--- 3.7 Compilation flags
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.
+ These three flags apply only to the kbuild makefile in which they
+ are assigned. They are used for all the normal cc, as and ld
+ invocations happening 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.
+ They are still supported but their usage is deprecated.
- ccflags-y specifies options for compiling C files with $(CC).
+ ccflags-y specifies options for compiling with $(CC).
Example:
- # drivers/sound/emu10k1/Makefile
- ccflags-y += -I$(obj)
- ccflags-$(DEBUG) += -DEMU10K1_DEBUG
-
+ # drivers/acpi/Makefile
+ ccflags-y := -Os
+ ccflags-$(CONFIG_ACPI_DEBUG) += -DACPI_DEBUG_OUTPUT
This variable is necessary because the top Makefile owns the
variable $(KBUILD_CFLAGS) and uses it for compilation flags for the
entire tree.
- asflags-y is a similar string for per-directory options
- when compiling assembly language source.
+ asflags-y specifies options for assembling with $(AS).
Example:
- #arch/x86_64/kernel/Makefile
- asflags-y := -traditional
-
+ #arch/sparc/kernel/Makefile
+ asflags-y := -ansi
- ldflags-y is a string for per-directory options to $(LD).
+ ldflags-y specifies options for linking with $(LD).
Example:
- #arch/m68k/fpsp040/Makefile
- ldflags-y := -x
+ #arch/cris/boot/compressed/Makefile
+ ldflags-y += -T $(srctree)/$(src)/decompress_$(arch-y).lds
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.
+ The two flags listed above are similar to ccflags-y and asflags-y.
+ The difference is that the subdir- variants have effect for the kbuild
+ file where they are present and all subdirectories.
Options specified using subdir-* are added to the commandline before
the options specified using the non-subdir variants.
CFLAGS_aha152x.o = -DAHA152X_STAT -DAUTOCONF
CFLAGS_gdth.o = # -DDEBUG_GDTH=2 -D__SERIAL__ -D__COM2__ \
-DGDTH_STATISTICS
- CFLAGS_seagate.o = -DARBITRATE -DPARITY -DSEAGATE_USE_ASM
- These three lines specify compilation flags for aha152x.o,
- gdth.o, and seagate.o
+ These two lines specify compilation flags for aha152x.o and gdth.o.
$(AFLAGS_$@) is a similar feature for source files in assembly
languages.
Example:
# arch/arm/kernel/Makefile
- AFLAGS_head-armv.o := -DTEXTADDR=$(TEXTADDR) -traditional
- AFLAGS_head-armo.o := -DTEXTADDR=$(TEXTADDR) -traditional
+ AFLAGS_head.o := -DTEXT_OFFSET=$(TEXT_OFFSET)
+ AFLAGS_crunch-bits.o := -Wa,-mcpu=ep9312
+ AFLAGS_iwmmxt.o := -Wa,-mcpu=iwmmxt
+
--- 3.9 Dependency tracking
The first example utilises the trick that a config option expands
to 'y' when selected.
- CFLAGS_KERNEL $(CC) options specific for built-in
+ KBUILD_AFLAGS_KERNEL $(AS) options specific for built-in
- $(CFLAGS_KERNEL) contains extra C compiler flags used to compile
+ $(KBUILD_AFLAGS_KERNEL) contains extra C compiler flags used to compile
resident kernel code.
- CFLAGS_MODULE $(CC) options specific for modules
+ 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).
- $(CFLAGS_MODULE) contains extra C compiler flags used to compile code
- for loadable kernel modules.
+ 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).
--- 6.2 Add prerequisites to archprepare:
=== 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
+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 is kernel internat (guarded by ifdef __KERNEL__)
+- drop all sections that are kernel internal (guarded by ifdef __KERNEL__)
-Each relevant directory contain a file name "Kbuild" which specify the
+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.
projects / firefly-linux-kernel-4.4.55.git / blobdiff