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[RFA:] Caveat for ARM in gcc-4.7/changes.html: unaligned accesses, take 2

Message ID 201206150207.q5F27NNC005016@ignucius.se.axis.com
State New
Headers show

Commit Message

Hans-Peter Nilsson June 15, 2012, 2:07 a.m. UTC 
Y is 28 for introduction of the quoted code in
arch/arm/mm/alignment.c, AFAICT, so how about this one, ok now?


brgds, H-P
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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	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.