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![Nicholas Piggin](/assets/img/avatar_default.png)
Allow architectures to create arch/xxx/Makefile.postlink with targets for vmlinux, modules.ko, and clean, which will be invoked after final linking of vmlinux and modules. powerpc will use this to check vmlinux linker relocations for sanity, and may use it to fix up alternate instruction patch branch addresses. Signed-off-by: Nicholas Piggin <npiggin@gmail.com> Signed-off-by: Michal Marek <mmarek@suse.com>
1448 lines
48 KiB
Text
1448 lines
48 KiB
Text
Linux Kernel Makefiles
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This document describes the Linux kernel Makefiles.
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=== Table of Contents
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=== 1 Overview
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=== 2 Who does what
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=== 3 The kbuild files
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--- 3.1 Goal definitions
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--- 3.2 Built-in object goals - obj-y
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--- 3.3 Loadable module goals - obj-m
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--- 3.4 Objects which export symbols
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--- 3.5 Library file goals - lib-y
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--- 3.6 Descending down in directories
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--- 3.7 Compilation flags
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--- 3.8 Command line dependency
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--- 3.9 Dependency tracking
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--- 3.10 Special Rules
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--- 3.11 $(CC) support functions
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--- 3.12 $(LD) support functions
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=== 4 Host Program support
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--- 4.1 Simple Host Program
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--- 4.2 Composite Host Programs
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--- 4.3 Using C++ for host programs
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--- 4.4 Controlling compiler options for host programs
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--- 4.5 When host programs are actually built
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--- 4.6 Using hostprogs-$(CONFIG_FOO)
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=== 5 Kbuild clean infrastructure
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=== 6 Architecture Makefiles
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--- 6.1 Set variables to tweak the build to the architecture
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--- 6.2 Add prerequisites to archheaders:
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--- 6.3 Add prerequisites to archprepare:
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--- 6.4 List directories to visit when descending
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--- 6.5 Architecture-specific boot images
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--- 6.6 Building non-kbuild targets
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--- 6.7 Commands useful for building a boot image
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--- 6.8 Custom kbuild commands
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--- 6.9 Preprocessing linker scripts
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--- 6.10 Generic header files
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--- 6.11 Post-link pass
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=== 7 Kbuild syntax for exported headers
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--- 7.1 header-y
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--- 7.2 genhdr-y
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--- 7.3 destination-y
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--- 7.4 generic-y
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--- 7.5 generated-y
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=== 8 Kbuild Variables
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=== 9 Makefile language
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=== 10 Credits
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=== 11 TODO
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=== 1 Overview
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The Makefiles have five parts:
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Makefile the top Makefile.
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.config the kernel configuration file.
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arch/$(ARCH)/Makefile the arch Makefile.
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scripts/Makefile.* common rules etc. for all kbuild Makefiles.
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kbuild Makefiles there are about 500 of these.
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The top Makefile reads the .config file, which comes from the kernel
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configuration process.
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The top Makefile is responsible for building two major products: vmlinux
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(the resident kernel image) and modules (any module files).
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It builds these goals by recursively descending into the subdirectories of
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the kernel source tree.
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The list of subdirectories which are visited depends upon the kernel
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configuration. The top Makefile textually includes an arch Makefile
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with the name arch/$(ARCH)/Makefile. The arch Makefile supplies
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architecture-specific information to the top Makefile.
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Each subdirectory has a kbuild Makefile which carries out the commands
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passed down from above. The kbuild Makefile uses information from the
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.config file to construct various file lists used by kbuild to build
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any built-in or modular targets.
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scripts/Makefile.* contains all the definitions/rules etc. that
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are used to build the kernel based on the kbuild makefiles.
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=== 2 Who does what
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People have four different relationships with the kernel Makefiles.
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*Users* are people who build kernels. These people type commands such as
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"make menuconfig" or "make". They usually do not read or edit
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any kernel Makefiles (or any other source files).
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*Normal developers* are people who work on features such as device
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drivers, file systems, and network protocols. These people need to
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maintain the kbuild Makefiles for the subsystem they are
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working on. In order to do this effectively, they need some overall
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knowledge about the kernel Makefiles, plus detailed knowledge about the
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public interface for kbuild.
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*Arch developers* are people who work on an entire architecture, such
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as sparc or ia64. Arch developers need to know about the arch Makefile
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as well as kbuild Makefiles.
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*Kbuild developers* are people who work on the kernel build system itself.
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These people need to know about all aspects of the kernel Makefiles.
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This document is aimed towards normal developers and arch developers.
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=== 3 The kbuild files
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Most Makefiles within the kernel are kbuild Makefiles that use the
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kbuild infrastructure. This chapter introduces the syntax used in the
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kbuild makefiles.
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The preferred name for the kbuild files are 'Makefile' but 'Kbuild' can
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be used and if both a 'Makefile' and a 'Kbuild' file exists, then the 'Kbuild'
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file will be used.
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Section 3.1 "Goal definitions" is a quick intro, further chapters provide
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more details, with real examples.
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--- 3.1 Goal definitions
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Goal definitions are the main part (heart) of the kbuild Makefile.
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These lines define the files to be built, any special compilation
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options, and any subdirectories to be entered recursively.
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The most simple kbuild makefile contains one line:
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Example:
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obj-y += foo.o
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This tells kbuild that there is one object in that directory, named
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foo.o. foo.o will be built from foo.c or foo.S.
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If foo.o shall be built as a module, the variable obj-m is used.
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Therefore the following pattern is often used:
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Example:
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obj-$(CONFIG_FOO) += foo.o
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$(CONFIG_FOO) evaluates to either y (for built-in) or m (for module).
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If CONFIG_FOO is neither y nor m, then the file will not be compiled
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nor linked.
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--- 3.2 Built-in object goals - obj-y
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The kbuild Makefile specifies object files for vmlinux
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in the $(obj-y) lists. These lists depend on the kernel
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configuration.
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Kbuild compiles all the $(obj-y) files. It then calls
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"$(LD) -r" to merge these files into one built-in.o file.
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built-in.o is later linked into vmlinux by the parent Makefile.
