New opcode: STATICCALL

EIPS/static_call.md

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+## Preamble
+
+    EIP: to be assigned
+    Title: New opcode STATIC_CALL
+    Author: Vitalik Buterin <[email protected]>, Christian Reitwiessner <[email protected]>;
+    Type: Standard Track
+    Category: Core
+    Status: Draft
+    Created: 2017-02-13
+
+## Simple Summary
+
+To increase smart contract security, this proposal adds a new opcode that can be used to call another contract (or itself) while disallowing any modifications to the state during the call (and its subcalls, if present).
+
+## Abstract
+
+
+## Motivation
+
+
+## Specification
+
+Opcode: `0xfa`.
+
+`STATIC_CALL` functions equivalently to a `CALL`, except it takes 6 arguments not including value, and calls the child with a `STATIC` flag on. Any calls, static or otherwise, made by an execution instance with a `STATIC` flag on will also have a `STATIC` flag on. Any attempts to make state-changing operations inside an execution instance with a `STATIC` flag on will instead throw an exception. These operations include nonzero-value calls, creates, `LOG` calls, `SSTORE`, `SSTOREBYTES` and `SUICIDE`.
+
+## Rationale
+
+This allows contracts to make calls that are clearly non-state-changing, reassuring developers and reviewers that re-entrancy bugs or other problems cannot possibly arise from that particular call; it is a pure function that returns an output and does nothing else. This may also make purely functional HLLs easier to implement.
+
+## Backwards Compatibility
+
+This proposal adds a new opcode but does not modify the behaviour of other opcodes and thus is backwards compatible for old contracts that do not use the new opcode.
+
+## Test Cases
+
+To be written.
+
+## Implementation
+