd7..332d26f5c6b6 100755
> --- a/livepatch-build
> +++ b/livepatch-build
> @@ -392,6 +392,10 @@ echo "Output directory: $outputarg"
>  echo "================================================"
>  echo
>
> +cleanup_version() {
> +    rm -rf "${SRCDIR}/xen/.scmversion"
> +}
> +
>  if [ "${SKIP}" != "build" ]; then
>      # Make sure output directory doesn't exist, and create it.
>      [ -e "$outputarg" ] && die "Output directory exists"
> @@ -417,6 +421,16 @@ if [ "${SKIP}" != "build" ]; then
>
>      export CROSS_COMPILE="${TOOLSDIR}/livepatch-gcc "
>
> +    # Force same date and time to prevent unwanted changes in version.c
> +    export XEN_BUILD_DATE=`LC_ALL=C date`
> +    export XEN_BUILD_TIME=`LC_ALL=C date +%T`
> +
> +    # Ensure uniform changeset between builds
> +    if [ ! -e "${SRCDIR}/xen/.scmversion" ]; then
> +        trap cleanup_version EXIT
> +        echo "unavailable" > "${SRCDIR}/xen/.scmversion"

Shouldn't this be "${SRCDIR}/.scmversion" since Xen runs
"$(srctree)/tools/scmversion $(XEN_ROOT)"?

Otherwise I still get spurious version.o changes...

With the 3 uses of that changed (can change during commit),

Reviewed-by: Ross Lagerwall <ross.lagerwall@citrix.com>

On Fri, Dec 15, 2023 at 11:47:18AM +0000, Ross Lagerwall wrote:
> On Thu, Dec 14, 2023 at 8:54 AM Roger Pau Monne <roger.pau@citrix.com> wrote:
> >
> > Currently version.o is explicitly ignored as the file would change as a result
> > of the orignal and the patched build having possibly different dates, times or
> > changeset strings (by the patched build appending -dirty).
> >
> > Fix such difference by exporting the date and time from the build script, so
> > that both builds share the same build time.  The changeset string gets set in
> > .scmversion, and is cleaned on script exit if it wasn't present initially. This
> > allows checking for changes in version.c, since the rest of fields need to be
> > manually changed in order to produce different output.
> >
> > Setting XEN_BUILD_{DATE,TIME} as an environment variable and .scmversion has
> > been supported since before livepatch support was added to Xen, so it's safe to
> > export those variables unconditionally.
> >
> > Reported-by: Andrew Cooper <andrew.cooper3@citrix.com>
> > Signed-off-by: Roger Pau Monné <roger.pau@citrix.com>
> > ---
> > Changes since v1:
> >  - Also ensure consistent changeset version.
> > ---
> >  livepatch-build | 14 ++++++++++++++
> >  livepatch-gcc   |  2 --
> >  2 files changed, 14 insertions(+), 2 deletions(-)
> >
> > diff --git a/livepatch-build b/livepatch-build
> > index e2ccce4f7fd7..332d26f5c6b6 100755
> > --- a/livepatch-build
> > +++ b/livepatch-build
> > @@ -392,6 +392,10 @@ echo "Output directory: $outputarg"
> >  echo "================================================"
> >  echo
> >
> > +cleanup_version() {
> > +    rm -rf "${SRCDIR}/xen/.scmversion"
> > +}
> > +
> >  if [ "${SKIP}" != "build" ]; then
> >      # Make sure output directory doesn't exist, and create it.
> >      [ -e "$outputarg" ] && die "Output directory exists"
> > @@ -417,6 +421,16 @@ if [ "${SKIP}" != "build" ]; then
> >
> >      export CROSS_COMPILE="${TOOLSDIR}/livepatch-gcc "
> >
> > +    # Force same date and time to prevent unwanted changes in version.c
> > +    export XEN_BUILD_DATE=`LC_ALL=C date`
> > +    export XEN_BUILD_TIME=`LC_ALL=C date +%T`
> > +
> > +    # Ensure uniform changeset between builds
> > +    if [ ! -e "${SRCDIR}/xen/.scmversion" ]; then
> > +        trap cleanup_version EXIT
> > +        echo "unavailable" > "${SRCDIR}/xen/.scmversion"
> 
> Shouldn't this be "${SRCDIR}/.scmversion" since Xen runs
> "$(srctree)/tools/scmversion $(XEN_ROOT)"?
> 
> Otherwise I still get spurious version.o changes...
> 
> With the 3 uses of that changed (can change during commit),
> 
> Reviewed-by: Ross Lagerwall <ross.lagerwall@citrix.com>

Great, I had a stale .scmversion in my Xen root and that's why I
wasn't seeing the path not being effective.

Please adjust on commit.

Thanks, Roger.