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The order of files in $(obj-y) is significant. Duplicates in
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the lists are allowed: the first instance will be linked into
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built-in.o and succeeding instances will be ignored.
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Link order is significant, because certain functions
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(module_init() / __initcall) will be called during boot in the
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order they appear. So keep in mind that changing the link
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order may e.g. change the order in which your SCSI
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controllers are detected, and thus your disks are renumbered.
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Example:
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#drivers/isdn/i4l/Makefile
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# Makefile for the kernel ISDN subsystem and device drivers.
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# Each configuration option enables a list of files.
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obj-$(CONFIG_ISDN_I4L) += isdn.o
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obj-$(CONFIG_ISDN_PPP_BSDCOMP) += isdn_bsdcomp.o
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--- 3.3 Loadable module goals - obj-m
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$(obj-m) specifies object files which are built as loadable
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kernel modules.
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A module may be built from one source file or several source
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files. In the case of one source file, the kbuild makefile
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simply adds the file to $(obj-m).
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Example:
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#drivers/isdn/i4l/Makefile
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obj-$(CONFIG_ISDN_PPP_BSDCOMP) += isdn_bsdcomp.o
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Note: In this example $(CONFIG_ISDN_PPP_BSDCOMP) evaluates to 'm'
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If a kernel module is built from several source files, you specify
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that you want to build a module in the same way as above; however,
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kbuild needs to know which object files you want to build your
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module from, so you have to tell it by setting a $(<module_name>-y)
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variable.
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Example:
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#drivers/isdn/i4l/Makefile
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obj-$(CONFIG_ISDN_I4L) += isdn.o
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isdn-y := isdn_net_lib.o isdn_v110.o isdn_common.o
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In this example, the module name will be isdn.o. Kbuild will
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compile the objects listed in $(isdn-y) and then run
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"$(LD) -r" on the list of these files to generate isdn.o.
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Due to kbuild recognizing $(<module_name>-y) for composite objects,
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you can use the value of a CONFIG_ symbol to optionally include an
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object file as part of a composite object.
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Example:
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#fs/ext2/Makefile
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obj-$(CONFIG_EXT2_FS) += ext2.o
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ext2-y := balloc.o dir.o file.o ialloc.o inode.o ioctl.o \
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namei.o super.o symlink.o
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ext2-$(CONFIG_EXT2_FS_XATTR) += xattr.o xattr_user.o \
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xattr_trusted.o
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In this example, xattr.o, xattr_user.o and xattr_trusted.o are only
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part of the composite object ext2.o if $(CONFIG_EXT2_FS_XATTR)
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evaluates to 'y'.
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Note: Of course, when you are building objects into the kernel,
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the syntax above will also work. So, if you have CONFIG_EXT2_FS=y,
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kbuild will build an ext2.o file for you out of the individual
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parts and then link this into built-in.o, as you would expect.
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--- 3.4 Objects which export symbols
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No special notation is required in the makefiles for
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modules exporting symbols.
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--- 3.5 Library file goals - lib-y
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Objects listed with obj-* are used for modules, or
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combined in a built-in.o for that specific directory.
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There is also the possibility to list objects that will
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be included in a library, lib.a.
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All objects listed with lib-y are combined in a single
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library for that directory.
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Objects that are listed in obj-y and additionally listed in
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lib-y will not be included in the library, since they will
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be accessible anyway.
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For consistency, objects listed in lib-m will be included in lib.a.
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Note that the same kbuild makefile may list files to be built-in
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and to be part of a library. Therefore the same directory
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may contain both a built-in.o and a lib.a file.
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Example:
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#arch/x86/lib/Makefile
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lib-y := delay.o
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This will create a library lib.a based on delay.o. For kbuild to
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actually recognize that there is a lib.a being built, the directory
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shall be listed in libs-y.
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See also "6.4 List directories to visit when descending".
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Use of lib-y is normally restricted to lib/ and arch/*/lib.
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--- 3.6 Descending down in directories
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A Makefile is only responsible for building objects in its own
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directory. Files in subdirectories should be taken care of by
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Makefiles in these subdirs. The build system will automatically
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invoke make recursively in subdirectories, provided you let it know of
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them.
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To do so, obj-y and obj-m are used.
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ext2 lives in a separate directory, and the Makefile present in fs/
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tells kbuild to descend down using the following assignment.
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Example:
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#fs/Makefile
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obj-$(CONFIG_EXT2_FS) += ext2/
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If CONFIG_EXT2_FS is set to either 'y' (built-in) or 'm' (modular)
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the corresponding obj- variable will be set, and kbuild will descend
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down in the ext2 directory.
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Kbuild only uses this information to decide that it needs to visit
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the directory, it is the Makefile in the subdirectory that
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specifies what is modular and what is built-in.
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It is good practice to use a CONFIG_ variable when assigning directory
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names. This allows kbuild to totally skip the directory if the
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corresponding CONFIG_ option is neither 'y' nor 'm'.
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--- 3.7 Compilation flags
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ccflags-y, asflags-y and ldflags-y
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These three flags apply only to the kbuild makefile in which they
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are assigned. They are used for all the normal cc, as and ld
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invocations happening during a recursive build.
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Note: Flags with the same behaviour were previously named:
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EXTRA_CFLAGS, EXTRA_AFLAGS and EXTRA_LDFLAGS.
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They are still supported but their usage is deprecated.
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ccflags-y specifies options for compiling with $(CC).
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Example:
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# drivers/acpi/Makefile
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ccflags-y := -Os
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ccflags-$(CONFIG_ACPI_DEBUG) += -DACPI_DEBUG_OUTPUT
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This variable is necessary because the top Makefile owns the
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variable $(KBUILD_CFLAGS) and uses it for compilation flags for the
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entire tree.
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asflags-y specifies options for assembling with $(AS).
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Example:
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#arch/sparc/kernel/Makefile
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asflags-y := -ansi
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ldflags-y specifies options for linking with $(LD).
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Example:
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#arch/cris/boot/compressed/Makefile
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ldflags-y += -T $(srctree)/$(src)/decompress_$(arch-y).lds
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subdir-ccflags-y, subdir-asflags-y
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The two flags listed above are similar to ccflags-y and asflags-y.
