diff options
Diffstat (limited to 'Documentation/kbuild')
| -rw-r--r-- | Documentation/kbuild/kbuild.txt | 115 | ||||
| -rw-r--r-- | Documentation/kbuild/kconfig-language.txt | 28 | ||||
| -rw-r--r-- | Documentation/kbuild/kconfig.txt | 201 | ||||
| -rw-r--r-- | Documentation/kbuild/makefiles.txt | 411 | ||||
| -rw-r--r-- | Documentation/kbuild/modules.txt | 733 |
5 files changed, 929 insertions, 559 deletions
diff --git a/Documentation/kbuild/kbuild.txt b/Documentation/kbuild/kbuild.txt index f3355b6812d..6466704d47b 100644 --- a/Documentation/kbuild/kbuild.txt +++ b/Documentation/kbuild/kbuild.txt @@ -1,3 +1,17 @@ +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. + + Environment variables KCPPFLAGS @@ -8,11 +22,37 @@ building C files and assembler files. KAFLAGS -------------------------------------------------- -Additional options to the assembler. +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. +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. + +LDFLAGS_vmlinux +-------------------------------------------------- +Additional options passed to final link of vmlinux. KBUILD_VERBOSE -------------------------------------------------- @@ -26,17 +66,25 @@ Set the directory to look for the kernel source when building external modules. The directory can be specified in several ways: 1) Use "M=..." on the command line -2) Environmnet variable KBUILD_EXTMOD -3) Environmnet variable SUBDIRS +2) Environment variable KBUILD_EXTMOD +3) Environment variable SUBDIRS The possibilities are listed in the order they take precedence. Using "M=..." will always override the others. KBUILD_OUTPUT -------------------------------------------------- Specify the output directory when building the kernel. -The output directory can also be specificed using "O=...". +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. @@ -51,7 +99,7 @@ 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 is some setups. +CROSS_COMPILE is also used for ccache in some setups. CF -------------------------------------------------- @@ -65,6 +113,22 @@ 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 -------------------------------------------------- @@ -86,7 +150,7 @@ 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 will used as the options to the strip command. +INSTALL_MOD_STRIP value will be used as the options to the strip command. INSTALL_FW_PATH -------------------------------------------------- @@ -132,3 +196,40 @@ 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_INIT +-------------------------------------------------- +All object files for the init (first) part of vmlinux. +Files specified with KBUILD_VMLINUX_INIT are linked first. + +KBUILD_VMLINUX_MAIN +-------------------------------------------------- +All object files for the main part of vmlinux. +KBUILD_VMLINUX_INIT and KBUILD_VMLINUX_MAIN together specify +all the object files used to link vmlinux. diff --git a/Documentation/kbuild/kconfig-language.txt b/Documentation/kbuild/kconfig-language.txt index c412c245848..350f733bf2c 100644 --- a/Documentation/kbuild/kconfig-language.txt +++ b/Documentation/kbuild/kconfig-language.txt @@ -112,7 +112,13 @@ applicable everywhere (see syntax). (no prompts anywhere) and for symbols with no dependencies. That will limit the usefulness but on the other hand avoid the illegal configurations all over. - kconfig should one day warn about such things. + +- limiting menu display: "visible if" <expr> + This attribute is only applicable to menu blocks, if the condition is + false, the menu block is not displayed to the user (the symbols + contained there can still be selected by other symbols, though). It is + similar to a conditional "prompt" attribute for individual menu + entries. Default value of "visible" is true. - numerical ranges: "range" <symbol> <symbol> ["if" <expr>] This allows to limit the range of possible input values for int @@ -141,6 +147,7 @@ applicable everywhere (see syntax). - "modules" This declares the symbol to be used as the MODULES symbol, which enables the third modular state for all config symbols. + At most one symbol may have the "modules" option set. - "env"=<value> This imports the environment variable into Kconfig. It behaves like @@ -150,6 +157,10 @@ applicable everywhere (see syntax). to the build environment (if this is desired, it can be done via another symbol). + - "allnoconfig_y" + This declares the symbol as one that should have the value y when + using "allnoconfig". Used for symbols that hide other symbols. + Menu dependencies ----------------- @@ -181,7 +192,7 @@ Expressions are listed in decreasing order of precedence. (7) Returns the result of max(/expr/, /expr/). An expression can have a value of 'n', 'm' or 'y' (or 0, 1, 2 -respectively for calculations). A menu entry becomes visible when it's +respectively for calculations). A menu entry becomes visible when its expression evaluates to 'm' or 'y'. There are two types of symbols: constant and non-constant symbols. @@ -268,7 +279,7 @@ separate list of options. choices: - "choice" + "choice" [symbol] <choice options> <choice block> "endchoice" @@ -282,6 +293,10 @@ single driver can be compiled/loaded into the kernel, but all drivers can be compiled as modules. A choice accepts another option "optional", which allows to set the choice to 'n' and no entry needs to be selected. +If no [symbol] is associated with a choice, then you can not have multiple +definitions of that choice. If a [symbol] is associated to the choice, +then you may define the same choice (ie. with the same entries) in another +place. comment: @@ -300,7 +315,8 @@ menu: "endmenu" This defines a menu block, see "Menu structure" above for more -information. The only possible options are dependencies. +information. The only possible options are dependencies and "visible" +attributes. if: @@ -322,7 +338,8 @@ mainmenu: "mainmenu" <prompt> This sets the config program's title bar if the config program chooses -to use it. +to use it. It should be placed at the top of the configuration, before any +other statement. Kconfig hints @@ -376,4 +393,3 @@ config FOO depends on BAR && m limits FOO to module (=m) or disabled (=n). - diff --git a/Documentation/kbuild/kconfig.txt b/Documentation/kbuild/kconfig.txt index 26a7c0a9319..bbc99c0c109 100644 --- a/Documentation/kbuild/kconfig.txt +++ b/Documentation/kbuild/kconfig.txt @@ -20,83 +20,52 @@ symbols have been introduced. To see a list of new config symbols when using "make oldconfig", use cp user/some/old.config .config - yes "" | make oldconfig >conf.new + make listnewconfig -and the config program will list as (NEW) any new symbols that have -unknown values. Of course, the .config file is also updated with -new (default) values, so you can use: - - grep "(NEW)" conf.new - -to see the new config symbols or you can 'diff' the previous and -new .config files to see the differences: - - diff .config.old .config | less - -(Yes, we need something better here.) - - -====================================================================== -menuconfig --------------------------------------------------- - -SEARCHING for CONFIG symbols - -Searching in menuconfig: - - The Search function searches for kernel configuration symbol - names, so you have to know something close to what you are - looking for. - - Example: - /hotplug - This lists all config symbols that contain "hotplug", - e.g., HOTPLUG, HOTPLUG_CPU, MEMORY_HOTPLUG. - - For search help, enter / followed TAB-TAB-TAB (to highlight - <Help>) and Enter. This will tell you that you can also use - regular expressions (regexes) in the search string, so if you - are not interested in MEMORY_HOTPLUG, you could try - - /^hotplug +and the config program will list any new symbols, one per line. + scripts/diffconfig .config.old .config | less ______________________________________________________________________ -Color Themes for 'menuconfig' +Environment variables for '*config' -It is possible to select different color themes using the variable -MENUCONFIG_COLOR. To select a theme use: +KCONFIG_CONFIG +-------------------------------------------------- +This environment variable can be used to specify a default kernel config +file name to override the default name of ".config". - make MENUCONFIG_COLOR=<theme> menuconfig +KCONFIG_OVERWRITECONFIG +-------------------------------------------------- +If you set KCONFIG_OVERWRITECONFIG in the environment, Kconfig will not +break symlinks when .config is a symlink to somewhere else. -Available themes are: - mono => selects colors suitable for monochrome displays - blackbg => selects a color scheme with black background - classic => theme with blue background. The classic look - bluetitle => a LCD friendly version of classic. (default) +CONFIG_ +-------------------------------------------------- +If you set CONFIG_ in the environment, Kconfig will prefix all symbols +with its value when saving the configuration, instead of using the default, +"CONFIG_". ______________________________________________________________________ -Environment variables in 'menuconfig' +Environment variables for '{allyes/allmod/allno/rand}config' KCONFIG_ALLCONFIG -------------------------------------------------- (partially based on lkml email from/by Rob Landley, re: miniconfig) -------------------------------------------------- -The allyesconfig/allmodconfig/allnoconfig/randconfig variants can -also use the environment variable KCONFIG_ALLCONFIG as a flag or a -filename that contains config symbols that