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Re: Debugging libgcj on cygwin

From: Thomas Pfaff <tpfaff at gmx dot net>
To: java at gcc dot gnu dot org
Cc: Danny Smith <dannysmith at clear dot net dot nz>
Date: Mon, 30 Jun 2003 10:02:32 +0200
Subject: Re: Debugging libgcj on cygwin
References: <3EF6F3BD.5090608@gmx.net>

Thomas Pfaff wrote:

Replying to myself:

Hi all,

i try to create gcj on cygwin. Gcc is gcc 3.3 with a cygwin-mingw specific patch from Danny Smith and configured with

../gcc-3.3/configure --prefix=/usr/gcc-3.3 --enable-sjlj-exceptions --disable-shared --enable-threads=posix --enable-languages=c,c++,java --enable-libgcj --disable-nls --target=i686-cygwin --host=i686-cygwin --with-gcc --with-gnu-ld --with-gnu-as --disable-win32-registry --without-included-gettext --with-system-zlib --disable-version-specific-runtime-libs --enable-haifa --enable-interpreter

Building gcj went fine, running the testsuite however results in segmentation faults on every compiled app. The backtrace is always the same for any app:

Program received signal SIGSEGV, Segmentation fault. _Jv_InterpMethod::run(void*, ffi_raw*) (this=0x1014be60, retp=0x22f730, args=0x22f750) at ../../../gcc-3.3/libjava/include/java-interp.h:230 230 next = *n;

which is located at java-interp.h:230
  _Jv_MethodChain (const _Jv_InterpMethod *s, _Jv_MethodChain **n)
  {
    self = s;
    ptr = n;
    next = *n;
    *n = this;
  }
(gdb) bt #0 _Jv_InterpMethod::run(void*, ffi_raw*) (this=0x1014be60, retp=0x22f730, args=0x22f750) at ../../../gcc-3.3/libjava/include/java-interp.h:230 #1 0x0022f698 in ?? () #2 0x00461e7a in ffi_closure_raw_SYSV (closure=0x0) at ../../../gcc-3.3/libffi/src/x86/ffi.c:379 #3 0x0040e219 in java::lang::Class::newInstance() (this=0x10148e80) at ../../../gcc-3.3/libjava/java/lang/natClass.cc:719 #4 0x00463973 in gnu.gcj.convert.UnicodeToBytes.getEncoder(java.lang.String) (encoding=0x10130c60) at ../../../gcc-3.3/libjava/gnu/gcj/convert/UnicodeToBytes.java:96 #5 0x004635b0 in gnu.gcj.convert.UnicodeToBytes.getDefaultEncoder() () at ../../../gcc-3.3/libjava/gnu/gcj/convert/UnicodeToBytes.java:62 #6 0x0043635e in java.io.PrintStream.PrintStream(java.io.OutputStream, boolean) (this=0x10130c80, out=0x10144678, af=269684225) at ../../../gcc-3.3/libjava/java/io/PrintStream.java:241 #7 0x0040661c in java.lang.System.<clinit>() () at ../../../gcc-3.3/libjava/java/lang/System.java:135 #8 0x0040e47d in java::lang::Class::initializeClass() (this=0x54dc10) at ../../../gcc-3.3/libjava/java/lang/natClass.cc:814 #9 0x00406008 in java.lang.System.getProperty(java.lang.String) (key=0x10131f00) at ../../../gcc-3.3/libjava/java/lang/System.java:393 #10 0x004154e3 in java.lang.Throwable.<clinit>() () at ../../../gcc-3.3/libjava/java/lang/Throwable.java:403 #11 0x0040e47d in java::lang::Class::initializeClass() (this=0x550250) at ../../../gcc-3.3/libjava/java/lang/natClass.cc:814 #12 0x0040e4d0 in java::lang::Class::initializeClass() (this=0x54dd70) at ../../../gcc-3.3/libjava/java/lang/Class.h:265 #13 0x0040e4d0 in java::lang::Class::initializeClass() (this=0x557a10) at ../../../gcc-3.3/libjava/java/lang/Class.h:265 #14 0x0040e4d0 in java::lang::Class::initializeClass() (this=0x54eff0) at ../../../gcc-3.3/libjava/java/lang/Class.h:265 #15 0x00402a93 in _Jv_AllocObjectNoFinalizer (klass=0x54eff0, size=24) at ../../../gcc-3.3/libjava/java/lang/Class.h:265 #16 0x00402abe in _Jv_AllocObject (klass=0x54eff0, size=24) at ../../../gcc-3.3/libjava/prims.cc:415 #17 0x00403a10 in _Jv_CreateJavaVM(void*) () at ../../../gcc-3.3/libjava/prims.cc:921 #18 0x00403c52 in _Jv_RunMain(java::lang::Class*, char const*, int, char const**, bool) (klass=0x54d0b0, name=0x0, argc=1, argv=0x101023f8, is_jar=false) at ../../../gcc-3.3/libjava/prims.cc:973 #19 0x00403e1f in JvRunMain (klass=0x54d0b0, argc=1, argv=0x101023f8) at ../../../gcc-3.3/libjava/prims.cc:1011 #20 0x0040108c in main (argc=1, argv=0x101023f8) at /c/DOKUME~1/pfaff/LOKALE~1/Temp/ccIEfgxx.i:11

It seems that n does not contain a valid address. This happens only if the app is running from a different directory (testsuite/Final.exe for example), if it is called from the same directory (./Final.exe) it works.

