Patchwork [RFA:] Caveat for ARM in gcc-4.7/changes.html: unaligned accesses

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Submitter Hans-Peter Nilsson
Date June 10, 2012, 11:16 p.m.
Message ID <201206102316.q5ANG9eF024439@ignucius.se.axis.com>
Download mbox | patch
Permalink /patch/164014/
State New
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Comments

Hans-Peter Nilsson - June 10, 2012, 11:16 p.m.
> From: Gerald Pfeifer <gerald@pfeifer.com>
> Date: Mon, 11 Jun 2012 00:27:21 +0200

> This is only a review wearing my web hat; it is orthogonal to the
> discussion with the ARM guys. ;-)
> 
> On Fri, 8 Jun 2012, Hans-Peter Nilsson wrote:
> > +    <li>On ARM, when compiling for ARMv6 (but not ARMv6-M), ARMv7-A,
> > +    ARMv7-R, or ARMv7-M, the default of the new option
> > +    <code>-munaligned-accesses</code> is on, which for some source
> 
> How about "the new option...is active by default"?
> 
> > +    This will require the OS of those systems to enable such accesses
> 
> Omit "of those systems" and spell out "operating system"?

I see the tautology to which you allude. 8]  Maybe "the kernel of
those systems" is better?

> > +    (controlled by CP15 register c1, refer to ARM documentation).
> 
> <code>c1</cdoe>
> 
> > +    Alternatively or for compatibility with OS versions that do not
> > +    enable unaligned accesses, all codes has to be compiled with
> 
> "enable" -> "support"

I wanted to emphasize that it's something you can configure to
be enabled or disabled (with the kernel catching an exception),
but maybe that doesn't really matter.  Clarity matters and that
part doesn't really have to explain in detail.

> "all code has"

I thought "codes" was a valid common reference to source code,
but I guess not.

Good suggestions, I hope I got them all below in one form or
another:


brgds, H-P

Patch

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	10 Jun 2012 23:12:02 -0000
@@ -43,6 +43,16 @@ 
 
     </li>
 
+    <li>On ARM, when compiling for ARMv6 (but not ARMv6-M), ARMv7-A,
+    ARMv7-R, or ARMv7-M, the new option
+    <code>-munaligned-accesses</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-accesses</code>.</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.