Attached patch fixes two problems:

1) gendef works from inside visual studio - use a tempfile instead of
redirection, because for some reason you can't redirect dumpbin from
inside (patch from Joachim Wieland)
2) gendef must process only *.obj, or you get weird errors in some build
scenarios when it tries to process a logfile

Magnus Hagander

Author: Neil Conway

src/tools/msvc/gendef.pl

@@ -10,9 +10,10 @@
 
 print "Generating $defname.DEF from directory $ARGV[0]\n";
 
-while (<$ARGV[0]/*>) {
+while (<$ARGV[0]/*.obj>) {
     print ".";
-	open(F,"dumpbin /symbols $_|") || die "Could not open $_\n";
+	system("dumpbin /symbols /out:symbols.out $_ >NUL") && die "Could not call dumpbin";
+	open(F, "<symbols.out") || die "Could not open symbols.out for $_\n";
 	while (<F>) {
 		s/\(\)//g;
 		next unless /^\d/;
@@ -31,6 +32,7 @@
 		push @def, $pieces[6];
 	}
 	close(F);
+	unlink("symbols.out");
 }
 print "\n";