RFR(M): 8201375: Add the AllowArchivingWithJavaAgent diagnostic vm option to allow the use of the -javaagent option during CDS dumping

Discussion:

Jiangli Zhou

2018-11-15 18:56:59 UTC

Permalink

+1

Adding serviceability-dev mailing list. It would be good to have this
reviewed by the JVMTI experts also to make sure all cases are covered.

Thanks,

Jiangli

Hi Calvin,
The changes look good.
Thanks
- Ioi

bug: https://bugs.openjdk.java.net/browse/JDK-8201375
webrev: http://cr.openjdk.java.net/~ccheung/8201375/webrev.00/
This change is for adding a diagnostic vm option
(AllowArchivingWithJavaAgent) to allow the -javaagent in the command
line during CDS dumping. Please refer to the corresponding CSR
(https://bugs.openjdk.java.net/browse/JDK-8213813) for details.
Testing: ran hs-tier{1,2,3} tests through mach5.
thanks,
Calvin

Calvin Cheung

2018-11-15 22:50:24 UTC

Permalink

Thanks for the review, Ioi and Jiangli.

Calvin

Post by Jiangli Zhou
+1
Adding serviceability-dev mailing list. It would be good to have this
reviewed by the JVMTI experts also to make sure all cases are covered.
Thanks,
Jiangli

Hi Calvin,
The changes look good.
Thanks
- Ioi

s***@oracle.com

2018-11-16 06:39:50 UTC

Permalink

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<div class="moz-cite-prefix">Hi Calvin, 
 
It seems the option name AllowArchivingWithJavaAgent is not right. 
In fact, it is about JVMTI (native) agents: <pre> // Create agents for -agentlib: -agentpath: and converted -Xrun // Invokes Agent_OnLoad // Called very early -- before JavaThreads exist void Threads::create_vm_init_agents() { + if (DumpSharedSpaces && !AllowArchivingWithJavaAgent) { + vm_exit_during_cds_dumping( + "Must enable AllowArchivingWithJavaAgent in order to run Java agent during CDS dumping"); + } extern struct JavaVM_ main_vm; AgentLibrary* agent; JvmtiExport::enter_onload_phase(); for (agent = Arguments::agents(); agent != NULL; agent = agent->next()) { + // CDS dumping does not support native JVMTI agent + if (DumpSharedSpaces && !agent->is_instrument_lib()) { + vm_exit_during_cds_dumping("CDS dumping does not support native JVMTI agent, name", agent->name());
+ }
+ 
 OnLoadEntry_t on_load_entry = lookup_agent_on_load(agent);</pre>
The flags -agentlib and -agentpath are to run JVMTI (native)
agents, 
and Agent_OnLoad is an entrypoint in native agent library. 
So, I'm thinking if it'd make sense to rename the option to
something like below: 
AllowArchivingWithJVMTIAgent or 
AllowArchivingWithNativeAgent or 
AllowArchivingWithAgent 
 
 
<a class="moz-txt-link-freetext" href="http://cr.openjdk.java.net/%7Eccheung/8201375/webrev.00/src/hotspot/share/memory/filemap.cpp.frames.html">http://cr.openjdk.java.net/%7Eccheung/8201375/webrev.00/src/hotspot/share/memory/filemap.cpp.frames.html</a> 
<pre> 212 _allow_archiving_with_java_agent = AllowArchivingWithJavaAgent;
...

1350 if (_allow_archiving_with_java_agent && !AllowArchivingWithJavaAgent) {
1351 FileMapInfo::fail_continue("The setting of the AllowArchivingWithJavaAgent is different "
1352 "from the setting in the shared archive.");
1353 return false;
1354 }

The _allow_archiving_with_java_agent is initialized with the AllowArchivingWithJavaAgent at line 212.
It is not clear from scratch how these two values can be different at line 1350.
At least, some comment explaining it is needed. </pre>
 
Thanks, 
Serguei 
 
 
On 11/15/18 10:56, Jiangli Zhou wrote: 
</div>
<blockquote type="cite"
cite="mid:4cb6dc63-31da-f479-6a44-***@oracle.com">+1
 
 
Adding serviceability-dev mailing list. It would be good to have
this reviewed by the JVMTI experts also to make sure all cases are
covered.
 
 
Thanks,
 
 
Jiangli
 
 
 
On 11/15/18 9:29 AM, Ioi Lam wrote:
 
<blockquote type="cite">Hi Calvin,
 
 
The changes look good.
 
 
Thanks
 
 
- Ioi
 
 
On 11/14/18 4:40 PM, Calvin Cheung wrote:
 
<blockquote type="cite">bug:
<a class="moz-txt-link-freetext" href="https://bugs.openjdk.java.net/browse/JDK-8201375">https://bugs.openjdk.java.net/browse/JDK-8201375</a>
 
 
webrev: <a class="moz-txt-link-freetext" href="http://cr.openjdk.java.net/~ccheung/8201375/webrev.00/">http://cr.openjdk.java.net/~ccheung/8201375/webrev.00/</a>
 
 
This change is for adding a diagnostic vm option
(AllowArchivingWithJavaAgent) to allow the -javaagent in the
command line during CDS dumping. Please refer to the
corresponding CSR
(<a class="moz-txt-link-freetext" href="https://bugs.openjdk.java.net/browse/JDK-8213813">https://bugs.openjdk.java.net/browse/JDK-8213813</a>) for
details.
 
 
Testing: ran hs-tier{1,2,3} tests through mach5.
 
 
thanks,
 
Calvin
 
</blockquote>
</blockquote>
 
</blockquote>
 
</body>
</html>

s***@oracle.com

2018-11-16 06:49:45 UTC

Permalink

Daniel D. Daugherty

2018-11-16 14:08:38 UTC

Permalink

The flags -agentlib and -agentpath are to run JVMTI (native) agents,
and Agent_OnLoad is an entrypoint in native agent library.

The '-agentlib' and '-agentpath' options are used to load and execute
a native library via the Agent_OnLoad() entry point. However, the
agent does not have to use JVM/TI (it could be pure JNI):

$ java -help

Â Â Â -agentlib:<libname>[=<options>]
Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â load native agent library <libname>, e.g. -agentlib:hprof
Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â see also, -agentlib:jdwp=help and -agentlib:hprof=help
Â Â Â -agentpath:<pathname>[=<options>]
Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â load native agent library by full pathname

The '-javaagent' option is used to load and execute a Java agent:

Â Â Â -javaagent:<jarpath>[=<options>]
Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â load Java programming language agent, see
java.lang.instrument

so I agree that the option is misnamed (a bit), but the reasons
needed to be clarified.