the user requires to be -set to a specific value. If KCONFIG_ALLCONFIG is used without a -filename, "make *config" checks for a file named -"all{yes/mod/no/random}.config" (corresponding to the *config command -that was used) for symbol values that are to be forced. If this file -is not found, it checks for a file named "all.config" to contain forced -values. +The allyesconfig/allmodconfig/allnoconfig/randconfig variants can also +use the environment variable KCONFIG_ALLCONFIG as a flag or a filename +that contains config symbols that the user requires to be set to a +specific value. If KCONFIG_ALLCONFIG is used without a filename where +KCONFIG_ALLCONFIG == "" or KCONFIG_ALLCONFIG == "1", "make *config" +checks for a file named "all{yes/mod/no/def/random}.config" +(corresponding to the *config command that was used) for symbol values +that are to be forced. If this file is not found, it checks for a +file named "all.config" to contain forced values. This enables you to create "miniature" config (miniconfig) or custom config files containing just the config symbols that you are interested in. Then the kernel config system generates the full .config file, -including dependencies of your miniconfig file, based on the miniconfig -file. +including symbols of your miniconfig file. This 'KCONFIG_ALLCONFIG' file is a config file which contains (usually a subset of all) preset config symbols. These variable @@ -113,45 +82,125 @@ These examples will disable most options (allnoconfig) but enable or disable the options that are explicitly listed in the specified mini-config files. -KCONFIG_NOSILENTUPDATE --------------------------------------------------- -If this variable has a non-blank value, it prevents silent kernel -config udpates (requires explicit updates). +______________________________________________________________________ +Environment variables for 'randconfig' -KCONFIG_CONFIG +KCONFIG_SEED -------------------------------------------------- -This environment variable can be used to specify a default kernel config -file name to override the default name of ".config". +You can set this to the integer value used to seed the RNG, if you want +to somehow debug the behaviour of the kconfig parser/frontends. +If not set, the current time will be used. -KCONFIG_OVERWRITECONFIG +KCONFIG_PROBABILITY -------------------------------------------------- -If you set KCONFIG_OVERWRITECONFIG in the environment, Kconfig will not -break symlinks when .config is a symlink to somewhere else. +This variable can be used to skew the probabilities. This variable can +be unset or empty, or set to three different formats: + KCONFIG_PROBABILITY y:n split y:m:n split + ----------------------------------------------------------------- + unset or empty 50 : 50 33 : 33 : 34 + N N : 100-N N/2 : N/2 : 100-N + [1] N:M N+M : 100-(N+M) N : M : 100-(N+M) + [2] N:M:L N : 100-N M : L : 100-(M+L) + +where N, M and L are integers (in base 10) in the range [0,100], and so +that: + [1] N+M is in the range [0,100] + [2] M+L is in the range [0,100] + +Examples: + KCONFIG_PROBABILITY=10 + 10% of booleans will be set to 'y', 90% to 'n' + 5% of tristates will be set to 'y', 5% to 'm', 90% to 'n' + KCONFIG_PROBABILITY=15:25 + 40% of booleans will be set to 'y', 60% to 'n' + 15% of tristates will be set to 'y', 25% to 'm', 60% to 'n' + KCONFIG_PROBABILITY=10:15:15 + 10% of booleans will be set to 'y', 90% to 'n' + 15% of tristates will be set to 'y', 15% to 'm', 70% to 'n' + +______________________________________________________________________ +Environment variables for 'silentoldconfig' -KCONFIG_NOTIMESTAMP +KCONFIG_NOSILENTUPDATE -------------------------------------------------- -If this environment variable exists and is non-null, the timestamp line -in generated .config files is omitted. +If this variable has a non-blank value, it prevents silent kernel +config updates (requires explicit updates). KCONFIG_AUTOCONFIG -------------------------------------------------- This environment variable can be set to specify the path & name of the "auto.conf" file. Its default value is "include/config/auto.conf". +KCONFIG_TRISTATE +-------------------------------------------------- +This environment variable can be set to specify the path & name of the +"tristate.conf" file. Its default value is "include/config/tristate.conf". + KCONFIG_AUTOHEADER -------------------------------------------------- This environment variable can be set to specify the path & name of the -"autoconf.h" (header) file. Its default value is "include/linux/autoconf.h". +"autoconf.h" (header) file. +Its default value is "include/generated/autoconf.h". + + +====================================================================== +menuconfig +-------------------------------------------------- + +SEARCHING for CONFIG symbols + +Searching in menuconfig: + + The Search function searches for kernel configuration symbol + names, so you have to know something close to what you are + looking for. + + Example: + /hotplug + This lists all config symbols that contain "hotplug", + e.g., HOTPLUG_CPU, MEMORY_HOTPLUG. + + For search help, enter / followed TAB-TAB-TAB (to highlight + <Help>) and Enter. This will tell you that you can also use + regular expressions (regexes) in the search string, so if you + are not interested in MEMORY_HOTPLUG, you could try + + /^hotplug + + When searching, symbols are sorted thus: + - first, exact matches, sorted alphabetically (an exact match + is when the search matches the complete symbol name); + - then, other matches, sorted alphabetically. + For example: ^ATH.K matches: + ATH5K ATH9K ATH5K_AHB ATH5K_DEBUG [...] ATH6KL ATH6KL_DEBUG + [...] ATH9K_AHB ATH9K_BTCOEX_SUPPORT ATH9K_COMMON [...] + of which only ATH5K and ATH9K match exactly and so are sorted + first (and in alphabetical order), then come all other symbols, + sorted in alphabetical order. ______________________________________________________________________ -menuconfig User Interface Options ----------------------------------------------------------------------- +User interface options for 'menuconfig' + +MENUCONFIG_COLOR +-------------------------------------------------- +It is possible to select different color themes using the variable +MENUCONFIG_COLOR. To select a theme use: + + make MENUCONFIG_COLOR=<theme> menuconfig + +Available themes are: + mono => selects colors suitable for monochrome displays + blackbg => selects a color scheme with black background + classic => theme with blue background. The classic look + bluetitle => a LCD friendly version of classic. (default) + MENUCONFIG_MODE -------------------------------------------------- This mode shows all sub-menus in one large tree. Example: - MENUCONFIG_MODE=single_menu make menuconfig + make MENUCONFIG_MODE=single_menu menuconfig + ====================================================================== xconfig diff --git a/Documentation/kbuild/makefiles.txt b/Documentation/kbuild/makefiles.txt index 51104f9194a..c600e2f44a6 100644 --- a/Documentation/kbuild/makefiles.txt +++ b/Documentation/kbuild/makefiles.txt @@ -18,6 +18,7 @@ This document describes the Linux kernel Makefiles. --- 3.9 Dependency tracking --- 3.10 Special Rules --- 3.11 $(CC) support functions + --- 3.12 $(LD) support functions === 4 Host Program support --- 4.1 Simple Host Program @@ -32,18 +33,26 @@ This document describes the Linux kernel Makefiles. === 6 Architecture Makefiles --- 6.1 Set variables to tweak the build to the architecture - --- 6.2 Add prerequisites to archprepare: - --- 6.3 List directories to visit when descending - --- 6.4 Architecture-specific boot images - --- 6.5 Building non-kbuild targets - --- 6.6 Commands useful for building a boot image - --- 6.7 Custom kbuild commands - --- 6.8 Preprocessing linker scripts - - === 7 Kbuild Variables - === 8 Makefile language - === 9 Credits - === 10 TODO + --- 6.2 Add prerequisites to archheaders: + --- 6.3 Add prerequisites to archprepare: + --- 6.4 List directories to visit when descending + --- 6.5 Architecture-specific boot images + --- 6.6 Building non-kbuild targets + --- 6.7 Commands useful for building a boot image + --- 6.8 Custom kbuild commands + --- 6.9 Preprocessing linker scripts + --- 6.10 Generic header files + + === 7 Kbuild syntax for exported headers + --- 7.1 header-y + --- 7.2 genhdr-y + --- 7.3 destination-y + --- 7.4 generic-y + + === 8 Kbuild Variables + === 9 Makefile language + === 10 Credits + === 11 TODO === 1 Overview @@ -161,7 +170,7 @@ more details, with real examples. #drivers/isdn/i4l/Makefile # Makefile for the kernel ISDN subsystem and device drivers. # Each configuration option enables a list of files. - obj-$(CONFIG_ISDN) += isdn.o + obj-$(CONFIG_ISDN_I4L) += isdn.o obj-$(CONFIG_ISDN_PPP_BSDCOMP) += isdn_bsdcomp.o --- 3.3 Loadable module goals - obj-m @@ -180,34 +189,35 @@ more details, with real examples. Note: In this example $(CONFIG_ISDN_PPP_BSDCOMP) evaluates to 'm' If a kernel module is built from several source files, you specify - that you want to build a module in the same way as above. - - Kbuild needs to know which the parts that you want to build your - module from, so you have to tell it by setting an - $(<module_name>-objs) variable. + that you want to build a module in the same way as above; however, + kbuild needs to know which object files you want to build your + module from, so you have to tell it by setting a $(<module_name>-y) + variable. Example: #drivers/isdn/i4l/Makefile - obj-$(CONFIG_ISDN) += isdn.o - isdn-objs := isdn_net_lib.o isdn_v110.o isdn_common.o + obj-$(CONFIG_ISDN_I4L) += isdn.o + isdn-y := isdn_net_lib.o isdn_v110.o isdn_common.o In this example, the module name will be isdn.o. Kbuild will - compile the objects listed in $(isdn-objs) and then run + compile the objects listed in $(isdn-y) and then run "$(LD) -r" on the list of these files to generate isdn.o. - Kbuild recognises objects used for composite objects by the suffix - -objs, and the suffix -y. This allows the Makefiles to use - the value of a CONFIG_ symbol to determine if an object is part - of a composite object. + Due to kbuild recognizing $(<module_name>-y) for composite objects, + you can use the value of a CONFIG_ symbol to optionally include an + object file as part of a composite object. Example: #fs/ext2/Makefile - obj-$(CONFIG_EXT2_FS) += ext2.o - ext2-y := balloc.o bitmap.o - ext2-$(CONFIG_EXT2_FS_XATTR) += xattr.o + obj-$(CONFIG_EXT2_FS) += ext2.o + ext2-y := balloc.o dir.o file.o ialloc.o inode.o ioctl.o \ + namei.o super.o symlink.o + ext2-$(CONFIG_EXT2_FS_XATTR) += xattr.o xattr_user.o \ + xattr_trusted.o - In this example, xattr.o is only part of the composite object - ext2.o if $(CONFIG_EXT2_FS_XATTR) evaluates to 'y'. + In this example, xattr.o, xattr_user.o and xattr_trusted.o are only + part of the composite object ext2.o if $(CONFIG_EXT2_FS_XATTR) + evaluates to 'y'. Note: Of course, when you are building objects into the kernel, the syntax above will also work. So, if you have CONFIG_EXT2_FS=y, @@ -237,13 +247,13 @@ more details, with real examples. may contain both a built-in.o and a lib.a file. Example: - #arch/i386/lib/Makefile - lib-y := checksum.o delay.o + #arch/x86/lib/Makefile + lib-y := delay.o - This will create a library lib.a based on checksum.o and delay.o. - For kbuild to actually recognize that there is a lib.a being built, - the directory shall be listed in libs-y. - See also "6.3 List directories to visit when descending". + This will create a library lib.a based on delay.o. For kbuild to + actually recognize that there is a lib.a being built, the directory + shall be listed in libs-y. + See also "6.4 List directories to visit when descending". Use of lib-y is normally restricted to lib/ and arch/*/lib. @@ -277,38 +287,45 @@ more details, with real examples. --- 3.7 Compilation flags ccflags-y, asflags-y and ldflags-y - The three flags listed above applies only to the kbuild makefile - where they are assigned. They are used for all the normal - cc, as and ld invocation happenign during a recursive build. + These three flags apply only to the kbuild makefile in which they + are assigned. They are used for all the normal cc, as and ld + invocations happening during a recursive build. Note: Flags with the same behaviour were previously named: EXTRA_CFLAGS, EXTRA_AFLAGS and EXTRA_LDFLAGS. - They are yet supported but their use are deprecated. + They are still supported but their usage is deprecated. - ccflags-y specifies options for compiling C files with $(CC). + ccflags-y specifies options for compiling with $(CC). Example: - # drivers/sound/emu10k1/Makefile - ccflags-y += -I$(obj) - ccflags-$(DEBUG) += -DEMU10K1_DEBUG - + # drivers/acpi/Makefile + ccflags-y := -Os + ccflags-$(CONFIG_ACPI_DEBUG) += -DACPI_DEBUG_OUTPUT This variable is necessary because the top Makefile owns the variable $(KBUILD_CFLAGS) and uses it for compilation flags for the entire tree. - asflags-y is a similar string for per-directory options - when compiling assembly language source. + asflags-y specifies options for assembling with $(AS). Example: - #arch/x86_64/kernel/Makefile - asflags-y := -traditional + #arch/sparc/kernel/Makefile + asflags-y := -ansi + ldflags-y specifies options for linking with $(LD). - ldflags-y is a string for per-directory options to $(LD). + Example: + #arch/cris/boot/compressed/Makefile + ldflags-y += -T $(srctree)/$(src)/decompress_$(arch-y).lds + + subdir-ccflags-y, subdir-asflags-y + The two flags listed above are similar to ccflags-y and asflags-y. + The difference is that the subdir- variants have effect for the kbuild + file where they are present and all subdirectories. + Options specified using subdir-* are added to the commandline before + the options specified using the non-subdir variants. Example: - #arch/m68k/fpsp040/Makefile - ldflags-y := -x + subdir-ccflags-y := -Werror CFLAGS_$@, AFLAGS_$@ @@ -323,18 +340,18 @@ more details, with real examples. CFLAGS_aha152x.o = -DAHA152X_STAT -DAUTOCONF CFLAGS_gdth.o = # -DDEBUG_GDTH=2 -D__SERIAL__ -D__COM2__ \ -DGDTH_STATISTICS - CFLAGS_seagate.o = -DARBITRATE -DPARITY -DSEAGATE_USE_ASM - These three lines specify compilation flags for aha152x.o, - gdth.o, and seagate.o + These two lines specify compilation flags for aha152x.o and gdth.o. $(AFLAGS_$@) is a similar feature for source files in assembly languages. Example: # arch/arm/kernel/Makefile - AFLAGS_head-armv.o := -DTEXTADDR=$(TEXTADDR) -traditional - AFLAGS_head-armo.o := -DTEXTADDR=$(TEXTADDR) -traditional + AFLAGS_head.o := -DTEXT_OFFSET=$(TEXT_OFFSET) + AFLAGS_crunch-bits.o := -Wa,-mcpu=ep9312 + AFLAGS_iwmmxt.o := -Wa,-mcpu=iwmmxt + --- 3.9 Dependency tracking @@ -419,14 +436,14 @@ more details, with real examples. The second argument is optional, and if supplied will be used if first argument is not supported. - ld-option - ld-option is used to check if $(CC) when used to link object files + cc-ldoption + cc-ldoption is used to check if $(CC) when used to link object files supports the given option. An optional second option may be specified if first option are not supported. Example: - #arch/i386/kernel/Makefile - vsyscall-flags += $(call ld-option, -Wl$(comma)--hash-style=sysv) + #arch/x86/kernel/Makefile + vsyscall-flags += $(call cc-ldoption, -Wl$(comma)--hash-style=sysv) In the above example, vsyscall-flags will be assigned the option -Wl$(comma)--hash-style=sysv if it is supported by $(CC). @@ -444,7 +461,7 @@ more details, with real examples. supported to use an optional second option. Example: - #arch/i386/Makefile + #arch/x86/Makefile cflags-y += $(call cc-option,-march=pentium-mmx,-march=i586) In the above example, cflags-y will be assigned the option @@ -485,6 +502,18 @@ more details, with real examples. gcc >= 3.00. For gcc < 3.00, -malign-functions=4 is used. Note: cc-option-align uses KBUILD_CFLAGS for $(CC) options + cc-disable-warning + cc-disable-warning checks if gcc supports a given warning and returns + the commandline switch to disable it. This special function is needed, + because gcc 4.4 and later accept any unknown -Wno-* option and only + warn about it if there is another warning in the source file. + + Example: + KBUILD_CFLAGS += $(call cc-disable-warning, unused-but-set-variable) + + In the above example, -Wno-unused-but-set-variable will be added to + KBUILD_CFLAGS only if gcc really accepts it. + cc-version cc-version returns a numerical version of the $(CC) compiler version. The format is <major><minor> where both are two digits. So for example @@ -494,7 +523,7 @@ more details, with real examples. even though the option was accepted by gcc. Example: - #arch/i386/Makefile + #arch/x86/Makefile cflags-y += $(shell \ if [ $(call cc-version) -ge 0300 ] ; then \ echo "-mregparm=3"; fi ;) @@ -554,6 +583,19 @@ more details, with real examples. endif endif +--- 3.12 $(LD) support functions + + ld-option + ld-option is used to check if $(LD) supports the supplied option. + ld-option takes two options as arguments. + The second argument is an optional option that can be used if the + first option is not supported by $(LD). + + Example: + #Makefile + LDFLAGS_vmlinux += $(call ld-option, -X) + + === 4 Host Program support Kbuild supports building executables on the host for use during the @@ -749,12 +791,19 @@ This will delete the directory debian, including all subdirectories. Kbuild will assume the directories to be in the same relative path as the Makefile if no absolute path is specified (path does not start with '/'). +To exclude certain files from make clean, use the $(no-clean-files) variable. +This is only a special case used in the top level Kbuild file: + + Example: + #Kbuild + no-clean-files := $(bounds-file) $(offsets-file) + Usually kbuild descends down in subdirectories due to "obj-* := dir/", but in the architecture makefiles where the kbuild infrastructure is not sufficient this sometimes needs to be explicit. Example: - #arch/i386/boot/Makefile + #arch/x86/boot/Makefile subdir- := compressed/ The above assignment instructs kbuild to descend down in the @@ -764,12 +813,12 @@ To support the clean infrastructure in the Makefiles that builds the final bootimage there is an optional target named archclean: Example: - #arch/i386/Makefile + #arch/x86/Makefile archclean: - $(Q)$(MAKE) $(clean)=arch/i386/boot + $(Q)$(MAKE) $(clean)=arch/x86/boot -When "make clean" is executed, make will descend down in arch/i386/boot, -and clean as usual. The Makefile located in arch/i386/boot/ may use +When "make clean" is executed, make will descend down in arch/x86/boot, +and clean as usual. The Makefile located in arch/x86/boot/ may use the subdir- trick to descend further down. Note 1: arch/$(ARCH)/Makefile cannot use "subdir-", because that file is @@ -834,7 +883,7 @@ When kbuild executes, the following steps are followed (roughly): LDFLAGS_vmlinux uses the LDFLAGS_$@ support. Example: - #arch/i386/Makefile + #arch/x86/Makefile LDFLAGS_vmlinux := -e stext OBJCOPYFLAGS objcopy flags @@ -872,14 +921,15 @@ When kbuild executes, the following steps are followed (roughly): Often, the KBUILD_CFLAGS variable depends on the configuration. Example: - #arch/i386/Makefile - cflags-$(CONFIG_M386) += -march=i386 + #arch/x86/boot/compressed/Makefile + cflags-$(CONFIG_X86_32) := -march=i386 + cflags-$(CONFIG_X86_64) := -mcmodel=small KBUILD_CFLAGS += $(cflags-y) Many arch Makefiles dynamically run the target C compiler to probe supported options: - #arch/i386/Makefile + #arch/x86/Makefile ... cflags-$(CONFIG_MPENTIUMII) += $(call cc-option,\ @@ -893,18 +943,53 @@ When kbuild executes, the following steps are followed (roughly): The first example utilises the trick that a config option expands to 'y' when selected. - CFLAGS_KERNEL $(CC) options specific for built-in + KBUILD_AFLAGS_KERNEL $(AS) options specific for built-in + + $(KBUILD_AFLAGS_KERNEL) contains extra C compiler flags used to compile + resident kernel code. + + KBUILD_AFLAGS_MODULE Options for $(AS) when building modules + + $(KBUILD_AFLAGS_MODULE) is used to add arch specific options that + are used for $(AS). + From commandline AFLAGS_MODULE shall be used (see kbuild.txt). + + KBUILD_CFLAGS_KERNEL $(CC) options specific for built-in - $(CFLAGS_KERNEL) contains extra C compiler flags used to compile + $(KBUILD_CFLAGS_KERNEL) contains extra C compiler flags used to compile resident kernel code. - CFLAGS_MODULE $(CC) options specific for modules + KBUILD_CFLAGS_MODULE Options for $(CC) when building modules - $(CFLAGS_MODULE) contains extra C compiler flags used to compile code - for loadable kernel modules. + $(KBUILD_CFLAGS_MODULE) is used to add arch specific options that + are used for $(CC). + From commandline CFLAGS_MODULE shall be used (see kbuild.txt). + KBUILD_LDFLAGS_MODULE Options for $(LD) when linking modules ---- 6.2 Add prerequisites to archprepare: + $(KBUILD_LDFLAGS_MODULE) is used to add arch specific options + used when linking modules. This is often a linker script. + From commandline LDFLAGS_MODULE shall be used (see kbuild.txt). + + KBUILD_ARFLAGS Options for $(AR) when creating archives + + $(KBUILD_ARFLAGS) set by the top level Makefile to "D" (deterministic + mode) if this option is supported by $(AR). + +--- 6.2 Add prerequisites to archheaders: + + The archheaders: rule is used to generate header files that + may be installed into user space by "make header_install" or + "make headers_install_all". In order to support + "make headers_install_all", this target has to be able to run + on an unconfigured tree, or a tree configured for another + architecture. + + It is run before "make archprepare" when run on the + architecture itself. + + +--- 6.3 Add prerequisites to archprepare: The archprepare: rule is used to list prerequisites that need to be built before starting to descend down in the subdirectories. @@ -920,7 +1005,7 @@ When kbuild executes, the following steps are followed (roughly): generating offset header files. ---- 6.3 List directories to visit when descending +--- 6.4 List directories to visit when descending An arch Makefile cooperates with the top Makefile to define variables which specify how to build the vmlinux file. Note that there is no @@ -949,7 +1034,7 @@ When kbuild executes, the following steps are followed (roughly): drivers-$(CONFIG_OPROFILE) += arch/sparc64/oprofile/ ---- 6.4 Architecture-specific boot images +--- 6.5 Architecture-specific boot images An arch Makefile specifies goals that take the vmlinux file, compress it, wrap it in bootstrapping code, and copy the resulting files @@ -968,8 +1053,8 @@ When kbuild executes, the following steps are followed (roughly): into the arch/$(ARCH)/boot/Makefile. Example: - #arch/i386/Makefile - boot := arch/i386/boot + #arch/x86/Makefile + boot := arch/x86/boot bzImage: vmlinux $(Q)$(MAKE) $(build)=$(boot) $(boot)/$@ @@ -981,7 +1066,7 @@ When kbuild executes, the following steps are followed (roughly): To support this, $(archhelp) must be defined. Example: - #arch/i386/Makefile + #arch/x86/Makefile define archhelp echo '* bzImage - Image (arch/$(ARCH)/boot/bzImage)' endif @@ -995,12 +1080,12 @@ When kbuild executes, the following steps are followed (roughly): from vmlinux. Example: - #arch/i386/Makefile + #arch/x86/Makefile all: bzImage When "make" is executed without arguments, bzImage will be built. ---- 6.5 Building non-kbuild targets +--- 6.6 Building non-kbuild targets extra-y @@ -1013,14 +1098,14 @@ When kbuild executes, the following steps are followed (roughly): 2) kbuild knows what files to delete during "make clean" Example: - #arch/i386/kernel/Makefile + #arch/x86/kernel/Makefile extra-y := head.o init_task.o In this example, extra-y is used to list object files that shall be built, but shall not be linked as part of built-in.o. ---- 6.6 Commands useful for building a boot image +--- 6.7 Commands useful for building a boot image Kbuild provides a few macros that are useful when building a boot image. @@ -1042,7 +1127,7 @@ When kbuild executes, the following steps are followed (roughly): always be built. Assignments to $(targets) are without $(obj)/ prefix. if_changed may be used in conjunction with custom commands as - defined in 6.7 "Custom kbuild commands". + defined in 6.8 "Custom kbuild commands". Note: It is a typical mistake to forget the FORCE prerequisite. Another common pitfall is that whitespace is sometimes @@ -1063,7 +1148,7 @@ When kbuild executes, the following steps are followed (roughly): Compress target. Use maximum compression to compress target. Example: - #arch/i386/boot/Makefile + #arch/x86/boot/Makefile LDFLAGS_bootsect := -Ttext 0x0 -s --oformat binary LDFLAGS_setup := -Ttext 0x0 -s --oformat binary -e begtext @@ -1085,8 +1170,47 @@ When kbuild executes, the following steps are followed (roughly): resulting in the target file being recompiled for no obvious reason. + dtc + Create flattened device tree blob object suitable for linking + into vmlinux. Device tree blobs linked into vmlinux are placed + in an init section in the image. Platform code *must* copy the + blob to non-init memory prior to calling unflatten_device_tree(). + + To use this command, simply add *.dtb into obj-y or targets, or make + some other target depend on %.dtb ---- 6.7 Custom kbuild commands + A central rule exists to create $(obj)/%.dtb from $(src)/%.dts; + architecture Makefiles do no need to explicitly write out that rule. + + Example: + targets += $(dtb-y) + clean-files += *.dtb + DTC_FLAGS ?= -p 1024 + + dtc_cpp + This is just like dtc as describe above, except that the C pre- + processor is invoked upon the .dtsp file before compiling the result + with dtc. + + In order for build dependencies to work, all files compiled using + dtc_cpp must use the C pre-processor's #include functionality and not + dtc's /include/ functionality. + + Using the C pre-processor allows use of #define to create named + constants. In turn, the #defines will typically appear in a header + file, which may be shared with regular C code. Since the dtc language + represents a data structure rather than code in C syntax, similar + restrictions are placed on a header file included by a device tree + file as for a header file included by an assembly language file. + In particular, the C pre-processor is passed -x assembler-with-cpp, + which sets macro __ASSEMBLY__. __DTS__ is also set. These allow header + files to restrict their content to that compatible with device tree + source. + + A central rule exists to create $(obj)/%.dtb from $(src)/%.dtsp; + architecture Makefiles do no need to explicitly write out that rule. + +--- 6.8 Custom kbuild commands When kbuild is executing with KBUILD_VERBOSE=0, then only a shorthand of a command is normally displayed. @@ -1108,12 +1232,12 @@ When kbuild executes, the following steps are followed (roughly): When updating the $(obj)/bzImage target, the line - BUILD arch/i386/boot/bzImage + BUILD arch/x86/boot/bzImage will be displayed with "make KBUILD_VERBOSE=0". ---- 6.8 Preprocessing linker scripts +--- 6.9 Preprocessing linker scripts When the vmlinux image is built, the linker script arch/$(ARCH)/kernel/vmlinux.lds is used. @@ -1122,7 +1246,7 @@ When kbuild executes, the following steps are followed (roughly): kbuild knows .lds files and includes a rule *lds.S -> *lds. Example: - #arch/i386/kernel/Makefile + #arch/x86/kernel/Makefile always := vmlinux.lds #Makefile @@ -1143,8 +1267,98 @@ When kbuild executes, the following steps are followed (roughly): The kbuild infrastructure for *lds file are used in several architecture-specific files. +--- 6.10 Generic header files + + The directory include/asm-generic contains the header files + that may be shared between individual architectures. + The recommended approach how to use a generic header file is + to list the file in the Kbuild file. + See "7.4 generic-y" for further info on syntax etc. + +=== 7 Kbuild syntax for exported headers + +The kernel include a set of headers that is exported to userspace. +Many headers can be exported as-is but other headers require a +minimal pre-processing before they are ready for user-space. +The pre-processing does: +- drop kernel specific annotations +- drop include of compiler.h +- drop all sections that are kernel internal (guarded by ifdef __KERNEL__) + +Each relevant directory contains a file name "Kbuild" which specifies the +headers to be exported. +See subsequent chapter for the syntax of the Kbuild file. + + --- 7.1 header-y + + header-y specify header files to be