Re: [PATCH 1/8] build: add maths library to libs in pkg-config file

[Aaron Conole <aconole@redhat.com>]

Luca Boccassi <bluca@debian.org> writes:

> On Wed, 2017-10-18 at 15:20 +0100, Bruce Richardson wrote:
>> On Wed, Oct 18, 2017 at 01:24:54PM +0100, Bruce Richardson wrote:
>> > On Wed, Oct 18, 2017 at 11:14:07AM +0100, Luca Boccassi wrote:
>> > > On Wed, 2017-10-18 at 10:51 +0100, Bruce Richardson wrote:
>> > > > On Wed, Oct 18, 2017 at 10:35:48AM +0100, Bruce Richardson
>> > > > wrote:
>> > > > > On Tue, Oct 17, 2017 at 07:17:09PM +0100, Luca Boccassi
>> > > > > wrote:
>> > > > > > On Tue, 2017-10-17 at 19:11 +0100, Luca Boccassi wrote:
>> > > > > > > On Tue, 2017-10-17 at 17:12 +0100, Bruce Richardson
>> > > > > > > wrote:
>> > > > > > > > Since a number of libraries depend on the maths lib, as
>> > > > > > > > well
>> > > > > > > > as
>> > > > > > > > adding it
>> > > > > > > > to the project args, we also need to add it to the
>> > > > > > > > pkgconfig
>> > > > > > > > file
>> > > > > > > > args.
>> > > > > > > > 
>> > > > > > > > Signed-off-by: Bruce Richardson <bruce.richardson@intel
>> > > > > > > > .com>
>> > > > > > > > ---
>> > > > > > > >  config/meson.build | 1 +
>> > > > > > > >  1 file changed, 1 insertion(+)
>> > > > > > > > 
>> > > > > > > > diff --git a/config/meson.build b/config/meson.build
>> > > > > > > > index db68a08d4..542fea4de 100644
>> > > > > > > > --- a/config/meson.build
>> > > > > > > > +++ b/config/meson.build
>> > > > > > > > @@ -35,6 +35,7 @@ dpdk_conf.set('RTE_MACHINE', machine)
>> > > > > > > >  add_project_arguments('-march=@0@'.format(machine),
>> > > > > > > > language: 'c')
>> > > > > > > >  # some libs depend on maths lib
>> > > > > > > >  add_project_link_arguments('-lm', language: 'c')
>> > > > > > > > +dpdk_extra_ldflags += '-lm'
>> > > > > > > >  
>> > > > > > > >  # add -include rte_config to cflags
>> > > > > > > >  add_project_arguments('-include', 'rte_config.h',
>> > > > > > > > language:
>> > > > > > > > 'c')
>> > > > > > > 
>> > > > > > > This is for static builds, right? If so it should go into
>> > > > > > > the
>> > > > > > > Libs.private section of the .pc file, so that it's only
>> > > > > > > used
>> > > > > > > when
>> > > > > > > calling pkg-config --static --libs
>> > > > > > 
>> > > > > > Bit of a brain fart - what I meant is, in order to have
>> > > > > > static
>> > > > > > builds
>> > > > > > work out of the box with pkg-config --static, -lm (and any
>> > > > > > other
>> > > > > > dependency used internally) could also be added to
>> > > > > > Libs.private
>> > > > > > in the
>> > > > > > .pc
>> > > > > 
>> > > > > Does that not assume that both static and dynamic libs are
>> > > > > installed
>> > > > > side-by-side? In DPDK case, we will either build static libs
>> > > > > or
>> > > > > shared
>> > > > > libs, but not both. If we require applications to use
>> > > > > different
>> > > > > pkg-config commands depending on the type of DPDK build that
>> > > > > was
>> > > > > done,
>> > > > > it makes things awkward for the apps. Right now by putting
>> > > > > all libs
>> > > > > and
>> > > > > flags into the libs section of pkgconfig, and having the
>> > > > > build
>> > > > > system
>> > > > > track whether it's static or dynamic and therefore what is
>> > > > > actually
>> > > > > necessary, we end up in a case where apps can be built
>> > > > > against DPDK
>> > > > > irrespective of the actual build type done. For this
>> > > > > particular -lm
>> > > > > flag, for instance, it only appears in the .pc file for
>> > > > > static
>> > > > > builds.
>> > > > > 
>> > > > > See the patches for the sample app Makefiles. Not sure how
>> > > > > that can
>> > > > > be
>> > > > > made to work if we use different pkg-config settings for
>> > > > > different
>> > > > > build
>> > > > > types.
>> > > > > 
>> > > > > Your input and suggestions here would be welcome.
>> > > 
>> > > Yes that works nicely when the libraries are rebuilt locally -
>> > > then it
>> > > can be chosen whether to build the static or dynamic ones.
>> > > 
>> > > In the packaging case though, at least in Debian and Ubuntu (not
>> > > sure
>> > > about RHEL/SUSE), we do ship both static and dynamic libraries at
>> > > the
>> > > same time, following best practices. So we'd have to choose and
>> > > either
>> > > cause applications linking dynamically to over-link (which is
>> > > what we
>> > > currently do in Debian/Ubuntu and many developers really don't
