Re: attributes

Okay ... so, attached are the two bytecodes that I would like to insert into method bodies. Only the "impdep1" bytecode as I've described it needs inserting beforehand. In the simplest model, I would like to do the following transformation with Soot:

non-native method call
return point
--->

impdep1 (operand = return point)
non-native method call
nop
return point

... and then when a non-speculative thread encounters the impdep1 bytecode, it tries to fork a speculative thread starting at the return point. If successful, it changes the code at run-time using one word replacement (which is atomic) to:

impdep1 (operand = return point)
non-native method call
impdep2 (count = 1)
return point

... and then when the non-speculative thread returns from the method call, it encounters the impdep2 bytecode, checks to see if it has started a speculative thread at the return point, and if so asks that thread to commit. If the commit is successful, it joins it somehow (to be determined). Either way, as long as it has started a spec. thread, it decrements the count by 1, and if the count = 0 then replaces it with a nop instruction again.

So in an attribute, I would need to give enough information to the VM to enable it to insert this special "impdep1" bytecode at specific points (we won't want to speculate on the return from _all_ methods) within a method body. However, if Soot currently destroys the code attribute, that sounds like you can't even run it on a VM at all.

I agree that attributes are a cleaner solution, because the bytecode will only get modified on a VM that recognizes / supports them.

Anyway, let me know what you think of my plan and if you can see a better way. Tips on getting started using attributes to do what I want to do are very much appreciated :-)

Cheers,
Chris

Ondrej Lhotak wrote:

Soot reads the following attributes:
SourceFile
ConstantValue
Code
Exceptions
LineNumberTable
LocalVariableTable

However, only LineNumberTable has a corresponding Tag implementation
allowing it to be represented as a Soot attribute. If you need to
preserve anything else, you need to implement a Tag to represent it, and
a TagAggregator to convert it from a Soot attribute into a bytecode
attribute.

Ondrej

On Sun, Mar 16, 2003 at 09:54:27PM -0500, Chris Pickett wrote:

 From the Soot tutorials ...

Known shortcomings:

Soot cannot currently preserve existing attributes in a class file when 
transforming and annotating it. In the foo example, any debug 
information from javac would be lost after annotation.

====

Is this still the case?

Chris

impdep1
branchbyte1
branchbyte2

impdep2
count