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Commit 92281c5d authored by Kai Germaschewski's avatar Kai Germaschewski
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Documentation/kbuild/makefiles.txt update 

Remove description of long obsolete (pre-2.4) Makefiles and describe the
current system.
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Documentation/kbuild/makefiles.txt
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...@@ -34,8 +34,7 @@ This document describes the Linux kernel Makefiles. ...@@ -34,8 +34,7 @@ This document describes the Linux kernel Makefiles.
8 New-style variables 8 New-style variables
8.1 New variables 8.1 New variables
8.2 Converting to old-style 8.2 Converting to old-style
9 Compatibility with Linux Kernel 2.2 9 Credits
10 Credits
=== 1 Overview === 1 Overview
...@@ -466,7 +465,7 @@ in the top Makefile: ...@@ -466,7 +465,7 @@ in the top Makefile:
=== 6 The structure of a subdirectory Makefile === 6 The structure of a subdirectory Makefile
A subdirectory Makefile has five sections. A subdirectory Makefile has four sections.
...@@ -488,20 +487,7 @@ special compilation options, and any subdirectories to be recursively ...@@ -488,20 +487,7 @@ special compilation options, and any subdirectories to be recursively
entered. The declarations in these lines depend heavily on the kernel entered. The declarations in these lines depend heavily on the kernel
configuration variables (CONFIG_* symbols). configuration variables (CONFIG_* symbols).
In some Makefiles ("old-style Makefiles"), the second section looks The second section looks like this:
like this:
# drivers/parport/Makefile
ifeq ($(CONFIG_PARPORT_PC),y)
LX_OBJS += parport_pc.o
else
ifeq ($(CONFIG_PARPORT_PC),m)
MX_OBJS += parport_pc.o
endif
endif
In most Makefiles ("new-style Makefiles"), the second section looks
like this:
# drivers/block/Makefile # drivers/block/Makefile
obj-$(CONFIG_MAC_FLOPPY) += swim3.o obj-$(CONFIG_MAC_FLOPPY) += swim3.o
...@@ -509,27 +495,10 @@ like this: ...@@ -509,27 +495,10 @@ like this:
obj-$(CONFIG_AMIGA_FLOPPY) += amiflop.o obj-$(CONFIG_AMIGA_FLOPPY) += amiflop.o
obj-$(CONFIG_ATARI_FLOPPY) += ataflop.o obj-$(CONFIG_ATARI_FLOPPY) += ataflop.o
The new-style Makefiles are more compact and easier to get correct
for certain features (such as CONFIG_* options that enable more than
one file). If you have a choice, please write a new-style Makefile.
--- 6.3 Adapter section
The third section is an adapter section. In old-style Makefiles, this
third section is not present. In new-style Makefiles, the third section
contains boilerplate code which converts from new-style variables to
old-style variables. This is because Rules.make processes only the
old-style variables.
See section 8.2 ("Converting to old-style") for examples.
--- 6.4 Rules.make section --- 6.4 Rules.make section
The fourth section is the single line: The third section is the single line:
include $(TOPDIR)/Rules.make include $(TOPDIR)/Rules.make
...@@ -537,7 +506,7 @@ The fourth section is the single line: ...@@ -537,7 +506,7 @@ The fourth section is the single line:
--- 6.5 Special rules --- 6.5 Special rules
The fifth section contains any special Makefile rules needed that are The fourth section contains any special Makefile rules needed that are
not available through the common rules in Rules.make. not available through the common rules in Rules.make.
...@@ -550,352 +519,166 @@ The public interface of Rules.make consists of the following variables: ...@@ -550,352 +519,166 @@ The public interface of Rules.make consists of the following variables:
--- 7.1 Subdirectories --- 7.1 Subdirectories
ALL_SUB_DIRS, SUB_DIRS, MOD_IN_SUB_DIRS, MOD_SUB_DIRS A Makefile is only responsible for building objects in its own
directory. Files in subdirectories should be taken care of by
$(ALL_SUB_DIRS) is an unconditional list of *all* the Makefiles in the these subdirs. The build system will automatically
subdirectories in a given directory. This list should not depend invoke make recursively in subdirectories, provided you let it know of
on the kernel configuration. them.
