+--- 6.8 Preprocessing linker scripts
+
+ When the vmlinux image is build the linker script:
+ arch/$(ARCH)/kernel/vmlinux.lds is used.
+ The script is a preprocessed variant of the file vmlinux.lds.S
+ located in the same directory.
+ kbuild knows .lds file and includes a rule *lds.S -> *lds.
+
+ Example:
+ #arch/i386/kernel/Makefile
+ always := vmlinux.lds
+
+ #Makefile
+ export CPPFLAGS_vmlinux.lds += -P -C -U$(ARCH)
+
+ The assigment to $(always) is used to tell kbuild to build the
+ target: vmlinux.lds.
+ The assignment to $(CPPFLAGS_vmlinux.lds) tell kbuild to use the
+ specified options when building the target vmlinux.lds.
+
+ When building the *.lds target kbuild used the variakles:
+ CPPFLAGS : Set in top-level Makefile
+ EXTRA_CPPFLAGS : May be set in the kbuild makefile
+ CPPFLAGS_$(@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.
+
+
+--- 6.9 $(CC) support functions
+
+ The kernel may be build 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).
+ $(CC) is useally the gcc compiler, but other alternatives are
+ available.
+
+ cc-option
+ cc-option is used to check if $(CC) support a given option, and not
+ supported to use an optional second option.
+
+ Example:
+ #arch/i386/Makefile
+ cflags-y += $(call cc-option,-march=pentium-mmx,-march=i586)
+
+ 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.
+
+ cc-option-yn
+ cc-option-yn is used to check if gcc supports a given option
+ and return 'y' if supported, otherwise 'n'.
+
+ Example:
+ #arch/ppc/Makefile
+ biarch := $(call cc-option-yn, -m32)
+ aflags-$(biarch) += -a32
+ cflags-$(biarch) += -m32
+
+ In the above example $(biarch) is set to y if $(CC) supports the -m32
+ option. When $(biarch) equals to y the expanded variables $(aflags-y)
+ and $(cflags-y) will be assigned the values -a32 and -m32.
+
+ cc-version
+ cc-version return a numerical version of the $(CC) compiler version.
+ The format is <major><minor> where both are two digits. So for example
+ gcc 3.41 would return 0341.
+ cc-version is useful when a specific $(CC) version is faulty in one
+ area, for example the -mregparm=3 were broken in some gcc version
+ even though the option was accepted by gcc.
+
+ Example:
+ #arch/i386/Makefile
+ GCC_VERSION := $(call cc-version)
+ cflags-y += $(shell \
+ if [ $(GCC_VERSION) -ge 0300 ] ; then echo "-mregparm=3"; fi ;)
+
+ In the above example -mregparm=3 is only used for gcc version greater
+ than or equal to gcc 3.0.
+
+