svn commit: r300167 - in head: contrib/bsnmp/snmpd usr.sbin/bsnmpd/bsnmpd

[Bruce Evans]

On Wed, 18 May 2016, Ian Lepore wrote:

> On Wed, 2016-05-18 at 22:02 +0000, Gleb Smirnoff wrote:
>> Log:
>>   Revert r299830, it has couple of fatal errors.
>>
>>   The CMSG_ family of macros take care of alignment, so we don't need
>> r299830
>>   at all, even if it was correct.  Put NO_WCAST_ALIGN into Makefile.

The breaks detection of cast-align bugs elsewhere in the program.

> So all of this was about a "cast increases required alignment" kind of
> warning for a macro that takes care of alignment?  Wouldn't the proper
> fix then be to change CMSG_DATA() so that its internal cast is void*
> instead of unsigned char* (he asked, knowing Bruce would come along
> soon and point out why that's a dumb question)?

I don't know much about CMSG*, so I wouldn't have if you didn't ask :-).

Changing its type might expose bugs.  Kernel code mostly casts it so
would get the same cast-align error if that were enabled in the kernel.
netinet6 passes it to a function without an explicit cast.  The function
does an implicit conversion to a struct pointer and there should be a
different warning for that.  char * and u_char * are required to be
binary compatible with void *, but it is bad style to depend on that.

So void * works better in all cases in the kernel.

LINUX_CMSG_DATA() already returns void *.

Bruce