$(SUB_DIRS) is a list of subdirectories which may contribute code
to vmlinux. This list may depend on the kernel configuration.
$(MOD_SUB_DIRS) and $(MOD_IN_SUB_DIRS) are lists of subdirectories To do so, use the subdir-{y,m,n,} variables:
which may build kernel modules. Both names have exactly the
same meaning. (In version 2.2 and earlier kernels, these
variables had different meanings -- hence the different names).
For new code, $(MOD_SUB_DIRS) is recommended and $(MOD_IN_SUB_DIRS) subdir-$(CONFIG_ISDN) += i4l
is deprecated. subdir-$(CONFIG_ISDN_CAPI) += capi
Example: When building the actual kernel, i.e. vmlinux ("make
{vmlinux,bzImage,...}"), make will recursively descend into
directories listed in $(subdir-y).
# fs/Makefile When building modules ("make modules"), make will recursively descend
ALL_SUB_DIRS = coda minix ext2 fat msdos vfat proc isofs nfs \ into directories listed in $(subdir-m).
umsdos ntfs hpfs sysv smbfs ncpfs ufs efs affs \
romfs autofs hfs lockd nfsd nls devpts devfs \
adfs partitions qnx4 udf bfs cramfs openpromfs \
autofs4 ramfs jffs
SUB_DIRS :=
... When building the dependencies ("make dep") make needs to visit every
subdir, so it'll descend into every directory listed in
$(subdir-y), $(subdir-m), $(subdir-n), $(subdir-).
ifeq ($(CONFIG_EXT2_FS),y) You may encounter the case where a config option may be set to "y", but
SUB_DIRS += ext2 you still want to possibly build modules in that subdirectory.
else
ifeq ($(CONFIG_EXT2_FS),m)
MOD_SUB_DIRS += ext2
endif
endif
ifeq ($(CONFIG_CRAMFS),y) For example, drivers/isdn/capi/Makefile has
SUB_DIRS += cramfs
else
ifeq ($(CONFIG_CRAMFS),m)
MOD_SUB_DIRS += cramfs
endif
endif
Example: obj-$(CONFIG_ISDN_CAPI) += kernelcapi.o capiutil.o
obj-$(CONFIG_ISDN_CAPI_CAPI20) += capi.o
# drivers/net/Makefile where it's possible that CONFIG_ISDN_CAPI=y, but
SUB_DIRS := CONFIG_ISDN_CAPI_CAPI20=m.
MOD_SUB_DIRS :=
MOD_IN_SUB_DIRS :=
ALL_SUB_DIRS := $(SUB_DIRS) fc hamradio irda pcmcia tokenring \
wan sk98lin arcnet skfp tulip appletalk
...
ifeq ($(CONFIG_IRDA),y) This is expressed by the following construct in the parent Makefile
SUB_DIRS += irda drivers/isdn/Makefile:
MOD_IN_SUB_DIRS += irda
else
ifeq ($(CONFIG_IRDA),m)
MOD_IN_SUB_DIRS += irda
endif
endif
ifeq ($(CONFIG_TR),y) mod-subdirs := i4l hisax capi eicon
SUB_DIRS += tokenring subdir-$(CONFIG_ISDN_CAPI) += capi
MOD_IN_SUB_DIRS += tokenring
else
ifeq ($(CONFIG_TR),m)
MOD_IN_SUB_DIRS += tokenring
endif
endif
Having a subdir ("capi") listed in the variable $(mod-subdirs) will
make the build system enter the specified subdirectory during "make
modules" also, even though the subdir ("capi") is listed only in
$(subdir-y), not $(subdir-m).
--- 7.2 Object file goals --- 7.2 Object file goals
O_TARGET, O_OBJS, OX_OBJS O_TARGET, obj-y
The subdirectory Makefile specifies object files for vmlinux in
the lists $(O_OBJS) and $(OX_OBJS). These lists depend on the
kernel configuration.
