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Date: Fri, 20 Jul 2012 17:40:32 +0200
From: Dimitry Andric <dim@FreeBSD.org>
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To: Kim Culhan <w8hdkim@gmail.com>
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Cc: freebsd-current@FreeBSD.org
Subject: Re: -current build failure
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On 2012-07-20 16:49, Kim Culhan wrote:
>  Seeing this for r:238655
...
> In file included from /usr/src/sys/modules/dtrace/dtrace/../../../sys/pcpu.h:44:
> ./machine/pcpu.h:226:13: error: indirection of non-volatile null
> pointer will be deleted, not trap
>       [-Werror,-Wnull-dereference]
>             : "m" (*(char *)OFFSETOF_CURTHREAD));
>                    ^~~~~~~~~~~~~~~~~~~~~~~~~~~
> ./machine/pcpu.h:226:13: note: consider using __builtin_trap() or
> qualifying pointer with 'volatile'

That's indeed a valid warning from clang, since OFFSETOF_CURTHREAD is
usually zero.  It's probably due to recent work on dtrace.  I'm not in
the neighborhood of a FreeBSD box right now to verify, but can you
please try to change the cast to "(volatile char *)"?  That should fix
the warning.