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    SubjectRe: module builds need improvement / top Makefile not good enough
    | > I am unhappy with the direction the 2.6 kernel builds have taken.
    | > Very much like Micro$loth DDKs we (linux users) are being forced to
    | > build modules by plugging into a framework that doesn't respect the
    | > aspects of dependency generation and analysis.
    | Ideas in form of patches are accepted,

    I think that one of the bigger firms that support linux, like IBM,
    Suse, ought to hire a contractor to redesign kbuild and get the linux
    community involved.

    | > Two problems I've identified
    | > 1. module builds are forcing me to use a particular make program
    | > make)
    | > Well, what if someone uses a different tool to express the DAG
    | > graph)?
    | with multiple stat()/clone()/exec(cc), i.e. `make' replacement, tools
    | support,
    | > 2. gnu make is a somewhat dated program and can't do profound
    | > generation and analysis like some newer tools. All it can do is
    | > produce
    | > .d from .c with the -MM option using an idiom like this
    | > -include f1.d f2.d
    | > %.d: %.c
    | > $(CC) -MM <whatever>
    | AFAIK GNU make have nothing to do with any kind of decencies,

    On the contrary. An attempt is made by gnu make to compute dependencies.
    As I pointed out earlier, it doesn't do a very good job of it.

    | > But that's not good enough for 2 reasons.
    | > a) version rollback that causes timestamp rollback in time does
    | > trigger regeneration of dependencies (e.g. clearcase based
    | > builds).
    | > b) dependencies on order of things can't be expressed in gnu
    | > for example -Iinc1 -Iinc2 causes different results from -Iinc2
    | > if you have 2 different header files that have the same name
    | > both directories. Same goes for "ld -r -o mod.o f1.o f2.o" vs
    | > "ld -r -o mod.o f2.o f1.o" if order mattered (which it doesn't
    | > this case).
    | see kbuild implementation to know how preparation done before GNU make
    | is used,

    How is this relevant to the point I was making about the deficiencies in
    make? The most important thing to remember when designing something like
    is that "make", no matter what kind, is nothing but a way to describe a
    (Directed Acyclic Graph). As soon as developers forget this all
    important fact
    you start seeing abominations, like Makefiles being used as a scripting
    and top level Makefiles invoking lower level Makefiles.

    | > Bottom line - there exist free tools that are vastly superior to
    | > make, one such example is omake, and I don't want you to force me
    to switch
    | > to inferior dependency analysis with gnu make.
    | (note: supported and well maintained free tools).

    That's not for you to decide.
    Just pass down all variables that may be relevant to my module builds
    and let me take it from there, for example
    chdir $(M)
    $(MYMAKE) CC="..." LD="..." AR="..." CFLAGS="..." MODFLAGS="..."
    WHATHAVE_YOU="whatever" modules

    Currently I face the following situation -- I try to build 2 drivers
    from the same Makefile
    CWD := $(shell pwd)
    obj-m := driver1.o driver2.o
    driver1-y := d1/d2/d3/f1.o d1/d2/f2.o
    driver2-y := d1/d5/file1.o d1/d6/file2.o
    # ill conceived kbuild framework doesn't allow me to reduce granularity
    # of EXTRA_FLAGS
    $(addprefix $(CWD)/,d1/d2/d3/f1.o d1/d5/file1.o: EXTRA_CFLAGS :=
    $(addprefix $(CWD)/,d1/d2/f2.o d1/d6/file2.o) : EXTRA_CFLAGS :=
    # fine grained scope for EXTRA_CFLAGS (supported by gnu make) doesn't
    There are 2 problems here
    1) kbuild is forcing me to declare EXTRA_CFLAGS in global scope and
    I can't build my drivers properly because the MASKs are incompatible.
    2) assuming that modules are buildable, if I do "make clean" there is
    junk in all of these places d1/d2/d3 d1/d5 d1/d2 d1/d6.
    There is a danger associated with that junk (or state), dependency
    may be broken which it provably is in some cases (remember -Iinc_dir1
    vs. -Iinc_dir2 -Iinc_dir1 example I gave earlier) and I can't rely on
    So then I need to be able to clean all, but the "clean:" target can't
    inexpensively in multiple directorie, i.e. must do recursive
    traversal to clean.

    | > My suggestion how to solve this problem is the following.
    | > Instead of
    | > gnumake -C /lib/modules/`uname -r`/build M=`pwd` modules
    | > it's better to be able to do
    | > gnumake -C /lib/modules/`uname -r`/build M=`pwd` MYMAKE=mymake
    | > and then inside your gnu Makefile you'd call mymake like so
    | >
    | > chdir $(M)
    | > mymake MODFLAGS="whatever modflags" INCFLAGS="whatever incflags"
    | > and pass on whatever flags are necessary.
    | >
    | > You can set MYMAKE to gmake if unspecified thus "MYMAKE ?= make"
    | >
    | > That would make the callback into the user's build environment clean
    | > unbind it from gnu make.
    | I doubt this suggestion. I think, as GNU make is current good and
    | supported stat()/clone()/exec(cc) tool, one must provide
    | gnu-make-with-kbuild-tools independent configuration and dependency
    | building process. And having multiple-pluging for dep-build and
    | tools, it may be suitable for guys like kbuild developers, you and me.

    See what happens to a person's thinking when he doesn't grasp the basics
    of building software -- it gets cloudy and he can't articulate his
    No wonder kbuild users like myself face the problems that they do.
    Here is a crash course in building software 101.
    Start off defining the DAG (dep. graph), then choose a tool that can
    express it, and extend the DAG by automatically making explicit some
    hidden (implicit) additional dependencies. The tool you pick may be
    stateless (gnu make for instance for the most part is stateless) or
    select state of the build machine and incorporate it into the DAG.
    A short example of a stateful build is where "make all DEBUG=false" does
    nothing when repeated after a successful build but does a complete
    when invoked thus "make all DEBUG=true", because the developer chose to
    include the variable $(DEBUG) in the DAG and the tool is able to express
    this dependency (gnu make can't do that btw). In addition to env.
    it may also be possible to express dependencies on order and other
    (but not in gnu make).

    So make sure whoever discusses build issues you understand building
    software 101 before jumping into discussions.

    > > Any replies, critique -- cc me, as I am not on this list.
    > If you can't follow LKML yet, please find little-nice kbuild ML in the
    > MAINTAINERS file. And IMHO, this (cc me) already must be in some kind of
    > "how to ask questions in the smart way" or Newbie's Netiquette, as bed
    > example of introduction of yourself.

    No, you can't send me off to some little kbuild mailing list.
    I've raised concerns that probably affects hundreds of module builders.
    kbuild works well only in the simplest of build scenarios but doesn't
    scale and that's a deficiency that should be urgently addressed.
    The leadership of the linux kernel is going to have to make
    a decision and possibly hire a competent contractor to fix these
    Are you guys perfectionists or what?

    Another item on my wish list is to see large chunks of the linux
    kernel, including most device drivers, rewritten in a DSL (domain
    language). Why?
    Because it's easier to reason about code correctness in a high level
    language, it's also easy to reason if the translation of constructs in
    this high level language to C/assembly chunks is correct.
    But it's incredibly difficult to prove correctness in large gobs
    of C code. I am not a prophet but I am fairly certain that in
    10-15 years there would be a big push to rewrite a lot of kernel
    code in a DSL. You might as well start thinking about it now.
    Goodbye everyone.

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