Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Date:   Wed, 6 Mar 2019 17:54:25 +0100
From:   Alexey Gladkov <gladkov.alexey@gmail.com>
To:     linux-kernel@vger.kernel.org, linux-kbuild@vger.kernel.org,
        linux-api@vger.kernel.org
Cc:     "Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>,
        Gleb Fotengauer-Malinovskiy <glebfm@altlinux.org>,
        "Dmitry V. Levin" <ldv@altlinux.org>
Subject: [PATCH v1] moduleparam: Save information about built-in modules in
 separate file
Message-ID: <20190306165425.GD14017@MacBook-PC.fortress>
MIME-Version: 1.0
Content-Type: multipart/signed; micalg=pgp-sha1;
        protocol="application/pgp-signature"; boundary="0OWHXb1mYLuhj1Ox"
Content-Disposition: inline
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk


--0OWHXb1mYLuhj1Ox
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
Content-Transfer-Encoding: quoted-printable

Problem:

When a kernel module is compiled as a separate module, some important
information about the kernel module is available via .modinfo section of
the module.  In contrast, when the kernel module is compiled into the
kernel, that information is not available.

Information about built-in modules is necessary in the following cases:

1. When it is necessary to find out what additional parameters can be
passed to the kernel at boot time.

2. When you need to know which module names and their aliases are in
the kernel. This is very useful for creating an initrd image.

Proposal:

The proposed patch does not remove .modinfo section with module
information from the vmlinux at the build time and saves it into a
separate file after kernel linking. So, the kernel does not increase in
size and no additional information remains in it. Information is stored
in the same format as in the separate modules (null-terminated string
array). Because the .modinfo section is already exported with a separate
modules, we are not creating a new API.

It can be easily read in the userspace:

$ tr '\0' '\n' < kernel.builtin.modinfo
ext4.softdep=3Dpre: crc32c
ext4.license=3DGPL
ext4.description=3DFourth Extended Filesystem
ext4.author=3DRemy Card, Stephen Tweedie, Andrew Morton, Andreas Dilger, Th=
eodore Ts'o and others
ext4.alias=3Dfs-ext4
ext4.alias=3Dext3
ext4.alias=3Dfs-ext3
ext4.alias=3Dext2
ext4.alias=3Dfs-ext2
md_mod.alias=3Dblock-major-9-*
md_mod.alias=3Dmd
md_mod.description=3DMD RAID framework
md_mod.license=3DGPL
md_mod.parmtype=3Dcreate_on_open:bool
md_mod.parmtype=3Dstart_dirty_degraded:int
=2E..

Signed-off-by: Alexey Gladkov <gladkov.alexey@gmail.com>
Signed-off-by: Gleb Fotengauer-Malinovskiy <glebfm@altlinux.org>
---
 Makefile                    |  1 +
 include/linux/moduleparam.h | 12 +++++-------
 scripts/link-vmlinux.sh     |  8 ++++++++
 3 files changed, 14 insertions(+), 7 deletions(-)

diff --git a/Makefile b/Makefile
index d5713e7b1e50..971102194c92 100644
--- a/Makefile
+++ b/Makefile
@@ -1288,6 +1288,7 @@ _modinst_:
 	fi
 	@cp -f $(objtree)/modules.order $(MODLIB)/
 	@cp -f $(objtree)/modules.builtin $(MODLIB)/
+	@cp -f $(objtree)/kernel.builtin.modinfo $(MODLIB)/
 	$(Q)$(MAKE) -f $(srctree)/scripts/Makefile.modinst
=20
 # This depmod is only for convenience to give the initial
diff --git a/include/linux/moduleparam.h b/include/linux/moduleparam.h
index ba36506db4fb..5ba250d9172a 100644
--- a/include/linux/moduleparam.h
+++ b/include/linux/moduleparam.h
@@ -10,23 +10,21 @@
    module name. */
 #ifdef MODULE
 #define MODULE_PARAM_PREFIX /* empty */
+#define __MODULE_INFO_PREFIX /* empty */
 #else
 #define MODULE_PARAM_PREFIX KBUILD_MODNAME "."
+/* We cannot use MODULE_PARAM_PREFIX because some modules override it. */
+#define __MODULE_INFO_PREFIX KBUILD_MODNAME "."
 #endif
=20
 /* Chosen so that structs with an unsigned long line up. */
 #define MAX_PARAM_PREFIX_LEN (64 - sizeof(unsigned long))
=20
-#ifdef MODULE
 #define __MODULE_INFO(tag, name, info)					  \
 static const char __UNIQUE_ID(name)[]					  \
   __used __attribute__((section(".modinfo"), unused, aligned(1)))	  \
-  =3D __stringify(tag) "=3D" info
-#else  /* !MODULE */
-/* This struct is here for syntactic coherency, it is not used */
-#define __MODULE_INFO(tag, name, info)					  \
-  struct __UNIQUE_ID(name) {}
-#endif
+  =3D __MODULE_INFO_PREFIX __stringify(tag) "=3D" info
+
 #define __MODULE_PARM_TYPE(name, _type)					  \
   __MODULE_INFO(parmtype, name##type, #name ":" _type)
=20
diff --git a/scripts/link-vmlinux.sh b/scripts/link-vmlinux.sh
index c8cf45362bd6..399d7e4d11ec 100755
--- a/scripts/link-vmlinux.sh
+++ b/scripts/link-vmlinux.sh
@@ -258,10 +258,12 @@ if [ -n "${CONFIG_KALLSYMS}" ]; then
=20
 	# step 1
 	vmlinux_link "" .tmp_vmlinux1
+	"${OBJCOPY}" -R .modinfo .tmp_vmlinux1
 	kallsyms .tmp_vmlinux1 .tmp_kallsyms1.o
=20
 	# step 2
 	vmlinux_link .tmp_kallsyms1.o .tmp_vmlinux2
+	"${OBJCOPY}" -R .modinfo .tmp_vmlinux2
 	kallsyms .tmp_vmlinux2 .tmp_kallsyms2.o
=20
 	# step 3
@@ -273,6 +275,7 @@ if [ -n "${CONFIG_KALLSYMS}" ]; then
 		kallsyms_vmlinux=3D.tmp_vmlinux3
=20
 		vmlinux_link .tmp_kallsyms2.o .tmp_vmlinux3
+		"${OBJCOPY}" -R .modinfo .tmp_vmlinux3
=20
 		kallsyms .tmp_vmlinux3 .tmp_kallsyms3.o
 	fi
@@ -281,6 +284,11 @@ fi
 info LD vmlinux
 vmlinux_link "${kallsymso}" vmlinux
=20
+info MODINFO kernel.builtin.modinfo
+"${OBJCOPY}" -j .modinfo -O binary vmlinux kernel.builtin.modinfo
+chmod 444 kernel.builtin.modinfo
+"${OBJCOPY}" -R .modinfo vmlinux
+
 if [ -n "${CONFIG_BUILDTIME_EXTABLE_SORT}" ]; then
 	info SORTEX vmlinux
 	sortextable vmlinux
--=20
2.19.2


--0OWHXb1mYLuhj1Ox
Content-Type: application/pgp-signature; name="signature.asc"

-----BEGIN PGP SIGNATURE-----
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=bKn9
-----END PGP SIGNATURE-----

--0OWHXb1mYLuhj1Ox--