[PATCH] D38214: [analyzer] Fix crash on modeling of pointer arithmetic

Alexander Shaposhnikov via Phabricator via cfe-commits cfe-commits at lists.llvm.org
Mon Sep 25 05:04:25 PDT 2017

alexshap created this revision.
Herald added a subscriber: xazax.hun.

This patch attempts to fix analyzer's crash on the newly added test case (see also https://bugs.llvm.org/show_bug.cgi?id=34374).
Pointer subtraction appears to be modeled incorrectly in the following example:

  char* p;
  long n = p - reinterpret_cast<char*>((unsigned long)1);

In this case the analyzer (built without this patch) tries to create a symbolic value for the difference 
treating reinterpret_cast<char*>((unsigned long)1) as an integer, that is not correct.

Test plan: make check-all




Index: test/Analysis/ptr-arith.cpp
--- test/Analysis/ptr-arith.cpp
+++ test/Analysis/ptr-arith.cpp
@@ -111,3 +111,9 @@
   __UINTPTR_TYPE__ y = (__UINTPTR_TYPE__)p - 1;
   return y == x;
+// Bug 34374
+bool integerAsPtrSubtractionNoCrash(char *p, __UINTPTR_TYPE__ m) {
+  auto n = p - reinterpret_cast<char*>((__UINTPTR_TYPE__)1);
+  return n == m;
Index: lib/StaticAnalyzer/Core/SimpleSValBuilder.cpp
--- lib/StaticAnalyzer/Core/SimpleSValBuilder.cpp
+++ lib/StaticAnalyzer/Core/SimpleSValBuilder.cpp
@@ -726,9 +726,11 @@
     if (Optional<loc::ConcreteInt> rInt = rhs.getAs<loc::ConcreteInt>()) {
       // If one of the operands is a symbol and the other is a constant,
       // build an expression for use by the constraint manager.
-      if (SymbolRef lSym = lhs.getAsLocSymbol(true))
-        return MakeSymIntVal(lSym, op, rInt->getValue(), resultTy);
+      if (SymbolRef lSym = lhs.getAsLocSymbol(true)) {
+        if (BinaryOperator::isComparisonOp(op))
+          return MakeSymIntVal(lSym, op, rInt->getValue(), resultTy);
+        return UnknownVal();
+      }
       // Special case comparisons to NULL.
       // This must come after the test if the LHS is a symbol, which is used to
       // build constraints. The address of any non-symbolic region is guaranteed

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