Dan

Hi Calvin,
It seems the option name AllowArchivingWithJavaAgent is not right.
*// Create agents for -agentlib: -agentpath: and converted -Xrun*
*// Invokes Agent_OnLoad*
*// Called very early -- before JavaThreads exist*
*void Threads::create_vm_init_agents() {*
*+ if (DumpSharedSpaces && !AllowArchivingWithJavaAgent) {*
*+ vm_exit_during_cds_dumping(*
*+ "Must enable AllowArchivingWithJavaAgent in order to run Java agent
during CDS dumping");*
*+ }*
*extern struct JavaVM_ main_vm;*
*AgentLibrary* agent;*
**
*JvmtiExport::enter_onload_phase();*
**
*for (agent = Arguments::agents(); agent != NULL; agent =
agent->next()) {*
*+ // CDS dumping does not support native JVMTI agent*
*+ if (DumpSharedSpaces && !agent->is_instrument_lib()) {*
*+ vm_exit_during_cds_dumping("CDS dumping does not support native
JVMTI agent, name", agent->name());*
*+ }*
*+ *
*OnLoadEntry_t on_load_entry = lookup_agent_on_load(agent);*
The flags -agentlib and -agentpath are to run JVMTI (native) agents,
and Agent_OnLoad is an entrypoint in native agent library.
So, I'm thinking if it'd make sense to rename the option to something
Â AllowArchivingWithJVMTIAgent or
Â AllowArchivingWithNativeAgent or
Â AllowArchivingWithAgent
http://cr.openjdk.java.net/%7Eccheung/8201375/webrev.00/src/hotspot/share/memory/filemap.cpp.frames.html
212 _allow_archiving_with_java_agent = AllowArchivingWithJavaAgent; ...
1350 if (_allow_archiving_with_java_agent &&
!AllowArchivingWithJavaAgent) { 1351 FileMapInfo::fail_continue("The
setting of the AllowArchivingWithJavaAgent is different " 1352 "from
the setting in the shared archive."); 1353 return false; 1354 } The
_allow_archiving_with_java_agent is initialized with the
AllowArchivingWithJavaAgent at line 212.
It is not clear from scratch how these two values can be different at
line 1350. At least, some comment explaining it is needed.
Thanks,
Serguei

Post by Jiangli Zhou
+1
Adding serviceability-dev mailing list. It would be good to have this
reviewed by the JVMTI experts also to make sure all cases are covered.
Thanks,
Jiangli

Hi Calvin,
The changes look good.
Thanks
- Ioi

bug: https://bugs.openjdk.java.net/browse/JDK-8201375
webrev: http://cr.openjdk.java.net/~ccheung/8201375/webrev.00/
This change is for adding a diagnostic vm option
(AllowArchivingWithJavaAgent) to allow the -javaagent in the
command line during CDS dumping. Please refer to the corresponding
CSR (https://bugs.openjdk.java.net/browse/JDK-8213813) for details.
Testing: ran hs-tier{1,2,3} tests through mach5.
thanks,
Calvin

Calvin Cheung

2018-11-16 17:26:18 UTC

Permalink

Serguei, Dan,

Thanks for taking a look.

I think the option name is correct but the comment for
Threads::create_vm_init_agents() is incorrect as I believe it will start
both Java native agents. Otherwise, my new tests won't work.

Below is my understanding:

In thread.cpp:

3697 if (Arguments::init_agents_at_startup()) {
3698 create_vm_init_agents();
3699 }

init_agents_at_startup() checks if the _agentList is empty in arguments.hpp:

static bool init_agents_at_startup() { return
!_agentList.is_empty(); }

In arguments.cpp, entries will be added to the _agentList during the
parsing of the -agentLib, -agentPath, and -javaagent arguments. See
lines around 2463-2502.
For the -agentLib and -agentPath args, the _agentList will be populated
via the add_init_agent() function. For the -javaagent, the _agentList
will be populated via the add_instrument_agent() function.

So in create_vm_init_agents(), it will just loop through the _agentList
and starts all the agents. There's a check for
!agent->is_instrument_agent() at line 4092 which is for not allowing any
JVMTI (native) agent to be run during dump time.

One more reply to Serguei's comment below...

thanks,
Calvin

Post by Daniel D. Daugherty

The flags -agentlib and -agentpath are to run JVMTI (native) agents,
and Agent_OnLoad is an entrypoint in native agent library.

The '-agentlib' and '-agentpath' options are used to load and execute
a native library via the Agent_OnLoad() entry point. However, the
$ java -help
-agentlib:<libname>[=<options>]
load native agent library <libname>, e.g.
-agentlib:hprof
see also, -agentlib:jdwp=help and -agentlib:hprof=help
-agentpath:<pathname>[=<options>]
load native agent library by full pathname
-javaagent:<jarpath>[=<options>]
load Java programming language agent, see
java.lang.instrument
so I agree that the option is misnamed (a bit), but the reasons
needed to be clarified.
Dan

Hi Calvin,
It seems the option name AllowArchivingWithJavaAgent is not right.
*// Create agents for -agentlib: -agentpath: and converted -Xrun*
*// Invokes Agent_OnLoad*
*// Called very early -- before JavaThreads exist*
*void Threads::create_vm_init_agents() {*
*+ if (DumpSharedSpaces && !AllowArchivingWithJavaAgent) {*
*+ vm_exit_during_cds_dumping(*
*+ "Must enable AllowArchivingWithJavaAgent in order to run Java
agent during CDS dumping");*
*+ }*
*extern struct JavaVM_ main_vm;*
*AgentLibrary* agent;*
**
*JvmtiExport::enter_onload_phase();*
**
*for (agent = Arguments::agents(); agent != NULL; agent =
agent->next()) {*
*+ // CDS dumping does not support native JVMTI agent*
*+ if (DumpSharedSpaces && !agent->is_instrument_lib()) {*
*+ vm_exit_during_cds_dumping("CDS dumping does not support native
JVMTI agent, name", agent->name());*
*+ }*
*+ *
*OnLoadEntry_t on_load_entry = lookup_agent_on_load(agent);*
The flags -agentlib and -agentpath are to run JVMTI (native) agents,
and Agent_OnLoad is an entrypoint in native agent library.
So, I'm thinking if it'd make sense to rename the option to something
AllowArchivingWithJVMTIAgent or
AllowArchivingWithNativeAgent or
AllowArchivingWithAgent
http://cr.openjdk.java.net/%7Eccheung/8201375/webrev.00/src/hotspot/share/memory/filemap.cpp.frames.html
212 _allow_archiving_with_java_agent = AllowArchivingWithJavaAgent; ...
1350 if (_allow_archiving_with_java_agent &&
!AllowArchivingWithJavaAgent) { 1351 FileMapInfo::fail_continue("The
setting of the AllowArchivingWithJavaAgent is different " 1352 "from
the setting in the shared archive."); 1353 return false; 1354 } The
_allow_archiving_with_java_agent is initialized with the
AllowArchivingWithJavaAgent at line 212.

