Re: [PATCH v5 3/4] arm64: mm: support ARCH_MMAP_RND_BITS.

From	Arnd Bergmann <arnd@arndb.de>
Newsgroups	linux.kernel
Subject	Re: [PATCH v5 3/4] arm64: mm: support ARCH_MMAP_RND_BITS.
Date	2015-12-08 11:10 +0100
Message-ID	<qDnnA-TA-9@gated-at.bofh.it> (permalink)
References	<qAZz4-5UF-13@gated-at.bofh.it> <qD1ZM-3Ks-11@gated-at.bofh.it> <qD8HU-8aH-9@gated-at.bofh.it>
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On Monday 07 December 2015 10:26:34 Daniel Cashman wrote:
> > Ideally we'd remove the #ifdef around the mmap_rnd_compat_bits declaration
> > and change this code to use
> > 
> >       if (IS_ENABLED(CONFIG_COMPAT) && test_thread_flag(TIF_32BIT))
> > 
> That would result in "undefined reference to mmap_rnd_compat_bits" in
> the not-defined case, no?

No. The compiler eliminates all code paths that it knows are unused.
The IS_ENABLED() macro is designed to let the compiler figure this out.

	Arnd
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[PATCH v5 3/4] arm64: mm: support ARCH_MMAP_RND_BITS. Daniel Cashman <dcashman@android.com> - 2015-12-01 21:20 +0100
  [PATCH v5 4/4] x86: mm: support ARCH_MMAP_RND_BITS. Daniel Cashman <dcashman@android.com> - 2015-12-01 21:20 +0100
  Re: [PATCH v5 3/4] arm64: mm: support ARCH_MMAP_RND_BITS. Will Deacon <will.deacon@arm.com> - 2015-12-03 13:20 +0100
    Re: [PATCH v5 3/4] arm64: mm: support ARCH_MMAP_RND_BITS. Daniel Cashman <dcashman@android.com> - 2015-12-03 17:20 +0100
  Re: [PATCH v5 3/4] arm64: mm: support ARCH_MMAP_RND_BITS. Jon Hunter <jonathanh@nvidia.com> - 2015-12-07 11:30 +0100
    Re: [PATCH v5 3/4] arm64: mm: support ARCH_MMAP_RND_BITS. Arnd Bergmann <arnd@arndb.de> - 2015-12-07 12:20 +0100
      Re: [PATCH v5 3/4] arm64: mm: support ARCH_MMAP_RND_BITS. Daniel Cashman <dcashman@android.com> - 2015-12-07 19:30 +0100
        Re: [PATCH v5 3/4] arm64: mm: support ARCH_MMAP_RND_BITS. Arnd Bergmann <arnd@arndb.de> - 2015-12-08 11:10 +0100

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