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The difference is that the subdir- variants have effect for the kbuild
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file where they are present and all subdirectories.
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Options specified using subdir-* are added to the commandline before
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the options specified using the non-subdir variants.
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Example:
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subdir-ccflags-y := -Werror
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CFLAGS_$@, AFLAGS_$@
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CFLAGS_$@ and AFLAGS_$@ only apply to commands in current
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kbuild makefile.
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$(CFLAGS_$@) specifies per-file options for $(CC). The $@
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part has a literal value which specifies the file that it is for.
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Example:
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# drivers/scsi/Makefile
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CFLAGS_aha152x.o = -DAHA152X_STAT -DAUTOCONF
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CFLAGS_gdth.o = # -DDEBUG_GDTH=2 -D__SERIAL__ -D__COM2__ \
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-DGDTH_STATISTICS
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These two lines specify compilation flags for aha152x.o and gdth.o.
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$(AFLAGS_$@) is a similar feature for source files in assembly
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languages.
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Example:
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# arch/arm/kernel/Makefile
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AFLAGS_head.o := -DTEXT_OFFSET=$(TEXT_OFFSET)
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AFLAGS_crunch-bits.o := -Wa,-mcpu=ep9312
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AFLAGS_iwmmxt.o := -Wa,-mcpu=iwmmxt
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--- 3.9 Dependency tracking
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Kbuild tracks dependencies on the following:
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1) All prerequisite files (both *.c and *.h)
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2) CONFIG_ options used in all prerequisite files
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3) Command-line used to compile target
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Thus, if you change an option to $(CC) all affected files will
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be re-compiled.
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--- 3.10 Special Rules
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Special rules are used when the kbuild infrastructure does
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not provide the required support. A typical example is
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header files generated during the build process.
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Another example are the architecture-specific Makefiles which
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need special rules to prepare boot images etc.
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Special rules are written as normal Make rules.
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Kbuild is not executing in the directory where the Makefile is
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located, so all special rules shall provide a relative
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path to prerequisite files and target files.
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Two variables are used when defining special rules:
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$(src)
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$(src) is a relative path which points to the directory
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where the Makefile is located. Always use $(src) when
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referring to files located in the src tree.
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$(obj)
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$(obj) is a relative path which points to the directory
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where the target is saved. Always use $(obj) when
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referring to generated files.
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Example:
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#drivers/scsi/Makefile
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$(obj)/53c8xx_d.h: $(src)/53c7,8xx.scr $(src)/script_asm.pl
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$(CPP) -DCHIP=810 - < $< | ... $(src)/script_asm.pl
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This is a special rule, following the normal syntax
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required by make.
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The target file depends on two prerequisite files. References
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to the target file are prefixed with $(obj), references
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to prerequisites are referenced with $(src) (because they are not
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generated files).
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$(kecho)
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echoing information to user in a rule is often a good practice
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but when execution "make -s" one does not expect to see any output
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except for warnings/errors.
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To support this kbuild defines $(kecho) which will echo out the
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text following $(kecho) to stdout except if "make -s" is used.
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Example:
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#arch/blackfin/boot/Makefile
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$(obj)/vmImage: $(obj)/vmlinux.gz
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$(call if_changed,uimage)
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@$(kecho) 'Kernel: $@ is ready'
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--- 3.11 $(CC) support functions
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The kernel may be built with several different versions of
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$(CC), each supporting a unique set of features and options.
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kbuild provides basic support to check for valid options for $(CC).
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$(CC) is usually the gcc compiler, but other alternatives are
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available.
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as-option
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as-option is used to check if $(CC) -- when used to compile
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assembler (*.S) files -- supports the given option. An optional
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second option may be specified if the first option is not supported.
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Example:
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#arch/sh/Makefile
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cflags-y += $(call as-option,-Wa$(comma)-isa=$(isa-y),)
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In the above example, cflags-y will be assigned the option
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-Wa$(comma)-isa=$(isa-y) if it is supported by $(CC).
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The second argument is optional, and if supplied will be used
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if first argument is not supported.
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cc-ldoption
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cc-ldoption is used to check if $(CC) when used to link object files
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supports the given option. An optional second option may be
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specified if first option are not supported.
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Example:
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#arch/x86/kernel/Makefile
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vsyscall-flags += $(call cc-ldoption, -Wl$(comma)--hash-style=sysv)
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In the above example, vsyscall-flags will be assigned the option
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-Wl$(comma)--hash-style=sysv if it is supported by $(CC).
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The second argument is optional, and if supplied will be used
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if first argument is not supported.
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as-instr
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as-instr checks if the assembler reports a specific instruction
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and then outputs either option1 or option2
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C escapes are supported in the test instruction
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Note: as-instr-option uses KBUILD_AFLAGS for $(AS) options
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cc-option
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cc-option is used to check if $(CC) supports a given option, and if
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not supported to use an optional second option.
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Example:
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#arch/x86/Makefile
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cflags-y += $(call cc-option,-march=pentium-mmx,-march=i586)
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In the above example, cflags-y will be assigned the option
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-march=pentium-mmx if supported by $(CC), otherwise -march=i586.
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The second argument to cc-option is optional, and if omitted,
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cflags-y will be assigned no value if first option is not supported.
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Note: cc-option uses KBUILD_CFLAGS for $(CC) options
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cc-option-yn
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cc-option-yn is used to check if gcc supports a given option
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and return 'y' if supported, otherwise 'n'.
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Example:
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#arch/ppc/Makefile
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biarch := $(call cc-option-yn, -m32)
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aflags-$(biarch) += -a32
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cflags-$(biarch) += -m32
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In the above example, $(biarch) is set to y if $(CC) supports the -m32
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option. When $(biarch) equals 'y', the expanded variables $(aflags-y)
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and $(cflags-y) will be assigned the values -a32 and -m32,
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respectively.
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Note: cc-option-yn uses KBUILD_CFLAGS for $(CC) options
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cc-option-align
|
|
gcc versions >= 3.0 changed the type of options used to specify
|
|
alignment of functions, loops etc. $(cc-option-align), when used
|
|
as prefix to the align options, will select the right prefix:
|
|
gcc < 3.00
|
|
cc-option-align = -malign
|
|
gcc >= 3.00
|
|
cc-option-align = -falign
|
|
|
|
Example:
|
|
KBUILD_CFLAGS += $(cc-option-align)-functions=4
|
|
|
|
In the above example, the option -falign-functions=4 is used for
|
|
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
|
|
gcc 3.41 would return 0341.
|
|
cc-version is useful when a specific $(CC) version is faulty in one
|
|
area, for example -mregparm=3 was broken in some gcc versions
|
|
even though the option was accepted by gcc.
|
|
|
|
Example:
|
|
#arch/x86/Makefile
|
|
cflags-y += $(shell \
|
|
if [ $(cc-version) -ge 0300 ] ; then \
|
|
echo "-mregparm=3"; fi ;)
|
|
|
|
In the above example, -mregparm=3 is only used for gcc version greater
|
|
than or equal to gcc 3.0.
|
|
|
|
cc-ifversion
|
|
cc-ifversion tests the version of $(CC) and equals the fourth parameter
|
|
if version expression is true, or the fifth (if given) if the version
|
|
expression is false.
|
|
|
|
Example:
|
|
#fs/reiserfs/Makefile
|
|
ccflags-y := $(call cc-ifversion, -lt, 0402, -O1)
|
|
|
|
In this example, ccflags-y will be assigned the value -O1 if the
|
|
$(CC) version is less than 4.2.
|
|
cc-ifversion takes all the shell operators:
|
|
-eq, -ne, -lt, -le, -gt, and -ge
|
|
The third parameter may be a text as in this example, but it may also
|
|
be an expanded variable or a macro.
|
|
|
|
cc-fullversion
|
|
cc-fullversion is useful when the exact version of gcc is needed.
|
|
One typical use-case is when a specific GCC version is broken.
|
|
cc-fullversion points out a more specific version than cc-version does.
|
|
|
|
Example:
|
|
#arch/powerpc/Makefile
|
|
$(Q)if test "$(cc-fullversion)" = "040200" ; then \
|
|
echo -n '*** GCC-4.2.0 cannot compile the 64-bit powerpc ' ; \
|
|
false ; \
|
|
fi
|
|
|
|
In this example for a specific GCC version the build will error out
|
|
explaining to the user why it stops.
|
|
|
|
cc-cross-prefix
|
|
cc-cross-prefix is used to check if there exists a $(CC) in path with
|
|
one of the listed prefixes. The first prefix where there exist a
|
|
prefix$(CC) in the PATH is returned - and if no prefix$(CC) is found
|
|
then nothing is returned.
|
|
Additional prefixes are separated by a single space in the
|
|
call of cc-cross-prefix.
|
|
This functionality is useful for architecture Makefiles that try
|
|
to set CROSS_COMPILE to well-known values but may have several
|
|
values to select between.
|
|
It is recommended only to try to set CROSS_COMPILE if it is a cross
|
|
build (host arch is different from target arch). And if CROSS_COMPILE
|
|
is already set then leave it with the old value.
|
|
|
|
Example:
|
|
#arch/m68k/Makefile
|
|
ifneq ($(SUBARCH),$(ARCH))
|
|
ifeq ($(CROSS_COMPILE),)
|
|
CROSS_COMPILE := $(call cc-cross-prefix, m68k-linux-gnu-)
|
|
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
|
|
compilation stage.
|
|
Two steps are required in order to use a host executable.
|
|
|
|
The first step is to tell kbuild that a host program exists. This is
|
|
done utilising the variable hostprogs-y.
|
|
|
|
The second step is to add an explicit dependency to the executable.
|
|
This can be done in two ways. Either add the dependency in a rule,
|
|
or utilise the variable $(always).
|
|
Both possibilities are described in the following.
|
|
|
|
--- 4.1 Simple Host Program
|
|
|
|
In some cases there is a need to compile and run a program on the
|
|
computer where the build is running.
|
|
The following line tells kbuild that the program bin2hex shall be
|
|
built on the build host.
|
|
|
|
Example:
|
|
hostprogs-y := bin2hex
|
|
|
|
Kbuild assumes in the above example that bin2hex is made from a single
|
|
c-source file named bin2hex.c located in the same directory as
|
|
the Makefile.
|
|
|
|
--- 4.2 Composite Host Programs
|
|
|
|
Host programs can be made up based on composite objects.
|
|
The syntax used to define composite objects for host programs is
|
|
similar to the syntax used for kernel objects.
|
|
$(<executable>-objs) lists all objects used to link the final
|
|
executable.
|
|
|
|
Example:
|
|
#scripts/lxdialog/Makefile
|
|
hostprogs-y := lxdialog
|
|
lxdialog-objs := checklist.o lxdialog.o
|
|
|
|
Objects with extension .o are compiled from the corresponding .c
|
|
files. In the above example, checklist.c is compiled to checklist.o
|
|
and lxdialog.c is compiled to lxdialog.o.
|
|
Finally, the two .o files are linked to the executable, lxdialog.
|
|
Note: The syntax <executable>-y is not permitted for host-programs.
|
|
|
|
--- 4.3 Using C++ for host programs
|
|
|
|
kbuild offers support for host programs written in C++. This was
|
|
introduced solely to support kconfig, and is not recommended
|
|
for general use.
|
|
|
|
Example:
|
|
#scripts/kconfig/Makefile
|
|
hostprogs-y := qconf
|
|
qconf-cxxobjs := qconf.o
|
|
|
|
In the example above the executable is composed of the C++ file
|
|
qconf.cc - identified by $(qconf-cxxobjs).
|
|
|
|
If qconf is composed of a mixture of .c and .cc files, then an
|
|
additional line can be used to identify this.
|
|
|
|
Example:
|
|
#scripts/kconfig/Makefile
|
|
hostprogs-y := qconf
|
|
qconf-cxxobjs := qconf.o
|
|
qconf-objs := check.o
|
|
|
|
--- 4.4 Controlling compiler options for host programs
|
|
|
|
When compiling host programs, it is possible to set specific flags.
