Build src/port files as a library with -fPIC, and use that in libpq.

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/interfaces/libpq/.gitignore

 /exports.list
 /libpq.rc
 # .c files that are symlinked in from elsewhere
-/chklocale.c
-/crypt.c
-/erand48.c
-/getaddrinfo.c
-/getpeereid.c
-/inet_aton.c
-/inet_net_ntop.c
-/noblock.c
-/open.c
-/system.c
-/pgsleep.c
-/pg_strong_random.c
-/pgstrcasecmp.c
-/pqsignal.c
-/snprintf.c
-/strerror.c
-/strlcpy.c
-/strnlen.c
-/thread.c
-/win32error.c
-/win32setlocale.c
 /ip.c
 /md5.c
 /base64.c

src/interfaces/libpq/Makefile

@@ -24,27 +24,11 @@ ifneq ($(PORTNAME), win32)
 override CFLAGS += $(PTHREAD_CFLAGS)
 endif
 
-# Need to recompile any external C files because we need
-# all object files to use the same compile flags as libpq; some
-# platforms require special flags.
-LIBS := $(LIBS:-lpgport=)
-
 # We can't use Makefile variables here because the MSVC build system scrapes
 # OBJS from this file.
 OBJS=	fe-auth.o fe-auth-scram.o fe-connect.o fe-exec.o fe-misc.o fe-print.o fe-lobj.o \
 	fe-protocol2.o fe-protocol3.o pqexpbuffer.o fe-secure.o \
 	libpq-events.o
-# libpgport C files we always use
-OBJS += chklocale.o inet_net_ntop.o noblock.o pgstrcasecmp.o pqsignal.o \
-	snprintf.o strerror.o thread.o
-# libpgport C files that are needed if identified by configure
-OBJS += $(filter crypt.o getaddrinfo.o getpeereid.o inet_aton.o open.o system.o strlcpy.o strnlen.o win32error.o win32setlocale.o, $(LIBOBJS))
-
-ifeq ($(enable_strong_random), yes)
-OBJS += pg_strong_random.o
-else
-OBJS += erand48.o
-endif
 
 # src/backend/utils/mb
 OBJS += encnames.o wchar.o
@@ -62,8 +46,7 @@ override shlib = cyg$(NAME)$(DLSUFFIX)
 endif
 
 ifeq ($(PORTNAME), win32)
-# pgsleep.o is from libpgport
-OBJS += pgsleep.o win32.o libpqrc.o
+OBJS += win32.o libpqrc.o
 
 libpqrc.o: libpq.rc
 	$(WINDRES) -i $< -o $@
@@ -76,11 +59,12 @@ endif
 
 # Add libraries that libpq depends (or might depend) on into the
 # shared library link.  (The order in which you list them here doesn't
-# matter.)
+# matter.)  Note that we filter out -lpgport from LIBS and instead
+# insert -lpgport_shlib, to get port files that are built correctly.
 ifneq ($(PORTNAME), win32)
-SHLIB_LINK += $(filter -lcrypt -ldes -lcom_err -lcrypto -lk5crypto -lkrb5 -lgssapi_krb5 -lgss -lgssapi -lssl -lsocket -lnsl -lresolv -lintl -lm, $(LIBS)) $(LDAP_LIBS_FE) $(PTHREAD_LIBS)
+SHLIB_LINK += -lpgport_shlib $(filter -lcrypt -ldes -lcom_err -lcrypto -lk5crypto -lkrb5 -lgssapi_krb5 -lgss -lgssapi -lssl -lsocket -lnsl -lresolv -lintl -lm, $(LIBS)) $(LDAP_LIBS_FE) $(PTHREAD_LIBS)
 else
-SHLIB_LINK += $(filter -lcrypt -ldes -lcom_err -lcrypto -lk5crypto -lkrb5 -lgssapi32 -lssl -lsocket -lnsl -lresolv -lintl -lm $(PTHREAD_LIBS), $(LIBS)) $(LDAP_LIBS_FE)
+SHLIB_LINK += -lpgport_shlib $(filter -lcrypt -ldes -lcom_err -lcrypto -lk5crypto -lkrb5 -lgssapi32 -lssl -lsocket -lnsl -lresolv -lintl -lm $(PTHREAD_LIBS), $(LIBS)) $(LDAP_LIBS_FE)
 endif
 ifeq ($(PORTNAME), win32)
 SHLIB_LINK += -lshell32 -lws2_32 -lsecur32 $(filter -leay32 -lssleay32 -lcomerr32 -lkrb5_32, $(LIBS))
@@ -90,22 +74,19 @@ SHLIB_EXPORTS = exports.txt
 
 all: all-lib
 
+all-lib: | submake-libpgport
+
 # Shared library stuff
 include $(top_srcdir)/src/Makefile.shlib
 backend_src = $(top_srcdir)/src/backend
 
