Re: [RESEND PATCH v1] moduleparam: Save information about built-in modules in separate file

From: Masahiro Yamada
Date: Wed Apr 03 2019 - 06:46:40 EST

Hi.

Sorry for the delay.
I added some comments from the
build system point of view.


On Wed, Mar 27, 2019 at 2:24 AM Alexey Gladkov <gladkov.alexey@xxxxxxxxx> wrote:
>
> On Fri, Mar 22, 2019 at 02:34:12PM +0900, Masahiro Yamada wrote:
> > Hi.
> >
> > (added some people to CC)
> >
> >
> > On Fri, Mar 15, 2019 at 7:10 PM Alexey Gladkov <gladkov.alexey@xxxxxxxxx> wrote:
> > >
> > > 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.
> >
> >
> > I might be missing something, but
> > vmlinux provides info of builtin modules
> > in /sys/module/.
>
> No. There are definitely not all modules. I have a builtin sha256_generic,
> but I can't find him in the /sys/module.
>
> > (Looks like currently only module_param and MODULE_VERSION)
> >
> > This patch is not exactly the same, but I see a kind of overwrap.
> > I'd like to be sure if we want this new scheme.
>
> The /sys/module is only for running kernel. One of my use cases is
> to create an initrd for a new kernel.
>
> >
> > > 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.
> >
> >
> > Actually, /sys/module/<module>/parameters/
> > exposes this information.
> >
> > Doesn't it work for your purpose?
>
> No, since creating an initrd needs to know all the modalias before
> I get the sysfs for new kernel. Also there are no modalias at all.
>
> > > 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=pre: crc32c
> > > ext4.license=GPL
> > > ext4.description=Fourth Extended Filesystem
> > > ext4.author=Remy Card, Stephen Tweedie, Andrew Morton, Andreas Dilger, Theodore Ts'o and others
> > > ext4.alias=fs-ext4
> > > ext4.alias=ext3
> > > ext4.alias=fs-ext3
> > > ext4.alias=ext2
> > > ext4.alias=fs-ext2
> > > md_mod.alias=block-major-9-*
> > > md_mod.alias=md
> > > md_mod.description=MD RAID framework
> > > md_mod.license=GPL
> > > md_mod.parmtype=create_on_open:bool
> > > md_mod.parmtype=start_dirty_degraded:int
> > > ...
> > >
> > > Co-Developed-by: Gleb Fotengauer-Malinovskiy <glebfm@xxxxxxxxxxxx>
> > > Signed-off-by: Gleb Fotengauer-Malinovskiy <glebfm@xxxxxxxxxxxx>
> > > Signed-off-by: Alexey Gladkov <gladkov.alexey@xxxxxxxxx>
> > > ---
> > > 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)/


This file should be cleaned up by 'make clean'.

Please add CLEAN_FILES around line 1336.


# Directories & files removed with 'make clean'
CLEAN_DIRS += $(MODVERDIR) include/ksym
CLEAN_FILES += ...




Also, shouldn't it be added to .gitignore?




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



As I pointed out before, I see lots of warnings for powerpc.

How about extracting modinfo before linking vmlinux?
You can extract it from vmlinux.o instead,
and discard it in the linker script.


diff --git a/scripts/link-vmlinux.sh b/scripts/link-vmlinux.sh
index dc0e8c5..994cd47 100755
--- a/scripts/link-vmlinux.sh
+++ b/scripts/link-vmlinux.sh
@@ -193,6 +193,9 @@ modpost_link vmlinux.o
# modpost vmlinux.o to check for section mismatches
${MAKE} -f "${srctree}/scripts/Makefile.modpost" vmlinux.o

+info MODINFO kernel.builtin.modinfo
+"${OBJCOPY}" -j .modinfo -O binary vmlinux kernel.builtin.modinfo
+
kallsymso=""
kallsyms_vmlinux=""
diff --git a/include/asm-generic/vmlinux.lds.h
b/include/asm-generic/vmlinux.lds.h
index f8f6f04..bbb9e33 100644
--- a/include/asm-generic/vmlinux.lds.h
+++ b/include/asm-generic/vmlinux.lds.h
@@ -844,6 +844,7 @@
EXIT_CALL \
*(.discard) \
*(.discard.*) \
+ *(.modinfo) \
}

/**



The code is simpler and I see no more warnings.


I also want you to check MODULE_VERSION.

If CONFIG_SYSFS is enabled, MODULE_VERSION
will not be contained in the file.



Thanks.


> > > --
> > > 2.19.2
> > >
> >
> >
> > --
> > Best Regards
> > Masahiro Yamada
> >
>
> --
> Rgrds, legion
>


--
Best Regards
Masahiro Yamada