|
|
The programs will always be compiled utilising $(HOSTCC) passed
|
|
the options specified in $(HOSTCFLAGS).
|
|
To set flags that will take effect for all host programs created
|
|
in that Makefile, use the variable HOST_EXTRACFLAGS.
|
|
|
|
Example:
|
|
#scripts/lxdialog/Makefile
|
|
HOST_EXTRACFLAGS += -I/usr/include/ncurses
|
|
|
|
To set specific flags for a single file the following construction
|
|
is used:
|
|
|
|
Example:
|
|
#arch/ppc64/boot/Makefile
|
|
HOSTCFLAGS_piggyback.o := -DKERNELBASE=$(KERNELBASE)
|
|
|
|
It is also possible to specify additional options to the linker.
|
|
|
|
Example:
|
|
#scripts/kconfig/Makefile
|
|
HOSTLOADLIBES_qconf := -L$(QTDIR)/lib
|
|
|
|
When linking qconf, it will be passed the extra option
|
|
"-L$(QTDIR)/lib".
|
|
|
|
--- 4.5 When host programs are actually built
|
|
|
|
Kbuild will only build host-programs when they are referenced
|
|
as a prerequisite.
|
|
This is possible in two ways:
|
|
|
|
(1) List the prerequisite explicitly in a special rule.
|
|
|
|
Example:
|
|
#drivers/pci/Makefile
|
|
hostprogs-y := gen-devlist
|
|
$(obj)/devlist.h: $(src)/pci.ids $(obj)/gen-devlist
|
|
( cd $(obj); ./gen-devlist ) < $<
|
|
|
|
The target $(obj)/devlist.h will not be built before
|
|
$(obj)/gen-devlist is updated. Note that references to
|
|
the host programs in special rules must be prefixed with $(obj).
|
|
|
|
(2) Use $(always)
|
|
When there is no suitable special rule, and the host program
|
|
shall be built when a makefile is entered, the $(always)
|
|
variable shall be used.
|
|
|
|
Example:
|
|
#scripts/lxdialog/Makefile
|
|
hostprogs-y := lxdialog
|
|
always := $(hostprogs-y)
|
|
|
|
This will tell kbuild to build lxdialog even if not referenced in
|
|
any rule.
|
|
|
|
--- 4.6 Using hostprogs-$(CONFIG_FOO)
|
|
|
|
A typical pattern in a Kbuild file looks like this:
|
|
|
|
Example:
|
|
#scripts/Makefile
|
|
hostprogs-$(CONFIG_KALLSYMS) += kallsyms
|
|
|
|
Kbuild knows about both 'y' for built-in and 'm' for module.
|
|
So if a config symbol evaluates to 'm', kbuild will still build
|
|
the binary. In other words, Kbuild handles hostprogs-m exactly
|
|
like hostprogs-y. But only hostprogs-y is recommended to be used
|
|
when no CONFIG symbols are involved.
|
|
|
|
=== 5 Kbuild clean infrastructure
|
|
|
|
"make clean" deletes most generated files in the obj tree where the kernel
|
|
is compiled. This includes generated files such as host programs.
|
|
Kbuild knows targets listed in $(hostprogs-y), $(hostprogs-m), $(always),
|
|
$(extra-y) and $(targets). They are all deleted during "make clean".
|
|
Files matching the patterns "*.[oas]", "*.ko", plus some additional files
|
|
generated by kbuild are deleted all over the kernel src tree when
|
|
"make clean" is executed.
|
|
|
|
Additional files can be specified in kbuild makefiles by use of $(clean-files).
|
|
|
|
Example:
|
|
#lib/Makefile
|
|
clean-files := crc32table.h
|
|
|
|
When executing "make clean", the file "crc32table.h" will be deleted.
|
|
Kbuild will assume files to be in the same relative directory as the
|
|
Makefile, except if prefixed with $(objtree).
|
|
|
|
To delete a directory hierarchy use:
|
|
|
|
Example:
|
|
#scripts/package/Makefile
|
|
clean-dirs := $(objtree)/debian/
|
|
|
|
This will delete the directory debian in the toplevel directory, including all
|
|
subdirectories.
|
|
|
|
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/x86/boot/Makefile
|
|
subdir- := compressed/
|
|
|
|
The above assignment instructs kbuild to descend down in the
|
|
directory compressed/ when "make clean" is executed.
|
|
|
|
To support the clean infrastructure in the Makefiles that build the
|
|
final bootimage there is an optional target named archclean:
|
|
|
|
Example:
|
|
#arch/x86/Makefile
|
|
archclean:
|
|
$(Q)$(MAKE) $(clean)=arch/x86/boot
|
|
|
|
When "make clean" is executed, make will descend down in arch/x86/boot,
|
|
and clean as usual. The Makefile located in arch/x86/boot/ may use
|
|
the subdir- trick to descend further down.
|
|
|
|
Note 1: arch/$(ARCH)/Makefile cannot use "subdir-", because that file is
|
|
included in the top level makefile, and the kbuild infrastructure
|
|
is not operational at that point.
|
|
|
|
Note 2: All directories listed in core-y, libs-y, drivers-y and net-y will
|
|
be visited during "make clean".
|
|
|
|
=== 6 Architecture Makefiles
|
|
|
|
The top level Makefile sets up the environment and does the preparation,
|
|
before starting to descend down in the individual directories.
|
|
The top level makefile contains the generic part, whereas
|
|
arch/$(ARCH)/Makefile contains what is required to set up kbuild
|
|
for said architecture.
|
|
To do so, arch/$(ARCH)/Makefile sets up a number of variables and defines
|
|
a few targets.
|
|
|
|
When kbuild executes, the following steps are followed (roughly):
|
|
1) Configuration of the kernel => produce .config
|
|
2) Store kernel version in include/linux/version.h
|
|
3) Updating all other prerequisites to the target prepare:
|
|
- Additional prerequisites are specified in arch/$(ARCH)/Makefile
|
|
4) Recursively descend down in all directories listed in
|
|
init-* core* drivers-* net-* libs-* and build all targets.
|
|
- The values of the above variables are expanded in arch/$(ARCH)/Makefile.
|
|
5) All object files are then linked and the resulting file vmlinux is
|
|
located at the root of the obj tree.
|
|
The very first objects linked are listed in head-y, assigned by
|
|
arch/$(ARCH)/Makefile.
|
|
6) Finally, the architecture-specific part does any required post processing
|
|
and builds the final bootimage.
|
|
- This includes building boot records
|
|
- Preparing initrd images and the like
|
|
|
|
|
|
--- 6.1 Set variables to tweak the build to the architecture
|
|
|
|
LDFLAGS Generic $(LD) options
|
|
|
|
Flags used for all invocations of the linker.
|
|
Often specifying the emulation is sufficient.
|
|
|
|
Example:
|
|
#arch/s390/Makefile
|
|
LDFLAGS := -m elf_s390
|
|
Note: ldflags-y can be used to further customise
|
|
the flags used. See chapter 3.7.
|
|
|
|
LDFLAGS_MODULE Options for $(LD) when linking modules
|
|
|
|
LDFLAGS_MODULE is used to set specific flags for $(LD) when
|
|
linking the .ko files used for modules.
|
|
Default is "-r", for relocatable output.
|
|
|
|
LDFLAGS_vmlinux Options for $(LD) when linking vmlinux
|
|
|
|
LDFLAGS_vmlinux is used to specify additional flags to pass to
|
|
the linker when linking the final vmlinux image.
|
|
LDFLAGS_vmlinux uses the LDFLAGS_$@ support.
|
|
|
|
Example:
|
|
#arch/x86/Makefile
|
|
LDFLAGS_vmlinux := -e stext
|
|
|
|
OBJCOPYFLAGS objcopy flags
|
|
|
|
When $(call if_changed,objcopy) is used to translate a .o file,
|
|
the flags specified in OBJCOPYFLAGS will be used.
|
|
$(call if_changed,objcopy) is often used to generate raw binaries on
|
|
vmlinux.
|
|
|
|
Example:
|
|
#arch/s390/Makefile
|
|
OBJCOPYFLAGS := -O binary
|
|
|
|
#arch/s390/boot/Makefile
|
|
$(obj)/image: vmlinux FORCE
|
|
$(call if_changed,objcopy)
|
|
|
|
In this example, the binary $(obj)/image is a binary version of
|
|
vmlinux. The usage of $(call if_changed,xxx) will be described later.
|
|
|
|
KBUILD_AFLAGS $(AS) assembler flags
|
|
|
|
Default value - see top level Makefile
|
|
Append or modify as required per architecture.
|
|
|
|
Example:
|
|
#arch/sparc64/Makefile
|
|
KBUILD_AFLAGS += -m64 -mcpu=ultrasparc
|
|
|
|
KBUILD_CFLAGS $(CC) compiler flags
|
|
|
|
Default value - see top level Makefile
|
|
Append or modify as required per architecture.
|
|
|
|
Often, the KBUILD_CFLAGS variable depends on the configuration.
|
|
|
|
Example:
|
|
#arch/x86/boot/compressed/Makefile
|
|
cflags-$(CONFIG_X86_32) := -march=i386
|
|
cflags-$(CONFIG_X86_64) := -mcmodel=small
|
|
KBUILD_CFLAGS += $(cflags-y)
|
|
|
|
Many arch Makefiles dynamically run the target C compiler to
|
|
probe supported options:
|
|
|
|
#arch/x86/Makefile
|
|
|
|
...
|
|
cflags-$(CONFIG_MPENTIUMII) += $(call cc-option,\
|
|
-march=pentium2,-march=i686)
|
|
...
|
|
# Disable unit-at-a-time mode ...
|
|
KBUILD_CFLAGS += $(call cc-option,-fno-unit-at-a-time)
|
|
...
|
|
|
|
|
|
The first example utilises the trick that a config option expands
|
|
to 'y' when selected.
|
|
|
|
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
|
|
|
|
$(KBUILD_CFLAGS_KERNEL) contains extra C compiler flags used to compile
|
|
resident kernel code.
|
|
|
|
KBUILD_CFLAGS_MODULE Options for $(CC) when building 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
|
|
|
|
$(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).
|
|
|
|
ARCH_CPPFLAGS, ARCH_AFLAGS, ARCH_CFLAGS Overrides the kbuild defaults
|
|
|
|
These variables are appended to the KBUILD_CPPFLAGS,
|
|
KBUILD_AFLAGS, and KBUILD_CFLAGS, respectively, after the
|
|
top-level Makefile has set any other flags. This provides a
|
|
means for an architecture to override the defaults.
|
|
|
|
|
|
--- 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.
|
|
This is usually used for header files containing assembler constants.
|
|
|
|
Example:
|
|
#arch/arm/Makefile
|
|
archprepare: maketools
|
|
|
|
In this example, the file target maketools will be processed
|
|
before descending down in the subdirectories.
|
|
See also chapter XXX-TODO that describe how kbuild supports
|
|
generating offset header files.
|
|
|
|
|
|
--- 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
|
|
corresponding arch-specific section for modules; the module-building
|
|
machinery is all architecture-independent.
|
|
|
|
|
|
head-y, init-y, core-y, libs-y, drivers-y, net-y
|
|
|
|
$(head-y) lists objects to be linked first in vmlinux.
|
|
$(libs-y) lists directories where a lib.a archive can be located.
|
|
The rest list directories where a built-in.o object file can be
|
|
located.
|
|
|
|
$(init-y) objects will be located after $(head-y).
|
|
Then the rest follows in this order:
|
|
$(core-y), $(libs-y), $(drivers-y) and $(net-y).
|
|
|
|
The top level Makefile defines values for all generic directories,
|
|
and arch/$(ARCH)/Makefile only adds architecture-specific directories.
|
|
|
|
Example:
|
|
#arch/sparc64/Makefile
|
|
core-y += arch/sparc64/kernel/
|
|
libs-y += arch/sparc64/prom/ arch/sparc64/lib/
|
|
drivers-$(CONFIG_OPROFILE) += arch/sparc64/oprofile/
|
|
|
|
|
|
--- 6.5 Architecture-specific boot images
|
|
|
|
An arch Makefile specifies goals that take the vmlinux file, compress
|
|
it, wrap it in bootstrapping code, and copy the resulting files
|
|
somewhere. This includes various kinds of installation commands.