 
-# We use several libpgport and backend modules verbatim, but since we need
+# We use a few backend modules verbatim, but since we need
 # to compile with appropriate options to build a shared lib, we can't
-# necessarily use the same object files built for libpgport and the backend.
+# use the same object files built for the backend.
 # Instead, symlink the source files in here and build our own object files.
-# For some libpgport modules, this only happens if configure decides
-# the module is needed (see filter hack in OBJS, above).
 # When you add a file here, remember to add it in the "clean" target below.
 
-chklocale.c crypt.c erand48.c getaddrinfo.c getpeereid.c inet_aton.c inet_net_ntop.c noblock.c open.c system.c pgsleep.c pg_strong_random.c pgstrcasecmp.c pqsignal.c snprintf.c strerror.c strlcpy.c strnlen.c thread.c win32error.c win32setlocale.c: % : $(top_srcdir)/src/port/%
-	rm -f $@ && $(LN_S) $< .
-
 ip.c md5.c base64.c link-canary.c scram-common.c sha2.c sha2_openssl.c saslprep.c unicode_norm.c: % : $(top_srcdir)/src/common/%
 	rm -f $@ && $(LN_S) $< .
 
@@ -123,6 +104,7 @@ libpq.rc libpq-dist.rc: libpq.rc.in
 # installations and is only updated by distprep.)
 libpq.rc: $(top_builddir)/src/Makefile.global
 
+# Make dependencies on pg_config_paths.h visible, too.
 fe-connect.o: fe-connect.c $(top_builddir)/src/port/pg_config_paths.h
 fe-misc.o: fe-misc.c $(top_builddir)/src/port/pg_config_paths.h
 
@@ -154,8 +136,7 @@ clean distclean: clean-lib
 	rm -f $(OBJS) pthread.h libpq.rc
 # Might be left over from a Win32 client-only build
 	rm -f pg_config_paths.h
-# Remove files we (may have) symlinked in from src/port and other places
-	rm -f chklocale.c crypt.c erand48.c getaddrinfo.c getpeereid.c inet_aton.c inet_net_ntop.c noblock.c open.c system.c pgsleep.c pg_strong_random.c pgstrcasecmp.c pqsignal.c snprintf.c strerror.c strlcpy.c strnlen.c thread.c win32error.c win32setlocale.c
+# Remove files we (may have) symlinked in from src/common and other places
 	rm -f ip.c md5.c base64.c link-canary.c scram-common.c sha2.c sha2_openssl.c saslprep.c unicode_norm.c
 	rm -f encnames.c wchar.c
 

src/port/.gitignore

 /libpgport.a
+/libpgport_shlib.a
 /libpgport_srv.a
 /pg_config_paths.h

src/port/Makefile

 #-------------------------------------------------------------------------
 #
 # Makefile
-#    Makefile for the port-specific subsystem of the backend
+#    Makefile for src/port
 #
-# These files are used in other directories for portability on systems
-# with broken/missing library files, and for common code sharing.
+# These files are used by the Postgres backend, and also by frontend
+# programs.  Primarily, they are meant to provide portability on systems
+# with broken/missing library files.
 #
-# This makefile generates two outputs:
+# This makefile generates three outputs:
 #
 #	libpgport.a - contains object files with FRONTEND defined,
-#		for use by client application and libraries
+#		for use by client applications
+#
+#	libpgport_shlib.a - contains object files with FRONTEND defined,
+#		built suitably for use in shared libraries; for use
+#		by libpq and other frontend libraries
 #
 #	libpgport_srv.a - contains object files without FRONTEND defined,
-#		for use only by the backend binaries
+#		for use only by the backend
 #
 # LIBOBJS is set by configure (via Makefile.global) to be the list of object
 # files that are conditionally needed as determined by configure's probing.
@@ -40,12 +45,15 @@ ifeq ($(enable_strong_random), yes)
 OBJS += pg_strong_random.o
 endif
 
