Java stack unwind enhancements have been added
to enable it to support unwinding across Java frames and provide an
effective way to examine stack traces containing mixed language frames
(Java and C/C++) of both live Java processes and core files. This
has been implemented by adding subcommands for Java VM debugging to gdb.
The following table shows which Java versions
on PA-RISC and Integrity systems have the stack unwind and the gdb Java subcommands features. These features are available
in gdb version 4.5 and later versions.
Table 1-8 Java Version Information for gdb Java VM
Debugging Features
| Platform | Stack
Unwind Enhancements | Java Subcommands | GDB Version |
|---|
| PA-RISC 32-bit -pa11 (PA_RISC) | SDK 1.3.1.02+ | SDK 1.4.1.05+ | 4.5+ |
| PA-RISC 32-bit (PA_RISC2.0) | SDK 1.3.1.02+ | SDK 1.4.1.05+ | 4.5+ |
| PA-RISC 64-bit (PA_RISC2.0W) | SDK 1.4.1.01+ | SDK 1.4.1.05+ | 4.5+ |
| Integrity 32-bit (IA64N) | SDK 1.3.1.06+ | SDK 1.4.1.05+ | 4.5–5.2 |
| Integrity 64-bit (IA64W) | SDK 1.4.0.01+ | SDK 1.4.1.05+ | 4.5–5.2 |
| Integrity 32 (IA64N), 64-bit (IA64W) | SDK
1.4.2.10+ | SDK 1.4.2.10+ | *5.3+ |
| Integrity 32 (IA64N), 64-bit (IA64W) | JDK
1.5.0.03+ | JDK 1.5.0.03+ | *5.3+ |
* gdb version 5.3 requires
SDK 1.4.2.10 and later versions or JDK 1.5.0.03 and later versions
in order to use the Java VM debugging features.
To use this functionality, the GDB_JAVA_UNWINDLIB environment variable must be set to the path name of the Java unwind library. The following
list contains the default locations of the Java unwind libraries on
various systems. The examples are for SDK 1.4; if you are using JDK
1.5, substitute /opt/java1.5 for /opt/java1.4.
/opt/java1.4/jre/lib/PA_RISC/server/libjunwind.sl
/opt/java1.4/jre/lib/PA_RISC2.0/server/libjunwind.sl
/opt/java1.4/jre/lib/PA_RISC2.0W/server/libjunwind.sl
/opt/java1.4/jre/lib/IA64N/server/libjunwind.so
/opt/java1.4/jre/lib/IA64W/server/libjunwind.so
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The following examples show how to set the GDB_JAVA_UNWINDLIB environment variable. If you are using ksh on a PA-RISC machine, this is how you set the environment
variable for a 32–bit Java application:
$ export GDB_JAVA_UNWINDLIB=/opt/java1.4/jre/lib/PA_RISC2.0/server/libjunwind.sl |
Additionally, this is how you set the environment
variable on an Integrity machine for a 32–bit Java application:
$ export GDB_JAVA_UNWINDLIB=/opt/java1.4/jre/lib/IA64N/server/libjunwind.so
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If the SDK is installed in a location other than
the default, substitute the nondefault location for /opt/java1.4 in the previous commands.
Java Stack Unwind Features |
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The Java stack unwind features are useful for
troubleshooting problems in the Java Virtual Machine (VM). The Java
stack unwind features are:
View mixed language frames
information, including Java frames and C/C++ native frames, in a gdb backtrace
Distinguish various Java
frame types including interpreted, compiled, and adapter frames
View Java method name,
signature, and class package name for Java method frames
Additional stack unwind features are available
starting with SDK 1.4.2. These features fall into three categories:
Java stack unwind enhancements, Java heap support, and Java threads
support.
These additional features are available as part
of the Java stack unwind enhancements:
View Java compiled frame
inlined methods
View Java interpreted
or compiled frame specific information.
View Java interpreted
or compiled frame arguments and local variables
Disassemble Java method
bytecodes
Print out the Java unwind
table
These additional features are available as part
of the Java heap support:
View Java heap parameters
Print Java heap histogram
Find all the instances
of a given Java class
Find all the references
to a given object in the Java heap
Find out the object OOP
(object-oriented pointer) of the given field address
These additional features are available as part
of Java threads support:
View Java threads state
information
View current Java thread
information
View Java interpreted
frame monitors information
gdb Subcommands for Java VM Debugging |
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To view the gdb commands that
support Java VM debugging, enter help java at the gdb prompt.
