AppletTalk.com Java discussions newsgroups   Archives   FAQ   Search   Memberlist   Usergroups   Register   Profile   Log in to check your private messages   Log in  modifying java.lang.String.java          AppletTalk.com Forum Index -> JVM, native methods and hardware View previous topic :: View next topic   Author Message danwichs@gmail.com Guest Posted: Mon Mar 26, 2007 3:00 am    Post subject: modifying java.lang.String.java Hi, I'm trying to modify java.lang.String.java and add the modified String.class to rt.jar [THIS IS FOR MYSELF ONLY AND WILL NOT BE DEPLOYED]. I cannot add "private final boolean tainted[] = new boolean[5];" to String.java. If I do, it still compiles and I can add it to rt.jar and compile a test program against it. However, the JVM crashes with a strange message: java.lang.IllegalArgumentException: name can't be empty at java.security.BasicPermission.init(Unknown Source) at java.security.BasicPermission.<init>(Unknown Source) at java.lang.RuntimePermission.<init>(Unknown Source) at java.lang.Thread.<clinit>(Unknown Source) I tried various ways of rewriting the above such as adding "private final boolean tainted[];" and initializing it in each constructor. Nothing works. I can add methods to String.java and even the member variable "private boolean isTainted;" and it works just fine. Do you have any ideas for why adding a boolean array does not work (or better yet how to get around this issue)? Thank you, Daniel Back to top Ralf Ullrich Guest Posted: Mon Mar 26, 2007 3:00 am    Post subject: Re: modifying java.lang.String.java danwichs (AT) gmail (DOT) com wrote: Quote: I'm trying to modify java.lang.String.java and add the modified String.class to rt.jar [THIS IS FOR MYSELF ONLY AND WILL NOT BE DEPLOYED]. Try running the VM with -Xshare:off If this works re-create the shared archives (JAVA_HOME/bin/(client|server)/classes.jsa). HTH cu Back to top Ralf Ullrich Guest Posted: Mon Mar 26, 2007 3:00 am    Post subject: Re: modifying java.lang.String.java danwichs (AT) gmail (DOT) com wrote: Quote: On Mar 25, 7:06 pm, "Ralf Ullrich" <n...@jnana.de> wrote: danwi...@gmail.com wrote: I'm trying to modify java.lang.String.java and add the modified String.class to rt.jar [THIS IS FOR MYSELF ONLY AND WILL NOT BE DEPLOYED]. Try running the VM with -Xshare:off If this works re-create the shared archives (JAVA_HOME/bin/(client|server)/classes.jsa). HTH cu That still does not work. I get the same error. Well, the offending code seems to be this line in java.lang.Thread: private static final RuntimePermission SUBCLASS_IMPLEMENTATION_PERMISSION = new RuntimePermission("enableContextClassLoaderOverride"); where "new RuntimePermission(...)" results in your observed error if the supplied string returns 0 for length(). So I would assume, that after you modified java.lang.String the magic trickery within the VM that creates String objects from String literals in class files is broken with regard to your modified String class. I'd try to look there for the problem. Sorry, that I cannot be of more help. cu Back to top danwichs@gmail.com Guest Posted: Mon Mar 26, 2007 5:58 am    Post subject: Re: modifying java.lang.String.java On Mar 25, 7:06 pm, "Ralf Ullrich" <n...@jnana.de> wrote: Quote: danwi...@gmail.com wrote: I'm trying to modify java.lang.String.java and add the modified String.class to rt.jar [THIS IS FOR MYSELF ONLY AND WILL NOT BE DEPLOYED]. Try running the VM with -Xshare:off If this works re-create the shared archives (JAVA_HOME/bin/(client|server)/classes.jsa). HTH cu That still does not work. I get the same error. Back to top danwichs@gmail.com Guest Posted: Mon Mar 26, 2007 6:34 am    Post subject: Re: modifying java.lang.String.java Thanks. I suspect you are right. I just wish that I knew exactly what the problem is. Unfortunatley since the error happens as the JVM is loading, I cannot attach a debugger. It is strange that adding "private final boolean tainted[] = new boolean[5];" causes a crash bud adding: "private final boolean tainted=false;" works fine. If anyone knows more about the internals of how the JVM makes strings out of string literals I would appreciate a lesson. On Mar 25, 9:21 pm, "Ralf Ullrich" <n...@jnana.de> wrote: Quote: danwi...@gmail.com wrote: On Mar 25, 7:06 pm, "Ralf Ullrich" <n...@jnana.de> wrote: danwi...@gmail.com wrote: I'm trying to modify java.lang.String.java and add the modified String.class to rt.jar [THIS IS FOR MYSELF ONLY AND WILL NOT BE DEPLOYED]. Try running the VM with -Xshare:off If this works re-create the shared archives (JAVA_HOME/bin/(client|server)/classes.jsa). HTH cu That still does not work. I get the same error. Well, the offending code seems to be this line in java.lang.Thread: private static final RuntimePermission SUBCLASS_IMPLEMENTATION_PERMISSION = new RuntimePermission("enableContextClassLoaderOverride"); where "new RuntimePermission(...)" results in your observed error if the supplied string returns 0 for length(). So I would assume, that after you modified java.lang.String the magic trickery within the VM that creates String objects from String literals in class files is broken with regard to your modified String class. I'd try to look there for the problem. Sorry, that I cannot be of more help. cu- Hide quoted text - - Show quoted text - Back to top danwichs@gmail.com Guest Posted: Mon Mar 26, 2007 7:10 am    Post subject: Re: modifying java.lang.String.java I think the error is caused by the intern() function in String.java. This is implemented in native code. I bet it somehow messes up. On Mar 25, 9:34 pm, "danwi...