--- 3.4 Objects which export symbols
--- 3.5 Library file goals - lib-y
--- 3.6 Descending down in directories
- --- 3.7 Compilation flags
- --- 3.8 Dependency tracking
- --- 3.9 Custom Rules
- --- 3.10 Command change detection
- --- 3.11 $(CC) support functions
- --- 3.12 $(LD) support functions
- --- 3.13 Script Invocation
+ --- 3.7 Non-builtin vmlinux targets - extra-y
+ --- 3.8 Always built goals - always-y
+ --- 3.9 Compilation flags
+ --- 3.10 Dependency tracking
+ --- 3.11 Custom Rules
+ --- 3.12 Command change detection
+ --- 3.13 $(CC) support functions
+ --- 3.14 $(LD) support functions
+ --- 3.15 Script Invocation
=== 4 Host Program support
--- 4.1 Simple Host Program
that directory specifies obj-y, those objects will be left orphan.
It is very likely a bug of the Makefile or of dependencies in Kconfig.
+ Kbuild also supports dedicated syntax, subdir-y and subdir-m, for
+ descending into subdirectories. It is a good fit when you know they
+ do not contain kernel-space objects at all. A typical usage is to let
+ Kbuild descend into subdirectories to build tools.
+
+ Examples::
+
+ # scripts/Makefile
+ subdir-$(CONFIG_GCC_PLUGINS) += gcc-plugins
+ subdir-$(CONFIG_MODVERSIONS) += genksyms
+ subdir-$(CONFIG_SECURITY_SELINUX) += selinux
+
+ Unlike obj-y/m, subdir-y/m does not need the trailing slash since this
+ syntax is always used for directories.
+
It is good practice to use a `CONFIG_` variable when assigning directory
names. This allows kbuild to totally skip the directory if the
corresponding `CONFIG_` option is neither 'y' nor 'm'.
-3.7 Compilation flags
+3.7 Non-builtin vmlinux targets - extra-y
+-----------------------------------------
+
+ extra-y specifies targets which are needed for building vmlinux,
+ but not combined into built-in.a.
+
+ Examples are:
+
+ 1) head objects
+
+ Some objects must be placed at the head of vmlinux. They are
+ directly linked to vmlinux without going through built-in.a
+ A typical use-case is an object that contains the entry point.
+
+ arch/$(SRCARCH)/Makefile should specify such objects as head-y.
+
+ Discussion:
+ Given that we can control the section order in the linker script,
+ why do we need head-y?
+
+ 2) vmlinux linker script
+
+ The linker script for vmlinux is located at
+ arch/$(SRCARCH)/kernel/vmlinux.lds
+
+ Example::
+
+ # arch/x86/kernel/Makefile
+ extra-y := head_$(BITS).o
+ extra-y += head$(BITS).o
+ extra-y += ebda.o
+ extra-y += platform-quirks.o
+ extra-y += vmlinux.lds
+
+ $(extra-y) should only contain targets needed for vmlinux.
+
+ Kbuild skips extra-y when vmlinux is apparently not a final goal.
+ (e.g. 'make modules', or building external modules)
+
+ If you intend to build targets unconditionally, always-y (explained
+ in the next section) is the correct syntax to use.
+
+3.8 Always built goals - always-y
+---------------------------------
+
+ always-y specifies targets which are literally always built when
+ Kbuild visits the Makefile.
+
+ Example::
+ # ./Kbuild
+ offsets-file := include/generated/asm-offsets.h
+ always-y += $(offsets-file)
+
+3.9 Compilation flags
---------------------
ccflags-y, asflags-y and ldflags-y
AFLAGS_iwmmxt.o := -Wa,-mcpu=iwmmxt
-3.8 Dependency tracking
------------------------
+3.10 Dependency tracking
+------------------------
Kbuild tracks dependencies on the following:
Thus, if you change an option to $(CC) all affected files will
be re-compiled.
-3.9 Custom Rules
-----------------
+3.11 Custom Rules
+-----------------
Custom rules are used when the kbuild infrastructure does
not provide the required support. A typical example is
will be displayed with "make KBUILD_VERBOSE=0".
-3.10 Command change detection
+3.12 Command change detection
-----------------------------
When the rule is evaluated, timestamps are compared between the target
unwanted results when the target is up to date and only the
tests on changed commands trigger execution of commands.
-3.11 $(CC) support functions
+3.13 $(CC) support functions
----------------------------
The kernel may be built with several different versions of
endif
endif
-3.12 $(LD) support functions
+3.14 $(LD) support functions
----------------------------
ld-option
#Makefile
LDFLAGS_vmlinux += $(call ld-option, -X)
-3.13 Script invocation
+3.15 Script invocation
----------------------
Make rules may invoke scripts to build the kernel. The rules shall
When "make" is executed without arguments, bzImage will be built.
-7.6 Building non-kbuild targets
--------------------------------
-
- extra-y
- 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:
-
- 1) Enable kbuild to check changes in command lines
-
- - When $(call if_changed,xxx) is used
-
- 2) kbuild knows what files to delete during "make clean"
-
- Example::
-
- #arch/x86/kernel/Makefile
- extra-y := head.o init_task.o
-
- In this example, extra-y is used to list object files that
- shall be built, but shall not be linked as part of built-in.a.
-
7.7 Commands useful for building a boot image
---------------------------------------------
projects / linux-2.6-microblaze.git / blobdiff