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SubjectRe: no version magic, tainting kernel.
On Sun, 26 Jan 2003, Christian Zander wrote:

> On Sun, Jan 26, 2003 at 11:51:22AM -0600, Kai Germaschewski wrote:
> >
> > Well, what I'm trying to say is that external build system will
> > always break one way or other. Since they're external, they're
> > naturally out of reach for me to influence, so there's really
> > nothing I can do it but telling people to using the internal system
> > instead.
> >
>
> External build systems have been working just fine even after kbuild
> was adopted as the build system of choice for the Linux kernel, there
> should be more convincing reasons for deliberately breaking them now.

That's not true. For example, how would an old external build system
magically starting to compile modules as .ko without updating? How would
it have added -DKBUILD_BASENAME and -DKBUILD_MODNAME, which are required
by the new module code. And, how did they avoid subtle breakage like not
giving the same switches on the command line? (This list goes on...)

Also, it's not true that they've been broken deliberately. As work
progresses, breakage occurs, that's just a fact of live. However,
introduction of __vermagic was not introduced in order to make live for
maintainers of external modules harder, it was introduced since loading
modules compiled with gcc3 into a kernel compiled with gcc2 caused crashes
for people.

> > When you're using the kernel build, the above cannot happen, since
> > the kernel build system knows about this dependency and builds a new
> > init/vermagic.o with the correct information before it gets linked
> > into the external module.
>
> Is that so? Does kbuild determine that vermagic.o needs rebuilding if
> the compiler version changed?

Okay, you have a point here, there's still a bug. vermagic.o will be
rebuilt when the version changes or any of the recorded config options
change, but it doesn't pick up changes in the compiler version, if the
new gcc has the same name.

That's a bug for internal use as well, the patch below fixes it.

Two more things:

o You say kbuild has been adopted as the build system of choice. That's
misleading, the new build system for 2.5, called kbuild-2.5 has never
been adopted. It's just that the existing build system has been improved
quite a bit by me and others.

o One thing I do not understand at all: What is the problem with using
the internal build system? It makes maintainance of external modules
much easier than keeping track of what happens in the kernel and
patching a private solution all the time.

I don't even see any license issues, first of all you don't even
distribute it, the user who's building the module will already have it
along with his kernel source. And if you're using it to compile
(possibly binary) modules you want to distribute, you can just use it
just like gcc without any further obligations, so no problem there
either. (IANAL, of course)

--Kai


===== init/Makefile 1.18 vs edited =====
--- 1.18/init/Makefile Tue Jan 14 14:29:02 2003
+++ edited/init/Makefile Sun Jan 26 15:24:21 2003
@@ -12,6 +12,13 @@

$(obj)/version.o: include/linux/compile.h

+# vermagic doesn't actually include compile.h, but it records
+# the compiler version. To make sure we notice when the compiler
+# changes, add a dependency on compile.h, which changes when the
+# compiler changes.
+
+$(obj)/vermagic.o: include/linux/compile.h
+
# compile.h changes depending on hostname, generation number, etc,
# so we regenerate it always.
# mkcompile_h will make sure to only update the

-
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