Status: Accepted
Owner: [email protected]
CC: [email protected], [email protected], [email protected]
Labels: Type-Bug Priority-Medium
New issue 3289 by [email protected]: Suspended generator activations can
become invalid when debugging is enabled
http://code.google.com/p/v8/issues/detail?id=3289
Generator objects represent suspended function activations. A generator
object encapsulates the state of a function by reifying it on the heap.
The data is the context, a slice of the operand stack, the receiver, the
function being called, and an offset within the function's code: the
continuation.
When a generator activation is resumed, we reconstruct a stack frame, and
then jump into the middle of the function, by looking up the function's
entry code pointer, then adding the continuation (the code offset) to that
pointer. This strategy allows for the function's code to be relocated.
However, if a function is recompiled for debugging mode, the offset is
invalid. This can lead to all kinds of bugs.
I guess we should hold onto the code object in the generator object, not
just the function. We should probably rely on deoptimization-on-return to
convert the continuation to debugging (or not-debugging) mode. Perhaps
GeneratorResume should check that it is restoring in the same mode it was
captured in.
Somewhat related would be LiveEdit of a generator function -- can you do
it? do suspended activations reflect the changes? (I would say yes and
no, respectively -- and no, it doesn't work now for the same reasons as
this bug.)
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