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java/8025: ICE when bytecode does array access on null
- From: ericb <ebb9 at email dot byu dot edu>
- To: gcc-gnats at gcc dot gnu dot org
- Date: Tue, 24 Sep 2002 17:30:55 -0600
- Subject: java/8025: ICE when bytecode does array access on null
>Number: 8025
>Category: java
>Synopsis: ICE when bytecode does array access on null
>Confidential: no
>Severity: serious
>Priority: medium
>Responsible: unassigned
>State: open
>Class: ice-on-legal-code
>Submitter-Id: net
>Arrival-Date: Tue Sep 24 16:36:00 PDT 2002
>Closed-Date:
>Last-Modified:
>Originator: Eric Blake
>Release: 3.1 20020501 (prerelease)
>Organization:
>Environment:
System: Linux quaffle 2.4.9-31smp #1 SMP Tue Feb 26 06:55:00 EST 2002 i686 unknown
Architecture: i686
host: i686-pc-linux-gnu
build: i686-pc-linux-gnu
target: i686-pc-linux-gnu
configured with: ../gcc/configure --enable-languages=c,c++,java --prefix=/fpga3/users/eblake/gcc
>Description:
The java .class file verifier is croaking when accessing array
elements of a null-typed local variable. This affects the 16
instructions [abcsilfd]a{load|store}.
Further analysis: In .java source code, no variable can have the null
type. But in .class bytecode, aconst_null is legal and has its own
type. The null type can therefore appear as the arrayref argument for
array stores and array loads - this must generate a
NullPointerException at runtime, but it is legal code and must pass
the verifier.
>How-To-Repeat:
Compile this program (which demonstrates the bug for iaload; the other
15 bytecodes with problems are similar) to bytecode, then from
bytecode to native.
$ cat Foo.java
class Foo
{
void m()
{
int[] a = null;
int i = a[0];
}
}
$ gcj -C Foo.java
$ gcj -o Foo --main=Foo Foo.class
Foo.java: In class `Foo':
Foo.java: In method `Foo.m()':
Foo.java:6: Internal compiler error in build_java_check_indexed_type, at java/expr.c:890
Please submit a full bug report,
with preprocessed source if appropriate.
See <URL:http://www.gnu.org/software/gcc/bugs.html> for instructions.
$
>Fix:
The following hack forces the compiler to store type information and
thus avoid the ICE:
class Foo1
{
void m()
{
int[] a = null;
Object o = a;
a = (int[]) o; // this causes a checkcast bytecode to appear,
// now the verifier knows a is int[] instead of null
int i = a[0]; // correctly throws the NullPointerException
}
}
>Release-Note:
>Audit-Trail:
>Unformatted: