Review Request: Shark

[Gary Benson]

Christian Thalinger wrote:
> On Tue, 2010-06-22 at 14:29 +0100, Gary Benson wrote:
> > Christian Thalinger wrote:
> > > hotspot/src/share/vm/compiler/disassembler.cpp:
> > > 
> > > +#ifdef SHARK
> > > +  SharkEntry* entry = (SharkEntry *) nm->instructions_begin();
> > > +  unsigned char* p = entry->code_start();
> > > +  unsigned char* end = entry->code_limit();
> > > +#else
> > > 
> > > Why do you need to stuff a SharkEntry into the address?
> > 
> > There's a few reasons for this:
> > 
> >  a) The server (and I think client) compilers generate code into a
> >     temporary CodeBuffer which the VM relocates into some "final"
> >     location when the nmethod is installed.  Shark can't control
> >     where its code is generated, it happens in some LLVM-allocated
> >     buffer, so we can't generate into a CodeBuffer and we certainly
> >     can't relocate that code afterwards.  So we generate a "dummy"
> >     CodeBuffer containing a pointer to the real native code.
> > 
> >  b) To free an LLVM-compiled method you need to keep track of the
> >     original IR it was compiled from.  The CodeBuffer is a convenient
> >     place to store that.
> > 
> >  c) Shark has no access to the code it generates (other than knowing
> >     where it is in memory) so it can't, for example, inline an oop
> >     and the rewrite it later.  Instead, Shark inlines oops into the
> >     method's CodeBuffer (with the appropriate relocations so they
> >     are rewritten as necessary) and loads them every time they're
> >     needed.
> 
> I see.  At least c) sounds familiar.

c) is the most recent.  There's other things it gets used for too.
There's quite a few things that are best inlined "somewhere", where
somewhere can't be in the real native code for one reason or another.

> > > hotspot/src/share/vm/includeDB_shark:
> > > 
> > > Still has the old Sun copyright header.
> > 
> > Ah, good catch.  I fixed this in:
> > http://cr.openjdk.java.net/~gbenson/shark-hotspot-01/
> 
> I guess you mean:  http://cr.openjdk.java.net/~gbenson/shark-hotspot-02/

Yes :)

Cheers,
Gary

-- 
http://gbenson.net/