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 ;)
