From 31fd66acf52749d4543200c84b8a388c9ea75c59 Mon Sep 17 00:00:00 2001
From: Joran Honig <joran.honig@gmail.com>
Date: Mon, 13 May 2019 10:58:14 +0200
Subject: [PATCH 1/2] ignore external calls to precompile contracts

---
 mythril/analysis/modules/external_calls.py | 20 +++++++++++++++++++-
 1 file changed, 19 insertions(+), 1 deletion(-)

diff --git a/mythril/analysis/modules/external_calls.py b/mythril/analysis/modules/external_calls.py
index 554cbb93..10f1eaa4 100644
--- a/mythril/analysis/modules/external_calls.py
+++ b/mythril/analysis/modules/external_calls.py
@@ -5,7 +5,7 @@ from mythril.analysis import solver
 from mythril.analysis.swc_data import REENTRANCY
 from mythril.analysis.modules.base import DetectionModule
 from mythril.analysis.report import Issue
-from mythril.laser.smt import UGT, symbol_factory
+from mythril.laser.smt import UGT, symbol_factory, Or, BitVec
 from mythril.laser.ethereum.state.global_state import GlobalState
 from mythril.exceptions import UnsatError
 from copy import copy
@@ -71,6 +71,8 @@ def _analyze_state(state):
             )
 
         except UnsatError:
+            if _is_precompile_call(state):
+                return []
 
             log.debug(
                 "[EXTERNAL_CALLS] Callee address cannot be modified. Reporting informational issue."
@@ -104,6 +106,22 @@ def _analyze_state(state):
     return [issue]
 
 
+def _is_precompile_call(global_state: GlobalState):
+    to = global_state.mstate.stack[-2]  # type: BitVec
+    try:
+        constraints = copy(global_state.mstate.constraints)
+        constraints += [
+            Or(
+                to < symbol_factory.BitVecVal(1, 256),
+                to > symbol_factory.BitVecVal(16, 256),
+            )
+        ]
+        solver.get_model(constraints)
+        return False
+    except UnsatError:
+        return True
+
+
 class ExternalCalls(DetectionModule):
     """This module searches for low level calls (e.g. call.value()) that
     forward all gas to the callee."""

From 6887fbdc06e1953c487a5bdafe0ae80f999c3840 Mon Sep 17 00:00:00 2001
From: Joran Honig <joran.honig@gmail.com>
Date: Tue, 14 May 2019 10:41:52 +0200
Subject: [PATCH 2/2] move constraint creation out of try context

---
 mythril/analysis/modules/external_calls.py | 15 ++++++++-------
 1 file changed, 8 insertions(+), 7 deletions(-)

diff --git a/mythril/analysis/modules/external_calls.py b/mythril/analysis/modules/external_calls.py
index 10f1eaa4..e24470a6 100644
--- a/mythril/analysis/modules/external_calls.py
+++ b/mythril/analysis/modules/external_calls.py
@@ -108,14 +108,15 @@ def _analyze_state(state):
 
 def _is_precompile_call(global_state: GlobalState):
     to = global_state.mstate.stack[-2]  # type: BitVec
+    constraints = copy(global_state.mstate.constraints)
+    constraints += [
+        Or(
+            to < symbol_factory.BitVecVal(1, 256),
+            to > symbol_factory.BitVecVal(16, 256),
+        )
+    ]
+
     try:
-        constraints = copy(global_state.mstate.constraints)
-        constraints += [
-            Or(
-                to < symbol_factory.BitVecVal(1, 256),
-                to > symbol_factory.BitVecVal(16, 256),
-            )
-        ]
         solver.get_model(constraints)
         return False
     except UnsatError: