--- 3.9 Dependency tracking
--- 3.10 Special Rules
--- 3.11 $(CC) support functions
+ --- 3.12 $(LD) support functions
=== 4 Host Program support
--- 4.1 Simple Host Program
--- 6.7 Custom kbuild commands
--- 6.8 Preprocessing linker scripts
- === 7 Kbuild Variables
- === 8 Makefile language
- === 9 Credits
- === 10 TODO
+ === 7 Kbuild syntax for exported headers
+ --- 7.1 header-y
+ --- 7.2 objhdr-y
+ --- 7.3 destination-y
+ --- 7.4 unifdef-y (deprecated)
+
+ === 8 Kbuild Variables
+ === 9 Makefile language
+ === 10 Credits
+ === 11 TODO
=== 1 Overview
#arch/m68k/fpsp040/Makefile
ldflags-y := -x
+ subdir-ccflags-y, subdir-asflags-y
+ The two flags listed above are similar to ccflags-y and as-falgs-y.
+ The difference is that the subdir- variants has effect for the kbuild
+ file where tey are present and all subdirectories.
+ Options specified using subdir-* are added to the commandline before
+ the options specified using the non-subdir variants.
+
+ Example:
+ subdir-ccflags-y := -Werror
+
CFLAGS_$@, AFLAGS_$@
CFLAGS_$@ and AFLAGS_$@ only apply to commands in current
to prerequisites are referenced with $(src) (because they are not
generated files).
+ $(kecho)
+ echoing information to user in a rule is often a good practice
+ but when execution "make -s" one does not expect to see any output
+ except for warnings/errors.
+ To support this kbuild define $(kecho) which will echo out the
+ text following $(kecho) to stdout except if "make -s" is used.
+
+ Example:
+ #arch/blackfin/boot/Makefile
+ $(obj)/vmImage: $(obj)/vmlinux.gz
+ $(call if_changed,uimage)
+ @$(kecho) 'Kernel: $@ is ready'
+
+
--- 3.11 $(CC) support functions
The kernel may be built with several different versions of
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)
+ 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).
to the user why it stops.
cc-cross-prefix
- cc-cross-prefix is used to check if there exist a $(CC) in path with
+ 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 usefull for architecture Makefile that try
- to set CROSS_COMPILE to well know values but may have several
+ 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 is it is a cross
- build (host arch is different from target arch). And is CROSS_COMPILE
+ 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:
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 really-ld-option, -X)
+
+
=== 4 Host Program support
Kbuild supports building executables on the host for use during the
The kbuild infrastructure for *lds file are used in several
architecture-specific files.
+=== 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 requires 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 is kernel internat (guarded by ifdef __KERNEL__)
+
+Each relevant directory contain a file name "Kbuild" which specify 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 objhdr-y
+
+ objhdr-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
+ objhdr-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 unifdef-y (deprecated)
+
+ unifdef-y is deprecated. A direct replacement is header-y.
+
-=== 7 Kbuild Variables
+=== 8 Kbuild Variables
The top Makefile exports the following variables:
INSTALL_MOD_STRIP will 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
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.
git://ftp.safe.ca / safe / jmp / linux-2.6 / blobdiff