Makefile.shared: update link_o.dawrin rule.

PR: 2306

Makefile.shared

@@ -70,7 +70,7 @@ LIBDEPS=
 # The rest is private to this makefile.
 
 SET_X=:
-#SET_X=set -x
+SET_X=set -x
 
 top:
 	echo "Trying to use this makefile interactively?  Don't."
@@ -135,7 +135,7 @@ LINK_SO_A_VIA_O=	\
   ALL=$$ALLSYMSFLAGS; ALLSYMSFLAGS=; NOALLSYMSFLAGS=; \
   ( $(SET_X); \
     ld $(LDFLAGS) -r -o lib$(LIBNAME).o $$ALL lib$(LIBNAME).a $(LIBEXTRAS) ); \
-  $(LINK_SO) && rm -f $(LIBNAME).o
+  $(LINK_SO) && rm -f lib$(LIBNAME).o
 
 LINK_SO_A_UNPACKED=	\
   UNPACKDIR=link_tmp.$$$$; rm -rf $$UNPACKDIR; mkdir $$UNPACKDIR; \
@@ -207,17 +207,27 @@ link_app.bsd:
 	fi; $(LINK_APP)
 
 # For Darwin AKA Mac OS/X (dyld)
-# link_o.darwin produces .so, because we let it use dso_dlfcn module,
-# which has .so extension hard-coded. One can argue that one should
-# develop special dso module for MacOS X. At least manual encourages
-# to use native NSModule(3) API and refers to dlfcn as termporary hack.
+# Originally link_o.darwin produced .so, because it was hard-coded
+# in dso_dlfcn module. At later point dso_dlfcn switched to .dylib
+# extension in order to allow for run-time linking with vendor-
+# supplied shared libraries such as libz, so that link_o.darwin had
+# to be harmonized with it. This caused minor controversy, because
+# it was believed that dlopen can't be used to dynamically load
+# .dylib-s, only so called bundle modules (ones linked with -bundle
+# flag). The belief seems to be originating from pre-10.4 release,
+# where dlfcn functionality was emulated by dlcompat add-on. In
+# 10.4 dlopen was rewritten as native part of dyld and is documented
+# to be capable of loading both dynamic libraries and bundles. In
+# order to provide compatibility with pre-10.4 dlopen, modules are
+# linked with -bundle flag, which makes .dylib extension misleading.
+# It works, because dlopen is [and always was] extension-agnostic.
 link_o.darwin:
 	@ $(CALC_VERSIONS); \
 	SHLIB=lib$(LIBNAME); \
-	SHLIB_SUFFIX=.so; \
+	SHLIB_SUFFIX=.dylib; \
 	ALLSYMSFLAGS='-all_load'; \
 	NOALLSYMSFLAGS=''; \
-	SHAREDFLAGS="$(CFLAGS) $(SHARED_LDFLAGS)"; \
+	SHAREDFLAGS="$(CFLAGS) `echo $(SHARED_LDFLAGS) | sed s/dynamiclib/bundle/"; \
 	if [ -n "$(LIBVERSION)" ]; then \
 		SHAREDFLAGS="$$SHAREDFLAGS -current_version $(LIBVERSION)"; \
 	fi; \