From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 7811 invoked by alias); 2 Apr 2009 19:38:37 -0000 Received: (qmail 7305 invoked by uid 22791); 2 Apr 2009 19:38:35 -0000 X-SWARE-Spam-Status: No, hits=0.0 required=5.0 tests=AWL,BAYES_00,J_CHICKENPOX_65 X-Spam-Check-By: sourceware.org Received: from mta2.cl.cam.ac.uk (HELO mta2.cl.cam.ac.uk) (128.232.0.14) by sourceware.org (qpsmtpd/0.43rc1) with ESMTP; Thu, 02 Apr 2009 19:38:30 +0000 Received: from font.cl.cam.ac.uk ([128.232.9.85]) by mta2.cl.cam.ac.uk with esmtp (Exim 3.092 #1) id 1LpSk7-0005Dn-00 for java@gcc.gnu.org; Thu, 02 Apr 2009 20:38:27 +0100 Received: from srk31 by font.cl.cam.ac.uk with local (Exim 4.66) (envelope-from ) id 1LpSk7-00078a-C3 for java@gcc.gnu.org; Thu, 02 Apr 2009 20:38:27 +0100 Date: Thu, 02 Apr 2009 19:38:00 -0000 From: Stephen Kell To: java@gcc.gnu.org Subject: CNI and interface methods Message-ID: <20090402193827.GD4939@font.cl.cam.ac.uk> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline User-Agent: Mutt/1.5.17 (2007-11-01) X-IsSubscribed: yes Mailing-List: contact java-help@gcc.gnu.org; run by ezmlm Precedence: bulk List-Id: List-Id: List-Subscribe: List-Archive: List-Post: List-Help: , Sender: java-owner@gcc.gnu.org X-SW-Source: 2009-04/txt/msg00003.txt.bz2 Hi, I'm using CNI for the first time and have hit a query. What exactly is and isn't supposed to work when invoking interface methods through *object* references (from C++, so I mean pointers), and passing these references around? The CNI chapter in the gcj manual says a lot about interface references, but not about the case of using object references where that object's class implements one or more interfaces. One thing that would appear to be worth mentioning is that clearly, passing them to methods wanting an interface reference won't compile without some sort of cast, since the gcjh-generated headers don't encode the subtyping relationship between interfaces and their implementing classes. I'm guessing a simple static cast isn't the right thing to do though, because I'm getting segfaults when I try. Specifically, I'm CNI-calling from C++ to Java code which, in turn, makes a call through an interface reference that I previously passed in to the Java object's constructor (i.e. I passed in an *object* reference, again from the C++ code, which required a cast as I just described). I get a segfault during the calling sequence of the interface call made by the Java code. The fault occurs just before the call to _Jv_LookupInterfaceMethodIdx. (This is all on a fresh build of vanilla gcc 4.3.3, on i686 Linux, by the way.) Program received signal SIGSEGV, Segmentation fault. [Switching to Thread 0xb7f5e8f0 (LWP 26704)] 0x080828ad in cakeJavaParser.toplevel()cakeJavaParser$toplevel_return () at cakeJavaParser.java:145 145 retval.start = input.LT(1); Current language: auto; currently java (gdb) bt #0 0x080828ad in cakeJavaParser.toplevel()cakeJavaParser$toplevel_return () at cakeJavaParser.java:145 #1 0x0805a4e2 in cake::request::process (this=@bffd0c18) at cake.cpp:33 #2 0x0805a7da in main (argc=2, argv=@bffd0cd4) at main.cpp:52 (Possibly significant: in earlier test runs, with a previous build of my code, I was getting the segfault *during* the call to _Jv_LookupInterfaceMethodIdx, with iface->ioffsets being null when it probably shouldn't. I can't reproduce that now for some reason.) The extent of my CNI code is JvCreateJavaVM(NULL); JvAttachCurrentThread(NULL, NULL); JvInitClass(&java::lang::System::class$); and shortly afterwards org::antlr::runtime::ANTLRInputStream *stream = new org::antlr::runtime::ANTLRInputStream(in_file); cakeJavaLexer *lexer = new cakeJavaLexer((org::antlr::runtime::CharStream*) stream); org::antlr::runtime::CommonTokenStream *tokenStream = new org::antlr::runtime::CommonTokenStream((org::antlr::runtime::TokenSource*) lexer); cakeJavaParser *parser = new cakeJavaParser((org::antlr::runtime::TokenStream*) tokenStream); parser->toplevel(); where the last statement triggers the segfault. The toplevel() method is Java code; it immediately calls a method on lexer (the object I passed earlier) and it's this call whose dispatch fails. Should this code work? I thought about class initialization, but having read the docs, it wouldn't appear that I need to add any JvInitClass calls manually in this case. There's a tarball at which should be sufficient to reproduce the above (just do 'make test'), unless I've forgotten to include something. Let me know if there's any more details that would be useful. Thanks for reading! Any answers or ideas appreciated, Stephen.