Review Request: Shark

[Christian Thalinger]

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.

> 
> > hotspot/src/share/vm/runtime/deoptimization.cpp:
> > 
> > +#ifndef SHARK
> >    assert(CodeCache::find_blob_unsafe(frame_pcs[0]) != NULL, "bad pc");
> > +#endif // SHARK
> > 
> > Why does this assert not hold?
> 
> Neither interpreter frames nor call stub frames exist in the code
> cache in Zero.

OK.

> 
> > 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/

-- Christian