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(gdb) help java Java and
JVM debugging commands.
List of java subcommands:
java args -- Show the current or specified Java frame arguments info
java bytecodes -- Disassemble the given Java method's bytecodes
java heap-histogram -- Show the Java heap object histogram
java instances -- Find all the instances of the given klassOop in the Java heap
java jvm-state -- Show Java virtual machine's current internal states
java locals -- Show the current or specified Java frame locals info
java mutex-info -- Print out details of the static mutexes
java object -- Print out the given Java object's fields info
java oop -- Find the Java object oop of the given Java heap address
java references -- Find all the references to the given Java object in the Java heap
java unwind-info -- Show the unwind info of the code where the given pc is located
java unwind-table -- Print out the dynamically generated Java Unwind Table
Type "help java" followed by java subcommand name for full documentation.
Command name abbreviations are allowed if unambiguous. |
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The following two tables list Java VM debugging
commands and Java subcommands:
Table 1-9 Java VM Debugging Commands
| backtrace | Print backtrace
of mixed Java and native frames |
| info frame | Print Java
frame specific information if this is a Java frame |
| info threads | Print state
information for all threads |
| thread | Print detailed
state information for the current thread |
Table 1-10 Java Subcommands
| java args | Show the current
or specified Java frame arguments information |
| java bytecodes | Disassemble
the given Java method's bytecodes |
| java heap-histogram | Show
the Java heap object histogram |
| java instances | Find
all the instances of the given klassOop in the Java heap |
| java jvm-state | Show the
current internal state of the Java VM |
| java locals | Show the
current or specified Java frame locals information |
| java object | Print the
given Java object's fields information |
| java oop | Find the Java
object OOP of the given Java heap address |
| java references | Find
all the references to the given Java object in the Java heap |
| java unwind-info | Show
the unwind information of the code where the given pc is located |
| java unwind-table | Print
the dynamically generated Java unwind table |
Enter help java followed by
the subcommand name for full documentation. Command name abbreviations
are allowed if they are unambiguous.
The following examples illustrate the gdb command-line options for invoking gdb on a core file and on a hung process.
The first set of examples illustrate how to execute gdb on a core file:
Invoke gdb on a core file generated
when running a 32-bit Java application on an Integrity system with /opt/java1.4/bin/java:
$ gdb /opt/java1.4/bin/IA64N/java core.java |
Invoke gdb on a core file generated
when running a 64-bit Java application on an Integrity system with /opt/java1.4/bin/java -d64:
$ gdb /opt/java1.4/bin/IA64W/java core.java |
Invoke gdb on a core file generated
when running a 32-bit Java application on PA-RISC using /opt/java1.4/bin/java:
$ gdb /opt/java1.4/bin/PA_RISC2.0/java core.java |
Invoke gdb on a core file generated
when running a 64-bit Java application on PA-RISC using /opt/java1.4/bin/java:
$ gdb /opt/java1.4/bin/PA_RISC2.0W/java core.java |
When debugging a core file, it is good practice
to rename the file from core to another name
to avoid accidentally overwriting it.
If the Java and system libraries used by the failed
application reside in nonstandard locations, then the GDB_SHLIB_PATH environment variable must be set to specify
the location of the libraries.
The following example illustrates how to execute gdb on a hung process:
Determine the process id:
$ ps -u user1 | grep java
23989 pts/9 8:52 java |
Attach gdb to the running process:
$ gdb -p 23989
HP gdb 5.0 for HP Itanium (32 or 64 bit) and target HP-UX 11.2x.
Copyright 1986 - 2001 Free Software Foundation, Inc.
Hewlett-Packard Wildebeest 5.0 (based on GDB) is covered by the GNU General Public License.
Type "show copying" to see the conditions to change it and/or distribute copies.
Type "show warranty" for warranty/support.
Reading symbols from /opt/java1.4/bin/IA64N/java...
(no debugging symbols found)...done.
Attaching to program: /opt/java1.4/bin/IA64N/java, process 23989
(no debugging symbols found)...
Reading symbols from /usr/lib/hpux32/libpthread.so.1...
(no debugging symbols found)...done.
Reading symbols from /usr/lib/hpux32/libdl.so.1...
... |
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 | NOTE: If the version of gdb on the
system is older than version 4.5, it is necessary to specify the full
path of the Java executable to use the gdb subcommands.
For example:$ gdb /opt/java1.4/bin/PA_RISC2.0/java –p 23989 |
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A tutorial on gdb can be found
at the following webpage:
http://www.hp.com/go/wdb
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