Re: [PATCH] [JAVA] Double.parseDouble(null) throw NullPointerException

Re: [PATCH] [JAVA] Double.parseDouble(null) throw NullPointerException

[Jie Liu]

Hi,

When I use gcj on an RTOS(RTEMS), Double.parseDouble(null) throw
NumberFormatException, but it should throw NullPointerException. So I
add the patch below:

Index: natVMDouble.cc
===================================================================
--- natVMDouble.cc	(revision 172224)
+++ natVMDouble.cc	(working copy)
@@ -19,6 +19,7 @@
 #include <java/lang/VMDouble.h>
 #include <java/lang/Character.h>
 #include <java/lang/NumberFormatException.h>
+#include <java/lang/NullPointerException.h>
 #include <jvm.h>

 #include <stdio.h>
@@ -162,6 +163,9 @@
 jdouble
 java::lang::VMDouble::parseDouble(jstring str)
 {
+  if(str == NULL)
+      throw new NullPointerException();
+
   int length = str->length();

   while (length > 0

The testsuite/Throw_2.java has been PASS after this patch. what do you
think about this patch?

Thanks,
Jie

Re: [PATCH] [JAVA] Double.parseDouble(null) throw NullPointerException

[Tom Tromey]

>>>>> "Jie" == Jie Liu <lj8175@gmail.com> writes:

Jie> +  if(str == NULL)
Jie> +      throw new NullPointerException();
Jie> +
Jie>    int length = str->length();

Why doesn't 'str->length()' throw the NPE?

Tom

Re: [PATCH] [JAVA] Double.parseDouble(null) throw NullPointerException

[Jie Liu]

Hi Tom,

RTEMS does not have virtual memory management, so there is no error
when access the 0 address on rtems.
So 'str->length()' donot throw NPE and just return an meaningless value.

Ps: There is a test:
http://code.google.com/p/rtemsgcj/source/browse/trunk/algorithm/20110810NPE/?r=127,
npe.c is the main file and *.scn is the output.

Thanks,
Jie

2011/8/8 Tom Tromey <tromey@redhat.com>:
>>>>>> "Jie" == Jie Liu <lj8175@gmail.com> writes:
>
> Jie> +  if(str == NULL)
> Jie> +      throw new NullPointerException();
> Jie> +
> Jie>    int length = str->length();
>
> Why doesn't 'str->length()' throw the NPE?
>
> Tom
>
=========== The first mail, for adding Joel ===========
Hi,

When I use gcj on an RTOS(RTEMS), Double.parseDouble(null) throw
NumberFormatException, but it should throw NullPointerException. So I
add the patch below:

Index: natVMDouble.cc
===================================================================
--- natVMDouble.cc	(revision 172224)
+++ natVMDouble.cc	(working copy)
@@ -19,6 +19,7 @@
 #include <java/lang/VMDouble.h>
 #include <java/lang/Character.h>
 #include <java/lang/NumberFormatException.h>
+#include <java/lang/NullPointerException.h>
 #include <jvm.h>

 #include <stdio.h>
@@ -162,6 +163,9 @@
 jdouble
 java::lang::VMDouble::parseDouble(jstring str)
 {
+  if(str == NULL)
+      throw new NullPointerException();
+
   int length = str->length();

   while (length > 0

The testsuite/Throw_2.java has been PASS after this patch. what do you
think about this patch?

Thanks,
Jie

Re: [PATCH] [JAVA] Double.parseDouble(null) throw NullPointerException

[Tom Tromey]

>>>>> "Jie" == Jie Liu <lj8175@gmail.com> writes:

Jie> RTEMS does not have virtual memory management, so there is no error
Jie> when access the 0 address on rtems.
Jie> So 'str->length()' donot throw NPE and just return an meaningless value.

If you compile the Java parts of the library with -fcheck-references, it
should work.  This is something you have to set up as part of the port,
as it is decided at (libgcj-) configure time.