@gmail.com" <danwi...@gmail.com> wrote: Quote: Thanks. I suspect you are right. I just wish that I knew exactly what the problem is. Unfortunatley since the error happens as the JVM is loading, I cannot attach a debugger. It is strange that adding "private final boolean tainted[] = new boolean[5];" causes a crash bud adding: "private final boolean tainted=false;" works fine. If anyone knows more about the internals of how the JVM makes strings out of string literals I would appreciate a lesson. On Mar 25, 9:21 pm, "Ralf Ullrich" <n...@jnana.de> wrote: danwi...@gmail.com wrote: On Mar 25, 7:06 pm, "Ralf Ullrich" <n...@jnana.de> wrote: danwi...@gmail.com wrote: I'm trying to modify java.lang.String.java and add the modified String.class to rt.jar [THIS IS FOR MYSELF ONLY AND WILL NOT BE DEPLOYED]. Try running the VM with -Xshare:off If this works re-create the shared archives (JAVA_HOME/bin/(client|server)/classes.jsa). HTH cu That still does not work. I get the same error. Well, the offending code seems to be this line in java.lang.Thread: private static final RuntimePermission SUBCLASS_IMPLEMENTATION_PERMISSION = new RuntimePermission("enableContextClassLoaderOverride"); where "new RuntimePermission(...)" results in your observed error if the supplied string returns 0 for length(). So I would assume, that after you modified java.lang.String the magic trickery within the VM that creates String objects from String literals in class files is broken with regard to your modified String class. I'd try to look there for the problem. Sorry, that I cannot be of more help. cu- Hide quoted text - - Show quoted text -- Hide quoted text - - Show quoted text - Back to top Moritz Hammer Guest Posted: Mon Mar 26, 2007 11:43 am    Post subject: Re: modifying java.lang.String.java On Sun, 25 Mar 2007 19:10:28 -0700, danwichs (AT) gmail (DOT) com wrote: Quote: I think the error is caused by the intern() function in String.java. This is implemented in native code. I bet it somehow messes up. Have you considered AspectJ or some other kind of bytecode instrumentation? I cannot predict whether it will work, but it might be worth a try, and your project would become much more publishable. But apart from technical realizability, I think Tom is right; your approach should not be dependent on the ability to modify the String class. Regards, Moritz Back to top Tom Hawtin Guest Posted: Mon Mar 26, 2007 1:30 pm    Post subject: Re: modifying java.lang.String.java danwichs (AT) gmail (DOT) com wrote: Quote: I'm trying to modify java.lang.String.java and add the modified String.class to rt.jar [THIS IS FOR MYSELF ONLY AND WILL NOT BE DEPLOYED]. I cannot add "private final boolean tainted[] = new Wouldn't it be easier to use WeakHashMap<String,boolean[]> (or something similar with the map value as a meaningful class type)? Quote: boolean[5];" to String.java. If I do, it still compiles and I can add it to rt.jar and compile a test program against it. However, the JVM crashes with a strange message: java.lang.IllegalArgumentException: name can't be empty at java.security.BasicPermission.init(Unknown Source) at java.security.BasicPermission.<init>(Unknown Source) at java.lang.RuntimePermission.<init>(Unknown Source) at java.lang.Thread.<clinit>(Unknown Source) So if you look at the source, it appears that the literal string "enableContextClassLoaderOverride" has a length of zero. As someone else mentioned it will be in the native code loading strings from class files. The exact details I don't know. Moving your field after the existing fields might help. It might be that reference fields are treated differently to primitive fields for object layout. I suggest your approach is probably poor. Tom Hawtin Back to top danwichs@gmail.com Guest Posted: Mon Mar 26, 2007 6:49 pm    Post subject: Re: modifying java.lang.String.java On Mar 26, 7:43 am, Moritz Hammer <newsgroup...@hammer-tour.com> wrote: Quote: On Sun, 25 Mar 2007 19:10:28 -0700, danwi...@gmail.com wrote: I think the error is caused by the intern() function in String.java. This is implemented in native code. I bet it somehow messes up. Have you considered AspectJ or some other kind of bytecode instrumentation? I cannot predict whether it will work, but it might be worth a try, and your project would become much more publishable. But apart from technical realizability, I think Tom is right; your approach should not be dependent on the ability to modify the String class. Regards, Moritz I tried instrumentation using JavaAssist and got the same problem. The reasons for why I want to modify the string class are rather complex so I'd rather not get into them. 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