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remarkable-linux/Documentation/kbuild/kbuild.txt
Alexey Gladkov 898490c010 moduleparam: Save information about built-in modules in separate file 
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.

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.

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' < modules.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>
Acked-by: Jessica Yu <jeyu@kernel.org>
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
2019-05-07 21:50:24 +09:00

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Output files
modules.order
--------------------------------------------------
This file records the order in which modules appear in Makefiles. This
is used by modprobe to deterministically resolve aliases that match
multiple modules.
modules.builtin
--------------------------------------------------
This file lists all modules that are built into the kernel. This is used
by modprobe to not fail when trying to load something builtin.
modules.builtin.modinfo
--------------------------------------------------
This file contains modinfo from all modules that are built into the kernel.
Unlike modinfo of a separate module, all fields are prefixed with module name.
Environment variables
KCPPFLAGS
--------------------------------------------------
Additional options to pass when preprocessing. The preprocessing options
will be used in all cases where kbuild does preprocessing including
building C files and assembler files.
KAFLAGS
--------------------------------------------------
Additional options to the assembler (for built-in and modules).
AFLAGS_MODULE
--------------------------------------------------
Additional module specific options to use for $(AS).
AFLAGS_KERNEL
--------------------------------------------------
Additional options for $(AS) when used for assembler
code for code that is compiled as built-in.
KCFLAGS
--------------------------------------------------
Additional options to the C compiler (for built-in and modules).
CFLAGS_KERNEL
--------------------------------------------------
Additional options for $(CC) when used to compile
code that is compiled as built-in.
CFLAGS_MODULE
--------------------------------------------------
Additional module specific options to use for $(CC).
LDFLAGS_MODULE
--------------------------------------------------
Additional options used for $(LD) when linking modules.
HOSTCFLAGS
--------------------------------------------------
Additional flags to be passed to $(HOSTCC) when building host programs.
HOSTCXXFLAGS
--------------------------------------------------
Additional flags to be passed to $(HOSTCXX) when building host programs.
HOSTLDFLAGS
--------------------------------------------------
Additional flags to be passed when linking host programs.
HOSTLDLIBS
--------------------------------------------------
Additional libraries to link against when building host programs.
KBUILD_KCONFIG
--------------------------------------------------
Set the top-level Kconfig file to the value of this environment
variable. The default name is "Kconfig".
KBUILD_VERBOSE
--------------------------------------------------
Set the kbuild verbosity. Can be assigned same values as "V=...".
See make help for the full list.
Setting "V=..." takes precedence over KBUILD_VERBOSE.
KBUILD_EXTMOD
--------------------------------------------------
Set the directory to look for the kernel source when building external
modules.
Setting "M=..." takes precedence over KBUILD_EXTMOD.
KBUILD_OUTPUT
--------------------------------------------------
Specify the output directory when building the kernel.
The output directory can also be specified using "O=...".
Setting "O=..." takes precedence over KBUILD_OUTPUT.
KBUILD_DEBARCH
--------------------------------------------------
For the deb-pkg target, allows overriding the normal heuristics deployed by
deb-pkg. Normally deb-pkg attempts to guess the right architecture based on
the UTS_MACHINE variable, and on some architectures also the kernel config.
The value of KBUILD_DEBARCH is assumed (not checked) to be a valid Debian
architecture.
ARCH
--------------------------------------------------
Set ARCH to the architecture to be built.
In most cases the name of the architecture is the same as the
directory name found in the arch/ directory.
But some architectures such as x86 and sparc have aliases.
x86: i386 for 32 bit, x86_64 for 64 bit
sh: sh for 32 bit, sh64 for 64 bit
sparc: sparc32 for 32 bit, sparc64 for 64 bit
CROSS_COMPILE
--------------------------------------------------
Specify an optional fixed part of the binutils filename.