|
|
The actual goals are not standardized across architectures.
|
|
|
|
It is common to locate any additional processing in a boot/
|
|
directory below arch/$(ARCH)/.
|
|
|
|
Kbuild does not provide any smart way to support building a
|
|
target specified in boot/. Therefore arch/$(ARCH)/Makefile shall
|
|
call make manually to build a target in boot/.
|
|
|
|
The recommended approach is to include shortcuts in
|
|
arch/$(ARCH)/Makefile, and use the full path when calling down
|
|
into the arch/$(ARCH)/boot/Makefile.
|
|
|
|
Example:
|
|
#arch/x86/Makefile
|
|
boot := arch/x86/boot
|
|
bzImage: vmlinux
|
|
$(Q)$(MAKE) $(build)=$(boot) $(boot)/$@
|
|
|
|
"$(Q)$(MAKE) $(build)=<dir>" is the recommended way to invoke
|
|
make in a subdirectory.
|
|
|
|
There are no rules for naming architecture-specific targets,
|
|
but executing "make help" will list all relevant targets.
|
|
To support this, $(archhelp) must be defined.
|
|
|
|
Example:
|
|
#arch/x86/Makefile
|
|
define archhelp
|
|
echo '* bzImage - Image (arch/$(ARCH)/boot/bzImage)'
|
|
endif
|
|
|
|
When make is executed without arguments, the first goal encountered
|
|
will be built. In the top level Makefile the first goal present
|
|
is all:.
|
|
An architecture shall always, per default, build a bootable image.
|
|
In "make help", the default goal is highlighted with a '*'.
|
|
Add a new prerequisite to all: to select a default goal different
|
|
from vmlinux.
|
|
|
|
Example:
|
|
#arch/x86/Makefile
|
|
all: bzImage
|
|
|
|
When "make" is executed without arguments, bzImage will be built.
|
|
|
|
--- 6.6 Building non-kbuild targets
|
|
|
|
extra-y
|
|
|
|
extra-y specifies additional targets created in the current
|
|
directory, in addition to any targets specified by obj-*.
|
|
|
|
Listing all targets in extra-y is required for two purposes:
|
|
1) Enable kbuild to check changes in command lines
|
|
- When $(call if_changed,xxx) is used
|
|
2) kbuild knows what files to delete during "make clean"
|
|
|
|
Example:
|
|
#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.
|
|
|
|
|
|
--- 6.7 Commands useful for building a boot image
|
|
|
|
Kbuild provides a few macros that are useful when building a
|
|
boot image.
|
|
|
|
if_changed
|
|
|
|
if_changed is the infrastructure used for the following commands.
|
|
|
|
Usage:
|
|
target: source(s) FORCE
|
|
$(call if_changed,ld/objcopy/gzip/...)
|
|
|
|
When the rule is evaluated, it is checked to see if any files
|
|
need an update, or the command line has changed since the last
|
|
invocation. The latter will force a rebuild if any options
|
|
to the executable have changed.
|
|
Any target that utilises if_changed must be listed in $(targets),
|
|
otherwise the command line check will fail, and the target will
|
|
always be built.
|
|
Assignments to $(targets) are without $(obj)/ prefix.
|
|
if_changed may be used in conjunction with custom commands as
|
|
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
|
|
significant; for instance, the below will fail (note the extra space
|
|
after the comma):
|
|
target: source(s) FORCE
|
|
#WRONG!# $(call if_changed, ld/objcopy/gzip/...)
|
|
|
|
ld
|
|
Link target. Often, LDFLAGS_$@ is used to set specific options to ld.
|
|
|
|
objcopy
|
|
Copy binary. Uses OBJCOPYFLAGS usually specified in
|
|
arch/$(ARCH)/Makefile.
|
|
OBJCOPYFLAGS_$@ may be used to set additional options.
|
|
|
|
gzip
|
|
Compress target. Use maximum compression to compress target.
|
|
|
|
Example:
|
|
#arch/x86/boot/Makefile
|
|
LDFLAGS_bootsect := -Ttext 0x0 -s --oformat binary
|
|
LDFLAGS_setup := -Ttext 0x0 -s --oformat binary -e begtext
|
|
|
|
targets += setup setup.o bootsect bootsect.o
|
|
$(obj)/setup $(obj)/bootsect: %: %.o FORCE
|
|
$(call if_changed,ld)
|
|
|
|
In this example, there are two possible targets, requiring different
|
|
options to the linker. The linker options are specified using the
|
|
LDFLAGS_$@ syntax - one for each potential target.
|
|
$(targets) are assigned all potential targets, by which kbuild knows
|
|
the targets and will:
|
|
1) check for commandline changes
|
|
2) delete target during make clean
|
|
|
|
The ": %: %.o" part of the prerequisite is a shorthand that
|
|
frees us from listing the setup.o and bootsect.o files.
|
|
Note: It is a common mistake to forget the "targets :=" assignment,
|
|
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
|
|
|
|
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
|
|
|
|
--- 6.8 Custom kbuild commands
|
|
|
|
When kbuild is executing with KBUILD_VERBOSE=0, then only a shorthand
|
|
of a command is normally displayed.
|
|
To enable this behaviour for custom commands kbuild requires
|
|
two variables to be set:
|
|
quiet_cmd_<command> - what shall be echoed
|
|
cmd_<command> - the command to execute
|
|
|
|
Example:
|
|
#
|
|
quiet_cmd_image = BUILD $@
|
|
cmd_image = $(obj)/tools/build $(BUILDFLAGS) \
|
|
$(obj)/vmlinux.bin > $@
|
|
|
|
targets += bzImage
|
|
$(obj)/bzImage: $(obj)/vmlinux.bin $(obj)/tools/build FORCE
|
|
$(call if_changed,image)
|
|
@echo 'Kernel: $@ is ready'
|
|
|
|
When updating the $(obj)/bzImage target, the line
|
|
|
|
BUILD arch/x86/boot/bzImage
|
|
|
|
will be displayed with "make KBUILD_VERBOSE=0".
