linux-kernel - [PATCH 0/5] Add support for GCC's __builtin_unreachable() and use it in BUG (v2.1).

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Date:	Fri, 04 Dec 2009 17:43:47 -0800
From:	David Daney <ddaney@...iumnetworks.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-arch@...r.kernel.org
CC:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: [PATCH 0/5] Add support for GCC's __builtin_unreachable() and use
 it in BUG (v2.1).

Greetings Linus et al.,

 From the announcement of the first version:

     Starting with version 4.5, GCC has a new built-in function called
     __builtin_unreachable().  The function tells the compiler that
     control flow will never reach that point.  Currently we trick the
     compiler by putting in for(;;); but this has the disadvantage that
     extra code is emitted for an endless loop.  For an i386 kernel
     using __builtin_unreachable() results in an defaultconfig that is
     nearly 4000 bytes smaller.

     This patch set adds support to compiler.h creating a new macro
     usable in the kernel called unreachable().  If the compiler lacks
     __builtin_unreachable(), it just expands to for(;;).


For version 2:

     I fixed a couple of checkpatch issues, and simplified the
     unreachable() macro for the pre-GCC-4.5 case (as suggested by
     Richard Henderson).  Also several Acked-by: were added.

For this version 2.1:

     I removed patches from the set for which there were no Acked-by,
     and rebased and tested against 2.6.32.

I will reply with the 5 patches.

David Daney (5):
   Add support for GCC-4.5's __builtin_unreachable() to compiler.h (v2)
   x86: Convert BUG() to use unreachable()
   MIPS: Convert BUG() to use unreachable()
   s390: Convert BUG() to use unreachable()
   avr32: Convert BUG() to use unreachable()

  arch/avr32/include/asm/bug.h  |    2 +-
  arch/mips/include/asm/bug.h   |    4 +---
  arch/s390/include/asm/bug.h   |    2 +-
  arch/x86/include/asm/bug.h    |    4 ++--
  include/linux/compiler-gcc4.h |   14 ++++++++++++++
  include/linux/compiler.h      |    5 +++++
  6 files changed, 24 insertions(+), 7 deletions(-)

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