Re: [PATCH] kbuild: depmod: fallback to /boot/System.map-KERNELRELEASE

[Nicolas Schier]

On Fri, Oct 16, 2026 at 01:11:06PM +0200, Adrián García Casado wrote:
> When installing external modules (M=...) against packaged kernel headers
> such as linux-headers built via 'make bindeb-pkg', ${objtree}/System.map
> is absent because System.map is located in:
> /boot/System.map-${KERNELRELEASE}
> 
> Currently, scripts/depmod.sh only checks ${objtree}/System.map and skips
> running depmod with a warning, leaving newly installed out-of-tree
> modules unindexed in modules.dep.
> 
> Fall back to ${INSTALL_MOD_PATH}/boot/System.map-${KERNELRELEASE} when
> ${objtree}/System.map is not readable so that depmod runs properly
> during external module installation.
> 
> Signed-off-by: Adrián García Casado <adriangarciacasado42@xxxxxxxxx>
> ---
>  scripts/depmod.sh | 13 +++++++++----
>  1 file changed, 9 insertions(+), 4 deletions(-)
> 
> diff --git a/scripts/depmod.sh b/scripts/depmod.sh
> index 3c34fecac..d6d1b9547 100755
> --- a/scripts/depmod.sh
> +++ b/scripts/depmod.sh
> @@ -12,9 +12,14 @@ KERNELRELEASE=$1
>  
>  : ${DEPMOD:=depmod}
>  
> -if ! test -r "${objtree}/System.map" ; then
> -	echo "Warning: modules_install: missing 'System.map' file. Skipping depmod." >&2
> -	exit 0
> +system_map="${objtree}/System.map"
> +if ! test -r "${system_map}" ; then
> +	if test -r "${INSTALL_MOD_PATH}/boot/System.map-${KERNELRELEASE}" ; then
> +		system_map="${INSTALL_MOD_PATH}/boot/System.map-${KERNELRELEASE}"
> +	else
> +		echo "Warning: modules_install: missing 'System.map' file. Skipping depmod." >&2
> +		exit 0
> +	fi
>  fi
>  
>  # legacy behavior: "depmod" in /sbin, no /sbin in PATH
> @@ -25,7 +30,7 @@ if [ -z $(command -v $DEPMOD) ]; then
>  	exit 0
>  fi
>  
> -set -- -ae -F "${objtree}/System.map"
> +set -- -ae -F "${system_map}"
>  if test -n "$INSTALL_MOD_PATH"; then
>  	set -- "$@" -b "$INSTALL_MOD_PATH"
>  fi
> -- 
> 2.39.5
> 

Thanks for report and patch.

For the record, this is what I can find in Debian's Linux packages:

Debian puts a dummy System.map to /lib/modules/$(KERNELVER)/System.map 
(linux-image-$(KVER)-$(DEBVER)-$(ARCH).deb) and the real System.map is 
only available in linux-image-$(KVER)-$(DEBVER)-$(ARCH)-dbg package 
at /usr/lib/debug/lib/modules/$(KVER)-$(ARCH)/System.map.

So, do we need a valid System.map for out-of-tree modules?

At a first glance, you patch looks good to me.  But lets way some days 
for other feedback.

Kind regards,
Nicolas