The "X" in "OX_OBJS" stands for "eXport". Files in $(OX_OBJS)
may use the EXPORT_SYMBOL macro to define public symbols which
loadable kernel modules can see. Files in $(O_OBJS) may not use
EXPORT_SYMBOL (and you will get a funky error message if you try).
[Yes, it's kludgy to do this by hand. Yes, you can define all
your objects as $(OX_OBJS) whether they define symbols or not;
but then you will notice a lot of extra compiles when you edit
any source file. Blame CONFIG_MODVERSIONS for this.]
Data that is passed to other objects via registration functions
(e.g. pci_register_driver, pm_register) does not need to be marked
as EXPORT_SYMBOL. The objects that pass data via registration
functions do not need to be marked as OX_OBJS, unless they also have
exported symbols.
Rules.make compiles all the $(O_OBJS) and $(OX_OBJS) files.
It then calls "$(LD) -r" to merge these files into one .o file
with the name $(O_TARGET). This $(O_TARGET) name also appears
in the top Makefile.
The order of files in $(O_OBJS) and $(OX_OBJS) is significant.
All $(OX_OBJS) files come first, in the order listed, followed by
all $(O_OBJS) files, in the order listed. Duplicates in the lists
are allowed: the first instance will be linked into $(O_TARGET)
and succeeding instances will be ignored. (Note: Rules.make may
emit warning messages for duplicates, but this is harmless).
Example:
# arch/alpha/kernel/Makefile
O_TARGET := kernel.o
O_OBJS := entry.o traps.o process.o osf_sys.o irq.o \
irq_alpha.o signal.o setup.o ptrace.o time.o \
semaphore.o
OX_OBJS := alpha_ksyms.o
ifdef CONFIG_SMP The subdirectory Makefile specifies object files for vmlinux
O_OBJS += smp.o irq_smp.o in the lists $(obj-y). These lists depend on the kernel
endif configuration.
ifdef CONFIG_PCI Rules.make compiles all the $(obj-y) files. It then calls
O_OBJS += pci.o pci_iommu.o "$(LD) -r" to merge these files into one .o file with the name
endif $(O_TARGET). This $(O_TARGET) is later linked into vmlinux by
a parent Makefile.
Even if a subdirectory Makefile has an $(O_TARGET), the .config The order of files in $(obj-y) is significant. Duplicates in
options still control whether or not its $(O_TARGET) goes into the lists are allowed: the first instance will be linked into
vmlinux. See the $(M_OBJS) example below. $(O_TARGET) and succeeding instances will be ignored.
Sometimes the ordering of all $(OX_OBJS) files before all
$(O_OBJS) files can be a problem, particularly if both
$(O_OBJS) files and $(OX_OBJS) files contain __initcall
declarations where order is important. To avoid this imposed
ordering, the use of $(OX_OBJS) can be dropped altogether and
$(MIX_OBJS) used instead.
If this approach is used, then:
- All objects to be linked into vmlinux should be listed in
$(O_OBJS) in the desired order.
- All objects to be created as modules should be listed in
$(M_OBJS)
- All objects that export symbols should also be listed in
$(MIX_OBJS).
This has the same effect as maintaining the
exported/non-exported split, except that there is more control
over the ordering of object files in vmlinux.
Link order is significant, because certain functions
--- 7.3 Library file goals (module_init() / __initcall) will be called during boot in the
order they appear. So keep in mind that changing the link
L_TARGET, L_OBJS, LX_OBJS order may e.g. change the order in which your SCSI
controllers are detected, and thus you disks are renumbered.
These names are similar to the O_* names. Once again, $(L_OBJS)
and $(LX_OBJS) specify object files for the resident kernel;
once again, the lists depend on the current configuration; and
once again, the files that call EXPORT_SYMBOL go on the "X" list.
The difference is that "L" stands for "Library". After making
$(L_OBJS) and $(LX_OBJS), Rules.make uses the "$(AR) rcs" command
to put these files into an archive file (a library) with the
name $(L_TARGET). This name also appears in the top Makefile.
Example: Example:
# arch/i386/lib/Makefile # Makefile for the kernel ISDN subsystem and device drivers.
L_TARGET = lib.a
L_OBJS = checksum.o old-checksum.o delay.o \
usercopy.o getuser.o putuser.o iodebug.o
ifdef CONFIG_X86_USE_3DNOW
L_OBJS += mmx.o
endif
ifdef CONFIG_HAVE_DEC_LOCK
L_OBJS += dec_and_lock.o
endif
The order of files in $(L_OBJS) and $(LX_OBJS) is not significant. # The target object and module list name.
Duplicates in the lists are allowed. (Note: Rules.make may emit
warning messages for duplicates, but this is harmless).
A subdirectory Makefile can specify either an $(O_TARGET), O_TARGET := vmlinux-obj.o
an $(L_TARGET), or both. Here is a discussion of the differences.
All of the files in an $(O_TARGET) are guaranteed to appear in # Each configuration option enables a list of files.
the resident vmlinux image. In an $(L_TARGET), only the files
that satisfy undefined symbol references from other files will
appear in vmlinux.
In a conventional link process, the linker processes some obj-$(CONFIG_ISDN) += isdn.o
object files and creates a list of unresolved external symbols. obj-$(CONFIG_ISDN_PPP_BSDCOMP) += isdn_bsdcomp.o
The linker then looks in a set of libraries to resolve these
symbols. Indeed, the Linux kernel used to be linked this way,
with the bulk of the code stored in libraries.
But vmlinux contains two types of object files that cannot be # The global Rules.make.
fetched out of libraries this way:
(1) object files that are purely EXPORT_SYMBOL definitions include $(TOPDIR)/Rules.make
(2) object files that use module_init or __initcall initializers
(instead of an initialization routine called externally)
These files contain autonomous initializer sections which provide --- 7.3 Library file goals
code and data without being explicitly called. If these files
were stored in $(L_TARGET) libraries, the linker would fail
to include them in vmlinux. Thus, most subdirectory Makefiles
specify an $(O_TARGET) and do not use $(L_TARGET).
Other considerations: $(O_TARGET) leads to faster re-link times L_TARGET
during development activity, but $(L_TARGET) gives better error
messages for unresolved symbols.
Instead of building an O_TARGET object file, you may also
build an archive which again contains objects listed in
$(obj-y). This is normally not necessary and only used in
the lib, arch/$(ARCH)/lib directories.
--- 7.4 Loadable module goals --- 7.4 Loadable module goals
M_OBJS, MX_OBJS obj-m
$(M_OBJS) and $(MX_OBJS) specify object files which are built $(obj-m) specify object files which are built as loadable
as loadable kernel modules. As usual, the "X" in $(MX_OBJS) kernel modules.
stands for "eXport"; source files that use EXPORT_SYMBOL must
appear on an $(MX_OBJS) list.
A module may be built from one source file or several source A module may be built from one source file or several source
files. In the case of one source file, the subdirectory files. In the case of one source file, the subdirectory
Makefile simply adds the file to either $(M_OBJS) or $(MX_OBJS), Makefile simply adds the file to $(obj-m)
as appropriate.
Example: Example:
# drivers/net/irda/Makefile obj-$(CONFIG_ISDN_PPP_BSDCOMP) += isdn_bsdcomp.o
ifeq ($(CONFIG_IRTTY_SIR),y)
L_OBJS += irtty.o
else
ifeq ($(CONFIG_IRTTY_SIR),m)
M_OBJS += irtty.o
endif
endif
ifeq ($(CONFIG_IRPORT_SIR),y) If a kernel module is built from several source files, you specify
LX_OBJS += irport.o that you want to build a module in the same way as above.
else
ifeq ($(CONFIG_IRPORT_SIR),m)
MX_OBJS += irport.o
endif
endif
If a kernel module is built from several source files, there However, the build system of course needs to know which the parts
are two ways to specify the set of source files. One way is to are that you want to build your module of, so you have to tell it
build a single module for the entire subdirectory. This way is by setting an $(<module_name>-objs) variable.
popular in the file system and network protocol stacks.
Example: Example:
# fs/ext2/Makefile obj-$(CONFIG_ISDN) += isdn.o
O_TARGET := ext2.o
O_OBJS := acl.o balloc.o bitmap.o dir.o file.o fsync.o \
ialloc.o inode.o ioctl.o namei.o super.o symlink.o \
truncate.o
M_OBJS := $(O_TARGET)
In this example, the module name will be ext2.o. Because this isdn-objs := isdn_net.o isdn_tty.o isdn_v110.o isdn_common.o
file has the same name has $(O_TARGET), Rules.make will use
the $(O_TARGET) rule to build ext2.o: it will run "$(LD) -r"
on the list of $(O_OBJS) files.
Note that this subdirectory Makefile defines both an $(O_TARGET) In this example, the module name will be isdn.o. Rules.make
and an $(M_OBJS). The control code, up in fs/Makefile, will will compile the objects listed in $(isdn-objs) and then run
select between these two. If CONFIG_EXT2_FS=y, then fs/Makefile "$(LD) -r" on the list of these files to generate isdn.o
will build $(O_TARGET); and if CONFIG_EXT_FS=m, then fs/Makefile
will build $(M_OBJS) instead. (Yes, this is a little delicate
and a little confusing).
Note: Of course, when you are building objects into the kernel,
the syntax above will also work. So, if you have CONFIG_ISDN=y,
the build system will build an isdn.o for you out of the individual
parts and then link this into the $(O_TARGET), as you'd expect.
--- 7.5 Multi-part modules --- 7.5 Objects which export symbols
MI_OBJS, MIX_OBJS export-objs
Some kernel modules are composed of several object files When using loadable modules, not every global symbol in the
linked together, but do not include every object file in their kernel / other modules is automatically available for your
subdirectory. $(MI_OBJS) and $(MIX_OBJS) are for this case. module, only those explicitly exported are.
"M" stands for Module. To make a symbol available for use in modules, to "export" it,
"I" stands for Intermediate. use the EXPORT_SYMBOL(<symbol>) directive in your source. In
"X", as usual, stands for "eXport symbol". addition, you need to list all object files which export symbols
(i.e. their source contains an EXPORT_SYMBOL() directive) in the
Makefile variable $(export-objs).
Example: Example:
# drivers/sound/Makefile # Objects that export symbols.
gus-objs := gus_card.o gus_midi.o gus_vol.o gus_wave.o ics2101.o
pas2-objs := pas2_card.o pas2_midi.o pas2_mixer.o pas2_pcm.o
sb-objs := sb_card.o
gus.o: $(gus-objs)
$(LD) -r -o $@ $(gus-objs)
pas2.o: $(pas2-objs)
$(LD) -r -o $@ $(pas2-objs)
sb.o: $(sb-objs) export-objs := isdn_common.o
$(LD) -r -o $@ $(sb-objs)
The kernel modules gus.o, pas2.o, and sb.o are the *composite since isdn_common.c contains
files*. The object files gus_card.o, gus_midi.o, gus_vol.o,
gus_wave.o, ics2101.o, pas2_card.o, pas2_midi.o, pas2_mixer.o,
pas2_pcm.o, and sb_card.o are *component files*. The component
files are also called *intermediate files*.
In another part of drivers/sound/Makefile (not shown), all of EXPORT_SYMBOL(register_isdn);
the component files are split out. For the resident drivers:
the component object files go onto $(O_OBJS) and $(OX_OBJS)
lists, depending on whether they export symbols or not; and the
composite files are never built. For the kernel modules: the
component object files go onto $(MI_OBJS) and $(MIX_OBJS);
the composite files go onto $(M_OBJS).
The subdirectory Makefile must also specify the linking rule which makes the function register_isdn available to
for a multi-object-file module: low-level ISDN drivers.