exported. + + Example: + #include/linux/Kbuild + header-y += usb/ + header-y += aio_abi.h + + The convention is to list one file per line and + preferably in alphabetic order. + + header-y also specify which subdirectories to visit. + A subdirectory is identified by a trailing '/' which + can be seen in the example above for the usb subdirectory. + + Subdirectories are visited before their parent directories. + + --- 7.2 genhdr-y + + genhdr-y specifies generated files to be exported. + Generated files are special as they need to be looked + up in another directory when doing 'make O=...' builds. + + Example: + #include/linux/Kbuild + genhdr-y += version.h + + --- 7.3 destination-y + + When an architecture have a set of exported headers that needs to be + exported to a different directory destination-y is used. + destination-y specify the destination directory for all exported + headers in the file where it is present. + + Example: + #arch/xtensa/platforms/s6105/include/platform/Kbuild + destination-y := include/linux + + In the example above all exported headers in the Kbuild file + will be located in the directory "include/linux" when exported. + + --- 7.4 generic-y + + If an architecture uses a verbatim copy of a header from + include/asm-generic then this is listed in the file + arch/$(ARCH)/include/asm/Kbuild like this: + + Example: + #arch/x86/include/asm/Kbuild + generic-y += termios.h + generic-y += rtc.h + + During the prepare phase of the build a wrapper include + file is generated in the directory: + + arch/$(ARCH)/include/generated/asm + + When a header is exported where the architecture uses + the generic header a similar wrapper is generated as part + of the set of exported headers in the directory: + + usr/include/asm + + The generated wrapper will in both cases look like the following: + + Example: termios.h + #include <asm-generic/termios.h> -=== 7 Kbuild Variables +=== 8 Kbuild Variables The top Makefile exports the following variables: @@ -1203,10 +1417,11 @@ The top Makefile exports the following variables: If this variable is specified, 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 will used as the option(s) to the strip command. + INSTALL_MOD_STRIP value will be used as the option(s) to the strip + command. -=== 8 Makefile language +=== 9 Makefile language The kernel Makefiles are designed to be run with GNU Make. The Makefiles use only the documented features of GNU Make, but they do use many @@ -1225,14 +1440,14 @@ time the left-hand side is used. There are some cases where "=" is appropriate. Usually, though, ":=" is the right choice. -=== 9 Credits +=== 10 Credits Original version made by Michael Elizabeth Chastain, <mailto:mec@shout.net> Updates by Kai Germaschewski <kai@tp1.ruhr-uni-bochum.de> Updates by Sam Ravnborg <sam@ravnborg.org> Language QA by Jan Engelhardt <jengelh@gmx.de> -=== 10 TODO +=== 11 TODO - Describe how kbuild supports shipped files with _shipped. - Generating offset header files. diff --git a/Documentation/kbuild/modules.txt b/Documentation/kbuild/modules.txt index b1096da953c..3fb39e0116b 100644 --- a/Documentation/kbuild/modules.txt +++ b/Documentation/kbuild/modules.txt @@ -1,215 +1,185 @@ +Building External Modules -In this document you will find information about: -- how to build external modules -- how to make your module use the kbuild infrastructure -- how kbuild will install a kernel -- how to install modules in a non-standard location +This document describes how to build an out-of-tree kernel module. === Table of Contents === 1 Introduction - === 2 How to build external modules - --- 2.1 Building external modules - --- 2.2 Available targets - --- 2.3 Available options - --- 2.4 Preparing the kernel tree for module build - --- 2.5 Building separate files for a module - === 3. Example commands - === 4. Creating a kbuild file for an external module - === 5. Include files - --- 5.1 How to include files from the kernel include dir - --- 5.2 External modules using an include/ dir - --- 5.3 External modules using several directories - === 6. Module installation - --- 6.1 INSTALL_MOD_PATH - --- 6.2 INSTALL_MOD_DIR - === 7. Module versioning & Module.symvers - --- 7.1 Symbols from the kernel (vmlinux + modules) - --- 7.2 Symbols and external modules - --- 7.3 Symbols from another external module - === 8. Tips & Tricks - --- 8.1 Testing for CONFIG_FOO_BAR + === 2 How to Build External Modules + --- 2.1 Command Syntax + --- 2.2 Options + --- 2.3 Targets + --- 2.4 Building Separate Files + === 3. Creating a Kbuild File for an External Module + --- 3.1 Shared Makefile + --- 3.2 Separate Kbuild file and Makefile + --- 3.3 Binary Blobs + --- 3.4 Building Multiple Modules + === 4. Include Files + --- 4.1 Kernel Includes + --- 4.2 Single Subdirectory + --- 4.3 Several Subdirectories + === 5. Module Installation + --- 5.1 INSTALL_MOD_PATH + --- 5.2 INSTALL_MOD_DIR + === 6. Module Versioning + --- 6.1 Symbols From the Kernel (vmlinux + modules) + --- 6.2 Symbols and External Modules + --- 6.3 Symbols From Another External Module + === 7. Tips & Tricks + --- 7.1 Testing for CONFIG_FOO_BAR === 1. Introduction -kbuild includes functionality for building modules both -within the kernel source tree and outside the kernel source tree. -The latter is usually referred to as external or "out-of-tree" -modules and is used both during development and for modules that -are not planned to be included in the kernel tree. +"kbuild" is the build system used by the Linux kernel. Modules must use +kbuild to stay compatible with changes in the build infrastructure and +to pick up the right flags to "gcc." Functionality for building modules +both in-tree and out-of-tree is provided. The method for building +either is similar, and all modules are initially developed and built +out-of-tree. -What is covered within this file is mainly information to authors -of modules. The author of an external module should supply -a makefile that hides most of the complexity, so one only has to type -'make' to build the module. A complete example will be presented in -chapter 4, "Creating a kbuild file for an external module". +Covered in this document is information aimed at developers interested +in building out-of-tree (or "external") modules. The author of an +external module should supply a makefile that hides most of the +complexity, so one only has to type "make" to build the module. This is +easily accomplished, and a complete example will be presented in +section 3. -=== 2. How to build external modules +=== 2. How to Build External Modules -kbuild offers functionality to build external modules, with the -prerequisite that there is a pre-built kernel available with full source. -A subset of the targets available when building the kernel is available -when building an external module. +To build external modules, you must have a prebuilt kernel available +that contains the configuration and header files used in the build. +Also, the kernel must have been built with modules enabled. If you are +using a distribution kernel, there will be a package for the kernel you +are running provided by your distribution. ---- 2.1 Building external modules +An alternative is to use the "make" target "modules_prepare." This will +make sure the kernel contains the information required. The target +exists solely as a simple way to prepare a kernel source tree for +building external modules. - Use the following command to build an external module: +NOTE: "modules_prepare" will not build Module.symvers even if +CONFIG_MODVERSIONS is set; therefore, a full kernel build needs to be +executed to make module versioning work. - make -C <path-to-kernel> M=`pwd` +--- 2.1 Command Syntax - For the running kernel use: + The command to build an external module is: - make -C /lib/modules/`uname -r`/build M=`pwd` + $ make -C <path_to_kernel_src> M=$PWD - For the above command to succeed, the kernel must have been - built with modules enabled. + The kbuild system knows that an external module is being built + due to the "M=<dir>" option given in the command. - To install the modules that were just built: + To build against the running kernel use: - make -C <path-to-kernel> M=`pwd` modules_install + $ make -C /lib/modules/`uname -r`/build M=$PWD - More complex examples will be shown later, the above should - be enough to get you started. + Then to install the module(s) just built, add the target + "modules_install" to the command: ---- 2.2 Available targets + $ make -C /lib/modules/`uname -r`/build M=$PWD modules_install - $KDIR refers to the path to the kernel source top-level directory +--- 2.2 Options - make -C $KDIR M=`pwd` - Will build the module(s) located in current directory. - All output files will be located in the same directory - as the module source. - No attempts are made to update the kernel source, and it is - a precondition that a successful make has been executed - for the kernel. + ($KDIR refers to the path of the kernel source directory.) - make -C $KDIR M=`pwd` modules - The modules target is implied when no target is given. - Same functionality as if no target was specified. - See description above. + make -C $KDIR M=$PWD - make -C $KDIR M=`pwd` modules_install - Install the external module(s). - Installation default is in /lib/modules/<kernel-version>/extra, - but may be prefixed with INSTALL_MOD_PATH - see separate - chapter. + -C $KDIR + The directory where the kernel source is located. + "make" will actually change to the specified directory + when