--- 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
+ --- 6.4 Architecture-specific boot images
--- 6.5 Building non-kbuild targets
--- 6.6 Commands useful for building a boot image
--- 6.7 Custom kbuild commands
Example:
obj-y += foo.o
- This tell kbuild that there is one object in that directory, named
+ This tells kbuild that there is one object in that directory, named
foo.o. foo.o will be built from foo.c or foo.S.
If foo.o shall be built as a module, the variable obj-m is used.
--- 3.7 Compilation flags
- EXTRA_CFLAGS, EXTRA_AFLAGS, EXTRA_LDFLAGS, EXTRA_ARFLAGS
+ 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.
+ 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.
- All the EXTRA_ variables apply only to the kbuild makefile
- where they are assigned. The EXTRA_ variables apply to all
- commands executed in the kbuild makefile.
-
- $(EXTRA_CFLAGS) specifies options for compiling C files with
- $(CC).
+ ccflags-y specifies options for compiling C files with $(CC).
Example:
# drivers/sound/emu10k1/Makefile
- EXTRA_CFLAGS += -I$(obj)
- ifdef DEBUG
- EXTRA_CFLAGS += -DEMU10K1_DEBUG
- endif
+ ccflags-y += -I$(obj)
+ ccflags-$(DEBUG) += -DEMU10K1_DEBUG
This variable is necessary because the top Makefile owns the
- variable $(CFLAGS) and uses it for compilation flags for the
+ variable $(KBUILD_CFLAGS) and uses it for compilation flags for the
entire tree.
- $(EXTRA_AFLAGS) is a similar string for per-directory options
+ asflags-y is a similar string for per-directory options
when compiling assembly language source.
Example:
#arch/x86_64/kernel/Makefile
- EXTRA_AFLAGS := -traditional
+ asflags-y := -traditional
- $(EXTRA_LDFLAGS) and $(EXTRA_ARFLAGS) are similar strings for
- per-directory options to $(LD) and $(AR).
+ ldflags-y is a string for per-directory options to $(LD).
Example:
#arch/m68k/fpsp040/Makefile
- EXTRA_LDFLAGS := -x
+ ldflags-y := -x
CFLAGS_$@, AFLAGS_$@
Special rules are used when the kbuild infrastructure does
not provide the required support. A typical example is
header files generated during the build process.
- Another example are the architecture specific Makefiles which
+ Another example are the architecture-specific Makefiles which
need special rules to prepare boot images etc.
Special rules are written as normal Make rules.
#arch/i386/kernel/Makefile
vsyscall-flags += $(call ld-option, -Wl$(comma)--hash-style=sysv)
- In the above example vsyscall-flags will be assigned the option
+ In the above example, vsyscall-flags will be assigned the option
-Wl$(comma)--hash-style=sysv if it is supported by $(CC).
The second argument is optional, and if supplied will be used
if first argument is not supported.
as-instr checks if the assembler reports a specific instruction
and then outputs either option1 or option2
C escapes are supported in the test instruction
+ 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
#arch/i386/Makefile
cflags-y += $(call cc-option,-march=pentium-mmx,-march=i586)
- In the above example cflags-y will be assigned the option
+ In the above example, cflags-y will be assigned the option
-march=pentium-mmx if supported by $(CC), otherwise -march=i586.
The second argument to cc-option is optional, and if omitted,
cflags-y will be assigned no value if first option is not supported.
+ Note: cc-option uses KBUILD_CFLAGS for $(CC) options
cc-option-yn
cc-option-yn is used to check if gcc supports a given option
option. When $(biarch) equals 'y', the expanded variables $(aflags-y)
and $(cflags-y) will be assigned the values -a32 and -m32,
respectively.
+ Note: cc-option-yn uses KBUILD_CFLAGS for $(CC) options
cc-option-align
gcc versions >= 3.0 changed the type of options used to specify
cc-option-align = -falign
Example:
- CFLAGS += $(cc-option-align)-functions=4
+ 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-version
cc-version returns a numerical version of the $(CC) compiler version.