# drivers/sound/Makefile
gus.o: $(gus-objs)
$(LD) -r -o $@ $(gus-objs)
pas2.o: $(pas2-objs)
$(LD) -r -o $@ $(pas2-objs)
sb.o: $(sb-objs)
$(LD) -r -o $@ $(sb-objs)
As is mentioned in section 7.2 ("Object file goals"),
$(MIX_OBJS) can also be used simply to list all objects that
export any symbols. If this approach is taken, then
$(O_OBJS), $(L_OBJS), $(M_OBJS) and $(MI_OBJS) should simply
lists all of the vmlinux object files, library object files,
module object files and intermediate module files
respectively. Duplication between $(MI_OBJS) and $(MIX_OBJS)
is not a problem.
--- 7.6 Compilation flags --- 7.6 Compilation flags
...@@ -1013,6 +796,10 @@ The public interface of Rules.make consists of the following variables: ...@@ -1013,6 +796,10 @@ The public interface of Rules.make consists of the following variables:
=== 8 New-style variables === 8 New-style variables
[ This sections dates back from a time where the way to write Makefiles
described above was "new-style". I'm leaving it in as it describes the
same thing in other words, so it may be of some use ]
The "new-style variables" are simpler and more powerful than the The "new-style variables" are simpler and more powerful than the
"old-style variables". As a result, many subdirectory Makefiles shrank "old-style variables". As a result, many subdirectory Makefiles shrank
more than 60%. This author hopes that, in time, all arch Makefiles and more than 60%. This author hopes that, in time, all arch Makefiles and
...@@ -1099,16 +886,14 @@ people define most variables using "new style" but then fall back to ...@@ -1099,16 +886,14 @@ people define most variables using "new style" but then fall back to
$(export-objs) list in a new-style Makefile is simpler and easier $(export-objs) list in a new-style Makefile is simpler and easier
to audit. to audit.
list-multi
$(foo)-objs $(foo)-objs
Some kernel modules are composed of multiple object files linked Some kernel modules are composed of multiple object files linked
together. $(list-multi) is a list of such kernel modules. together.
This is a static list; it does not depend on the configuration.
For each kernel module in $(list-multi) there is another list For each multi-part kernel modul there is a list of all the
of all the object files which make up that module. For a kernel object files which make up that module. For a kernel module
module named foo.o, its object file list is foo-objs. named foo.o, its object file list is foo-objs.
Example: Example:
...@@ -1135,44 +920,16 @@ people define most variables using "new style" but then fall back to ...@@ -1135,44 +920,16 @@ people define most variables using "new style" but then fall back to
obj-$(CONFIG_SCSI_INIA100) += a100u2w.o obj-$(CONFIG_SCSI_INIA100) += a100u2w.o
Suppose that CONFIG_SCSI=y. Then vmlinux needs to link in all Suppose that CONFIG_SCSI=y. Then vmlinux needs to link in all
14 components of scsi_mod.o, so these components will go onto 14 components of scsi_mod.o.
$(O_OBJS) and $(OX_OBJS). The composite file scsi_mod.o will
never be created. The boilerplate conversion code produces this
result with a few lines of list processing commands.
Suppose that CONFIG_BLK_DEV_SR=m. Then the 3 components Suppose that CONFIG_BLK_DEV_SR=m. Then the 3 components
of sr_mod.o will linked together with "$(LD) -r" to make the of sr_mod.o will be linked together with "$(LD) -r" to make the
kernel module sr_mod.o, so these 3 components need to go onto kernel module sr_mod.o.
the $(MI_OBJS) and $(MIX_OBJS) lists; the composite file sr_mod.o
goes onto $(M_OBJS). The boilerplate conversion code takes care
of this, too.
And suppose CONFIG_SCSI_INITIO=n. Then initio.o goes onto the And suppose CONFIG_SCSI_INITIO=n. Then initio.o goes onto the
$(obj-n) list and that's the end of it. Its component files $(obj-n) list and that's the end of it. Its component files
are not compiled, and the composite file is not created. are not compiled, and the composite file is not created.
Finally, the subdirectory Makefile needs to define rules to
build each multi-object kernel module from its component list.
