Subject: Re: [Bluez-devel] Alignment issue
From: Marcel Holtmann <marcel@holtmann.org>
To: Daryl Van Vorst <daryl@wideray.com>
Cc: "'BlueZ Mailing List'" <bluez-devel@lists.sourceforge.net>
In-Reply-To: <001301c47f09$3900e650$1301010a@baked>
References: <001301c47f09$3900e650$1301010a@baked>
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Message-Id: <1092208405.4564.227.camel@pegasus>
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Sender: bluez-devel-admin@lists.sourceforge.net
Errors-To: bluez-devel-admin@lists.sourceforge.net
Date: Wed, 11 Aug 2004 09:13:25 +0200

Hi Daryl,

> The attached patch should fix the problem (it does as far as I can tell).
> The compiler probably thinks both arguments to memcpy() are aligned and so
> makes an optimization which breaks the copy (because the destination is not
> actually aligned). Perhaps this is a compiler bug... I'm using gcc 3.3.3.
> After googling and reading some discussion on the topic it seems that it's
> probably not a compiler bug. I'll leave that for someone else to decide. :)

after checking some more resources, you may be right and the compiler
optimizes here where it should not. I found a comment about gcc and
using its __builtin_memcpy. Try to replace the memcpy with memmove and
see if this works.

--- bluetooth.h 2004/07/04 15:38:11     1.14
+++ bluetooth.h 2004/08/11 07:07:12     1.15
@@ -93,10 +93,10 @@ enum {
 #define bt_put_unaligned(val, ptr) ((void)( *(ptr) = (val) ))
 #else
 #define bt_get_unaligned(ptr) \
-       ({ __typeof__(*(ptr)) __tmp; memcpy(&__tmp, (ptr), sizeof(*(ptr))); __tmp; })
+       ({ __typeof__(*(ptr)) __tmp; memmove(&__tmp, (ptr), sizeof(*(ptr))); __tmp; })
 #define bt_put_unaligned(val, ptr) \
        ({ __typeof__(*(ptr)) __tmp = (val); \
-       memcpy((ptr), &__tmp, sizeof(*(ptr))); \
+       memmove((ptr), &__tmp, sizeof(*(ptr))); \
        (void)0; })
 #endif

Regards

Marcel


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