|
|
|
|
|
|
--- 6.9 Preprocessing linker scripts
|
|
|
|
When the vmlinux image is built, the linker script
|
|
arch/$(ARCH)/kernel/vmlinux.lds is used.
|
|
The script is a preprocessed variant of the file vmlinux.lds.S
|
|
located in the same directory.
|
|
kbuild knows .lds files and includes a rule *lds.S -> *lds.
|
|
|
|
Example:
|
|
#arch/x86/kernel/Makefile
|
|
always := vmlinux.lds
|
|
|
|
#Makefile
|
|
export CPPFLAGS_vmlinux.lds += -P -C -U$(ARCH)
|
|
|
|
The assignment to $(always) is used to tell kbuild to build the
|
|
target vmlinux.lds.
|
|
The assignment to $(CPPFLAGS_vmlinux.lds) tells kbuild to use the
|
|
specified options when building the target vmlinux.lds.
|
|
|
|
When building the *.lds target, kbuild uses the variables:
|
|
KBUILD_CPPFLAGS : Set in top-level Makefile
|
|
cppflags-y : May be set in the kbuild makefile
|
|
CPPFLAGS_$(@F) : Target-specific flags.
|
|
Note that the full filename is used in this
|
|
assignment.
|
|
|
|
The kbuild infrastructure for *lds files is 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.
|
|
|
|
--- 6.11 Post-link pass
|
|
|
|
If the file arch/xxx/Makefile.postlink exists, this makefile
|
|
will be invoked for post-link objects (vmlinux and modules.ko)
|
|
for architectures to run post-link passes on. Must also handle
|
|
the clean target.
|
|
|
|
This pass runs after kallsyms generation. If the architecture
|
|
needs to modify symbol locations, rather than manipulate the
|
|
kallsyms, it may be easier to add another postlink target for
|
|
.tmp_vmlinux? targets to be called from link-vmlinux.sh.
|
|
|
|
For example, powerpc uses this to check relocation sanity of
|
|
the linked vmlinux file.
|
|
|
|
=== 7 Kbuild syntax for exported headers
|
|
|
|
The kernel includes 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 specifies 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 specifies 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 has a set of exported headers that needs to be
|
|
exported to a different directory destination-y is used.
|
|
destination-y specifies 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>
|
|
|
|
--- 7.5 generated-y
|
|
|
|
If an architecture generates other header files alongside generic-y
|
|
wrappers, and not included in genhdr-y, then generated-y specifies
|
|
them.
|
|
|
|
This prevents them being treated as stale asm-generic wrappers and
|
|
removed.
|
|
|
|
Example:
|
|
#arch/x86/include/asm/Kbuild
|
|
generated-y += syscalls_32.h
|
|
|
|
=== 8 Kbuild Variables
|
|
|
|
The top Makefile exports the following variables:
|
|
|
|
VERSION, PATCHLEVEL, SUBLEVEL, EXTRAVERSION
|
|
|
|
These variables define the current kernel version. A few arch
|
|
Makefiles actually use these values directly; they should use
|
|
$(KERNELRELEASE) instead.
|
|
|
|
$(VERSION), $(PATCHLEVEL), and $(SUBLEVEL) define the basic
|
|
three-part version number, such as "2", "4", and "0". These three
|
|
values are always numeric.
|
|
|
|
$(EXTRAVERSION) defines an even tinier sublevel for pre-patches
|
|
or additional patches. It is usually some non-numeric string
|
|
such as "-pre4", and is often blank.
|
|
|
|
KERNELRELEASE
|
|
|
|
$(KERNELRELEASE) is a single string such as "2.4.0-pre4", suitable
|
|
for constructing installation directory names or showing in
|
|
version strings. Some arch Makefiles use it for this purpose.
|
|
|
|
ARCH
|
|
|
|
This variable defines the target architecture, such as "i386",
|
|
"arm", or "sparc". Some kbuild Makefiles test $(ARCH) to
|
|
determine which files to compile.
|
|
|
|
By default, the top Makefile sets $(ARCH) to be the same as the
|
|
host system architecture. For a cross build, a user may
|
|
override the value of $(ARCH) on the command line:
|
|
|
|
make ARCH=m68k ...
|
|
|
|
|
|
INSTALL_PATH
|
|
|
|
This variable defines a place for the arch Makefiles to install
|
|
the resident kernel image and System.map file.
|
|
Use this for architecture-specific install targets.
|
|
|
|
INSTALL_MOD_PATH, MODLIB
|
|
|
|
$(INSTALL_MOD_PATH) specifies a prefix to $(MODLIB) for module
|
|
installation. This variable is not defined in the Makefile but
|
|
may be passed in by the user if desired.
|
|
|
|
$(MODLIB) specifies the directory for module installation.
|
|
The top Makefile defines $(MODLIB) to
|
|
$(INSTALL_MOD_PATH)/lib/modules/$(KERNELRELEASE). The user may
|
|
override this value on the command line if desired.
|
|
|
|
INSTALL_MOD_STRIP
|
|
|
|
If this variable is specified, it 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, the
|
|
INSTALL_MOD_STRIP value will be used as the option(s) to the strip
|
|
command.
|
|
|
|
|
|
=== 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
|
|
GNU extensions.
|
|
|
|
GNU Make supports elementary list-processing functions. The kernel
|
|
Makefiles use a novel style of list building and manipulation with few
|
|
"if" statements.
|
|
|
|
GNU Make has two assignment operators, ":=" and "=". ":=" performs
|
|
immediate evaluation of the right-hand side and stores an actual string
|
|
into the left-hand side. "=" is like a formula definition; it stores the
|
|
right-hand side in an unevaluated form and then evaluates this form each
|
|
time the left-hand side is used.
|
|
|
|
There are some cases where "=" is appropriate. Usually, though, ":="
|
|
is the right choice.
|
|
|
|
=== 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>
|
|
|
|
=== 11 TODO
|
|
|
|
- Describe how kbuild supports shipped files with _shipped.
|
|
- Generating offset header files.
|
|
- Add more variables to section 7?
|
|
|
|
|
|
|