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Date:   Tue, 26 Mar 2019 18:24:12 +0100
From:   Alexey Gladkov <gladkov.alexey@gmail.com>
To:     Masahiro Yamada <yamada.masahiro@socionext.com>
Cc:     Michal Marek <michal.lkml@markovi.net>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Linux Kbuild mailing list <linux-kbuild@vger.kernel.org>,
        linux-api@vger.kernel.org,
        "Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>,
        Gleb Fotengauer-Malinovskiy <glebfm@altlinux.org>,
        "Dmitry V. Levin" <ldv@altlinux.org>,
        Dmitry Torokhov <dmitry.torokhov@gmail.com>,
        Rusty Russell <rusty@rustcorp.com.au>,
        Jessica Yu <jeyu@kernel.org>
Subject: Re: [RESEND PATCH v1] moduleparam: Save information about built-in
 modules in separate file
Message-ID: <20190326172411.GA15936@Legion-PC.fortress>
References: <20190315101013.GN8455@Legion-PC.fortress>
 <CAK7LNATsm23e_CuyfFw7_CR8xZQ3HnwNHCXhEm_zQZU2PUGK5A@mail.gmail.com>
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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