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

[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
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, serguei.spitsyn at oracle.com wrote:
> 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
>
>
> 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
>
>
> On 11/15/18 10:56, Jiangli Zhou wrote:
>> +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:
>>> Hi Calvin,
>>>
>>> The changes look good.
>>>
>>> Thanks
>>>
>>> - Ioi
>>>
>>> On 11/14/18 4:40 PM, Calvin Cheung wrote:
>>>> 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
>>
>

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