This won't help with the native code.  IIRC in the end we just gave up
on that; if you wanted real correctness you would have to add a null
check at every dereference in the C++ code.  I believe Andrew had a g++
patch to do this in the compiler, but it was rejected.

Tom

Re: [PATCH] [JAVA] Double.parseDouble(null) throw NullPointerException

[Jie Liu]

2011/8/10 Tom Tromey <tromey@redhat.com>:
>>>>>> "Jie" == Jie Liu <lj8175@gmail.com> writes:
>
> Jie> RTEMS does not have virtual memory management, so there is no error
> Jie> when access the 0 address on rtems.
> Jie> So 'str->length()' donot throw NPE and just return an meaningless value.
>
> If you compile the Java parts of the library with -fcheck-references, it
> should work.  This is something you have to set up as part of the port,
> as it is decided at (libgcj-) configure time.
>
Thank you very much for the information you provide. :)

I add the following patch for -fcheck-references:
Index: configure.host
===================================================================
--- configure.host	(revision 172224)
+++ configure.host	(working copy)
@@ -347,8 +347,14 @@
 	slow_pthread_self=
 	can_unwind_signal=yes
 	;;
+  *-*-rtems*)
+	can_unwind_signal=no
+	CHECKREFSPEC=-fcheck-references
+	DIVIDESPEC=-fuse-divide-subroutine
+	;;
 esac

+
 case "${host}" in
   *-cygwin* | *-mingw*)
 	fallback_backtrace_h=sysdep/i386/backtrace.h

And we can see the following have -fcheck-references:
/mnt/gcj/mytoolchain/libexec/gcc/i386-rtems/4.7.0/jc1
/tmp/ccYuDgD5.jar -fsource-filename=HelloWorld.java
-fhash-synchronization -fuse-divide-subroutine -fcheck-references
-fuse-boehm-gc -fkeep-inline-functions -quiet -dumpbase
HelloWorld.java -mtune=i386 -march=i386 -auxbase HelloWorld -g -g
-Wall -version -fsaw-java-file
-fbootclasspath=./:/usr/share/java/ecj.jar:/mnt/gcj/mytoolchain/share/java/libgcj-4.7.0.jar
-faux-classpath /tmp/cc6nFx0I.zip -o /tmp/ccCuf7ju.s
GNU Java (GCC) version 4.7.0 20110409 (experimental) (i386-rtems)

But it does not work as we want, is there something wrong?

Thanks,
Jie

> This won't help with the native code.  IIRC in the end we just gave up
> on that; if you wanted real correctness you would have to add a null
> check at every dereference in the C++ code.  I believe Andrew had a g++
> patch to do this in the compiler, but it was rejected.
>
> Tom
>

Re: [PATCH] [JAVA] Double.parseDouble(null) throw NullPointerException

[Tom Tromey]

>>>>> "Jie" == Jie Liu <lj8175@gmail.com> writes:

Jie> +  *-*-rtems*)
Jie> +	can_unwind_signal=no
Jie> +	CHECKREFSPEC=-fcheck-references
Jie> +	DIVIDESPEC=-fuse-divide-subroutine
Jie> +	;;

This part is OK with a ChangeLog entry.

Jie> +

Spurious newline addition.

Jie> But it does not work as we want, is there something wrong?

Did you rebuild all of libgcj?

If you did, then I don't know, you'll have to debug it, sorry.

I vaguely recollect that -fcheck-references adds a check for 'this' at
the start of final methods.  If I'm misremembering, then that is
probably the problem.

Tom

Re: [PATCH] [JAVA] Double.parseDouble(null) throw NullPointerException

[Jie Liu]

> Jie> But it does not work as we want, is there something wrong?
>
> Did you rebuild all of libgcj?