The assignment at line 212 is for populating the archive header during
CDS dump time.

Post by Daniel D. Daugherty

It is not clear from scratch how these two values can be different at
line 1350. At least, some comment explaining it is needed.

The value retrieved from the archive header could be different from the
run time setting.
I will add a comment.

Post by Daniel D. Daugherty

Thanks,
Serguei

Post by Jiangli Zhou
+1
Adding serviceability-dev mailing list. It would be good to have
this reviewed by the JVMTI experts also to make sure all cases are
covered.
Thanks,
Jiangli

Hi Calvin,
The changes look good.
Thanks
- Ioi

bug: https://bugs.openjdk.java.net/browse/JDK-8201375
webrev: http://cr.openjdk.java.net/~ccheung/8201375/webrev.00/
This change is for adding a diagnostic vm option
(AllowArchivingWithJavaAgent) to allow the -javaagent in the
command line during CDS dumping. Please refer to the corresponding
CSR (https://bugs.openjdk.java.net/browse/JDK-8213813) for details.
Testing: ran hs-tier{1,2,3} tests through mach5.
thanks,
Calvin

s***@oracle.com

2018-11-16 17:45:53 UTC

Permalink

Hi Calvin,

Post by Calvin Cheung
Serguei, Dan,
Thanks for taking a look.
I think the option name is correct but the comment for
Threads::create_vm_init_agents() is incorrect as I believe it will
start both Java native agents. Otherwise, my new tests won't work.

It works because there is the system JVMTI (native) agent library
libinstrument.so that is supporting java agents.
It means that new option first impacts native agents and transitively
java agents as well via the libinstrument.so.

Dan already asked the question about your original reasoning/intention.
If your intention is to control java agent only then the fix is wrong as
the real impact is much bigger.
If you wanted to control all the agents then the new option name is
misleading.

Post by Calvin Cheung
3697   if (Arguments::init_agents_at_startup()) {
3698     create_vm_init_agents();
3699   }
init_agents_at_startup() checks if the _agentList is empty in
static bool init_agents_at_startup()      { return
!_agentList.is_empty(); }
In arguments.cpp, entries will be added to the _agentList during the
parsing of the -agentLib, -agentPath, and -javaagent arguments. See
lines around 2463-2502.
For the -agentLib and -agentPath args, the _agentList will be
populated via the add_init_agent() function. For the -javaagent, the
_agentList will be populated via the add_instrument_agent() function.
So in create_vm_init_agents(), it will just loop through the
_agentList and starts all the agents. There's a check for
!agent->is_instrument_agent() at line 4092 which is for not allowing
any JVMTI (native) agent to be run during dump time.
One more reply to Serguei's comment below...

Okay, thank you for the update!

Thanks,
Serguei

Post by Calvin Cheung
thanks,
Calvin

Post by Daniel D. Daugherty

The flags -agentlib and -agentpath are to run JVMTI (native) agents,
and Agent_OnLoad is an entrypoint in native agent library.

The '-agentlib' and '-agentpath' options are used to load and execute
a native library via the Agent_OnLoad() entry point. However, the
$ java -help
 -agentlib:<libname>[=<options>]
 load native agent library <libname>, e.g.
-agentlib:hprof
 see also, -agentlib:jdwp=help and -agentlib:hprof=help
 -agentpath:<pathname>[=<options>]
 load native agent library by full pathname
 -javaagent:<jarpath>[=<options>]
 load Java programming language agent, see
java.lang.instrument
so I agree that the option is misnamed (a bit), but the reasons
needed to be clarified.
Dan

Hi Calvin,
It seems the option name AllowArchivingWithJavaAgent is not right.
*// Create agents for -agentlib: -agentpath: and converted -Xrun*
*// Invokes Agent_OnLoad*
*// Called very early -- before JavaThreads exist*
*void Threads::create_vm_init_agents() {*
*+ if (DumpSharedSpaces && !AllowArchivingWithJavaAgent) {*
*+ vm_exit_during_cds_dumping(*
*+ "Must enable AllowArchivingWithJavaAgent in order to run Java
agent during CDS dumping");*
*+ }*
*extern struct JavaVM_ main_vm;*
*AgentLibrary* agent;*
**
*JvmtiExport::enter_onload_phase();*
**
*for (agent = Arguments::agents(); agent != NULL; agent =
agent->next()) {*
*+ // CDS dumping does not support native JVMTI agent*
*+ if (DumpSharedSpaces && !agent->is_instrument_lib()) {*
*+ vm_exit_during_cds_dumping("CDS dumping does not support native
JVMTI agent, name", agent->name());*
*+ }*
*+ *
*OnLoadEntry_t on_load_entry = lookup_agent_on_load(agent);*
The flags -agentlib and -agentpath are to run JVMTI (native) agents,
and Agent_OnLoad is an entrypoint in native agent library.
So, I'm thinking if it'd make sense to rename the option to
AllowArchivingWithJVMTIAgent or
AllowArchivingWithNativeAgent or
AllowArchivingWithAgent
http://cr.openjdk.java.net/%7Eccheung/8201375/webrev.00/src/hotspot/share/memory/filemap.cpp.frames.html
212 _allow_archiving_with_java_agent = AllowArchivingWithJavaAgent; ...
1350 if (_allow_archiving_with_java_agent &&
!AllowArchivingWithJavaAgent) { 1351 FileMapInfo::fail_continue("The
setting of the AllowArchivingWithJavaAgent is different " 1352 "from
the setting in the shared archive."); 1353 return false; 1354 } The
_allow_archiving_with_java_agent is initialized with the
AllowArchivingWithJavaAgent at line 212.

