extable, core_kernel_data(): Make sure all archs define _sdata

A new utility function (core_kernel_data()) is used to determine if a
passed in address is part of core kernel data or not. It may or may not
return true for RO data, but this utility must work for RW data.

Thus both _sdata and _edata must be defined and continuous,
without .init sections that may later be freed and replaced by
volatile memory (memory that can be freed).

This utility function is used to determine if data is safe from
ever being freed. Thus it should return true for all RW global
data that is not in a module or has been allocated, or false
otherwise.

Also change core_kernel_data() back to the more precise _sdata condition
and document the function.

Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Acked-by: Ralf Baechle <ralf@linux-mips.org>
Acked-by: Hirokazu Takata <takata@linux-m32r.org>
Cc: Richard Henderson <rth@twiddle.net>
Cc: Ivan Kokshaysky <ink@jurassic.park.msu.ru>
Cc: Matt Turner <mattst88@gmail.com>
Cc: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: Roman Zippel <zippel@linux-m68k.org>
Cc: linux-m68k@lists.linux-m68k.org
Cc: Kyle McMartin <kyle@mcmartin.ca>
Cc: Helge Deller <deller@gmx.de>
Cc: JamesE.J.Bottomley <jejb@parisc-linux.org>
Link: http://lkml.kernel.org/r/1305855298.1465.19.camel@gandalf.stny.rr.com


Signed-off-by: Ingo Molnar <mingo@elte.hu>
----
 arch/alpha/kernel/vmlinux.lds.S   |    1 +
 arch/m32r/kernel/vmlinux.lds.S    |    1 +
 arch/m68k/kernel/vmlinux-std.lds  |    2 ++
 arch/m68k/kernel/vmlinux-sun3.lds |    1 +
 arch/mips/kernel/vmlinux.lds.S    |    1 +
 arch/parisc/kernel/vmlinux.lds.S  |    3 +++
 kernel/extable.c                  |   12 +++++++++++-
 7 files changed, 20 insertions(+), 1 deletion(-)