Re: [PATCH] modutils: prevent "Invalid ELF header magic" warning

On Sat, Jul 25, 2026 at 12:24:12PM +0200, S=F6ren Tempel via busybox wrote:
> This patch has the minor caveat that it causes modprobe to no longer
> load uncomprossed modules, which do not have a .ko filename suffix via
> finit_module, iff. CONFIG_DECOMPRESS is not set (it would still load
> them via init_module).
> =

> The best, but more invasive change, would be to improve the check
> determining if the given module is compressed. Currently, this is
> achieved by looking at the file extension. Instead, we should check
> if the file has a valid ELF header. This would allow us to eliminate
> logic that invokes finit_module(2) twice (once with and once without
> MODULE_INIT_COMPRESSED_FILE).
> =

> If there is an interest in improving handling of compressed modules
> on kernels without CONFIG_DECOMPRESS, then I would be willing to revise
> the patch accordingly.

Back to Jul 6, 2024, I sent a patch to check whether a module is
compressed by poking the ELF magic number[1].

Regards,
Yao Zi

[1]: https://lists.busybox.net/pipermail/busybox/2024-July/090802.html

> Cheers
> S=F6ren
> =

> S=F6ren Tempel <[email protected]> wrote:
> > On Alpine Linux, I noticed a lot of "Invalid ELF header magic" warnings
> > in the kernel log. These are caused by the fact that BusyBox calls
> > finit_module(2) twice. Once with, and once w/o MODULE_INIT_COMPRESSED_F=
ILE.
> > On Alpine, the first call fails because the kernel is configured without
> > kernel-space module decompression (i.e., CONFIG_MODULE_DECOMPRESS is
> > not set). The second call then causes the aforementioned error message
> > to be emitted as all of Alpine's Kernel modules are actually compressed.
> > =

> > This is fixed in this patch by not re-trying finit_module(2) when the
> > error return value indicates that CONFIG_MODULE_DECOMPRESS is not set
> > in the kernel configuration (i.e., EOPNOTSUPP is set in errno). The
> > module is then decompressed in userspace and loaded using init_module(2=
).
> > =

> > Downstream issues:
> > =

> > * https://gitlab.alpinelinux.org/alpine/aports/-/work_items/13427
> > * https://gitlab.alpinelinux.org/alpine/aports/-/merge_requests/105839
> > =

> > See also: af5277f883e8fc2e0236aa9ecc5115ecaffd0ccb
> > =

> > Signed-off-by: S=F6ren Tempel <[email protected]>
> > ---
> >  modutils/modprobe-small.c | 2 ++
> >  modutils/modutils.c       | 2 ++
> >  2 files changed, 4 insertions(+)
> > =

> > diff --git a/modutils/modprobe-small.c b/modutils/modprobe-small.c
> > index 7f584102d..4fa1c462c 100644
> > --- a/modutils/modprobe-small.c
> > +++ b/modutils/modprobe-small.c
> > @@ -271,6 +271,8 @@ static int load_module(const char *fname, const cha=
r *options)
> >  				r =3D finit_module(fd, options, flags);
> >  				if (r =3D=3D 0 || flags =3D=3D 0)
> >  					break;
> > +				else if (errno =3D=3D EOPNOTSUPP) /* kernel compression disabled -=
> don't retry */
> > +					break;
> >  				/* Loading non-.ko named uncompressed module? Not likely, but let'=
s try it */
> >  				flags =3D 0;
> >  			}
> > diff --git a/modutils/modutils.c b/modutils/modutils.c
> > index 862f71f57..cf619fc46 100644
> > --- a/modutils/modutils.c
> > +++ b/modutils/modutils.c
> > @@ -216,6 +216,8 @@ int FAST_FUNC bb_init_module(const char *filename, =
const char *options)
> >  				rc =3D finit_module(fd, options, flags);
> >  				if (rc =3D=3D 0 || flags =3D=3D 0)
> >  					break;
> > +				else if (errno =3D=3D EOPNOTSUPP) /* kernel compression disabled -=
> don't retry */
> > +					break;
> >  				/* Loading non-.ko named uncompressed module? Not likely, but let'=
s try it */
> >  				flags =3D 0;
> >  			}
> > _______________________________________________
> > busybox mailing list
> > [email protected]
> > https://lists.busybox.net/mailman/listinfo/busybox
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