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

[serguei.spit...@oracle.com]

On 8/6/13 11:57 AM, serguei.spit...@oracle.com wrote:
On 8/5/13 7:41 AM, Bob Vandette wrote:
On Aug 2, 2013, at 11:11 PM, Bill Pittore wrote:
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.

I'd rather leave this undefined since the behavior is very platform 
specific.
The way we determine if a library is statically linked is by the 
presence of the Agent_OnLoad_L function.
If this function exists in a dynamically linked library, it will be 
treated as a static library if by some chance
it's attempted to be loaded twice, since the symbol will may be 
visible in the running process.
(I've added Alan and Coleen to the cc-list)

It is still not clear to me how the second load might happen.

It is inaccurate statement above.
I wanted to say "such a second load" that will determine the dynamically 
loaded agent as statically loaded.

Thanks,
Serguei


The agent is determined as statically loaded if the Agent_OnLoad_L 
function
is found in the main program, not in the dynamic library.
At least, the dll_lookup is done for the main program (for 
DefaultProcessHandle).
If the agent is loaded dynamically, the Agent_OnLoad_L function in the 
agent library
can be ignored because the dll_lookup in the main program will not 
find it.
In a case of the second load this function will be ignored again.
So that there is no conflict with the dynamically loaded agent here.

We can skip this issue for now.
Alan is going to review the JEP from the dynamic Attach point of view 
and hopefully will pay attention to these details.

Thanks,
Serguei


Bob.


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