CROSS_COMPILE can be a part of the filename or the full path.
CROSS_COMPILE is also used for ccache in some setups.
CF
--------------------------------------------------
Additional options for sparse.
CF is often used on the command-line like this:
make CF=-Wbitwise C=2
INSTALL_PATH
--------------------------------------------------
INSTALL_PATH specifies where to place the updated kernel and system map
images. Default is /boot, but you can set it to other values.
INSTALLKERNEL
--------------------------------------------------
Install script called when using "make install".
The default name is "installkernel".
The script will be called with the following arguments:
$1 - kernel version
$2 - kernel image file
$3 - kernel map file
$4 - default install path (use root directory if blank)
The implementation of "make install" is architecture specific
and it may differ from the above.
INSTALLKERNEL is provided to enable the possibility to
specify a custom installer when cross compiling a kernel.
MODLIB
--------------------------------------------------
Specify where to install modules.
The default value is:
$(INSTALL_MOD_PATH)/lib/modules/$(KERNELRELEASE)
The value can be overridden in which case the default value is ignored.
INSTALL_MOD_PATH
--------------------------------------------------
INSTALL_MOD_PATH specifies a prefix to MODLIB for module directory
relocations required by build roots. This is not defined in the
makefile but the argument can be passed to make if needed.
INSTALL_MOD_STRIP
--------------------------------------------------
INSTALL_MOD_STRIP, if defined, will cause modules to be
stripped after they are installed. If INSTALL_MOD_STRIP is '1', then
the default option --strip-debug will be used. Otherwise,
INSTALL_MOD_STRIP value will be used as the options to the strip command.
INSTALL_HDR_PATH
--------------------------------------------------
INSTALL_HDR_PATH specifies where to install user space headers when
executing "make headers_*".
The default value is:
$(objtree)/usr
$(objtree) is the directory where output files are saved.
The output directory is often set using "O=..." on the commandline.
The value can be overridden in which case the default value is ignored.
KBUILD_SIGN_PIN
--------------------------------------------------
This variable allows a passphrase or PIN to be passed to the sign-file
utility when signing kernel modules, if the private key requires such.
KBUILD_MODPOST_WARN
--------------------------------------------------
KBUILD_MODPOST_WARN can be set to avoid errors in case of undefined
symbols in the final module linking stage. It changes such errors
into warnings.
KBUILD_MODPOST_NOFINAL
--------------------------------------------------
KBUILD_MODPOST_NOFINAL can be set to skip the final link of modules.
This is solely useful to speed up test compiles.
KBUILD_EXTRA_SYMBOLS
--------------------------------------------------
For modules that use symbols from other modules.
See more details in modules.txt.
ALLSOURCE_ARCHS
--------------------------------------------------
For tags/TAGS/cscope targets, you can specify more than one arch
to be included in the databases, separated by blank space. E.g.:
$ make ALLSOURCE_ARCHS="x86 mips arm" tags
To get all available archs you can also specify all. E.g.:
$ make ALLSOURCE_ARCHS=all tags
KBUILD_ENABLE_EXTRA_GCC_CHECKS
--------------------------------------------------
If enabled over the make command line with "W=1", it turns on additional
gcc -W... options for more extensive build-time checking.
KBUILD_BUILD_TIMESTAMP
--------------------------------------------------
Setting this to a date string overrides the timestamp used in the
UTS_VERSION definition (uname -v in the running kernel). The value has to
be a string that can be passed to date -d. The default value
is the output of the date command at one point during build.
KBUILD_BUILD_USER, KBUILD_BUILD_HOST
--------------------------------------------------
These two variables allow to override the user@host string displayed during
boot and in /proc/version. The default value is the output of the commands
whoami and host, respectively.
KBUILD_LDS
--------------------------------------------------
The linker script with full path. Assigned by the top-level Makefile.
KBUILD_VMLINUX_OBJS
--------------------------------------------------
All object files for vmlinux. They are linked to vmlinux in the same
order as listed in KBUILD_VMLINUX_OBJS.
KBUILD_VMLINUX_LIBS
--------------------------------------------------
All .a "lib" files for vmlinux. KBUILD_VMLINUX_OBJS and KBUILD_VMLINUX_LIBS
together specify all the object files used to link vmlinux.
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