>> > > like
>> > > that) or to cause applications that use the static libraries to
>> > > have to
>> > > manually add the missing flags.
>> > > 
>> > > From what I can see, the most common workflow for applications
>> > > that
>> > > want to do static builds when using packaged libraries is to use
>> > > the --
>> > > static flag of pkgconfig.
>> > > This has the advantage of being a ""standardised"" workflow,
>> > > expected
>> > > to work across any dependency, not just DPDK. Of course that's
>> > > not
>> > > always the case, but one can dream :-)
>> > > 
>> > > If you prefer to optimise for the local build workflow that's
>> > > fine, we
>> > > can patch it in the distro, it's not too much overhead (I need to
>> > > do it
>> > > anyway for the old build system at some point).
>> > > 
>> > > > 
>> > > > +Thomas, Olivier, Sergio to get more input
>> > > > 
>> > > > Thinking about it some more, is there any reason why we can't
>> > > > or
>> > > > shouldn't do both static and dynamic libs in all builds, and
>> > > > then let
>> > > > apps use pkg-config to determine what they want to link
>> > > > against? It
>> > > > wouldn't be a massive change to the new build system to do
>> > > > that, I
>> > > > think.
>> > > > 
>> > > > /Bruce
>> > > 
>> > > Yes that would be ideal! Right now in Debian/Ubuntu we have to
>> > > build
>> > > twice, doubling the required time unfortunately.
>> > > 
>> > > In theory the same objects could be packed into .ar and .so but
>> > > sadly
>> > > Meson doesn't support that yet like autotools/cmake do:
>> > > 
>> > > https://github.com/mesonbuild/meson/issues/484
>> > > 
>> > > (please do add some feedback there as developers!)
>> > > 
>> > > It looks like it could be possible with some extensive hacking,
>> > > not
>> > > sure if it would be worth it.
>> > > 
>> > 
>> > Actually, I think it's workable using extract_objects. Build the
>> > static
>> > lib first, then extract_all_objects() and then use those to build
>> > the .so.
>> > I can prototype it very easily by changing lib/meson.build and see
>> > what
>> > happens.
>> > 
>> 
>> Seems to work fine. This change makes all the libraries (bar EAL,
>> which
>> is special-cased) appear as both .a and .so. Testpmd links against
>> the
>> dynamic versions and still works.
>> 
>> When I get the chance I'll see about doing the same for EAL and
>> drivers,
>> and then having the pkgconfig file reflect both possibilities. Then I
>> can test with some examples linking both dynamically and statically
>> and
>> check all is as expected.
>> 
>> /Bruce
>> 
>> diff --git a/lib/meson.build b/lib/meson.build
>> index f04cb2791..29c88548b 100644
>> --- a/lib/meson.build
>> +++ b/lib/meson.build
>> @@ -76,6 +76,20 @@ foreach l:libraries
>>                         dep_objs += [get_variable('dep_rte_' + d)]
>>                 endforeach
>> 
>> +               libname = 'rte_' + name
>> +
>> +# first build static library
>> +               static_lib = static_library(libname, sources,
>> +                       objects: objs,
>> +                       c_args: cflags,
>> +                       dependencies: dep_objs,
>> +                       include_directories:
>> include_directories(dir_name),
>> +                       install: true)
>> +
>> +# now use those objects to build dynamic library
>> +               sources = []
>> +               objs += static_lib.extract_all_objects()
>> +
>>                 if get_option('per_library_versions')
>>                         lib_version = '@0@.1'.format(version)
>>                         so_version = '@0@'.format(version)
>> @@ -87,8 +101,7 @@ foreach l:libraries
>> 
>>                 version_map = '@0@/@1@/rte_@2@_version.map'.format(
>>                                 meson.current_source_dir(), dir_name,
>> name)
>> -               libname = 'rte_' + name
>> -               lib = library(libname,
>> +               lib = shared_library(libname,
>>                                 sources,
>>                                 objects: objs,
>>                                 c_args: cflags,
>
> Nice! Much easier than I thought reading that thread :-)
>
> I'll try to give it a test run in the next few days. Thanks!

Would there be any opposition if someone were to feel ambitious and
attempt this for the existing build system as well?  Not me, of course.
Asking for a friend, that's all. ;)

Having both library types spit out is really useful.  One less config
option, etc.