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From:   Masahiro Yamada <yamada.masahiro@socionext.com>
Date:   Fri, 22 Mar 2019 14:34:12 +0900
Message-ID: <CAK7LNATsm23e_CuyfFw7_CR8xZQ3HnwNHCXhEm_zQZU2PUGK5A@mail.gmail.com>
Subject: Re: [RESEND PATCH v1] moduleparam: Save information about built-in
 modules in separate file
To:     Alexey Gladkov <gladkov.alexey@gmail.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>
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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/.

(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.


> 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?


> 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