Yes. :)
>
> If you did, then I don't know, you'll have to debug it, sorry.
>
> I vaguely recollect that -fcheck-references adds a check for 'this' at
> the start of final methods.  If I'm misremembering, then that is
> probably the problem.
>
The method length() is not a final method, as java/lang/String.java line 447:

  public int length()
  {
    return count;
  }

Is this the problem?

Thanks,
Jie
> Tom
>

Re: [PATCH] [JAVA] Double.parseDouble(null) throw NullPointerException

[Bryce McKinlay]

On Fri, Aug 12, 2011 at 8:27 AM, Jie Liu <lj8175@gmail.com> wrote:

> The method length() is not a final method, as java/lang/String.java line 447:
>
>  public int length()
>  {
>    return count;
>  }
>
> Is this the problem?

As String is a final class, all its methods are implicitly final.

Bryce

Re: [PATCH] [JAVA] Double.parseDouble(null) throw NullPointerException

[Jie Liu]

> If you did, then I don't know, you'll have to debug it, sorry.
>
> I vaguely recollect that -fcheck-references adds a check for 'this' at
> the start of final methods.  If I'm misremembering, then that is
> probably the problem.

In my debug, there appears no check for 'this' at start of String.length():

(gdb) s
java::lang::VMDouble::parseDouble (str=0x0)
    at ../../../gcc-trunk/libjava/java/lang/natVMDouble.cc:165
165	  int length = str->length();
(gdb) s
java.lang.String.length()int (this=@336e44)
    at /mnt/gcj/gcj-rtems-work/gcc-trunk/libjava/java/lang/String.java:451
451	    return count;
(gdb) p count
$5 = -268370093
(gdb) p this
$6 = (java.lang.String *) 0x0

Thanks,
Jie

Re: [PATCH] [JAVA] Double.parseDouble(null) throw NullPointerException

[Tom Tromey]

>>>>> "Jie" == Jie Liu <lj8175@gmail.com> writes:

Jie> In my debug, there appears no check for 'this' at start of String.length():

Yeah, I looked for uses of flag_check_references and didn't see one when
building a method's body.  So I guess I mis-remembered this.

In any case, the spot you found is just the tip of the problem.  Any
method call in any of the C++ code could potentially have the same
issue.

Tom

Re: [PATCH] [JAVA] Double.parseDouble(null) throw NullPointerException

[Andrew Haley]

On 08/07/2011 12:00 PM, Jie Liu wrote:

> When I use gcj on an RTOS(RTEMS), Double.parseDouble(null) throw
> NumberFormatException, but it should throw NullPointerException. So I
> add the patch below:
> 
> Index: natVMDouble.cc
> ===================================================================
> --- natVMDouble.cc	(revision 172224)
> +++ natVMDouble.cc	(working copy)
> @@ -19,6 +19,7 @@
>  #include <java/lang/VMDouble.h>
>  #include <java/lang/Character.h>
>  #include <java/lang/NumberFormatException.h>
> +#include <java/lang/NullPointerException.h>
>  #include <jvm.h>
> 
>  #include <stdio.h>
> @@ -162,6 +163,9 @@
>  jdouble
>  java::lang::VMDouble::parseDouble(jstring str)
>  {
> +  if(str == NULL)
> +      throw new NullPointerException();
> +
>    int length = str->length();
> 
>    while (length > 0
> 
> The testsuite/Throw_2.java has been PASS after this patch. what do you
> think about this patch?

This patch is not OK, and must not go in.

Look at the comment at the top of Throw_2:

// Check that NullPointerExceptions thrown from library code are
// caught.  This detects a number of failures that can be caused by
// libgcj being built incorrectly.  In particular, we ensure that a
// SEGV in native (i.e. C++) code in libgcj is handled correctly.

// Regrettably, we cannot guarantee that Double.parseDouble() will
// always be native code, or that it will never be inlined.  It could
// be argued that we should add a method to libgcj that will be
// guaranteed forever to be native, but I'm reluctant to add to the
// library for the sole purpose of performing this test.

Andrew.