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ea53100d56
libpq and ecpg need shared-library-friendly versions of assorted src/port/ and src/common/ modules. Up to now, they got those by symlinking the individual source files and compiling them locally. That's baroque, and a pain to maintain, and it results in some amount of duplicated compile work. It might've made sense when only a couple of files were needed, but the list has grown and grown and grown :-( It makes more sense to have the originating directory build a third variant of libpgport.a/libpgcommon.a containing modules built with $(CFLAGS_SL), and just link that into the shared library. Unused files won't get linked, so the end result should be the same. This patch makes a down payment on that idea by having src/port/ build such a library and making libpq use it. If the buildfarm doesn't expose fatal problems with the approach, I'll extend it to the other cases. Discussion: https://postgr.es/m/13022.1538003440@sss.pgh.pa.us
src/port/README
libpgport
=========
libpgport must have special behavior. It supplies functions to both
libraries and applications. However, there are two complexities:
1) Libraries need to use object files that are compiled with exactly
the same flags as the library. libpgport might not use the same flags,
so it is necessary to recompile the object files for individual
libraries. This is done by removing -lpgport from the link line:
# Need to recompile any libpgport object files
LIBS := $(filter-out -lpgport, $(LIBS))
and adding infrastructure to recompile the object files:
OBJS= execute.o typename.o descriptor.o data.o error.o prepare.o memory.o \
connect.o misc.o path.o exec.o \
$(filter strlcat.o, $(LIBOBJS))
The problem is that there is no testing of which object files need to be
added, but missing functions usually show up when linking user
applications.
2) For applications, we use -lpgport before -lpq, so the static files
from libpgport are linked first. This avoids having applications
dependent on symbols that are _used_ by libpq, but not intended to be
exported by libpq. libpq's libpgport usage changes over time, so such a
dependency is a problem. Windows, Linux, and macOS use an export list to
control the symbols exported by libpq.