The assignment at line 212 is for populating the archive header during
CDS dump time.

Post by Daniel D. Daugherty

It is not clear from scratch how these two values can be different
at line 1350. At least, some comment explaining it is needed.

The value retrieved from the archive header could be different from
the run time setting.
I will add a comment.

Post by Daniel D. Daugherty

Thanks,
Serguei

Post by Jiangli Zhou
+1
Adding serviceability-dev mailing list. It would be good to have
this reviewed by the JVMTI experts also to make sure all cases are
covered.
Thanks,
Jiangli

Hi Calvin,
The changes look good.
Thanks
- Ioi

bug: https://bugs.openjdk.java.net/browse/JDK-8201375
webrev: http://cr.openjdk.java.net/~ccheung/8201375/webrev.00/
This change is for adding a diagnostic vm option
(AllowArchivingWithJavaAgent) to allow the -javaagent in the
command line during CDS dumping. Please refer to the
corresponding CSR
(https://bugs.openjdk.java.net/browse/JDK-8213813) for details.
Testing: ran hs-tier{1,2,3} tests through mach5.
thanks,
Calvin

Ioi Lam

2018-11-16 18:18:29 UTC

Permalink

Hi Calvin,

It works because there is the system JVMTI (native) agent library
libinstrument.so that is supporting java agents.
It means that new option first impacts native agents and transitively
java agents as well via the libinstrument.so.
Dan already asked the question about your original reasoning/intention.
If your intention is to control java agent only then the fix is wrong
as the real impact is much bigger.
If you wanted to control all the agents then the new option name is
misleading.

The intention of this change is:

Disallow all use of native and java agents by default. -- using agents
during dump time will cause undesirable side effects and make the CDS
archive unsuitable for production environments.

However, for testing CDS itself, we want to use the Java agent (to run
arbitrary Java code during dump time, such as causing GC at specific times).

As a result, what we are doing is:

+ Always disallow non-Java agents.
+ Allow java agents only if AllowArchivingWithJavaAgent is specified.

I think we should clean up the bug title and description if necessary.
However, the behavior of this patch is what we want. And I think the
naming of the AllowArchivingWithJavaAgent option is correct (as least in
the sense of "anything not explicitly allow are strictly forbidden" :-)

Thanks
- Ioi

Okay, thank you for the update!
Thanks,
Serguei

Post by Calvin Cheung
thanks,
Calvin

Post by Daniel D. Daugherty

The flags -agentlib and -agentpath are to run JVMTI (native) agents,
and Agent_OnLoad is an entrypoint in native agent library.

The '-agentlib' and '-agentpath' options are used to load and execute
a native library via the Agent_OnLoad() entry point. However, the
$ java -help
 -agentlib:<libname>[=<options>]
 load native agent library <libname>, e.g.
-agentlib:hprof
 see also, -agentlib:jdwp=help and
-agentlib:hprof=help
 -agentpath:<pathname>[=<options>]
 load native agent library by full pathname
 -javaagent:<jarpath>[=<options>]
 load Java programming language agent, see
java.lang.instrument
so I agree that the option is misnamed (a bit), but the reasons
needed to be clarified.
Dan

Hi Calvin,
It seems the option name AllowArchivingWithJavaAgent is not right.
*// Create agents for -agentlib: -agentpath: and converted -Xrun*
*// Invokes Agent_OnLoad*
*// Called very early -- before JavaThreads exist*
*void Threads::create_vm_init_agents() {*
*+ if (DumpSharedSpaces && !AllowArchivingWithJavaAgent) {*
*+ vm_exit_during_cds_dumping(*
*+ "Must enable AllowArchivingWithJavaAgent in order to run Java
agent during CDS dumping");*
*+ }*
*extern struct JavaVM_ main_vm;*
*AgentLibrary* agent;*
**
*JvmtiExport::enter_onload_phase();*
**
*for (agent = Arguments::agents(); agent != NULL; agent =
agent->next()) {*
*+ // CDS dumping does not support native JVMTI agent*
*+ if (DumpSharedSpaces && !agent->is_instrument_lib()) {*
*+ vm_exit_during_cds_dumping("CDS dumping does not support native
JVMTI agent, name", agent->name());*
*+ }*
*+ *
*OnLoadEntry_t on_load_entry = lookup_agent_on_load(agent);*
The flags -agentlib and -agentpath are to run JVMTI (native) agents,
and Agent_OnLoad is an entrypoint in native agent library.
So, I'm thinking if it'd make sense to rename the option to
AllowArchivingWithJVMTIAgent or
AllowArchivingWithNativeAgent or
AllowArchivingWithAgent
http://cr.openjdk.java.net/%7Eccheung/8201375/webrev.00/src/hotspot/share/memory/filemap.cpp.frames.html
212 _allow_archiving_with_java_agent = AllowArchivingWithJavaAgent; ...
1350 if (_allow_archiving_with_java_agent &&
!AllowArchivingWithJavaAgent) { 1351
FileMapInfo::fail_continue("The setting of the
AllowArchivingWithJavaAgent is different " 1352 "from the setting
in the shared archive."); 1353 return false; 1354 } The
_allow_archiving_with_java_agent is initialized with the
AllowArchivingWithJavaAgent at line 212.

The assignment at line 212 is for populating the archive header
during CDS dump time.

Post by Daniel D. Daugherty

It is not clear from scratch how these two values can be different
at line 1350. At least, some comment explaining it is needed.

The value retrieved from the archive header could be different from
the run time setting.
I will add a comment.

Post by Daniel D. Daugherty

Thanks,
Serguei

Post by Jiangli Zhou
+1
Adding serviceability-dev mailing list. It would be good to have
this reviewed by the JVMTI experts also to make sure all cases are
covered.
Thanks,
Jiangli

Hi Calvin,
The changes look good.
Thanks
- Ioi

bug: https://bugs.openjdk.java.net/browse/JDK-8201375
webrev: http://cr.openjdk.java.net/~ccheung/8201375/webrev.00/
This change is for adding a diagnostic vm option
(AllowArchivingWithJavaAgent) to allow the -javaagent in the
command line during CDS dumping. Please refer to the
corresponding CSR
(https://bugs.openjdk.java.net/browse/JDK-8213813) for details.
Testing: ran hs-tier{1,2,3} tests through mach5.
thanks,
Calvin

s***@oracle.com

2018-11-16 18:41:39 UTC

Permalink

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<div class="moz-cite-prefix">Hi Ioi, 
 
Thank you for the clarifications! 
 
