core/vm: implement RETURNDATA metropolis opcodes

[karalabe]

Implements ethereum/EIPs#211.

[holiman]

Minor nitpick, it's not only "unimportant to preserve the old buffer", it's required to clear the buffer here - otherwise a child-call could access the returndata from a parent context.

[karalabe]

I think Jeff meant that clearing it only/setting to zero len (but keeping the allocated memory area) is useless because the entire buffer will be replaced, so we might as well set to nil and discard the allocated memory.

…

On Aug 16, 2017 14:22, "Martin Holst Swende" ***@***.***> wrote: ***@***.**** approved this pull request. ------------------------------ In core/vm/interpreter.go <#14981 (comment)> : > @@ -113,6 +114,10 @@ func (in *Interpreter) Run(snapshot int, contract *Contract, input []byte) (ret in.evm.depth++ defer func() { in.evm.depth-- }() + // Reset the previous call's return data. It's unimportant to preserve the old buffer + // as every returning call will return new data anyway. + in.returnData = nil Minor nitpick, it's not only "unimportant to preserve the old buffer", it's *required* to clear the buffer here - otherwise a child-call could access the returndata from a parent context. — You are receiving this because you authored the thread. Reply to this email directly, view it on GitHub <#14981 (review)>, or mute the thread <https://github.com/notifications/unsubscribe-auth/AAH6GQ9D7DJeryfhfcL7IyQ4zhnPQqZrks5sYtEAgaJpZM4O4usr> .

[holiman]

Ah, yeah that makes more sense, thanks