Example:
# drivers/scsi/Makefile
scsi_mod.o: $(scsi_mod-objs)
$(LD) -r -o $@ $(scsi_mod-objs)
sr_mod.o: $(sr_mod-objs)
$(LD) -r -o $@ $(sr_mod-objs)
initio.o: $(initio-objs)
$(LD) -r -o $@ $(initio-objs)
a100u2w.o: $(a100u2w-objs)
$(LD) -r -o $@ $(a100u2w-objs)
These rules are very regular; it would be nice for the boilerplate
code or Rules.make to synthesize these rules automatically.
But until that happens, the subdirectory Makefile needs to define
these rules explicitly.
subdir-y subdir-m subdir-n subdir- subdir-y subdir-m subdir-n subdir-
...@@ -1217,72 +974,7 @@ people define most variables using "new style" but then fall back to ...@@ -1217,72 +974,7 @@ people define most variables using "new style" but then fall back to
This means nls should be added to (subdir-y) and $(subdir-m) if This means nls should be added to (subdir-y) and $(subdir-m) if
CONFIG_NFS = y. CONFIG_NFS = y.
--- 8.2 Converting to old-style === 9 Credits
The following example is taken from drivers/usb/Makefile.
Note that this uses MIX_OBJS to avoid the need for OX_OBJS and
MX_OBJS and thus to maintain the ordering of objects in $(obj-y)
# Translate to Rules.make lists.
multi-used := $(filter $(list-multi), $(obj-y) $(obj-m))
multi-objs := $(foreach m, $(multi-used), $($(basename $(m))-objs))
active-objs := $(sort $(multi-objs) $(obj-y) $(obj-m))
O_OBJS := $(obj-y)
M_OBJS := $(obj-m)
MIX_OBJS := $(filter $(export-objs), $(active-objs))
An example for libraries from drivers/acorn/scsi/Makefile:
# Translate to Rules.make lists.
L_OBJS := $(filter-out $(export-objs), $(obj-y))
LX_OBJS := $(filter $(export-objs), $(obj-y))
M_OBJS := $(sort $(filter-out $(export-objs), $(obj-m)))
MX_OBJS := $(sort $(filter $(export-objs), $(obj-m)))
As ordering is not so important in libraries, this still uses
LX_OBJS and MX_OBJS, though (presumably) it could be changed to
use MIX_OBJS as follows:
active-objs := $(sort $(obj-y) $(obj-m))
L_OBJS := $(obj-y)
M_OBJS := $(obj-m)
MIX_OBJS := $(filter $(export-objs), $(active-objs))
which is clearly shorted and arguably clearer.
=== 9 Compatibility with Linux Kernel 2.2
Most of the information in this document also applies to 2.2, although
there is no indication of which things have changed when. Here are some
hints for writing subdirectory Makefiles that are compatible with Linux
kernel 2.2.
You can write either an old-style Makefile or a new-style Makefile
with a boilerplate adapter section. See the 2.2 version of
drivers/sound/Makefile for a copy of the boilerplate code.
In 2.2, Rules.make makes a distinction between $(MOD_SUB_DIRS)
and $(MOD_IN_SUB_DIRS). If you have a single directory with no
subdirectories, this will not matter to you. If you have a whole
tree, then you need to know the difference between $(MOD_SUB_DIRS)
and $(MOD_IN_SUB_DIRS). For example code: $(MOD_SUB_DIRS) is used
extensively in fs/Makefile; $(MOD_IN_SUB_DIRS) is used extensively in
drivers/net/Makefile.
If you are already using MOD_LIST_NAME, go ahead and keep using it.
If you don't already have a MOD_LIST_NAME, go ahead and keep not using
one; your module will be a 'misc' module in 2.2.
Assembly language rules were a mess in 2.2. If you have assembly language
files, this author recommends that you write your own explicit rules
for each file by name.
=== 10 Credits
Thanks to the members of the linux-kbuild mailing list for reviewing Thanks to the members of the linux-kbuild mailing list for reviewing
drafts of this document, with particular thanks to Peter Samuelson drafts of this document, with particular thanks to Peter Samuelson
......
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