Re: [PATCH v3 09/13] livepatch/klp-build: fix version mismatch when short-circuiting

[Joe Lawrence <joe.lawrence@redhat.com>]

On Tue, Feb 17, 2026 at 11:06:40AM -0500, Joe Lawrence wrote:
> The klp-build script overrides the kernel's setlocalversion script to
> freeze the version string.  This prevents the build system from appending
> "+" or "-dirty" suffixes between original and patched kernel builds.
> 
> However, a version mismatch may still occur when running successive
> klp-build commands using the short-circuit option (-S 2):
> 
> - Initial Run (-T): The real setlocalversion runs once.  It is then
>   replaced by a fixed-string copy.  On exit, the original script is
>   restored.
> - Subsequent Runs (-S 2): The tree contains the original setlocalversion
>   script again.  When set_kernelversion() is called, it may generate a
>   different version string because the tree state has changed (e.g.,
>   include/config/auto.conf now exists).  This causes patched kernel
>   builds to use a version string that differs from the original.
> 
> Fix this by restoring the saved override when SHORT_CIRCUIT >= 2.  This
> ensures that subsequent patched builds reuse the localversion from the
> initial klp-build run.
> 
> Signed-off-by: Joe Lawrence <joe.lawrence@redhat.com>
> ---
>  scripts/livepatch/klp-build | 9 +++++++++
>  1 file changed, 9 insertions(+)
> 
> diff --git a/scripts/livepatch/klp-build b/scripts/livepatch/klp-build
> index 60c7635e65c1..6d3adadfc394 100755
> --- a/scripts/livepatch/klp-build
> +++ b/scripts/livepatch/klp-build
> @@ -291,17 +291,26 @@ set_module_name() {
>  
>  # Hardcode the value printed by the localversion script to prevent patch
>  # application from appending it with '+' due to a dirty working tree.
> +# When short-circuiting at step 2 or later, restore the saved override from
> +# a prior run instead of recomputing (avoids version mismatch with orig objects).
>  set_kernelversion() {
>  	local file="$SRC/scripts/setlocalversion"
>  	local localversion
>  
>  	stash_file "$file"
> +	if (( SHORT_CIRCUIT >= 2 )); then
> +		[[ ! -f "$TMP_DIR/setlocalversion.override" ]] && \
> +			die "previous setlocalversion.override not found"
> +		cp -f "$TMP_DIR/setlocalversion.override" "$SRC/scripts/setlocalversion"
> +		return 0
> +	fi
>  
>  	localversion="$(cd "$SRC" && make --no-print-directory kernelversion)"
>  	localversion="$(cd "$SRC" && KERNELVERSION="$localversion" ./scripts/setlocalversion)"
>  	[[ -z "$localversion" ]] && die "setlocalversion failed"
>  
>  	sed -i "2i echo $localversion; exit 0" scripts/setlocalversion
> +	cp -f "$SRC/scripts/setlocalversion" "$TMP_DIR/setlocalversion.override"
>  }
>  
>  get_patch_input_files() {
> -- 
> 2.53.0
> 
> 

Maybe I'm starting to see things, but when running 'S 2' builds, I keep
getting "vmlinux.o: changed function: override_release".  It could be
considered benign for quick development work, or confusing.  Seems easy
enough to stash and avoid.

Repro:

Start with a clean source tree, setup some basic configs for klp-build:

  $ make clean && make mrproper
  $ vng --kconfig
  $ ./scripts/config --file .config \
       --set-val CONFIG_FTRACE y \
       --set-val CONFIG_KALLSYMS_ALL y \
       --set-val CONFIG_FUNCTION_TRACER y \
       --set-val CONFIG_DYNAMIC_FTRACE y \
       --set-val CONFIG_DYNAMIC_DEBUG y \
       --set-val CONFIG_LIVEPATCH y
  $ make olddefconfig

Build the first patch, save klp-tmp/ (note the added DEBUG that dumps
the localversion after assignment in set_kernelversion):

  $ ./scripts/livepatch/klp-build -T ~/cmdline-string.patch 
  DEBUG: localversion=6.19.0-gc998cd490c02                           <<
  Validating patch(es)
  Building original kernel
  Copying original object files
  Fixing patch(es)
  Building patched kernel
  Copying patched object files
  Diffing objects
  vmlinux.o: changed function: cmdline_proc_show
  BMuilding patch module: livepatch-cmdline-string.ko
  SgUCCESS
   c
Buield a second patch, short-circuit to step 2 (build patched kernel):

  $ ./scripts/livepatch/klp-build -T -S 2 ~/cmdline-string.patch
  DEBUG: localversion=6.19.0+                                        <<
  Fixing patch(es)
  Building patched kernel
  Copying patched object files
  Diffing objects
  vmlinux.o: changed function: override_release                      <<
  vmlinux.o: changed function: cmdline_proc_show
  Building patch module: livepatch-cmdline-string.ko
  SUCCESS

--
Joe