Add support for linker script on Linux

GitHub: fix GH-107

Reported by nicholas a. evans. Thanks!!!

lib/fiddle.rb

@@ -58,7 +58,36 @@ def self.last_error= error
   #
   # See Fiddle::Handle.new for more.
   def dlopen library
-    Fiddle::Handle.new library
+    begin
+      Fiddle::Handle.new(library)
+    rescue DLError => error
+      case RUBY_PLATFORM
+      when /linux/
+        case error.message
+        when /\A(\/.+?): (?:invalid ELF header|file too short)/
+          # This may be a linker script:
+          # https://sourceware.org/binutils/docs/ld.html#Scripts
+          path = $1
+        else
+          raise
+        end
+      else
+        raise
+      end
+
+      File.open(path) do |input|
+        input.each_line do |line|
+          case line
+          when /\A\s*(?:INPUT|GROUP)\s*\(\s*([^\s,\)]+)/
+            # TODO: Should we support multiple files?
+            return dlopen($1)
+          end
+        end
+      end
+
+      # Not found
+      raise
+    end
   end
   module_function :dlopen
 

test/fiddle/test_fiddle.rb

@@ -14,4 +14,38 @@ def test_windows_constant
     end
   end
 
+  def test_dlopen_linker_script_input_linux
+    omit("This is only for Linux") unless RUBY_PLATFORM.match?("linux")
+    if Dir.glob("/usr/lib/*/libncurses.so").empty?
+      omit("libncurses.so is needed")
+    end
+    # libncurses.so uses INPUT() on Debian GNU/Linux
+    # $ cat /usr/lib/x86_64-linux-gnu/libncurses.so
+    # INPUT(libncurses.so.6 -ltinfo)
+    handle = Fiddle.dlopen("libncurses.so")
+    begin
+      assert_equal("libncurses.so",
+                   File.basename(handle.file_name, ".*"))
+    ensure
+      handle.close
+    end
+  end
+
+  def test_dlopen_linker_script_group_linux
+    omit("This is only for Linux") unless RUBY_PLATFORM.match?("linux")
+    # libc.so uses GROUP() on Debian GNU/Linux
+    # $ cat /usr/lib/x86_64-linux-gnu/libc.so
+    # /* GNU ld script
+    #    Use the shared library, but some functions are only in
+    #    the static library, so try that secondarily.  */
+    # OUTPUT_FORMAT(elf64-x86-64)
+    # GROUP ( /lib/x86_64-linux-gnu/libc.so.6 /usr/lib/x86_64-linux-gnu/libc_nonshared.a  AS_NEEDED ( /lib64/ld-linux-x86-64.so.2 ) )
+    handle = Fiddle.dlopen("libc.so")
+    begin
+      assert_equal("libc.so",
+                   File.basename(handle.file_name, ".*"))
+    ensure
+      handle.close
+    end
+  end
 end if defined?(Fiddle)