Teach `klee::getDirectCallTarget()` to resolve weak aliases. This is

controlled by a new parameter `moduleIsFullyLinked`. When
true the linkage type of a weak alias is ignored. It is legal to do
this when the module is fully linked because there won't be another
function that could override the weak alias.

This fixes a previous assertion failure in `klee::getDirectCallTarget()`
triggered by the `test/regression/2016-11-24-bitcast-weak-alias.c` test case.

2 files changed, 30 insertions, 18 deletions

diff --git a/lib/Core/StatsTracker.cpp b/lib/Core/StatsTracker.cpp
index 97ed26ea..dbd86524 100644
--- a/lib/Core/StatsTracker.cpp
+++ b/lib/Core/StatsTracker.cpp
@@ -167,7 +167,8 @@ static bool instructionIsCoverable(Instruction *i) {
     } else {
       Instruction *prev = --it;
       if (isa<CallInst>(prev) || isa<InvokeInst>(prev)) {
-        Function *target = getDirectCallTarget(prev);
+        Function *target =
+            getDirectCallTarget(prev, /*moduleIsFullyLinked=*/true);
         if (target && target->doesNotReturn())
           return false;
       }
@@ -690,7 +691,8 @@ void StatsTracker::computeReachableUncovered() {
               // (which should be correct anyhow).
               callTargets.insert(std::make_pair(it,
                                                 std::vector<Function*>()));
-            } else if (Function *target = getDirectCallTarget(cs)) {
+            } else if (Function *target = getDirectCallTarget(
+                           cs, /*moduleIsFullyLinked=*/true)) {
               callTargets[it].push_back(target);
             } else {
               callTargets[it] = 
diff --git a/lib/Module/ModuleUtil.cpp b/lib/Module/ModuleUtil.cpp
index a5394067..2cd41c89 100644
--- a/lib/Module/ModuleUtil.cpp
+++ b/lib/Module/ModuleUtil.cpp
@@ -436,23 +436,33 @@ Module *klee::linkWithLibrary(Module *module,
 #endif
 }
 
-
-
-Function *klee::getDirectCallTarget(CallSite cs) {
+Function *klee::getDirectCallTarget(CallSite cs, bool moduleIsFullyLinked) {
   Value *v = cs.getCalledValue();
-  if (Function *f = dyn_cast<Function>(v)) {
-    return f;
-  } else if (llvm::ConstantExpr *ce = dyn_cast<llvm::ConstantExpr>(v)) {
-    if (ce->getOpcode()==Instruction::BitCast)
-      if (Function *f = dyn_cast<Function>(ce->getOperand(0)->stripPointerCasts()))
-        return f;
-
-    // NOTE: This assert may fire, it isn't necessarily a problem and
-    // can be disabled, I just wanted to know when and if it happened.
-    assert(0 && "FIXME: Unresolved direct target for a constant expression.");
-  }
-  
-  return 0;
+  bool viaConstantExpr = false;
+  // Walk through aliases and bitcasts to try to find
+  // the function being called.
+  do {
+    if (Function *f = dyn_cast<Function>(v)) {
+      return f;
+    } else if (llvm::GlobalAlias *ga = dyn_cast<GlobalAlias>(v)) {
+      if (moduleIsFullyLinked || !(ga->mayBeOverridden())) {
+        v = ga->getAliasee();
+      } else {
+        v = NULL;
+      }
+    } else if (llvm::ConstantExpr *ce = dyn_cast<llvm::ConstantExpr>(v)) {
+      viaConstantExpr = true;
+      v = ce->getOperand(0)->stripPointerCasts();
+    } else {
+      v = NULL;
+    }
+  } while (v != NULL);
+
+  // NOTE: This assert may fire, it isn't necessarily a problem and
+  // can be disabled, I just wanted to know when and if it happened.
+  assert((!viaConstantExpr) &&
+         "FIXME: Unresolved direct target for a constant expression");
+  return NULL;
 }
 
 static bool valueIsOnlyCalled(const Value *v) {