Patchwork Commit: ARM: Document -munaligned-access

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Submitter Hans-Peter Nilsson
Date July 20, 2012, 1:41 p.m.
Message ID <201207201341.q6KDfB3J014174@ignucius.se.axis.com>
Download mbox | patch
Permalink /patch/172279/
State New
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Hans-Peter Nilsson - July 20, 2012, 1:41 p.m.
> From: nick clifton <nickc@redhat.com>
> Date: Fri, 20 Jul 2012 09:18:52 +0200

> "approved - please apply".

Thanks!  I see the last sentence could do with better
punctuation, so I added the obvious comma.  Installed as
follows.



brgds, H-P

Patch

Index: changes.html
===================================================================
RCS file: /cvs/gcc/wwwdocs/htdocs/gcc-4.7/changes.html,v
retrieving revision 1.121
diff -p -u -r1.121 changes.html
--- changes.html	15 Jul 2012 15:04:38 -0000	1.121
+++ changes.html	20 Jul 2012 13:35:48 -0000
@@ -43,6 +43,19 @@ 
 
     </li>
 
+    <li>On ARM, when compiling for ARMv6 (but not ARMv6-M), ARMv7-A,
+    ARMv7-R, or ARMv7-M, the new option
+    <code>-munaligned-access</code> is active by default, which for
+    some source codes generates code that accesses memory on unaligned
+    adresses.  This will require the kernel of those systems to enable
+    such accesses (controlled by CP15 register <code>c1</code>, refer
+    to ARM documentation).  Alternatively or for compatibility with
+    kernels where unaligned accesses are not supported, all code has
+    to be compiled with <code>-mno-unaligned-access</code>.
+    Linux/ARM in official releases has automatically and
+    unconditionally supported unaligned accesses as emitted by GCC due
+    to this option being active, since Linux version 2.6.28.</li>
+
     <li>Support on ARM for the legacy floating-point accelerator (FPA) and
     the mixed-endian floating-point format that it used has been obsoleted.
     The ports that still use this format have been obsoleted as well.