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There is a common pattern on how to allocate memory for a flexible-size
structure, e.g.
union {
struct flex f; /* Structure that contains a flexible array. */
char buf[MAX_SIZE]; /* Memory buffer for structure 'flex' and
its flexible array. */
};
There is another example of such thing in CMSG manpage with the
alignment purposes:
union { /* Ancillary data buffer, wrapped in a union
in order to ensure it is suitably aligned */
char buf[CMSG_SPACE(sizeof(myfds))];
struct cmsghdr align;
} u;
Such unions could form an array in case user wants multiple
instances of them. For example, if you want receive up to
32 network packets via recvmmsg(), you will need 32 unions like 'u'.
Open vSwitch does exactly that and fails the check.
So, add a new option, -W[no-]flex-array-union, to enable or disable
any warning concerning flexible arrays and unions. This option needs
at least one of -Wflex-array-{array,nested,union} to be enabled in
order to have any effect.
Signed-off-by: Ilya Maximets <i.maximets@ovn.org>
Signed-off-by: Luc Van Oostenryck <luc.vanoostenryck@gmail.com>
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