But then I have one more question to the fix in webrev. <a class="moz-txt-link-freetext" href="http://cr.openjdk.java.net/%7Eccheung/8201375/webrev.00/src/hotspot/share/runtime/thread.cpp.udiff.html">http://cr.openjdk.java.net/%7Eccheung/8201375/webrev.00/src/hotspot/share/runtime/thread.cpp.udiff.html</a> <pre> // Create agents for -agentlib: -agentpath: and converted -Xrun // Invokes Agent_OnLoad // Called very early -- before JavaThreads exist void Threads::create_vm_init_agents() { + if (DumpSharedSpaces && !AllowArchivingWithJavaAgent) { + vm_exit_during_cds_dumping( + "Must enable AllowArchivingWithJavaAgent in order to run Java agent during CDS dumping"); + } extern struct JavaVM_ main_vm; AgentLibrary* agent; JvmtiExport::enter_onload_phase(); for (agent = Arguments::agents(); agent != NULL; agent = agent->next()) { + // CDS dumping does not support native JVMTI agent + if (DumpSharedSpaces && !agent->is_instrument_lib()) { + vm_exit_during_cds_dumping("CDS dumping does not support native JVMTI agent, name", agent->name()); + } + OnLoadEntry_t on_load_entry = lookup_agent_on_load(agent); if (on_load_entry != NULL) { // Invoke the Agent_OnLoad function jint err = (*on_load_entry)(&main_vm, agent->options(), NULL);</pre>
 
If !agent->is_instrument_lib()
is passed then it will be rejected with the message: 
"Must enable AllowArchivingWithJavaAgent in order to run
Java agent during CDS dumping" 
which is incorrect. 
 
Probably, the fix needs to be something like this: <pre> for (agent = Arguments::agents(); agent != NULL; agent = agent->next()) { + // CDS dumping does not support native JVMTI agent + if (DumpSharedSpaces && !agent->is_instrument_lib()) { + vm_exit_during_cds_dumping("CDS dumping does not support native JVMTI agent, name", agent->name()); + } + // CDS dumping does not support native JVMTI agent + else if (DumpSharedSpaces && !agent->is_instrument_lib()) { + vm_exit_during_cds_dumping("CDS dumping does not support native JVMTI agent, name", agent->name());
+ }
</pre>
 
Thanks, 
Serguei 
 
 
 
 
 
On 11/16/18 10:18, Ioi Lam wrote: 
</div>
<blockquote type="cite"
cite="mid:25737bd7-9333-480b-8ee6-***@oracle.com">
 
 
On 11/16/18 9:45 AM, <a class="moz-txt-link-abbreviated" href="mailto:***@oracle.com">***@oracle.com</a> wrote:
 
<blockquote type="cite">Hi Calvin,
 
 
On 11/16/18 09:26, Calvin Cheung wrote:
 
<blockquote type="cite">Serguei, Dan,
 
 
Thanks for taking a look.
 
 
I think the option name is correct but the comment for
Threads::create_vm_init_agents() is incorrect as I believe it
will start both Java native agents. Otherwise, my new tests
won't work.
 
</blockquote>
 
It works because there is the system JVMTI (native) agent
library libinstrument.so that is supporting java agents.
 
It means that new option first impacts native agents and
transitively java agents as well via the libinstrument.so.
 
 
Dan already asked the question about your original
reasoning/intention.
 
If your intention is to control java agent only then the fix is
wrong as the real impact is much bigger.
 
If you wanted to control all the agents then the new option name
is misleading.
 
 
 
</blockquote>
The intention of this change is:
 
 
Disallow all use of native and java agents by default. -- using
agents during dump time will cause undesirable side effects and
make the CDS archive unsuitable for production environments.
 
 
However, for testing CDS itself, we want to use the Java agent (to
run arbitrary Java code during dump time, such as causing GC at
specific times).
 
 
As a result, what we are doing is:
 
 
 + Always disallow non-Java agents.
 
 + Allow java agents only if AllowArchivingWithJavaAgent is
specified.
 
 
I think we should clean up the bug title and description if
necessary. However, the behavior of this patch is what we want.
And I think the naming of the AllowArchivingWithJavaAgent option
is correct (as least in the sense of "anything not explicitly
allow are strictly forbidden" :-)
 
 
Thanks
 
- Ioi
 
 
 
<blockquote type="cite">
<blockquote type="cite">Below is my understanding:
 
 
In thread.cpp:
 
 
3697 if (Arguments::init_agents_at_startup()) {
 
3698 create_vm_init_agents();
 
3699 }
 
 
init_agents_at_startup() checks if the _agentList is empty in
arguments.hpp:
 
 
static bool init_agents_at_startup() { return
!_agentList.is_empty(); }
 
 
In arguments.cpp, entries will be added to the _agentList
during the parsing of the -agentLib, -agentPath, and
-javaagent arguments. See lines around 2463-2502.
 
For the -agentLib and -agentPath args, the _agentList will be
populated via the add_init_agent() function. For the
-javaagent, the _agentList will be populated via the
add_instrument_agent() function.
 
 
So in create_vm_init_agents(), it will just loop through the
_agentList and starts all the agents. There's a check for
!agent->is_instrument_agent() at line 4092 which is for not
allowing any JVMTI (native) agent to be run during dump time.
 
 
One more reply to Serguei's comment below...
 
</blockquote>
 
Okay, thank you for the update!
 
 
Thanks,
 
Serguei
 
 
<blockquote type="cite">
 
thanks,
 
Calvin
 
 
On 11/16/18, 6:08 AM, Daniel D. Daugherty wrote: <blockquote type="cite">> The flags -agentlib and
-agentpath are to run JVMTI (native) agents,
 
> and Agent_OnLoad is an entrypoint in native agent
library.
 
 
The '-agentlib' and '-agentpath' options are used to load
and execute
 
a native library via the Agent_OnLoad() entry point.
However, the
 
agent does not have to use JVM/TI (it could be pure JNI):
 
 
$ java -help
 
 
 -agentlib:<libname>[=<options>]
 
 load native agent library <libname>,
e.g. -agentlib:hprof
 
 see also, -agentlib:jdwp=help and
-agentlib:hprof=help
 
 -agentpath:<pathname>[=<options>]
 
 load native agent library by full pathname
 
 
The '-javaagent' option is used to load and execute a Java
agent:
 
 
 -javaagent:<jarpath>[=<options>]
 
 load Java programming language agent, see
java.lang.instrument
 
 
so I agree that the option is misnamed (a bit), but the
reasons
 
needed to be clarified.
 
