Re: cast errors reported by a OsX cmake build

[Evan Huus <eapache () gmail com>]

On Mon, Jun 17, 2013 at 5:45 PM, Guy Harris <guy () alum mit edu> wrote:
> On Jun 17, 2013, at 5:22 PM, Dirk Jagdmann <doj () cubic org> wrote:
>
> > I just tried to use cmake to build current Wireshark SVN trunk source code. It fails early on with errors like:
> >
> > [  5%] Building C object tools/lemon/CMakeFiles/lemon.dir/lemon.c.o
> > /Users/djagdmann/ws-trunk/trunk/tools/lemon/lemon.c:443:8: error: cast from 'char *' to 'struct action *' increases 
> > required
> >      alignment from 1 to 8 [-Werror,-Wcast-align]
> >  ap = (struct action *)msort((char *)ap,(char **)&ap->next,
> >       ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> > /Users/djagdmann/ws-trunk/trunk/tools/lemon/lemon.c:457:24: error: cast from 'char *' to 'struct state *' increases 
> > required
> >      alignment from 1 to 8 [-Werror,-Wcast-align]
> >    newaction->x.stp = (struct state *)arg;
> >
> > and many more of this type. Is somebody looking into cmake builds on OsX?
>
> This isn't a cmake issue, it's a clang issue.  Clang is a bit less forgiving when it comes to playing games with 
> alignment. Cmake's only contribution to the problem is that it defaults to clang (probably because it defaults to cc 
> rather than gcc).

Lemon isn't our code, and is only used as an intermediate in the build
process. It should probably be in the non-fatal (dirty) group in
automake and cmake.

> SPARC is even less forgiving, as in "your program crashes if it tries to do an unaligned load or store", so, unless 
> we want to abandon support for SPARC-based machines, we should seriously consider fixing those complaints *AND*, if 
> there's a gcc option to warn about those errors, turning that on to make it more likely that the build will fail if 
> somebody submits code that "gee, it worked on my PC, what's the problem?"

GCC has -Wcast-align which is already enabled on my current
configuration, but it doesn't produce this warning (at least with my
current GCC, which is relatively old).

> (There may be other processors that either trap on unaligned accesses, as SPARC processors do, or do other 
> non-unaligned-fetch/store things, such as ignoring the low-order bits of the address.  I think Alpha and MIPS did 
> that.  Yes, PowerPC/Power Architecture processors, these days, do unaligned fetches/stores, as far as I know, and 
> recent ARM processors might, but....)
>
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