-# foo_srv.o and foo.o are both built from foo.c, but only foo.o has -DFRONTEND
+# libpgport.a, libpgport_shlib.a, and libpgport_srv.a contain the same files
+# foo.o, foo_shlib.o, and foo_srv.o are all built from foo.c
+OBJS_SHLIB = $(OBJS:%.o=%_shlib.o)
 OBJS_SRV = $(OBJS:%.o=%_srv.o)
 
-all: libpgport.a libpgport_srv.a
+all: libpgport.a libpgport_shlib.a libpgport_srv.a
 
 # libpgport is needed by some contrib
+# currently we don't install libpgport_shlib.a, maybe we should?
 install: all installdirs
 	$(INSTALL_STLIB) libpgport.a '$(DESTDIR)$(libdir)/libpgport.a'
 
@@ -59,17 +67,37 @@ libpgport.a: $(OBJS)
 	rm -f $@
 	$(AR) $(AROPT) $@ $^
 
-# thread.o needs PTHREAD_CFLAGS (but thread_srv.o does not)
+# thread.o and thread_shlib.o need PTHREAD_CFLAGS (but thread_srv.o does not)
 thread.o: CFLAGS+=$(PTHREAD_CFLAGS)
+thread_shlib.o: CFLAGS+=$(PTHREAD_CFLAGS)
 
-# pg_crc32c_sse42.o and its _srv.o version need CFLAGS_SSE42
+# all versions of pg_crc32c_sse42.o need CFLAGS_SSE42
 pg_crc32c_sse42.o: CFLAGS+=$(CFLAGS_SSE42)
+pg_crc32c_sse42_shlib.o: CFLAGS+=$(CFLAGS_SSE42)
 pg_crc32c_sse42_srv.o: CFLAGS+=$(CFLAGS_SSE42)
 
-# pg_crc32c_armv8.o and its _srv.o version need CFLAGS_ARMV8_CRC32C
+# all versions of pg_crc32c_armv8.o need CFLAGS_ARMV8_CRC32C
 pg_crc32c_armv8.o: CFLAGS+=$(CFLAGS_ARMV8_CRC32C)
+pg_crc32c_armv8_shlib.o: CFLAGS+=$(CFLAGS_ARMV8_CRC32C)
 pg_crc32c_armv8_srv.o: CFLAGS+=$(CFLAGS_ARMV8_CRC32C)
 
+#
+# Shared library versions of object files
+#
+
+libpgport_shlib.a: $(OBJS_SHLIB)
+	rm -f $@
+	$(AR) $(AROPT) $@ $^
+
+# Because this uses its own compilation rule, it doesn't use the
+# dependency tracking logic from Makefile.global.  To make sure that
+# dependency tracking works anyway for the *_shlib.o files, depend on
+# their *.o siblings as well, which do have proper dependencies.  It's
+# a hack that might fail someday if there is a *_shlib.o without a
+# corresponding *.o, but there seems little reason for that.
+%_shlib.o: %.c %.o
+	$(CC) $(CFLAGS) $(CFLAGS_SL) $(CPPFLAGS) -c $< -o $@
+
 #
 # Server versions of object files
 #
@@ -92,6 +120,8 @@ libpgport_srv.a: $(OBJS_SRV)
 
 path.o: path.c pg_config_paths.h
 
+path_shlib.o: path.c pg_config_paths.h
+
 path_srv.o: path.c pg_config_paths.h
 
 # We create a separate file rather than put these in pg_config.h
@@ -112,4 +142,5 @@ pg_config_paths.h: $(top_builddir)/src/Makefile.global
 	echo "#define MANDIR \"$(mandir)\"" >>$@
 
 clean distclean maintainer-clean:
-	rm -f libpgport.a libpgport_srv.a $(OBJS) $(OBJS_SRV) pg_config_paths.h
+	rm -f libpgport.a libpgport_shlib.a libpgport_srv.a
+	rm -f $(OBJS) $(OBJS_SHLIB) $(OBJS_SRV) pg_config_paths.h