svn commit: r358655 - head/sbin/mount_nfs

[Dimitry Andric]

On 5 Mar 2020, at 18:44, Gleb Smirnoff <glebius at FreeBSD.org> wrote:
> 
> On Thu, Mar 05, 2020 at 08:35:15PM +0300, Slawa Olhovchenkov wrote:
> S> > > D> sbin/mount_nfs/mount_nfs.c:549:10: error: cast from 'char *' to 'struct
> S> > > D> if_msghdr *' increases required alignment from 1 to 4
> S> > > D> [-Werror,-Wcast-align]
> S> > > D>                         ifm = (struct if_msghdr *)buf;
> S> > > D>                               ^~~~~~~~~~~~~~~~~~~~~~~
> S> > > D> 1 error generated.
> S> > > D>
> S> > > D> In practice I don't think the buffer can ever get misaligned, so can you
> S> > > D> please add a NO_WCAST_ALIGN= to the Makefile?
> S> > >
> S> > > route(8) handles the same problem via intermediate (void *) cast. What is
> S> > > preferred way to solve the problem? Change compiler flags file wide, or
> S> > > just through (void *) cast?
> S> >
> S> > Copy to aligned buffer or got SIGBUS on some architectures?
> S>
> S> char buf[2048] __aligned(__alignof(struct if_msghdr));
> S>
> S> resolve this watning.
> 
> Thanks, Slawa! I think this is the most elegant solution.

Why don't just declare the buffer as:

  struct if_msghdr buf;

and then do:

  nread = read(s, &buf, sizeof buf);

?  You are never reading more than one if_msghdr anyway, and then there
is no need to cast anything.

-Dimitry

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