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

[Nathan Chancellor <nathan@kernel.org>]

On 2026-10-16 16:22 +0200, Nicolas Schier wrote:
> 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@gmail.com>
> > ---
> >  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?

Yeah, how does this work for the main Debian packages? Do they just not
expecte modules.dep to be generated for external modules if System.map
is not in a standard location? Or maybe nobody cares?

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

I don't have a particular opinion on this patch other than maybe this is
being patched in the wrong place? Perhaps we should be fixing this in
scripts/package/install-extmod-build? scripts/package/PKGBUILD copies
System.map to its external module build folder already.
scripts/package/kernel.spec copies it to /lib/modules/<rel>, not
/lib/modules/<rel>/build. Unifying those in in install-extmod-build
would avoid having to change it here (since /boot/System.map-<rel> seems
like a Debian-ism that we are hard coding here). I trust your judgement
though.

-- 
Cheers,
Nathan