m4/ax_realpath_lib.m4: recognize "GNU ld script" files which redirect…

… to a real library

Signed-off-by: Jim Klimov <[email protected]>

m4/ax_realpath_lib.m4

@@ -156,16 +156,44 @@ AC_DEFUN([AX_REALPATH_LIB],
         AS_IF([test -n "${myLIBPATH}" && test -s "${myLIBPATH}"], [
             AC_MSG_RESULT([initially '${myLIBPATH}'])
 
-            dnl # Resolving the directory location is a nice bonus
-            dnl # (usually the paths are relative to toolkit and ugly,
-            dnl # though maybe arguably portable with regard to symlinks).
-            dnl # The primary goal is to resolve the actual library file
-            dnl # name like "libnetsnmp.so.1.2.3", so we can preferentially
-            dnl # try to dlopen() it on a system with a packaged footprint
-            dnl # that does not serve short (developer-friendly) links like
-            dnl # "libnetsnmp.so".
-            myLIBPATH_REAL="${myLIBPATH}"
-            AX_REALPATH([${myLIBPATH}], [myLIBPATH_REAL])
+            AC_MSG_CHECKING([whether the file is a "GNU ld script" and not a binary])
+            AS_IF([LANG=C LC_ALL=C file "${myLIBPATH}" | grep -Ei '(ascii|text)' && grep -w GROUP "${myLIBPATH}" >/dev/null], [
+                # dnl e.g. # cat /usr/lib/x86_64-linux-gnu/libusb.so
+                # dnl    /* GNU ld script.  */
+                # dnl    GROUP ( /lib/x86_64-linux-gnu/libusb-0.1.so.4.4.4 )
+                # dnl Note that spaces around parentheses vary, more keywords
+                # dnl may be present in a group (e.g. AS_NEEDED), and comment
+                # dnl strings are inconsistent (useless to match by).
+                AC_MSG_RESULT([yes, iterate further])
+                myLIBPATH_LDSCRIPT="`grep -w GROUP "${myLIBPATH}" | sed 's,^.*GROUP *( *\(/@<:@^ @:>@*\.so@<:@^ @:>@*\)@<:@^0-9a-zA-Z_.-@:>@.*$,\1,'`"
+                AS_IF([test -n "${myLIBPATH_LDSCRIPT}" && test -s "${myLIBPATH_LDSCRIPT}"], [
+                    AC_MSG_NOTICE([will dig into ${myLIBPATH_LDSCRIPT}])
+
+                    dnl # See detailed comments just below
+                    myLIBPATH_REAL="${myLIBPATH_LDSCRIPT}"
+                    AX_REALPATH([${myLIBPATH_LDSCRIPT}], [myLIBPATH_REAL])
+                ], [
+                    AC_MSG_NOTICE([could not determine a further path name, will use what we have])
+
+                    dnl # See detailed comments just below
+                    myLIBPATH_REAL="${myLIBPATH}"
+                    AX_REALPATH([${myLIBPATH}], [myLIBPATH_REAL])
+                ])
+            ],[
+                AC_MSG_RESULT([no, seems like a normal binary])
+
+                dnl # Resolving the directory location is a nice bonus
+                dnl # (usually the paths are relative to toolkit and ugly,
+                dnl # though maybe arguably portable with regard to symlinks).
+                dnl # The primary goal is to resolve the actual library file
+                dnl # name like "libnetsnmp.so.1.2.3", so we can preferentially
+                dnl # try to dlopen() it on a system with a packaged footprint
+                dnl # that does not serve short (developer-friendly) links like
+                dnl # "libnetsnmp.so".
+                myLIBPATH_REAL="${myLIBPATH}"
+                AX_REALPATH([${myLIBPATH}], [myLIBPATH_REAL])
+            ])
+
             AC_MSG_RESULT(${myLIBPATH_REAL})
             $2="${myLIBPATH_REAL}"
         ],[