After some debug sessions i think that i got the problem:

When running the testsuite from the libjava directory
gnu.gcj.convert.UnicodeToBytes.getDefaultEncoder() tries to load the
encoder class for "gnu.gcj.convert.Output_ASCII". It will search for
this class on the filesystem first and sees that a class exists at
"./gnu/gcj/convert/Output_ASCII.class".

An attempt to load and run this class via _Jv_InterpMethod::run is made.
A call to java::lang::Thread *thread = java::lang::Thread::currentThread
is made which returns NULL since the main thread is not initialized yet
(a call to _Jv_AttachCurrentThread will be later done in _Jv_RunMain,
the backtrace above shows that it is still in _Jv_CreateJavaVM).

What makes me wonder is that this seems to happen only on cygwin.

I have created a small patch to URLClassLoader.java

--- URLClassLoader.java.org 2003-01-02 10:36:05.000000000 +0100 +++ URLClassLoader.java 2003-06-30 09:54:03.000000000 +0200 @@ -756,6 +756,12 @@ public class URLClassLoader extends Secu protected Class findClass(final String className) throws ClassNotFoundException { + // Do not try to load a class from URL + // until the calling thread is registered + Thread current = Thread.currentThread(); + if (current == null) + throw new ClassNotFoundException(className + " not found in " + urls); + // Just try to find the resource by the (almost) same name String resourceName = className.replace('.', '/') + ".class"; Resource resource = findURLResource(resourceName);

With this patch the test result was

Running /usr/src/gcc-3/gcc-3.3/libjava/testsuite/libjava.lang/lang.exp ... FAIL: Array_3 execution - source compiled test FAIL: Array_3 execution - bytecode->native test FAIL: Array_3 -O execution - source compiled test FAIL: Array_3 -O execution - bytecode->native test FAIL: Divide_1 execution - source compiled test FAIL: Divide_1 execution - bytecode->native test FAIL: Divide_1 -O execution - source compiled test FAIL: Divide_1 -O execution - bytecode->native test FAIL: SyncTest execution - bytecode->native test FAIL: SyncTest -O execution - bytecode->native test FAIL: TLtest execution - source compiled test FAIL: TLtest output - bytecode->native test FAIL: TLtest -O execution - source compiled test FAIL: TLtest -O execution - bytecode->native test FAIL: TestProxy execution - source compiled test FAIL: TestProxy execution - bytecode->native test FAIL: TestProxy -O execution - source compiled test FAIL: TestProxy -O execution - bytecode->native test FAIL: Thread_Alive execution - source compiled test FAIL: Thread_Alive execution - bytecode->native test FAIL: Thread_Alive -O execution - source compiled test FAIL: Thread_Alive -O execution - bytecode->native test FAIL: Thread_Join execution - source compiled test FAIL: Thread_Join execution - bytecode->native test FAIL: Thread_Join -O execution - source compiled test FAIL: Thread_Join -O execution - bytecode->native test FAIL: Thread_Wait_2 execution - source compiled test FAIL: Thread_Wait_2 execution - bytecode->native test FAIL: Thread_Wait_2 -O execution - source compiled test FAIL: Thread_Wait_2 -O execution - bytecode->native test FAIL: Thread_Wait_Interrupt execution - source compiled test FAIL: Thread_Wait_Interrupt execution - bytecode->native test FAIL: Thread_Wait_Interrupt -O execution - source compiled test FAIL: Thread_Wait_Interrupt -O execution - bytecode->native test FAIL: Throw_2 execution - source compiled test FAIL: Throw_2 execution - bytecode->native test FAIL: Throw_2 -O execution - source compiled test FAIL: Throw_2 -O execution - bytecode->native test Running /usr/src/gcc-3/gcc-3.3/libjava/testsuite/libjava.loader/loader.exp ... FAIL: /usr/src/gcc-3/BUILD.cygwin/i686-cygwin/libjava/testsuite/TestEarlyGC.exe output - /usr/src/gc c-3/BUILD.cygwin/i686-cygwin/libjava/testsuite/TestEarlyGC.exe FAIL: /usr/src/gcc-3/BUILD.cygwin/i686-cygwin/libjava/testsuite/TestLeak.exe execution - /usr/src/gc c-3/BUILD.cygwin/i686-cygwin/libjava/testsuite/TestLeak.exe FAIL: /usr/src/gcc-3/BUILD.cygwin/i686-cygwin/libjava/testsuite/TestMultiple.exe execution - /usr/sr c/gcc-3/BUILD.cygwin/i686-cygwin/libjava/testsuite/TestMultiple.exe FAIL: /usr/src/gcc-3/BUILD.cygwin/i686-cygwin/libjava/testsuite/TestParent.exe execution - /usr/src/ gcc-3/BUILD.cygwin/i686-cygwin/libjava/testsuite/TestParent.exe Running /usr/src/gcc-3/gcc-3.3/libjava/testsuite/libjava.mauve/mauve.exp ...

=== libjava Summary ===

# of expected passes            2343
# of unexpected failures        55
# of expected failures          29
# of untested testcases         52


The java interpreter seems to have a similar problem, therefore i
configured with --disable-interpreter, the jni tests have also failed.

Thomas

Follow-Ups:
- Re: Debugging libgcj on cygwin
  - From: Tom Tromey

References:
- Debugging libgcj on cygwin
  - From: Thomas Pfaff

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