--- 3.3 Loadable module goals - obj-m
- $(obj-m) specify object files which are built as loadable
+ $(obj-m) specifies object files which are built as loadable
kernel modules.
A module may be built from one source file or several source
down in the ext2 directory.
Kbuild only uses this information to decide that it needs to visit
the directory, it is the Makefile in the subdirectory that
- specifies what is modules and what is built-in.
+ specifies what is modular and what is built-in.
It is good practice to use a CONFIG_ variable when assigning directory
names. This allows kbuild to totally skip the directory if the
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
+ To support this kbuild defines $(kecho) which will echo out the
text following $(kecho) to stdout except if "make -s" is used.
Example:
The kernel may be built with several different versions of
$(CC), each supporting a unique set of features and options.
- kbuild provide basic support to check for valid options for $(CC).
+ kbuild provides basic support to check for valid options for $(CC).
$(CC) is usually the gcc compiler, but other alternatives are
available.
Note: as-instr-option uses KBUILD_AFLAGS for $(AS) options
cc-option
- cc-option is used to check if $(CC) supports a given option, and not
- supported to use an optional second option.
+ cc-option is used to check if $(CC) supports a given option, and if
+ not supported to use an optional second option.
Example:
#arch/x86/Makefile
false ; \
fi
- In this example for a specific GCC version the build will error out explaining
- to the user why it stops.
+ 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
In the example above the executable is composed of the C++ file
qconf.cc - identified by $(qconf-cxxobjs).
- If qconf is composed by a mixture of .c and .cc files, then an
+ If qconf is composed of a mixture of .c and .cc files, then an
additional line can be used to identify this.
Example:
hostprogs-$(CONFIG_KALLSYMS) += kallsyms
Kbuild knows about both 'y' for built-in and 'm' for module.
- So if a config symbol evaluate to 'm', kbuild will still build
+ 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.
#drivers/pci/Makefile
clean-files := devlist.h classlist.h
-When executing "make clean", the two files "devlist.h classlist.h" will
-be deleted. Kbuild will assume files to be in same relative directory as the
+When executing "make clean", the two files "devlist.h classlist.h" will be
+deleted. Kbuild will assume files to be in the same relative directory as the
Makefile except if an absolute path is specified (path starting with '/').
To delete a directory hierarchy use:
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 builds the
+To support the clean infrastructure in the Makefiles that build the
final bootimage there is an optional target named archclean:
Example:
KBUILD_AFLAGS_MODULE Options for $(AS) when building modules
- $(KBUILD_AFLAGS_MODULE) is used to add arch specific options that
+ $(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_MODULE Options for $(CC) when building modules
- $(KBUILD_CFLAGS_MODULE) is used to add arch specific options that
+ $(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
+ $(KBUILD_LDFLAGS_MODULE) is used to add arch-specific options
used when linking modules. This is often a linker script.
From commandline LDFLAGS_MODULE shall be used (see kbuild.txt).
extra-y
- extra-y specify additional targets created in the current
+ extra-y specifies additional targets created in the current
directory, in addition to any targets specified by obj-*.
Listing all targets in extra-y is required for two purposes:
2) delete target during make clean
The ": %: %.o" part of the prerequisite is a shorthand that
- free us from listing the setup.o and bootsect.o files.
+ frees us from listing the setup.o and bootsect.o files.
Note: It is a common mistake to forget the "targets :=" assignment,
resulting in the target file being recompiled for no
obvious reason.
When building the *.lds target, kbuild uses the variables:
KBUILD_CPPFLAGS : Set in top-level Makefile
cppflags-y : May be set in the kbuild makefile
- CPPFLAGS_$(@F) : Target specific flags.
+ CPPFLAGS_$(@F) : Target-specific flags.
Note that the full filename is used in this
assignment.
- The kbuild infrastructure for *lds file are used in several
+ The kbuild infrastructure for *lds files is used in several
architecture-specific files.
--- 6.10 Generic header files
=== 7 Kbuild syntax for exported headers
-The kernel include a set of headers that is exported to userspace.
+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 kernel-specific annotations
- drop include of compiler.h
- drop all sections that are kernel internal (guarded by ifdef __KERNEL__)
--- 7.1 header-y
- header-y specify header files to be exported.
+ header-y specifies header files to be exported.
Example:
#include/linux/Kbuild
The convention is to list one file per line and
preferably in alphabetic order.
- header-y also specify which subdirectories to visit.
+ 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.
--- 7.3 destination-y
- When an architecture have a set of exported headers that needs to be
+ When an architecture has 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
+ destination-y specifies the destination directory for all exported
headers in the file where it is present.
Example:
INSTALL_MOD_STRIP
- If this variable is specified, will cause modules to be stripped
+ 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,
+ default option --strip-debug will be used. Otherwise, the
INSTALL_MOD_STRIP value will be used as the option(s) to the strip
command.
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