The module alias support in the kernel have a consistency
check where it is checked that the size of a structure
in the kernel and on the build host are the same.
For cross builds this check does not make sense so detect
when we do cross builds and silently skip the check in these
situations.
This fixes a build bug for a wireless driver when cross building
for arm.

Acked-by: Michael Buesch <mb@bu3sch.de>
Tested-by: Gordon Farquharson <gordonfarquharson@gmail.com>
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Cc: stable@kernel.org

* git://git.kernel.org/pub/scm/linux/kernel/git/sam/kbuild:
  kbuild: explain why DEBUG_SECTION_MISMATCH is UNDEFINED
  kbuild: fix building vmlinux.o
  kbuild: allow -fstack-protector to take effect
  kconfig: fix select in combination with default

Ingo Molnar wrote:
>
> i've got a build log from a weird build error below:
>
>   LD      init/built-in.o
> distcc[12023] ERROR: compile (null) on localhost failed
> make: *** [vmlinux.o] Error 1
> make: *** Waiting for unfinished jobs....
>   LD      .tmp_vmlinux1
>

Building vmlinux.o were moved up in the dependency chain so we started
to build it before the kallsym stuff. This was done to let modpost
report section mismatch bugs even when the final link failed.

Originally I had expected the dependency of $(kallsyms.o) to
cover this but it turns out that we need to be even more explicit.
Fix this by adding a conditional dependency on firat target
used in the kallsyms serie of builds.

Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Roland McGrath <roland@redhat.com>

Arjan van de Ven <arjan@infradead.org> wrote:
===
I just read the excellent LWN writeup of the vmsplice
security thing, and that got me wondering why this attack
wasn't stopped by the CONFIG_CC_STACKPROTECTOR option...
because it plain should have been...

Some analysis later.. it turns out that the following line
in the top level Makefile, added by you in October 2007,
entirely disables CONFIG_CC_STACKPROTECTOR ;(
With this line removed the exploit will be nicely stopped.

CFLAGS          += $(call cc-option, -fno-stack-protector)

Now I realize that certain distros have patched gcc to
compensate for their lack of distro wide CFLAGS, and it's
great to work around that... but would there be a way to NOT
disable this for CONFIG_CC_STACKPROTECTOR please?
It would have made this exploit not possible for those kernels
that enable this feature (and that includes distros like Fedora)
===

Move the assignment to KBUILD_CFLAGS up before including
the arch specific Makefile so arch makefiles may override
the setting.

Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Cc: Arjan van de Ven <arjan@infradead.org>
Cc: stable@kernel.org