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SubjectRe: [RESEND PATCH v1] moduleparam: Save information about built-in modules in separate file
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@gmail.com> 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@altlinux.org>
> > Signed-off-by: Gleb Fotengauer-Malinovskiy <glebfm@altlinux.org>
> > Signed-off-by: Alexey Gladkov <gladkov.alexey@gmail.com>
> > ---
> > 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 $(srctree)/scripts/Makefile.modinst
> >
> > # This depmod is only for convenience to give the initial
> > diff --git a/include/linux/moduleparam.h b/include/linux/moduleparam.h
> > index ba36506db4fb..5ba250d9172a 100644
> > --- a/include/linux/moduleparam.h
> > +++ b/include/linux/moduleparam.h
> > @@ -10,23 +10,21 @@
> > module name. */
> > #ifdef MODULE
> > #define MODULE_PARAM_PREFIX /* empty */
> > +#define __MODULE_INFO_PREFIX /* empty */
> > #else
> > #define MODULE_PARAM_PREFIX KBUILD_MODNAME "."
> > +/* We cannot use MODULE_PARAM_PREFIX because some modules override it. */
> > +#define __MODULE_INFO_PREFIX KBUILD_MODNAME "."
> > #endif
> >
> > /* Chosen so that structs with an unsigned long line up. */
> > #define MAX_PARAM_PREFIX_LEN (64 - sizeof(unsigned long))
> >
> > -#ifdef MODULE
> > #define __MODULE_INFO(tag, name, info) \
> > static const char __UNIQUE_ID(name)[] \
> > __used __attribute__((section(".modinfo"), unused, aligned(1))) \
> > - = __stringify(tag) "=" info
> > -#else /* !MODULE */
> > -/* This struct is here for syntactic coherency, it is not used */
> > -#define __MODULE_INFO(tag, name, info) \
> > - struct __UNIQUE_ID(name) {}
> > -#endif
> > + = __MODULE_INFO_PREFIX __stringify(tag) "=" info
> > +
> > #define __MODULE_PARM_TYPE(name, _type) \
> > __MODULE_INFO(parmtype, name##type, #name ":" _type)
> >
> > diff --git a/scripts/link-vmlinux.sh b/scripts/link-vmlinux.sh
> > index c8cf45362bd6..399d7e4d11ec 100755
> > --- a/scripts/link-vmlinux.sh
> > +++ b/scripts/link-vmlinux.sh
> > @@ -258,10 +258,12 @@ if [ -n "${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
> > --
> > 2.19.2
> >
>
>
> --
> Best Regards
> Masahiro Yamada
>

--
Rgrds, legion

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