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SubjectPATCH - kbuild documentation.

Linus,
I thought I would document what I had learnt about Makefiles in
making the initialisation of drivers/md work better.

This patch (minus a few typos that I have since found and corrected)
was blessed by Michael Chastain on linux-kbuild.

Ofcourse, running "make vmlinux" doesn't convert documentation
patches into changes in a running kernel like it does for code
patches, so:

Linux Developers:
Please apply this patch to your brain. It works for me, bit if you
get a cerebral Oops, or a live-lock (hopefully no deadlock!!), please
send me a brain-dump and I will try to fix the problem :-)

NeilBrown




--- ./Documentation/kbuild/makefiles.txt 2000/11/29 20:44:19 1.1
+++ ./Documentation/kbuild/makefiles.txt 2000/11/29 23:27:10 1.2
@@ -32,6 +32,8 @@
7.6 Compilation flags
7.7 Miscellaneous variables
8 New-style variables
+ 8.1 New variables
+ 8.2 Converting to old-style
9 Compatibility with Linux Kernel 2.2
10 Credits

@@ -521,6 +523,8 @@
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
@@ -679,6 +683,25 @@
options still control whether or not its $(O_TARGET) goes into
vmlinux. See the $(M_OBJS) example below.

+ 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.
+


--- 7.3 Library file goals
@@ -865,6 +888,14 @@
$(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

@@ -993,6 +1024,8 @@
people define most variables using "new style" but then fall back to
"old style" for a few lines.

+--- 8.1 New variables
+
obj-y obj-m obj-n obj-

These variables replace $(O_OBJS), $(OX_OBJS), $(M_OBJS),
@@ -1184,6 +1217,41 @@
This means nls should be added to (subdir-y) and $(subdir-m) if
CONFIG_NFS = y.

+--- 8.2 Converting to old-style
+
+ 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

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