notes on symbol versioning

TODO

@@ -5,6 +5,52 @@ Next
    to build and test cleanly in 2.3.1.  Hopefully the next release
    will include 64-bit binary distributions and external libraries.
 
+ * Add versioned symbols.  Fix below to not use AM_CONDITIONAL.  Just
+   set some variable that can be part of LDFLAGS, like
+   LD_VERSION_SCRIPT, instead.
+
+# Check if LD supports linker scripts, and define conditional
+# HAVE_LD_VERSION_SCRIPT if so.  This functionality is currently
+# constrained to compilers using GNU ld on ELF systems or systems
+# which provide an adequate emulation thereof.
+AC_ARG_ENABLE([ld-version-script],
+  AS_HELP_STRING([--enable-ld-version-script],
+    [enable linker version script (default is disabled)]),
+    [have_ld_version_script=$enableval], [have_ld_version_script=no])
+if test "$have_ld_version_script" != no; then
+  AC_MSG_CHECKING([if LD -Wl,--version-script works])
+  save_LDFLAGS="$LDFLAGS"
+  LDFLAGS="$LDFLAGS -Wl,--version-script=conftest.map"
+  cat > conftest.map <<EOF
+VERS_1 {
+        global: sym;
+};
+
+VERS_2 {
+        global: sym;
+} VERS_1;
+EOF
+  AC_LINK_IFELSE([AC_LANG_PROGRAM([], [])],
+                 [have_ld_version_script=yes], [have_ld_version_script=no])
+  rm -f conftest.map
+  LDFLAGS="$save_LDFLAGS"
+  AC_MSG_RESULT($have_ld_version_script)
+fi
+AM_CONDITIONAL(HAVE_LD_VERSION_SCRIPT, test "$have_ld_version_script" = "yes")
+
+----
+
+if HAVE_LD_VERSION_SCRIPT
+libtiff_la_LDFLAGS += -Wl,--version-script=$(srcdir)/libtiff.map
+endif
+
+----
+
+LIBQPDF_3 {
+  global:
+    *;
+};
+
 
 Better 64-bit support on Windows
 ================================