svn commit: r358655 - head/sbin/mount_nfs

[Gleb Smirnoff]

On Thu, Mar 05, 2020 at 09:30:41PM +0300, Slawa Olhovchenkov wrote:
S> > > On Thu, Mar 05, 2020 at 08:35:15PM +0300, Slawa Olhovchenkov wrote:
S> > > S> > > D> sbin/mount_nfs/mount_nfs.c:549:10: error: cast from 'char *' to 'struct
S> > > S> > > D> if_msghdr *' increases required alignment from 1 to 4
S> > > S> > > D> [-Werror,-Wcast-align]
S> > > S> > > D>                         ifm = (struct if_msghdr *)buf;
S> > > S> > > D>                               ^~~~~~~~~~~~~~~~~~~~~~~
S> > > S> > > D> 1 error generated.
S> > > S> > > D>
S> > > S> > > D> In practice I don't think the buffer can ever get misaligned, so can you
S> > > S> > > D> please add a NO_WCAST_ALIGN= to the Makefile?
S> > > S> > >
S> > > S> > > route(8) handles the same problem via intermediate (void *) cast. What is
S> > > S> > > preferred way to solve the problem? Change compiler flags file wide, or
S> > > S> > > just through (void *) cast?
S> > > S> >
S> > > S> > Copy to aligned buffer or got SIGBUS on some architectures?
S> > > S>
S> > > S> char buf[2048] __aligned(__alignof(struct if_msghdr));
S> > > S>
S> > > S> resolve this watning.
S> > > 
S> > > Thanks, Slawa! I think this is the most elegant solution.
S> > 
S> > Why don't just declare the buffer as:
S> > 
S> >   struct if_msghdr buf;
S> > 
S> > and then do:
S> > 
S> >   nread = read(s, &buf, sizeof buf);
S> > 
S> > ?  You are never reading more than one if_msghdr anyway, and then there
S> > is no need to cast anything.
S> 
S> My inspiration: route socket can return other messages (man 4 route)

Yes, exactly. We don't know what size next datagram is going to be.

-- 
Gleb Smirnoff