Re: [linux-next:master 4174/4356] kernel/built-in.o:undefined reference to `mmap_rnd_bits'

[Andrew Morton <akpm@linux-foundation.org>]

On Sat, 5 Dec 2015 00:18:47 +0800 kbuild test robot <fengguang.wu@intel.com> wrote:

> tree:   https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git master
> head:   dcccebc04ddba852aad354270986d508e8f011c0
> commit: a8f025e63718534d6a9224a0b069b772ef21cb5d [4174/4356] arm: mm: support ARCH_MMAP_RND_BITS
> config: arm-vf610m4_defconfig (attached as .config)
> reproduce:
>         wget https://git.kernel.org/cgit/linux/kernel/git/wfg/lkp-tests.git/plain/sbin/make.cross -O ~/bin/make.cross
>         chmod +x ~/bin/make.cross
>         git checkout a8f025e63718534d6a9224a0b069b772ef21cb5d
>         # save the attached .config to linux build tree
>         make.cross ARCH=arm 
> 
> All errors (new ones prefixed by >>):
> 
> >> kernel/built-in.o:(.data+0x754): undefined reference to `mmap_rnd_bits'
> >> kernel/built-in.o:(.data+0x76c): undefined reference to `mmap_rnd_bits_min'
> >> kernel/built-in.o:(.data+0x770): undefined reference to `mmap_rnd_bits_max'

OK, the patches are pretty broken when HAVE_ARCH_MMAP_RND_BITS=n.  I
guess a pile of new ifdefs need adding for this case.

There's also the matter of CONFIG_MMU=n.  mm/mmap.o doesn't get
included in the build in this case, so that will also break things.  I
suggest that can be fixed by making HAVE_ARCH_MMAP_RND_BITS and
HAVE_ARCH_MMAP_RND_COMPAT_BITS depend on MMU.  That should fix things
up when combined with the new ifdef-sprinkling.

This stuff is going to break quite a lot of test builds so I think I'll
consolidate the patches then drop 'em for now.

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