 
Dan
 
 
 
On 11/16/18 1:39 AM, <a class="moz-txt-link-abbreviated" href="mailto:***@oracle.com">***@oracle.com</a> wrote:
 
<blockquote type="cite">Hi Calvin,
 
 
It seems the option name AllowArchivingWithJavaAgent is
not right.
 
In fact, it is about JVMTI (native) agents:
 
 
*// Create agents for -agentlib: -agentpath: and converted
-Xrun*
 
*// Invokes Agent_OnLoad*
 
*// Called very early -- before JavaThreads exist*
 
*void Threads::create_vm_init_agents() {*
 
*+ if (DumpSharedSpaces &&
!AllowArchivingWithJavaAgent) {*
 
*+ vm_exit_during_cds_dumping(*
 
*+ "Must enable AllowArchivingWithJavaAgent in order to
run Java agent during CDS dumping");*
 
*+ }*
 
*extern struct JavaVM_ main_vm;*
 
*AgentLibrary* agent;*
 
**
 
*JvmtiExport::enter_onload_phase();*
 
**
 
*for (agent = Arguments::agents(); agent != NULL; agent =
agent->next()) {*
 
*+ // CDS dumping does not support native JVMTI agent*
 
*+ if (DumpSharedSpaces &&
!agent->is_instrument_lib()) {*
 
*+ vm_exit_during_cds_dumping("CDS dumping does not
support native JVMTI agent, name", agent->name());*
 
*+ }*
 
*+ *
 
*OnLoadEntry_t on_load_entry =
lookup_agent_on_load(agent);*
 
The flags -agentlib and -agentpath are to run JVMTI
(native) agents,
 
and Agent_OnLoad is an entrypoint in native agent library.
 
So, I'm thinking if it'd make sense to rename the option
to something like below:
 
AllowArchivingWithJVMTIAgent or
 
AllowArchivingWithNativeAgent or
 
AllowArchivingWithAgent
 
 
 
<a class="moz-txt-link-freetext" href="http://cr.openjdk.java.net/%7Eccheung/8201375/webrev.00/src/hotspot/share/memory/filemap.cpp.frames.html">http://cr.openjdk.java.net/%7Eccheung/8201375/webrev.00/src/hotspot/share/memory/filemap.cpp.frames.html</a>
 
212 _allow_archiving_with_java_agent =
AllowArchivingWithJavaAgent; ...
 
1350 if (_allow_archiving_with_java_agent &&
!AllowArchivingWithJavaAgent) { 1351
FileMapInfo::fail_continue("The setting of the
AllowArchivingWithJavaAgent is different " 1352 "from the
setting in the shared archive."); 1353 return false; 1354
} The _allow_archiving_with_java_agent is initialized with
the AllowArchivingWithJavaAgent at line 212.
 
</blockquote>
</blockquote>
The assignment at line 212 is for populating the archive
header during CDS dump time.
 
<blockquote type="cite">
<blockquote type="cite">It is not clear from scratch how
these two values can be different at line 1350. At least,
some comment explaining it is needed.
 
</blockquote>
</blockquote>
The value retrieved from the archive header could be different
from the run time setting.
 
I will add a comment.
 
 
<blockquote type="cite">
<blockquote type="cite">Thanks,
 
Serguei
 
 
 
On 11/15/18 10:56, Jiangli Zhou wrote:
 
<blockquote type="cite">+1
 
 
Adding serviceability-dev mailing list. It would be good
to have this reviewed by the JVMTI experts also to make
sure all cases are covered.
 
 
Thanks,
 
 
Jiangli
 
 
 
On 11/15/18 9:29 AM, Ioi Lam wrote:
 
<blockquote type="cite">Hi Calvin,
 
 
The changes look good.
 
 
Thanks
 
 
- Ioi
 
 
On 11/14/18 4:40 PM, Calvin Cheung wrote:
 
<blockquote type="cite">bug:
<a class="moz-txt-link-freetext" href="https://bugs.openjdk.java.net/browse/JDK-8201375">https://bugs.openjdk.java.net/browse/JDK-8201375</a>
 
 
webrev:
<a class="moz-txt-link-freetext" href="http://cr.openjdk.java.net/~ccheung/8201375/webrev.00/">http://cr.openjdk.java.net/~ccheung/8201375/webrev.00/</a>
 
 
This change is for adding a diagnostic vm option
(AllowArchivingWithJavaAgent) to allow the
-javaagent in the command line during CDS dumping.
Please refer to the corresponding CSR
(<a class="moz-txt-link-freetext" href="https://bugs.openjdk.java.net/browse/JDK-8213813">https://bugs.openjdk.java.net/browse/JDK-8213813</a>)
for details.
 
 
Testing: ran hs-tier{1,2,3} tests through mach5.
 
 
thanks,
 
Calvin
 
</blockquote>
</blockquote>
 
</blockquote>
 
</blockquote>
 
</blockquote>
</blockquote>
 
</blockquote>
 
</blockquote>
 
</body>
</html>

s***@oracle.com

2018-11-16 19:16:05 UTC

Permalink

<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
</head>
<body text="#000000" bgcolor="#FFFFFF">
<div class="moz-cite-prefix">On 11/16/18 10:41,
<a class="moz-txt-link-abbreviated" href="mailto:***@oracle.com">***@oracle.com</a> wrote: 
</div>
<blockquote type="cite"
cite="mid:6a5f2f33-6342-cae3-d47e-***@oracle.com">
<div class="moz-cite-prefix">Hi Ioi, 
 
Thank you for the clarifications! 
 
But then I have one more question to the fix in webrev. 
 
