Re: Aliasing violations in gnu_java_nio_VMChannel.c

Andrew John Hughes wrote:
> 2009/10/22 Andrew Haley <[email protected]>:
>> This:
>>
>>
>> #ifdef HAVE_GETPEERNAME
>> #ifdef HAVE_INET6
>>  struct sockaddr_in6 *addr6;
>>  struct sockaddr_in6 sock_storage;
>>  socklen_t socklen = sizeof (struct sockaddr_in6);
>> #else
>>  struct sockaddr_in sock_storage;
>>  socklen_t socklen = sizeof (struct sockaddr_in);
>> #endif /* HAVE_INET6 */
>>
>>  struct sockaddr *sockaddr = (struct sockaddr *) &sock_storage;
>>
>>
>> is clearly an aliasing violation: sock_storage is of type struct sockaddr_in6,
>> and *sockaddr is of type struct sockaddr.
>>
>> It would be easy enough to fix the code with a union, but I can't test it
>> because gcj doesn't use this code.  I could simply compile with
>> -fno-strict-aliasing.
>>
>> Thoughts?
>>
>> Andrew.
>>
>>
> 
> I posted a patch sometime ago to do exactly that (use a union), but
> received no response:
> 
> http://developer.classpath.org/pipermail/classpath-patches/2009-June/006341.html
> 
> It does need more testing than I've had chance to give it so far, I
> just haven't had time to do any more work on it.

I seriously wonder if it's worth the effort.  I just did this:

Index: configure.ac
===================================================================
RCS file: /sources/classpath/classpath/configure.ac,v
retrieving revision 1.244
diff -c -u -r1.244 configure.ac
--- configure.ac        6 Feb 2009 02:21:23 -0000       1.244
+++ configure.ac        23 Oct 2009 09:10:33 -0000
@@ -514,7 +514,7 @@
     dnl CFLAGS that are used for all native code.  We want to compile
     dnl everything with unwinder data so that backtrace() will always
     dnl work.
-    EXTRA_CFLAGS='-fexceptions -fasynchronous-unwind-tables'
+    EXTRA_CFLAGS='-fexceptions -fasynchronous-unwind-tables -fno-strict-aliasing'
     AC_SUBST(EXTRA_CFLAGS)

     dnl Strict warning flags which not every module uses.

which is a much safer change.  It will somewhat pessimize other native code,
that's true, but will that make any real difference to anyone these days?

Andrew.