Adding the Serviceability team to the thread since JVM/TI is owned
by them...
Dan
On 7/2/14 10:15 AM, Maynard Johnson wrote:
Cross-posting to see if Hotspot developers can help.
-Maynard
-------- Original Message --------
Subject: PowerPC issue: Some JVMTI dynamic code generated events have code size
of zero
Date: Wed, 25 Jun 2014 10:18:17 -0500
From: Maynard Johnson <mayna...@us.ibm.com>
To: ppc-aix-port-...@openjdk.java.net <ppc-aix-port-...@openjdk.java.net>
Hello, PowerPC OpenJDK folks,
I am just now starting to get involved in the OpenJDK project. My goal is to
ensure that the standard serviceability tools and tooling (jdb, JVMTI, jmap,
etc.) work correctly on the PowerLinux platform. I selected JVMTI to start
with since I have some experience from a client perspective with the JVMTI API.
An OSS profiling tool for which I am the maintainer (oprofile) provides an
agent library that implements the JVMTI API. Using this agent library to
profile Java apps on my Intel-based laptop with OpenJDK (using various
versions, up to current jdk9-dev) works fine. But the same profiling scenario
attempted on my PowerLinux box (POWER7/Fedora 20) fails miserably.
The oprofile agent library registers for callbacks for CompiledMethodLoad,
CompiledMethodUnload, and DynamicCodeGenerated. In the callback functions, it
writes information about the JVMTI event to a file. After profiling completes,
oprofile's post-processing phase involves interpreting the information from the
agent library's output file and generating an ELF file to represent the JITed
code. When I profile an OpenJDK app on my Power system, the post-processing
phase fails while trying to resolve overlapping symbols. The failure is due to
the fact that it is unexpectedly finding symbols with code size of zero
overlapping at the starting address of some other symbol with non-zero code
size. The symbols in question here are from DynamicCodeGenerated events.
Are these "code size=0" events valid? If so, I can fix the oprofile code to
handle them. If they're not valid, then below is some debug information I've collected
so far.
----------------------------
I instrumented JvmtiExport::post_dynamic_code_generated_internal (in
hotspot/src/share/vm/prims/jvmtiExport.cpp) to print a debug line when a symbol
with code size of zero was detected and then ran the following command:
java
-agentpath:<jdk9-install-dir>/jvm/openjdk-1.9.0-internal/demo/jvmti/CodeLoadInfo/lib/libCodeLoadInfo.so
-version
The debug output from my instrumentation was as follows:
Code size is ZERO!! Dynamic code generated event sent for flush_icache_stub;
code begin: 0x3fff68000080; code end: 0x3fff68000080
Code size is ZERO!! Dynamic code generated event sent for throw_exception;
code begin: 0x3fff68000a90; code end: 0x3fff68000a90
Code size is ZERO!! Dynamic code generated event sent for throw_exception;
code begin: 0x3fff68016600; code end: 0x3fff68016600
Code size is ZERO!! Dynamic code generated event sent for throw_exception;
code begin: 0x3fff68016600; code end: 0x3fff68016600
Code size is ZERO!! Dynamic code generated event sent for throw_exception;
code begin: 0x3fff68016600; code end: 0x3fff68016600
Code size is ZERO!! Dynamic code generated event sent for verify_oop; code
begin: 0x3fff6801665c; code end: 0x3fff6801665c
openjdk version "1.9.0-internal"
OpenJDK Runtime Environment (build 1.9.0-internal-mpj_2014_06_18_09_55-b00)
OpenJDK 64-Bit Server VM (build 1.9.0-internal-mpj_2014_06_18_09_55-b00,
mixed mode)
I don't have access to an AIX system to know if the same issue would be seen
there. Let me know if there's any other information I can provide.
Thanks for the help.
-Maynard
