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Re: Commit: ARM: Document -munaligned-access
- From: Hans-Peter Nilsson <hans-peter dot nilsson at axis dot com>
- To: nickc at redhat dot com
- Cc: gcc-patches at gcc dot gnu dot org
- Date: Fri, 20 Jul 2012 15:41:11 +0200
- Subject: Re: Commit: ARM: Document -munaligned-access
> 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.
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.
brgds, H-P