Example:
#fs/reiserfs/Makefile
- EXTRA_CFLAGS := $(call cc-ifversion, -lt, 0402, -O1)
+ ccflags-y := $(call cc-ifversion, -lt, 0402, -O1)
- In this example, EXTRA_CFLAGS will be assigned the value -O1 if the
+ 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
+ $(Q)if test "$(call 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 := $(call cc-cross-prefix, m68k-linux-gnu-)
+ endif
+ endif
=== 4 Host Program support
located at the root of the obj tree.
The very first objects linked are listed in head-y, assigned by
arch/$(ARCH)/Makefile.
-7) Finally, the architecture specific part does any required post processing
+7) Finally, the architecture-specific part does any required post processing
and builds the final bootimage.
- This includes building boot records
- - Preparing initrd images and thelike
+ - Preparing initrd images and the like
--- 6.1 Set variables to tweak the build to the architecture
Example:
#arch/s390/Makefile
LDFLAGS := -m elf_s390
- Note: EXTRA_LDFLAGS and LDFLAGS_$@ can be used to further customise
- the flags used. See chapter 7.
+ Note: ldflags-y can be used to further customise
+ the flags used. See chapter 3.7.
LDFLAGS_MODULE Options for $(LD) when linking modules
In this example, the binary $(obj)/image is a binary version of
vmlinux. The usage of $(call if_changed,xxx) will be described later.
- AFLAGS $(AS) assembler flags
+ KBUILD_AFLAGS $(AS) assembler flags
Default value - see top level Makefile
Append or modify as required per architecture.
Example:
#arch/sparc64/Makefile
- AFLAGS += -m64 -mcpu=ultrasparc
+ KBUILD_AFLAGS += -m64 -mcpu=ultrasparc
- CFLAGS $(CC) compiler flags
+ KBUILD_CFLAGS $(CC) compiler flags
Default value - see top level Makefile
Append or modify as required per architecture.
- Often, the CFLAGS variable depends on the configuration.
+ Often, the KBUILD_CFLAGS variable depends on the configuration.
Example:
#arch/i386/Makefile
cflags-$(CONFIG_M386) += -march=i386
- CFLAGS += $(cflags-y)
+ KBUILD_CFLAGS += $(cflags-y)
Many arch Makefiles dynamically run the target C compiler to
probe supported options:
-march=pentium2,-march=i686)
...
# Disable unit-at-a-time mode ...
- CFLAGS += $(call cc-option,-fno-unit-at-a-time)
+ KBUILD_CFLAGS += $(call cc-option,-fno-unit-at-a-time)
...
$(head-y) lists objects to be linked first in vmlinux.
$(libs-y) lists directories where a lib.a archive can be located.
- The rest lists directories where a built-in.o object file can be
+ The rest list directories where a built-in.o object file can be
located.
$(init-y) objects will be located after $(head-y).
$(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.
+ and arch/$(ARCH)/Makefile only adds architecture-specific directories.
Example:
#arch/sparc64/Makefile
drivers-$(CONFIG_OPROFILE) += arch/sparc64/oprofile/
---- 6.4 Architecture specific boot images
+--- 6.4 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
"$(Q)$(MAKE) $(build)=<dir>" is the recommended way to invoke
make in a subdirectory.
- There are no rules for naming architecture specific targets,
+ 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.
$(call if_changed,ld/objcopy/gzip)
When the rule is evaluated, it is checked to see if any files
- needs an update, or the command line has changed since the last
+ 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 $(targets),
specified options when building the target vmlinux.lds.
When building the *.lds target, kbuild uses the variables:
- CPPFLAGS : Set in top-level Makefile
- EXTRA_CPPFLAGS : May be set in the kbuild makefile
+ KBUILD_CPPFLAGS : Set in top-level Makefile
+ cppflags-y : May be set in the kbuild makefile
CPPFLAGS_$(@F) : Target specific flags.
Note that the full filename is used in this
assignment.
The kbuild infrastructure for *lds file are used in several
- architecture specific files.
+ architecture-specific files.
=== 7 Kbuild Variables
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.
+ Use this for architecture-specific install targets.
INSTALL_MOD_PATH, MODLIB
git.openpandora.org / pandora-kernel.git / blobdiff