r278483 - This patch implements PR#22821.

[Joerg Sonnenberger via cfe-commits]

On Mon, Oct 03, 2016 at 07:10:08AM +0000, Roger Ferrer Ibanez wrote:
> Hi Joerg,
> 
> thanks for your comments. I agree that these false positives are annoying.
> 
> I submitted a while ago a patch to address those false positives in
> https://reviews.llvm.org/D23657 but it is pending approval.

I'm trying this patch now. Two instances here show false positives. Some
others are misuse/overuse of __packed, it is time consuming to check all
of them.

--- sbin/route

https://nxr.netbsd.org/xref/src/sbin/route/route.c#1009
triggers the warning:
    union mpls_shim *ms = &su->smpls.smpls_addr;
where su is defined as:
    union sockunion {
        ...
	struct	sockaddr_mpls smpls;
    };

and sockaddr_mpls in turn is
https://nxr.netbsd.org/xref/src/sys/netmpls/mpls.h#66 

    struct sockaddr_mpls {
        uint8_t smpls_len;
	uint8_t smpls_family;
	uint8_t smpls_pad[2];
	union mpls_shim smpls_addr;
    } __packed;

smpls_addr is a union of a uint32_t and matching bit field. The
alignment of sockunion and the explicit padding ensures that all fields
can be accessed correctly.

--- sbin/ifconfig

Member access is
https://nxr.netbsd.org/xref/src/sbin/ifconfig/ieee80211.c#969
The macro is defined at
https://nxr.netbsd.org/xref/src/sbin/ifconfig/ieee80211.c#928

Most importantly, this effective casts immediately to (unsigned) char
and therefore doesn't care about any misalignment.

Joerg