On Wed, Jul 01, 2020 at 04:42:33PM +0200, Thomas Monjalon wrote: > 30/06/2020 16:14, Bruce Richardson: > > When calling pkg-config --static --libs, pkg-config will always output the > > regular libs first, and then the extra libs from libraries.private field, > > s/libraries.private/Libs.private/ > > > since the assumption is that those are additional dependencies for building > > statically that the .a files depend upon. > > > > However, for DPDK, we only link the driver files for static builds, and > > those need to come *before* the regular libraries. To get this result, we > > need two pkgconfig files for DPDK, one for the shared libs, and a second > > for the static libs and drivers, which depends upon the first. Using a > > dependency means that the shared libs are printed only after the > > libraries.private field rather than before. > > s/libraries.private/Libs.private/ > > > Without this patch, the linking works in DPDK because in all cases we > > specify the libraries after the drivers in the Libs.private line, ensuring > > that the references to the libs from the drivers can be resolved. The > > current output is therefore of the form, "(shared)libs, drivers, > > (static)libs", while after this patch the output is, "drivers, > > (static)libs, (shared)libs". The former case will not work if we use the > > --whole-archive flag on the static libs as it will lead to duplicate > > definitions due to some references having been previously resolved from the > > shared libraries. By ensuring the shared libraries come last in the link > > link, this issue does not occur, as duplicate references when linking the > > shared libs will be ignored. > > > > Signed-off-by: Bruce Richardson <bruce.richard...@intel.com> > > Acked-by: Luca Boccassi <bl...@debian.org> > > Acked-by: Sunil Pai G <sunil.pa...@intel.com> > > --- > > +# When calling pkg-config --static --libs, pkg-config will always output > > the > > +# regular libs first, and then the extra libs from libraries.private field, > > +# since the assumption is that those are additional dependencies for > > building > > +# statically that the .a files depend upon. However, for DPDK, we only link > > +# the driver files for static builds, and those need to come *before* the > > +# regular libraries. To get this result, we need two pkgconfig files for > > DPDK, > > +# one for the shared libs, and a second for the static libs and drivers, > > which > > +# depends upon the first. Using a dependency means that the shared libs are > > +# printed only after the libraries.private field rather than before. > > This is not obvious. In order to avoid messing it up in future, > I suggest this longer reword: > > # When calling pkg-config --static --libs, pkg-config will always output the > # regular libs first, and then the extra libs from Libs.private field, > # since the assumption is that those are additional dependencies for building > # statically that the .a files depend upon. The output order of .pc fields is: > # Cflags Libs Libs.private Requires Requires.private > # The fields Requires* are for package names. > # The flags of the DPDK libraries must be defined in Libs* fields. > # However, the DPDK drivers are linked only in static builds (Libs.private), > # and those need to come *before* the regular libraries (Libs field). > # This requirement is satisfied by moving the regular libs in a separate file > # included in the field Requires (after Libs.private). > # Another requirement is to allow linking dependencies as shared libraries, > # while linking static DPDK libraries and drivers. It is satisfied by > # listing the static files in Libs.private with the explicit syntax > -l:libfoo.a. > # As a consequence, the regular DPDK libraries are already listed as static > # in the field Libs.private. The second occurences of DPDK libraries, > # included from Requires and used for shared library linkage case, > # are skipped in the case of static linkage thanks to the flag --as-needed. > > # Link order summary: > # libdpdk.Libs.private: whole-archive(static drivers/libs), drivers deps > flags > # libdpdk.Requires: libdpdk-libs package > # libdpdk-libs.Libs: as-needed(shared libs) > # libdpdk-libs.Libs.private: libs deps flags > # libdpdk.pc.Requires.private: deps packages > > > If you agree, I could change this comment while merging. > I would add my Signed-off ;) >
This seems generally ok, but probably should just be added as part of patch #7 when all parts of the above have been applied. Couple of comments: * One small nit is that cflags are not output as part of the --libs call, so you can remove them from the list on line 5 of the comment. They aren't really relevant to this comment/essay. * I find the link-order summary to actually be more confusing than helpful. I think the text block is explanatory enough. It just confuses things introducing the extra details of what goes in the requires-private or libs-private of the libdpdk.pc file. That's just regular stuff, unrelated to the changes or to DPDK special-case of needing private libs first. /Bruce
