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

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