Commit: ARM: Document -munaligned-access

[nick clifton]

Hi H-P,

> *cough*
>
> Sounds like a call for a note in changes.html, to warn people
> that they have to turn on the alignment feature in their startup
> code (for whatever OS) for their ARMv6-or-later targets, if they
> have not already done so.

What a good idea :-)

>
> Maybe something like:
>
>>> Index: changes.html
>>> ===================================================================
>>> RCS file: /cvs/gcc/wwwdocs/htdocs/gcc-4.7/changes.html,v
>>> retrieving revision 1.113
>>> diff -p -u -r1.113 changes.html
>>> --- changes.html	5 Jun 2012 11:03:53 -0000	1.113
>>> +++ changes.html	15 Jun 2012 02:04:46 -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.
>>>
>>
>
> <http://gcc.gnu.org/ml/gcc-patches/2012-07/msg00282.html>
>
> Sorry, but I couldn't miss the opportunity to ping this now that
> the ARM maintainers have this issue in their L1-cache.  A simple
> yes or no would do; I don't see what could possibly need any
> contemplation regarding this note.

Agreed - in fact agreed so much that as an ARM maintainer I say 
"approved - please apply".

Cheers
   Nick