<a class="moz-txt-link-freetext"
href="http://cr.openjdk.java.net/%7Eccheung/8201375/webrev.00/src/hotspot/share/runtime/thread.cpp.udiff.html"
moz-do-not-send="true">http://cr.openjdk.java.net/%7Eccheung/8201375/webrev.00/src/hotspot/share/runtime/thread.cpp.udiff.html</a> <pre> // Create agents for -agentlib: -agentpath: and converted -Xrun // Invokes Agent_OnLoad // Called very early -- before JavaThreads exist void Threads::create_vm_init_agents() { + if (DumpSharedSpaces && !AllowArchivingWithJavaAgent) { + vm_exit_during_cds_dumping( + "Must enable AllowArchivingWithJavaAgent in order to run Java agent during CDS dumping"); + } extern struct JavaVM_ main_vm; AgentLibrary* agent; JvmtiExport::enter_onload_phase(); for (agent = Arguments::agents(); agent != NULL; agent = agent->next()) { + // CDS dumping does not support native JVMTI agent + if (DumpSharedSpaces && !agent->is_instrument_lib()) { + vm_exit_during_cds_dumping("CDS dumping does not support native JVMTI agent, name", agent->name()); + } + OnLoadEntry_t on_load_entry = lookup_agent_on_load(agent); if (on_load_entry != NULL) { // Invoke the Agent_OnLoad function jint err = (*on_load_entry)(&main_vm, agent->options(), NULL);</pre>
 
If !agent->is_instrument_lib() is passed then it will
be rejected with the message: 
"Must enable AllowArchivingWithJavaAgent in order to run
Java agent during CDS dumping" 
which is incorrect. 
 
Probably, the fix needs to be something like this: <pre> for (agent = Arguments::agents(); agent != NULL; agent = agent->next()) { + // CDS dumping does not support native JVMTI agent + if (DumpSharedSpaces && !agent->is_instrument_lib()) { + vm_exit_during_cds_dumping("CDS dumping does not support native JVMTI agent, name", agent->name()); + } + // CDS dumping does not support native JVMTI agent + else if (DumpSharedSpaces && !agent->is_instrument_lib()) { + vm_exit_during_cds_dumping("CDS dumping does not support native JVMTI agent, name", agent->name());
+ }
</pre>
</div>
</blockquote>
Sorry, somehow I've copy-pasted wrong fragment. 
It has to be: <pre> for (agent = Arguments::agents(); agent != NULL; agent = agent->next()) {
+ // CDS dumping does not support native JVMTI agent
+ if (DumpSharedSpaces) {
+ if(!agent->is_instrument_lib()) { + vm_exit_during_cds_dumping("CDS dumping does not support native JVMTI agent, name", agent->name());
+ }
+ else if (!AllowArchivingWithJavaAgent) {
+ vm_exit_during_cds_dumping(
+ "Must enable AllowArchivingWithJavaAgent in order to run Java agent during CDS dumping");
+ }
+ }
</pre>
And this fragment at the begin of the function needs to be removed: 
<pre>+ if (DumpSharedSpaces && !AllowArchivingWithJavaAgent) {
+ vm_exit_during_cds_dumping(
+ "Must enable AllowArchivingWithJavaAgent in order to run Java agent during CDS dumping");
+ }</pre>
 
Thanks, 
Serguei 
 
<blockquote type="cite"
cite="mid:6a5f2f33-6342-cae3-d47e-***@oracle.com">
<div class="moz-cite-prefix"> Thanks, 
Serguei 
 
 
 
 
 
On 11/16/18 10:18, Ioi Lam wrote: 
</div>
<blockquote type="cite"
cite="mid:25737bd7-9333-480b-8ee6-***@oracle.com"> 
 
On 11/16/18 9:45 AM, <a class="moz-txt-link-abbreviated"
href="mailto:***@oracle.com"
moz-do-not-send="true">***@oracle.com</a> wrote: 
<blockquote type="cite">Hi Calvin, 
 
On 11/16/18 09:26, Calvin Cheung wrote: 
<blockquote type="cite">Serguei, Dan, 
 
Thanks for taking a look. 
 
I think the option name is correct but the comment for
Threads::create_vm_init_agents() is incorrect as I believe
it will start both Java native agents. Otherwise, my new
tests won't work. 
</blockquote>
 
It works because there is the system JVMTI (native) agent
library libinstrument.so that is supporting java agents. 
It means that new option first impacts native agents and
transitively java agents as well via the libinstrument.so. 
 
Dan already asked the question about your original
reasoning/intention. 
If your intention is to control java agent only then the fix
is wrong as the real impact is much bigger. 
If you wanted to control all the agents then the new option
name is misleading. 
 
 
</blockquote>
The intention of this change is: 
 
Disallow all use of native and java agents by default. -- using
agents during dump time will cause undesirable side effects and
make the CDS archive unsuitable for production environments. 
 
However, for testing CDS itself, we want to use the Java agent
(to run arbitrary Java code during dump time, such as causing GC
at specific times). 
 
As a result, what we are doing is: 
 
 + Always disallow non-Java agents. 
 + Allow java agents only if AllowArchivingWithJavaAgent is
specified. 
 
I think we should clean up the bug title and description if
necessary. However, the behavior of this patch is what we want.
And I think the naming of the AllowArchivingWithJavaAgent option
is correct (as least in the sense of "anything not explicitly
allow are strictly forbidden" :-) 
 
Thanks 
- Ioi 
 
 
<blockquote type="cite">
<blockquote type="cite">Below is my understanding: 
 
In thread.cpp: 
 
3697 if (Arguments::init_agents_at_startup()) { 
3698 create_vm_init_agents(); 
3699 } 
 
init_agents_at_startup() checks if the _agentList is empty
in arguments.hpp: 
 
static bool init_agents_at_startup() { return
!_agentList.is_empty(); } 
 
In arguments.cpp, entries will be added to the _agentList
during the parsing of the -agentLib, -agentPath, and
-javaagent arguments. See lines around 2463-2502. 
For the -agentLib and -agentPath args, the _agentList will
be populated via the add_init_agent() function. For the
-javaagent, the _agentList will be populated via the
add_instrument_agent() function. 
 
So in create_vm_init_agents(), it will just loop through the
_agentList and starts all the agents. There's a check for
!agent->is_instrument_agent() at line 4092 which is for
not allowing any JVMTI (native) agent to be run during dump
time. 
 
One more reply to Serguei's comment below... 
</blockquote>
 
Okay, thank you for the update! 
 
Thanks, 
Serguei 
 
<blockquote type="cite"> 
thanks, 
Calvin 
 
On 11/16/18, 6:08 AM, Daniel D. Daugherty wrote: <blockquote type="cite">> The flags -agentlib and
-agentpath are to run JVMTI (native) agents, 
> and Agent_OnLoad is an entrypoint in native agent
library. 
 
