--- 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_$@
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
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
-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
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 := $(call cc-cross-prefix, m68k-linux-gnu-)
+ endif
+ endif
+
=== 4 Host Program support
Kbuild supports building executables on the host for use during the
Example:
#arch/s390/Makefile
LDFLAGS := -m elf_s390
- Note: EXTRA_LDFLAGS and LDFLAGS_$@ 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 += $(call cc-option,-fno-unit-at-a-time)
...
specified options when building the target vmlinux.lds.
When building the *.lds target, kbuild uses the variables:
- CPPFLAGS : Set in top-level Makefile
- EXTRA_CPPFLAGS : May be set in the kbuild makefile
+ KBUILD_CPPFLAGS : Set in top-level Makefile
+ cppflags-y : May be set in the kbuild makefile
CPPFLAGS_$(@F) : Target specific flags.
Note that the full filename is used in this
assignment.
git.samba.org / sfrench / cifs-2.6.git / blobdiff