Re: [PATCH XEN v3 01/22] tools/Rules.mk: Properly handle libraries with recursive dependencies.

[Ian Campbell <ian.campbell@citrix.com>]

On Thu, 2015-10-08 at 12:21 +0100, Ian Jackson wrote:
> Ian Campbell writes ("[PATCH XEN v3 01/22] tools/Rules.mk: Properly
> handle libraries with recursive dependencies."):
> > In tree libraries which link against other in tree libraries in a way
> > which is opaque to their callers need special handling, specifically
> > correct use of -Wl,-rpath-link for the recusively used libraries.
> > 
> > Currently this is rather simple, but up coming changes are going to
> > introduce transitive dependencies more than 1 step deep.
> > 
> > Introduce a SHDEPS idiom to contain all the recursive deps for a
> > library and include those in both LDLIBS (for linking) and SHLIB (for
> > recursive uses).
> > 
> > Try and document the whole thing.
> ...
> 
> Thanks.
> 
> > +# Compiling and linking against in tree libraries.
> > +#
> > +# In order to compile and link against an in-tree library various
> > +# cpp/compiler/linker options are required.
> > +#
> > +# For example consider a library "libfoo" which itself uses two other
> > +# libraries:
> > +#  libbar - whose use is entirely internal to libfoo and not exposed
> > +#           to users of libfoo at all.
> > +#  libbaz - whose use is entirely internal to libfoo but libfoo's
> > +#           public headers include libbaz's one or more of libbaz's
> > +#           public headers. Users of libfoo are therefore transitively
> > +#           using libbaz's header but not linking against libbaz.
> 
> The first sentence seems slightly mangled.

Ah yes. I think I meant:

+#  libbaz - whose use is entirely internal to libfoo but libfoo's
+#           public headers include one or more of libbaz's
+#           public headers. Users of libfoo are therefore transitively
+#           using libbaz's header but not linking against libbaz.

(dropping a stray "libbaz's" from the middle)

> You seem to have reinvented half of pkg-config.  But it's small, so,
> with the docs fix,
> 
> Acked-by: Ian Jackson <ian.jackson@eu.citrix.com>

Thanks.

Probably we should look at shipping pkg-config files for these libraries,
for the benefit of third parties. I'm not sure how well pkg-config can be
made to work for in-tree users. I suppose it can be directed to examine
some $PATH thing for .pc files, but I'm less sure about having it ignore
system installed versions of things (i.e. older versions).

Ian.