The '-agentlib' and '-agentpath' options are used to load
and execute 
a native library via the Agent_OnLoad() entry point.
However, the 
agent does not have to use JVM/TI (it could be pure JNI):
 
 
$ java -help 
 
 -agentlib:<libname>[=<options>] 
 load native agent library
<libname>, e.g. -agentlib:hprof 
 see also, -agentlib:jdwp=help and
-agentlib:hprof=help 
 -agentpath:<pathname>[=<options>] 
 load native agent library by full
pathname 
 
The '-javaagent' option is used to load and execute a Java
agent: 
 
 -javaagent:<jarpath>[=<options>] 
 load Java programming language agent,
see java.lang.instrument 
 
so I agree that the option is misnamed (a bit), but the
reasons 
needed to be clarified. 
 
Dan 
 
 
On 11/16/18 1:39 AM, <a class="moz-txt-link-abbreviated"
href="mailto:***@oracle.com"
moz-do-not-send="true">***@oracle.com</a>
wrote: 
<blockquote type="cite">Hi Calvin, 
 
It seems the option name AllowArchivingWithJavaAgent is
not right. 
In fact, it is about JVMTI (native) agents: 
 
*// Create agents for -agentlib: -agentpath: and
converted -Xrun* 
*// Invokes Agent_OnLoad* 
*// Called very early -- before JavaThreads exist* 
*void Threads::create_vm_init_agents() {* 
*+ if (DumpSharedSpaces &&
!AllowArchivingWithJavaAgent) {* 
*+ vm_exit_during_cds_dumping(* 
*+ "Must enable AllowArchivingWithJavaAgent in order to
run Java agent during CDS dumping");* 
*+ }* 
*extern struct JavaVM_ main_vm;* 
*AgentLibrary* agent;* 
** 
*JvmtiExport::enter_onload_phase();* 
** 
*for (agent = Arguments::agents(); agent != NULL; agent
= agent->next()) {* 
*+ // CDS dumping does not support native JVMTI agent* 
*+ if (DumpSharedSpaces &&
!agent->is_instrument_lib()) {* 
*+ vm_exit_during_cds_dumping("CDS dumping does not
support native JVMTI agent, name", agent->name());* 
*+ }* 
*+ * 
*OnLoadEntry_t on_load_entry =
lookup_agent_on_load(agent);* 
The flags -agentlib and -agentpath are to run JVMTI
(native) agents, 
and Agent_OnLoad is an entrypoint in native agent
library. 
So, I'm thinking if it'd make sense to rename the option
to something like below: 
AllowArchivingWithJVMTIAgent or 
AllowArchivingWithNativeAgent or 
AllowArchivingWithAgent 
 
 
<a class="moz-txt-link-freetext"
href="http://cr.openjdk.java.net/%7Eccheung/8201375/webrev.00/src/hotspot/share/memory/filemap.cpp.frames.html"
moz-do-not-send="true">http://cr.openjdk.java.net/%7Eccheung/8201375/webrev.00/src/hotspot/share/memory/filemap.cpp.frames.html</a>
 
212 _allow_archiving_with_java_agent =
AllowArchivingWithJavaAgent; ... 
1350 if (_allow_archiving_with_java_agent &&
!AllowArchivingWithJavaAgent) { 1351
FileMapInfo::fail_continue("The setting of the
AllowArchivingWithJavaAgent is different " 1352 "from
the setting in the shared archive."); 1353 return false;
1354 } The _allow_archiving_with_java_agent is
initialized with the AllowArchivingWithJavaAgent at
line 212. 
</blockquote>
</blockquote>
The assignment at line 212 is for populating the archive
header during CDS dump time. 
<blockquote type="cite">
<blockquote type="cite">It is not clear from scratch how
these two values can be different at line 1350. At
least, some comment explaining it is needed. 
</blockquote>
</blockquote>
The value retrieved from the archive header could be
different from the run time setting. 
I will add a comment. 
 
<blockquote type="cite">
<blockquote type="cite">Thanks, 
Serguei 
 
 
On 11/15/18 10:56, Jiangli Zhou wrote: 
<blockquote type="cite">+1 
 
Adding serviceability-dev mailing list. It would be
good to have this reviewed by the JVMTI experts also
to make sure all cases are covered. 
 
Thanks, 
 
Jiangli 
 
 
On 11/15/18 9:29 AM, Ioi Lam wrote: 
<blockquote type="cite">Hi Calvin, 
 
The changes look good. 
 
Thanks 
 
- Ioi 
 
On 11/14/18 4:40 PM, Calvin Cheung wrote: 
<blockquote type="cite">bug: <a
class="moz-txt-link-freetext"
href="https://bugs.openjdk.java.net/browse/JDK-8201375"
moz-do-not-send="true">https://bugs.openjdk.java.net/browse/JDK-8201375</a>
 
 
webrev: <a class="moz-txt-link-freetext"
href="http://cr.openjdk.java.net/%7Eccheung/8201375/webrev.00/"
moz-do-not-send="true">http://cr.openjdk.java.net/~ccheung/8201375/webrev.00/</a>
 
 
This change is for adding a diagnostic vm option
(AllowArchivingWithJavaAgent) to allow the
-javaagent in the command line during CDS dumping.
Please refer to the corresponding CSR (<a
class="moz-txt-link-freetext"
href="https://bugs.openjdk.java.net/browse/JDK-8213813"
moz-do-not-send="true">https://bugs.openjdk.java.net/browse/JDK-8213813</a>)
for details. 
 
Testing: ran hs-tier{1,2,3} tests through mach5. 
 
thanks, 
Calvin 
</blockquote>
</blockquote>
 
</blockquote>
 
</blockquote>
 
</blockquote>
</blockquote>
 
</blockquote>
 
</blockquote>
 
</blockquote>
 
</body>
</html>

Calvin Cheung

2018-11-16 20:09:28 UTC

Permalink

Hi Serguei,

I've updated the webrev based on your suggestions:
http://cr.openjdk.java.net/~ccheung/8201375/webrev.01/

Files changed since last time:
thead.cpp - your suggestion below
filemap.cpp - added a comment
DumpWithJavaAgent.java - some @ tag cleanup
DumpWithJvmtiAgent.java - some @ tag cleanup and added another test
scenario (-agentlib without AllowArchivingWithJavaAgent)

thanks,
Calvin