executing and will change back when finished. - make -C $KDIR M=`pwd` clean - Remove all generated files for the module - the kernel - source directory is not modified. + M=$PWD + Informs kbuild that an external module is being built. + The value given to "M" is the absolute path of the + directory where the external module (kbuild file) is + located. - make -C $KDIR M=`pwd` help - help will list the available target when building external - modules. +--- 2.3 Targets ---- 2.3 Available options: + When building an external module, only a subset of the "make" + targets are available. - $KDIR refers to the path to the kernel source top-level directory + make -C $KDIR M=$PWD [target] - make -C $KDIR - Used to specify where to find the kernel source. - '$KDIR' represent the directory where the kernel source is. - Make will actually change directory to the specified directory - when executed but change back when finished. + The default will build the module(s) located in the current + directory, so a target does not need to be specified. All + output files will also be generated in this directory. No + attempts are made to update the kernel source, and it is a + precondition that a successful "make" has been executed for the + kernel. - make -C $KDIR M=`pwd` - M= is used to tell kbuild that an external module is - being built. - The option given to M= is the directory where the external - module (kbuild file) is located. - When an external module is being built only a subset of the - usual targets are available. + modules + The default target for external modules. It has the + same functionality as if no target was specified. See + description above. - make -C $KDIR SUBDIRS=`pwd` - Same as M=. The SUBDIRS= syntax is kept for backwards - compatibility. + modules_install + Install the external module(s). The default location is + /lib/modules/<kernel_release>/extra/, but a prefix may + be added with INSTALL_MOD_PATH (discussed in section 5). ---- 2.4 Preparing the kernel tree for module build + clean + Remove all generated files in the module directory only. - To make sure the kernel contains the information required to - build external modules the target 'modules_prepare' must be used. - 'modules_prepare' exists solely as a simple way to prepare - a kernel source tree for building external modules. - Note: modules_prepare will not build Module.symvers even if - CONFIG_MODVERSIONS is set. Therefore a full kernel build - needs to be executed to make module versioning work. + help + List the available targets for external modules. ---- 2.5 Building separate files for a module - It is possible to build single files which are part of a module. - This works equally well for the kernel, a module and even for - external modules. - Examples (module foo.ko, consist of bar.o, baz.o): - make -C $KDIR M=`pwd` bar.lst - make -C $KDIR M=`pwd` bar.o - make -C $KDIR M=`pwd` foo.ko - make -C $KDIR M=`pwd` / - - -=== 3. Example commands - -This example shows the actual commands to be executed when building -an external module for the currently running kernel. -In the example below, the distribution is supposed to use the -facility to locate output files for a kernel compile in a different -directory than the kernel source - but the examples will also work -when the source and the output files are mixed in the same directory. +--- 2.4 Building Separate Files -# Kernel source -/lib/modules/<kernel-version>/source -> /usr/src/linux-<version> - -# Output from kernel compile -/lib/modules/<kernel-version>/build -> /usr/src/linux-<version>-up - -Change to the directory where the kbuild file is located and execute -the following commands to build the module: + It is possible to build single files that are part of a module. + This works equally well for the kernel, a module, and even for + external modules. - cd /home/user/src/module - make -C /usr/src/`uname -r`/source \ - O=/lib/modules/`uname-r`/build \ - M=`pwd` + Example (The module foo.ko, consist of bar.o and baz.o): + make -C $KDIR M=$PWD bar.lst + make -C $KDIR M=$PWD baz.o + make -C $KDIR M=$PWD foo.ko + make -C $KDIR M=$PWD / -Then, to install the module use the following command: - make -C /usr/src/`uname -r`/source \ - O=/lib/modules/`uname-r`/build \ - M=`pwd` \ - modules_install +=== 3. Creating a Kbuild File for an External Module -If you look closely you will see that this is the same command as -listed before - with the directories spelled out. +In the last section we saw the command to build a module for the +running kernel. The module is not actually built, however, because a +build file is required. Contained in this file will be the name of +the module(s) being built, along with the list of requisite source +files. The file may be as simple as a single line: -The above are rather long commands, and the following chapter -lists a few tricks to make it all easier. + obj-m := <module_name>.o +The kbuild system will build <module_name>.o from <module_name>.c, +and, after linking, will result in the kernel module <module_name>.ko. +The above line can be put in either a "Kbuild" file or a "Makefile." +When the module is built from multiple sources, an additional line is +needed listing the files: -=== 4. Creating a kbuild file for an external module + <module_name>-y := <src1>.o <src2>.o ... -kbuild is the build system for the kernel, and external modules -must use kbuild to stay compatible with changes in the build system -and to pick up the right flags to gcc etc. +NOTE: Further documentation describing the syntax used by kbuild is +located in Documentation/kbuild/makefiles.txt. -The kbuild file used as input shall follow the syntax described -in Documentation/kbuild/makefiles.txt. This chapter will introduce a few -more tricks to be used when dealing with external modules. +The examples below demonstrate how to create a build file for the +module 8123.ko, which is built from the following files: -In the following a Makefile will be created for a module with the -following files: 8123_if.c 8123_if.h 8123_pci.c 8123_bin.o_shipped <= Binary blob ---- 4.1 Shared Makefile for module and kernel +--- 3.1 Shared Makefile - An external module always includes a wrapper Makefile supporting - building the module using 'make' with no arguments. - The Makefile provided will most likely include additional - functionality such as test targets etc. and this part shall - be filtered away from kbuild since it may impact kbuild if - name clashes occurs. + An external module always includes a wrapper makefile that + supports building the module using "make" with no arguments. + This target is not used by kbuild; it is only for convenience. + Additional functionality, such as test targets, can be included + but should be filtered out from kbuild due to possible name + clashes. Example 1: --> filename: Makefile @@ -219,11 +189,11 @@ following files: 8123-y := 8123_if.o 8123_pci.o 8123_bin.o else - # Normal Makefile + # normal makefile + KDIR ?= /lib/modules/`uname -r`/build - KERNELDIR := /lib/modules/`uname -r`/build - all:: - $(MAKE) -C $(KERNELDIR) M=`pwd` $@ + default: + $(MAKE) -C $(KDIR) M=$$PWD # Module specific targets genbin: @@ -231,15 +201,20 @@ following files: endif - In example 1, the check for KERNELRELEASE is used to separate - the two parts of the Makefile. kbuild will only see the two - assignments whereas make will see everything except the two - kbuild assignments. + The check for KERNELRELEASE is used to separate the two parts + of the makefile. In the example, kbuild will only see the two + assignments, whereas "make" will see everything except these + two assignments. This is due to two passes made on the file: + the first pass is by the "make" instance run on the command + line; the second pass is by the kbuild system, which is + initiated by the parameterized "make" in the default target. + +--- 3.2 Separate Kbuild File and Makefile - In recent versions of the kernel, kbuild will look for a file named - Kbuild and as second option look for a file named Makefile. - Utilising the Kbuild file makes us split up the Makefile in example 1 - into two files as shown in example 2: + In newer versions of the kernel, kbuild will first look for a + file named "Kbuild," and only if that is not found, will it + then look for a makefile. Utilizing a "Kbuild" file allows us + to split up the makefile from example 1 into two files: Example 2: --> filename: Kbuild @@ -247,20 +222,21 @@ following files: 8123-y := 8123_if.o 8123_pci.o 8123_bin.o --> filename: Makefile - KERNELDIR := /lib/modules/`uname -r`/build - all:: - $(MAKE) -C $(KERNELDIR) M=`pwd` $@ + KDIR ?= /lib/modules/`uname -r`/build + + default: + $(MAKE) -C $(KDIR) M=$$PWD # Module specific targets genbin: echo "X" > 8123_bin.o_shipped + The split in example 2 is questionable due to the simplicity of + each file; however, some external modules use makefiles + consisting of several hundred lines, and here it really pays + off to separate the kbuild part from the rest. - In example 2, we are down to two fairly simple files and for simple - files as used in this example the split is questionable. But some - external modules use Makefiles of several hundred lines and here it - really pays off to separate the kbuild part from the rest. - Example 3 shows a backward compatible version. + The next example shows a backward compatible version. Example 3: --> filename: Kbuild @@ -269,13 +245,15 @@ following files: --> filename: Makefile ifneq ($(KERNELRELEASE),) + # kbuild part of makefile include Kbuild + else - # Normal Makefile + # normal makefile + KDIR ?