Re: RFR - Changes to address CCC 8014135: Support for statically linked agents

Fri, 02 Aug 2013 20:12:25 -0700 

On 8/2/2013 9:12 PM, serguei.spit...@oracle.com wrote:

Hi Bill,

A couple of more questions.

webrev.01/jvmti.html
An agent L whose image has been combined with the VM *is defined* as /statically linked/ 
if and only if the agent exports a function called Agent_OnLoad_L.

A question to the above.
Are we going to allow to link a library dynamically if it exports both
the Agent_OnLoad and Agent_OnLoad_L functions?
It can be convenient if a library exports both Agent_OnLoad and Agent_OnLoad_L as it can be linked statically or dynamically depending on the need without changes.
It would be nice but the problem is that you could only link one agent into the VM if it exported Agent_OnLoad. Otherwise there would be a symbol collision with the second agent you linked in that also had Agent_OnLoad. As an agent developer you will have to select one or the other at build time, either statically linked in or dynamic. 
You already added the following statement to the JVMTI spec:
If a /statically linked/ agent L exports a function called Agent_OnLoad_L and a function called Agent_OnLoad, the Agent_OnLoad function will be ignored. 

Could we say it in a shorter form?:
If a /statically linked/ agent L exports a function called Agent_OnLoad,
  the Agent_OnLoad function will be ignored.
I believe I copied this from JNI static linking JEP. If so, I'll probably leave it as is just for consistency with JNI static spec. JVM TI static linking spec is closely related to JNI static linking spec. 

In this context would it be reasonable to add another statement:
If a /dynamically linked/ agent L exports a function called Agent_OnLoad_L, 
  the Agent_OnLoad_L function will be ignored.
The same questions apply to the Agent_OnAttach and Agent_OnAttach_L entry points.
I'm out on vacation for a couple of weeks so I'll leave it up to Bob V. and yourself if you guys want to hash out better/different wording. 

bill


Thanks,
Serguei


On 7/30/13 12:17 PM, bill.pitt...@oracle.com wrote:
Thanks Serguei for the comments. Some comments inline. I updated the webrevs at 
http://cr.openjdk.java.net/~bpittore/8014135/jdk/webrev.02/
http://cr.openjdk.java.net/~bpittore/8014135/hotspot/webrev.01/

http://cr.openjdk.java.net/~bpittore/8014135/javadoc/index.html
http://cr.openjdk.java.net/~bpittore/8014135/hotspot/webrev.01/jvmti.html


On 7/26/2013 5:00 AM, serguei.spit...@oracle.com wrote:

Hi Bill,

Sorry for the big delay.


http://cr.openjdk.java.net/~bpittore/8014135/jdk/webrev.01/


 src/share/classes/com/sun/tools/attach/VirtualMachine.java:
I'm suggesting to use the reference *<code>Agent_OnAttach[_L]</code>**||* even more consistently. (If, in some cases, you prefer the longer form to underline the difference between dynamically and statically linked libraries then feel free to leave it as it is.) 

It would simplify the following fragments:

304      * It then causes the target VM to invoke the 
<code>Agent_OnAttach</code> function
305      * or, for a statically linked agent named 'L', the 
<code>Agent_OnAttach_L</code> function
   ==>

304      * It then causes the target VM to invoke the 
<code>Agent_OnAttach[_L]</code> function

409      * It then causes the target VM to invoke the 
<code>Agent_OnAttach</code>
410      * function or, for a statically linked agent named 'L', the
411      * <code>Agent_OnAttach_L</code> function as specified in the
  ==>
  409      * It then causes the target VM to invoke the 
<code>Agent_OnAttach[_L]</code>
  410      * function as specified in the
I left the above as is since it's part of the method description. The following fragments below I simplified as you suggested. 



the following 4 identical fragments:

  341      *          If the <code>Agent_OnAttach</code> function returns an 
error
  342      *          or, for a statically linked agent named 'L', if the
  343      *          <code>Agent_OnAttach_L</code> function returns
  344      *          an error.
  375      *          If the <code>Agent_OnAttach</code> function returns an 
error
  376      *          or, for a statically linked agent named 'L', if the
  377      *          <code>Agent_OnAttach_L</code> function returns
  378      *          an error.
  442      *          If the <code>Agent_OnAttach</code> function returns an 
error
  443      *          or, for a statically linked agent named 'L', if the
  444      *          <code>Agent_OnAttach_L</code> function returns an error
  475      *          If the <code>Agent_OnAttach</code> function returns an 
error
  476      *          or, for a statically linked agent named 'L', if the
  477      *          <code>Agent_OnAttach_L</code> function returns
  478      *          an error.
  ==>
336 * If the <code>Agent_OnAttach[_L]</code> function returns an error. 






http://cr.openjdk.java.net/~bpittore/8014135/hotspot/webrev.00/


http://cr.openjdk.java.net/~bpittore/8014135/hotspot/webrev.00/jvmti.html
  src/share/vm/prims/jvmti.xml

 Lines 442-462:  many extra <p/>'s. The fragment does not look well.
 I'd suggest to remove most of them.
 Also, these lines are too long. Could you make them shorter, please?
 The same is applied to other long new lines in this file.

Cleaned this up a bit.


 Lines 490-491, 502-503, 505-506:
The same sentence is repeated 3 times: "the agent library may be statically linked ..."
490 Note that the agent library may be statically linked into the executable 
491     in which case no actual loading takes place.

Fixed.
501 <code>-agentpath:c:\myLibs\foo.dll=opt1,opt2</code> is specified, the VM will attempt to 502 load the shared library <code>c:\myLibs\foo.dll</code>. As mentioned above, the agent library may be statically linked into the executable 
 503         in which case no actual loading takes place
505 Note that the agent library may be statically linked into the executable 
 506     in which case no actual loading takes place.


Tweaked the above a bit to make it less wordy.


 Lines 677-678: The dot is missed at the end of line 677:

 677     and enabled the event


Fixed.


 src/os/posix/vm/os_posix.cpp

   - no comments

 src/os/windows/vm/os_windows.cpp

   - no comments

 src/share/vm/prims/jvmtiExport.cpp

   - no comments

 src/share/vm/runtime/arguments.hpp

   - no comments

 src/share/vm/runtime/os.cpp

 Space is missed after the 'if':
   471     if(entryName != NULL) {


Fixed.

 Extra space after the '*':
  483   void * saveHandle;


Fixed.

 src/share/vm/runtime/os.hpp

   - no comments

 src/share/vm/runtime/thread.cpp

  The line has been removed:
  3866         break;


Correct, the inner for loop was removed so no need for the break;


I'm still in process of reading the code.
Another pass is needed to make sure that nothing is missed.
But in general, the code quality is pretty good.

Thanks,
Serguei



On 7/25/13 10:47 AM, bill.pitt...@oracle.com wrote:
Still need an official reviewer for the hotspot changes for statically linked agents. 

thanks,
bill
These changes address bug 8014135 which adds support for statically linked agents in the VM. This is a followup to the recent JNI spec changes that addressed statically linked JNI libraries( 8005716). 
The JEP for this change is the same JEP as the JNI changes:
http://openjdk.java.net/jeps/178

Webrevs are here:

http://cr.openjdk.java.net/~bpittore/8014135/jdk/webrev.00/
http://cr.openjdk.java.net/~bpittore/8014135/hotspot/webrev.00/
The changes to jvmti.xml can also be seen in the output file that I placed here: http://cr.openjdk.java.net/~bpittore/8014135/hotspot/webrev.00/jvmti.html 

Thanks,
bill

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