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References: <20180108172904.8772-1-f4bug@amsat.org>
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From: Thomas Huth <thuth@redhat.com>
Message-ID: <0b5bb4bf-3f85-1b09-fa6b-2a2269a203f1@redhat.com>
Date: Tue, 9 Jan 2018 18:08:06 +0100
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Subject: Re: [Qemu-devel] [PATCH 04/12] slirp: add in6_multicast() and use
 it instead of IN6_IS_ADDR_MULTICAST()
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To: Richard Henderson <richard.henderson@linaro.org>, =?UTF-8?Q?Philippe_Mathieu-Daud=c3=a9?= <f4bug@amsat.org>, Samuel Thibault <samuel.thibault@ens-lyon.org>, Jan Kiszka <jan.kiszka@siemens.com>, "Michael S . Tsirkin" <mst@redhat.com>, Paolo Bonzini <pbonzini@redhat.com>, Eric Blake <eblake@redhat.com>
Cc: qemu-devel@nongnu.org

On 09.01.2018 17:33, Richard Henderson wrote:
> On 01/08/2018 09:28 AM, Philippe Mathieu-Daud=C3=A9 wrote:
>> Host: Mac OS 10.12.5
>> Compiler: Apple LLVM version 8.1.0 (clang-802.0.42)
>>
>>   slirp/ip6_icmp.c:79:32: warning: taking address of packed member 'ip=
_src' of class or
>>         structure 'ip6' may result in an unaligned pointer value
>>         [-Waddress-of-packed-member]
>>       if (IN6_IS_ADDR_MULTICAST(&ip->ip_src) ||
>>                                  ^~~~~~~~~~
>>   /usr/include/netinet6/in6.h:299:36: note: expanded from macro 'IN6_I=
S_ADDR_MULTICAST'
>>   #define IN6_IS_ADDR_MULTICAST(a)        ((a)->s6_addr[0] =3D=3D 0xff=
)
>=20
> The fact that you replace a macro with a function of exactly the same c=
ode in
> order to avoid a diagnostic sure looks like a compiler bug to me.

I think this might also be a bug in the macro definitions. On Linux, it
is defined like this:

#define IN6_IS_ADDR_MULTICAST(a) (((const uint8_t *) (a))[0] =3D=3D 0xff)

 Thomas