= /lib/modules/`uname -r`/build - KERNELDIR := /lib/modules/`uname -r`/build - all:: - $(MAKE) -C $KERNELDIR M=`pwd` $@ + default: + $(MAKE) -C $(KDIR) M=$$PWD # Module specific targets genbin: @@ -283,260 +261,271 @@ following files: endif - The trick here is to include the Kbuild file from Makefile, so - if an older version of kbuild picks up the Makefile, the Kbuild - file will be included. + Here the "Kbuild" file is included from the makefile. This + allows an older version of kbuild, which only knows of + makefiles, to be used when the "make" and kbuild parts are + split into separate files. ---- 4.2 Binary blobs included in a module +--- 3.3 Binary Blobs - Some external modules needs to include a .o as a blob. kbuild - has support for this, but requires the blob file to be named - <filename>_shipped. In our example the blob is named - 8123_bin.o_shipped and when the kbuild rules kick in the file - 8123_bin.o is created as a simple copy off the 8213_bin.o_shipped file - with the _shipped part stripped of the filename. - This allows the 8123_bin.o filename to be used in the assignment to - the module. + Some external modules need to include an object file as a blob. + kbuild has support for this, but requires the blob file to be + named <filename>_shipped. When the kbuild rules kick in, a copy + of <filename>_shipped is created with _shipped stripped off, + giving us <filename>. This shortened filename can be used in + the assignment to the module. + + Throughout this section, 8123_bin.o_shipped has been used to + build the kernel module 8123.ko; it has been included as + 8123_bin.o. - Example 4: - obj-m := 8123.o 8123-y := 8123_if.o 8123_pci.o 8123_bin.o - In example 4, there is no distinction between the ordinary .c/.h files - and the binary file. But kbuild will pick up different rules to create - the .o file. + Although there is no distinction between the ordinary source + files and the binary file, kbuild will pick up different rules + when creating the object file for the module. + +--- 3.4 Building Multiple Modules + kbuild supports building multiple modules with a single build + file. For example, if you wanted to build two modules, foo.ko + and bar.ko, the kbuild lines would be: -=== 5. Include files + obj-m := foo.o bar.o + foo-y := <foo_srcs> + bar-y := <bar_srcs> -Include files are a necessity when a .c file uses something from other .c -files (not strictly in the sense of C, but if good programming practice is -used). Any module that consists of more than one .c file will have a .h file -for one of the .c files. + It is that simple! -- If the .h file only describes a module internal interface, then the .h file - shall be placed in the same directory as the .c files. -- If the .h files describe an interface used by other parts of the kernel - located in different directories, the .h files shall be located in - include/linux/ or other include/ directories as appropriate. -One exception for this rule is larger subsystems that have their own directory -under include/ such as include/scsi. Another exception is arch-specific -.h files which are located under include/asm-$(ARCH)/*. +=== 4. Include Files -External modules have a tendency to locate include files in a separate include/ -directory and therefore need to deal with this in their kbuild file. +Within the kernel, header files are kept in standard locations +according to the following rule: ---- 5.1 How to include files from the kernel include dir + * If the header file only describes the internal interface of a + module, then the file is placed in the same directory as the + source files. + * If the header file describes an interface used by other parts + of the kernel that are located in different directories, then + the file is placed in include/linux/. - When a module needs to include a file from include/linux/, then one - just uses: + NOTE: There are two notable exceptions to this rule: larger + subsystems have their own directory under include/, such as + include/scsi; and architecture specific headers are located + under arch/$(ARCH)/include/. - #include <linux/modules.h> +--- 4.1 Kernel Includes - kbuild will make sure to add options to gcc so the relevant - directories are searched. - Likewise for .h files placed in the same directory as the .c file. + To include a header file located under include/linux/, simply + use: - #include "8123_if.h" + #include <linux/module.h> - will do the job. + kbuild will add options to "gcc" so the relevant directories + are searched. ---- 5.2 External modules using an include/ dir +--- 4.2 Single Subdirectory - External modules often locate their .h files in a separate include/ - directory although this is not usual kernel style. When an external - module uses an include/ dir then kbuild needs to be told so. - The trick here is to use either EXTRA_CFLAGS (take effect for all .c - files) or CFLAGS_$F.o (take effect only for a single file). + External modules tend to place header files in a separate + include/ directory where their source is located, although this + is not the usual kernel style. To inform kbuild of the + directory, use either ccflags-y or CFLAGS_<filename>.o. - In our example, if we move 8123_if.h to a subdirectory named include/ - the resulting Kbuild file would look like: + Using the example from section 3, if we moved 8123_if.h to a + subdirectory named include, the resulting kbuild file would + look like: --> filename: Kbuild - obj-m := 8123.o + obj-m := 8123.o - EXTRA_CFLAGS := -Iinclude + ccflags-y := -Iinclude 8123-y := 8123_if.o 8123_pci.o 8123_bin.o - Note that in the assignment there is no space between -I and the path. - This is a kbuild limitation: there must be no space present. + Note that in the assignment there is no space between -I and + the path. This is a limitation of kbuild: there must be no + space present. ---- 5.3 External modules using several directories - - If an external module does not follow the usual kernel style, but - decides to spread files over several directories, then kbuild can - handle this too. +--- 4.3 Several Subdirectories + kbuild can handle files that are spread over several directories. Consider the following example: - | - +- src/complex_main.c - | +- hal/hardwareif.c - | +- hal/include/hardwareif.h - +- include/complex.h - - To build a single module named complex.ko, we then need the following + . + |__ src + | |__ complex_main.c + | |__ hal + | |__ hardwareif.c + | |__ include + | |__ hardwareif.h + |__ include + |__ complex.h + + To build the module complex.ko, we then need the following kbuild file: - Kbuild: + --> filename: Kbuild obj-m := complex.o complex-y := src/complex_main.o complex-y += src/hal/hardwareif.o - EXTRA_CFLAGS := -I$(src)/include - EXTRA_CFLAGS += -I$(src)src/hal/include + ccflags-y := -I$(src)/include + ccflags-y += -I$(src)/src/hal/include + As you can see, kbuild knows how to handle object files located + in other directories. The trick is to specify the directory + relative to the kbuild file's location. That being said, this + is NOT recommended practice. - kbuild knows how to handle .o files located in another directory - - although this is NOT recommended practice. The syntax is to specify - the directory relative to the directory where the Kbuild file is - located. + For the header files, kbuild must be explicitly told where to + look. When kbuild executes, the current directory is always the + root of the kernel tree (the argument to "-C") and therefore an + absolute path is needed. $(src) provides the absolute path by + pointing to the directory where the currently executing kbuild + file is located. - To find the .h files, we have to explicitly tell kbuild where to look - for the .h files. When kbuild executes, the current directory is always - the root of the kernel tree (argument to -C) and therefore we have to - tell kbuild how to find the .h files using absolute paths. - $(src) will specify the absolute path to the directory where the - Kbuild file are located when being build as an external module. - Therefore -I$(src)/ is used to point out the directory of the Kbuild - file and any additional path are just appended. -=== 6. Module installation +=== 5. Module Installation -Modules which are included in the kernel are installed in the directory: +Modules which are included in the kernel are installed in the +directory: - /lib/modules/$(KERNELRELEASE)/kernel + /lib/modules/$(KERNELRELEASE)/kernel/ -External modules are installed in the directory: +And external modules are installed in: - /lib/modules/$(KERNELRELEASE)/extra + /lib/modules/$(KERNELRELEASE)/extra/ ---- 6.1 INSTALL_MOD_PATH +--- 5.1 INSTALL_MOD_PATH - Above are the default directories, but as always, some level of - customization is possible. One can prefix the path using the variable - INSTALL_MOD_PATH: + Above are the default directories but as always some level of + customization is possible. A prefix can be added to the + installation path using the variable INSTALL_MOD_PATH: $ make INSTALL_MOD_PATH=/frodo modules_install - => Install dir: /frodo/lib/modules/$(KERNELRELEASE)/kernel - - INSTALL_MOD_PATH may be set as an ordinary shell variable or as in the - example above, can be specified on the command line when calling make. - INSTALL_MOD_PATH has effect both when installing modules included in - the kernel as well as when installing external modules. + => Install dir: /frodo/lib/modules/$(KERNELRELEASE)/kernel/ ---- 6.2 INSTALL_MOD_DIR + INSTALL_MOD_PATH may be set as an ordinary shell variable or, + as shown above, can be specified on the command line when + calling "make." This has effect when installing both in-tree + and out-of-tree modules. - When installing external modules they are by default installed to a - directory under /lib/modules/$(KERNELRELEASE)/extra, but one may wish - to locate modules for a specific functionality in a separate - directory. For this purpose, one can use INSTALL_MOD_DIR to specify an - alternative name to 'extra'. +--- 5.2 INSTALL_MOD_DIR - $ make INSTALL_MOD_DIR=gandalf -C KERNELDIR \ - M=`pwd` modules_install - => Install dir: /lib/modules/$(KERNELRELEASE)/gandalf + External modules are by default installed to a directory under + /lib/modules/$(KERNELRELEASE)/extra/, but you may wish to + locate modules for a specific functionality in a separate + directory. For this purpose, use INSTALL_MOD_DIR to specify an + alternative name to "extra." + $ make INSTALL_MOD_DIR=gandalf -C $KDIR \ + M=$PWD modules_install + => Install dir: /lib/modules/$(KERNELRELEASE)/gandalf/ -=== 7. Module versioning & Module.symvers -Module versioning is enabled by the CONFIG_MODVERSIONS tag. +=== 6. Module Versioning -Module versioning is used as a simple ABI consistency check. The Module -versioning creates a CRC value of the full prototype for an exported symbol and -when a module is loaded/used then the CRC values contained in the kernel are -compared with similar values in the module. If they are not equal, then the -kernel refuses to load the module. +Module versioning is enabled by the CONFIG_MODVERSIONS tag, and is used +as a simple ABI consistency check. A CRC value of the full prototype +for an exported symbol is created. When a module is loaded/used, the +CRC values contained in the kernel are compared with similar values in +the module; if they are not equal, the kernel refuses to load the +module. -Module.symvers contains a list of all exported symbols from a kernel build. +Module.symvers contains a list of all exported symbols from a kernel +build. ---- 7.1 Symbols from the kernel (vmlinux + modules) +--- 6.1 Symbols From the Kernel (vmlinux + modules) - During a kernel build, a file named Module.symvers will be generated. - Module.symvers contains all exported symbols from the kernel and - compiled modules. For each symbols, the corresponding CRC value - is stored too. + During a kernel build, a file named Module.symvers will be + generated. Module.symvers contains all exported symbols from + the kernel and compiled modules. For each symbol, the + corresponding CRC value is also stored. The syntax of the Module.symvers file is: - <CRC> <Symbol> <module> - Sample: + <CRC> <Symbol> <module> + 0x2d036834 scsi_remove_host drivers/scsi/scsi_mod - For a kernel build without CONFIG_MODVERSIONS enabled, the crc - would read: 0x00000000 + For a kernel build without CONFIG_MODVERSIONS enabled, the CRC + would read 0x00000000. Module.symvers serves two purposes: - 1) It lists all exported symbols both from vmlinux and all modules - 2) It lists the CRC if CONFIG_MODVERSIONS is enabled - ---- 7.2 Symbols and external modules - - When building an external module, the build system needs access to - the symbols from the kernel to check if all external symbols are - defined. This is done in the MODPOST step and to obtain all - symbols, modpost reads Module.symvers from the kernel. - If a Module.symvers file is present in the directory where - the external module is being built, this file will be read too. - During the MODPOST step, a new Module.symvers file will be written - containing all exported symbols that were not defined in the kernel. - ---- 7.3 Symbols from another external module - - Sometimes, an external module uses exported symbols from another - external module. Kbuild needs to have full knowledge on all symbols - to avoid spitting out warnings about undefined symbols. - Three solutions exist to let kbuild know all symbols of more than - one external module. - The method with a top-level kbuild file is recommended but may be - impractical in certain situations. - - Use a top-level Kbuild file - If you have two modules: 'foo' and 'bar', and 'foo' needs - symbols from 'bar', then one can use a common top-level kbuild - file so both modules are compiled in same build. - - Consider following directory layout: - ./foo/ <= contains the foo module - ./bar/ <= contains the bar module - The top-level Kbuild file would then look like: - - #./Kbuild: (this file may also be named Makefile) + 1) It lists all exported symbols from vmlinux and all modules. + 2) It lists the CRC if CONFIG_MODVERSIONS is enabled. + +--- 6.2 Symbols and External Modules + + When building an external module, the build system needs access + to the symbols from the kernel to check if all external symbols + are defined. This is done in the MODPOST step. modpost obtains + the symbols by reading Module.symvers from the kernel source + tree. If a Module.symvers file is present in the directory + where the external module is being built, this file will be + read too. During the MODPOST step, a new Module.symvers file + will be written containing all exported symbols that were not + defined in the kernel. + +--- 6.3 Symbols From Another External Module + + Sometimes, an external module uses exported symbols from + another external module. kbuild needs to have full knowledge of + all symbols to avoid spitting out warnings about undefined + symbols. Three solutions exist for this situation. + + NOTE: The method with a top-level kbuild file is recommended + but may be impractical in certain situations. + + Use a top-level kbuild file + If you have two modules, foo.ko and bar.ko, where + foo.ko needs symbols from bar.ko, you can use a + common top-level kbuild file so both modules are + compiled in the same build. Consider the following + directory layout: + + ./foo/ <= contains foo.ko + ./bar/ <= contains bar.ko + + The top-level kbuild file would then look like: + + #./Kbuild (or ./Makefile): obj-y := foo/ bar/ - Executing: - make -C $KDIR M=`pwd` + And executing + + $ make -C $KDIR M=$PWD - will then do the expected and compile both modules with full - knowledge on symbols from both modules. + will then do the expected and compile both modules with + full knowledge of symbols from either module. Use an extra Module.symvers file - When an external module is built, a Module.symvers file is - generated containing all exported symbols which are not - defined in the kernel. - To get access to symbols from module 'bar', one can copy the - Module.symvers file from the compilation of the 'bar' module - to the directory where the 'foo' module is built. - During the module build, kbuild will read the Module.symvers - file in the directory of the external module and when the - build is finished, a new Module.symvers file is created - containing the sum of all symbols defined and not part of the - kernel. - - Use make variable KBUILD_EXTRA_SYMBOLS in the Makefile - If it is impractical to copy Module.symvers from another - module, you can assign a space separated list of files to - KBUILD_EXTRA_SYMBOLS in your Makfile. These files will be - loaded by modpost during the initialisation of its symbol - tables. - -=== 8. Tips & Tricks - ---- 8.1 Testing for CONFIG_FOO_BAR - - Modules often need to check for certain CONFIG_ options to decide if - a specific feature shall be included in the module. When kbuild is used - this is done by referencing the CONFIG_ variable directly. + When an external module is built, a Module.symvers file + is generated containing all exported symbols which are + not defined in the kernel. To get access to symbols + from bar.ko, copy the Module.symvers file from the + compilation of bar.ko to the directory where foo.ko is + built. During the module build, kbuild will read the + Module.symvers file in the directory of the external + module, and when the build is finished, a new + Module.symvers file is created containing the sum of + all symbols defined and not part of the kernel. + + Use "make" variable KBUILD_EXTRA_SYMBOLS + If it is impractical to copy Module.symvers from + another module, you can assign a space separated list + of files to KBUILD_EXTRA_SYMBOLS in your build file. + These files will be loaded by modpost during the + initialization of its symbol tables. + + +=== 7. Tips & Tricks + +--- 7.1 Testing for CONFIG_FOO_BAR + + Modules often need to check for certain CONFIG_ options to + decide if a specific feature is included in the module. In + kbuild this is done by referencing the CONFIG_ variable + directly. #fs/ext2/Makefile obj-$(CONFIG_EXT2_FS) += ext2.o @@ -544,9 +533,9 @@ Module.symvers contains a list of all exported symbols from a kernel build. ext2-y := balloc.o bitmap.o dir.o ext2-$(CONFIG_EXT2_FS_XATTR) += xattr.o - External modules have traditionally used grep to check for specific - CONFIG_ settings directly in .config. This usage is broken. - As introduced before, external modules shall use kbuild when building - and therefore can use the same methods as in-kernel modules when - testing for CONFIG_ definitions. + External modules have traditionally used "grep" to check for + specific CONFIG_ settings directly in .config. This usage is + broken. As introduced before, external modules should use + kbuild for building and can therefore use the same methods as + in-tree modules when testing for CONFIG_ definitions. |