Re: [v4l-utils PATCH 1/1] Fix static linking of v4l2-compliance and v4l2-ctl

[Mauro Carvalho Chehab <mchehab@s-opensource.com>]

Em Tue, 27 Sep 2016 00:40:51 +0300
Sakari Ailus <sakari.ailus@iki.fi> escreveu:

> Hi Mauro,
> 
> On Mon, Sep 26, 2016 at 01:59:45PM -0300, Mauro Carvalho Chehab wrote:
> > Em Mon, 26 Sep 2016 18:46:40 +0300
> > Sakari Ailus <sakari.ailus@iki.fi> escreveu:
> >   
> > > Hi Mauro,
> > > 
> > > On Mon, Sep 19, 2016 at 11:19:12AM -0300, Mauro Carvalho Chehab wrote:  
> > > > Em Mon, 19 Sep 2016 16:21:30 +0300
> > > > Sakari Ailus <sakari.ailus@linux.intel.com> escreveu:
> > > >     
> > > > > Hi Mauro,
> > > > > 
> > > > > On 09/19/16 14:22, Mauro Carvalho Chehab wrote:    
> > > > > > Em Mon, 19 Sep 2016 13:50:25 +0300
> > > > > > Sakari Ailus <sakari.ailus@linux.intel.com> escreveu:
> > > > > >       
> > > > > >> v4l2-compliance and v4l2-ctl depend on librt and libpthread. The symbols
> > > > > >> are found by the linker only if these libraries are specified after the
> > > > > >> objects that depend on them.
> > > > > >>
> > > > > >> As LDFLAGS variable end up expanded on libtool command line before LDADD,
> > > > > >> move the libraries to LDADD after local objects. -lpthread is added as on
> > > > > >> some systems librt depends on libpthread. This is the case on Ubuntu 16.04
> > > > > >> for instance.
> > > > > >>
> > > > > >> After this patch, creating a static build using the command
> > > > > >>
> > > > > >> LDFLAGS="--static -static" ./configure --disable-shared --enable-static      
> > > > > > 
> > > > > > It sounds weird to use LDFLAGS="--static -static" here, as the
> > > > > > configure options are already asking for static.
> > > > > > 
> > > > > > IMHO, the right way would be to change configure.ac to add those LDFLAGS
> > > > > > when --disable-shared is used.      
> > > > > 
> > > > > That's one option, but then shared libraries won't be built at all.    
> > > > 
> > > > Well, my understanding is that  --disable-shared is meant to disable
> > > > building the shared library build :)
> > > >     
> > > > > I'm
> > > > > not sure what would be the use cases for that, though: static linking
> > > > > isn't very commonly needed except when you need to run the binaries
> > > > > elsewhere (for whatever reason) where you don't have the libraries you
> > > > > linked against available.    
> > > > 
> > > > Yeah, that's the common usage. It is also interesting if someone
> > > > wants to build 2 versions of the same utility, each using a
> > > > different library, for testing purposes.
> > > > 
> > > > The usecase I can't see is to use --disable-shared but keeping
> > > > using the dynamic library for the exec files.    
> > > 
> > > There are three primary options here,
> > > 
> > > 1. build an entirely static binary,
> > > 2. build a binary that relies on dynamic libraries as well and
> > > 3. build a binary that relies on dynamic libraries outside v4l-utils package
> > >    but that links v4l-utils originating libraries statically.
> > > 
> > > If you say 3. is not needed then we could just use --disable-shared also to
> > > tell that static binaries are to be built.
> > > 
> > > 3. is always used for libv4l2subdev and libmediactl as the libraries do not
> > > have stable APIs.  
> > 
> > Sakari,
> > 
> > I can't see what you mean by scenario (2). I mean, if 
> > --disable-shared is called, it *should not* use dynamic libraries
> > for any library provided by v4l-utils, as the generated binaries will
> > either:
> > 
> > a) don't work, because those libraries weren't built;
> > b) will do the wrong thing, as they'll be dynamically linked
> >    to an older version of the library.
> > 
> > So, there are only 3 possible scenarios, IMHO:
> > 
> > 1) dynamic libraries, dynamic execs
> > 2) static v4l-utils libraries, static execs
> > 3) static v4l-utils libraries, static links for v4l-utils libs, dyn for the rest.
> > 
> > In practice, I don't see any reason for keeping support for both (2)
> > and (3), as all usecases for (3) can be covered by a fully static
> > exec. It is also very confusing for one to understand that.
> > For example, right now, we have those static/shared options:
> > 
> >   --enable-static[=PKGS]  build static libraries [default=yes]
> >   --enable-shared[=PKGS]  build shared libraries [default=yes]
> > 
> > with, IMHO, sounds confusing, as those options don't seem to be
> > orthogonal. I mean, what happens someone calls ./configure with:
> > 
> > 	./configure --disable-static --disable-shared  
> 
> That doesn't make much sense --- to disable the build for both static and
> dynamic libraries.

Yes, but it is still a "valid" set of options, as configure won't 
complain. Yet, this will cause build errors:

/usr/bin/ld: ../../lib/libdvbv5/.libs/libdvbv5.a(libdvbv5_la-dvb-dev-local.o): undefined reference to symbol 'pthread_cancel@@GLIBC_2.2.5'
/usr/lib64/libpthread.so.0: error adding symbols: DSO missing from command line
collect2: error: ld returned 1 exit status

> What would you prefer? Link binaries statically iff shared libraries are not
> built? I'd just like to get this fixed. Currently building static binaries
> is simply broken.

IMHO, if --disable-shared is issued, it should do static linking for
all libraries.

Gregor may have a different opinion, as I think he knows a lot more
about how distros usually expect those options to be handled.

Thanks,
Mauro