introduce HAVE_EFFICIENT_UNALIGNED_ACCESS Kconfig symbol
In many cases, especially in networking, it can be beneficial to know at
compile time whether the architecture can do unaligned accesses efficiently.
This patch introduces a new Kconfig symbol
HAVE_EFFICIENT_UNALIGNED_ACCESS
for that purpose and adds it to the powerpc and x86 architectures. Also add
some documentation about alignment and networking, and especially one intended
use of this symbol.
Signed-off-by: Johannes Berg <johannes@sipsolutions.net>
Acked-by: Sam Ravnborg <sam@ravnborg.org>
Acked-by: Ingo Molnar <mingo@elte.hu> [x86 architecture part]
Cc: <linux-arch@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/arch/Kconfig b/arch/Kconfig
index 6093c0b..b0fabfa 100644
--- a/arch/Kconfig
+++ b/arch/Kconfig
@@ -27,6 +27,25 @@
for kernel debugging, non-intrusive instrumentation and testing.
If in doubt, say "N".
+config HAVE_EFFICIENT_UNALIGNED_ACCESS
+ def_bool n
+ help
+ Some architectures are unable to perform unaligned accesses
+ without the use of get_unaligned/put_unaligned. Others are
+ unable to perform such accesses efficiently (e.g. trap on
+ unaligned access and require fixing it up in the exception
+ handler.)
+
+ This symbol should be selected by an architecture if it can
+ perform unaligned accesses efficiently to allow different
+ code paths to be selected for these cases. Some network
+ drivers, for example, could opt to not fix up alignment
+ problems with received packets if doing so would not help
+ much.
+
+ See Documentation/unaligned-memory-access.txt for more
+ information on the topic of unaligned memory accesses.
+
config KRETPROBES
def_bool y
depends on KPROBES && HAVE_KRETPROBES