[analyzer] CStringChecker: pr34460: Avoid a crash when a cast is not modeled.

The checker used to crash when a mempcpy's length argument is symbolic. In this
case the cast from 'void *' to 'char *' failed because the respective
ElementRegion that represents cast is hard to add on top of the existing
ElementRegion that represents the offset to the last copied byte, while
preseving a sane memory region structure.

Additionally, a few test cases are added (to casts.c) which demonstrate problems
caused by existing sloppy work we do with multi-layer ElementRegions. If said
cast would be modeled properly in the future, these tests would need to be
taken into account.

Differential Revision: https://reviews.llvm.org/D38797

llvm-svn: 315742

clang/lib/StaticAnalyzer/Checkers/CStringChecker.cpp

@@ -1050,31 +1050,22 @@ void CStringChecker::evalCopyCommon(CheckerContext &C,
     // If this is mempcpy, get the byte after the last byte copied and
     // bind the expr.
     if (IsMempcpy) {
-      loc::MemRegionVal destRegVal = destVal.castAs<loc::MemRegionVal>();
-
-      // Get the length to copy.
-      if (Optional<NonLoc> lenValNonLoc = sizeVal.getAs<NonLoc>()) {
-        // Get the byte after the last byte copied.
-        SValBuilder &SvalBuilder = C.getSValBuilder();
-        ASTContext &Ctx = SvalBuilder.getContext();
-        QualType CharPtrTy = Ctx.getPointerType(Ctx.CharTy);
-        loc::MemRegionVal DestRegCharVal = SvalBuilder.evalCast(destRegVal,
-          CharPtrTy, Dest->getType()).castAs<loc::MemRegionVal>();
-        SVal lastElement = C.getSValBuilder().evalBinOpLN(state, BO_Add,
-                                                          DestRegCharVal,
-                                                          *lenValNonLoc,
-                                                          Dest->getType());
-
-        // The byte after the last byte copied is the return value.
-        state = state->BindExpr(CE, LCtx, lastElement);
-      } else {
-        // If we don't know how much we copied, we can at least
-        // conjure a return value for later.
-        SVal result = C.getSValBuilder().conjureSymbolVal(nullptr, CE, LCtx,
+      // Get the byte after the last byte copied.
+      SValBuilder &SvalBuilder = C.getSValBuilder();
+      ASTContext &Ctx = SvalBuilder.getContext();
+      QualType CharPtrTy = Ctx.getPointerType(Ctx.CharTy);
+      SVal DestRegCharVal =
+          SvalBuilder.evalCast(destVal, CharPtrTy, Dest->getType());
+      SVal lastElement = C.getSValBuilder().evalBinOp(
+          state, BO_Add, DestRegCharVal, sizeVal, Dest->getType());
+      // If we don't know how much we copied, we can at least
+      // conjure a return value for later.
+      if (lastElement.isUnknown())
+        lastElement = C.getSValBuilder().conjureSymbolVal(nullptr, CE, LCtx,
                                                           C.blockCount());
-        state = state->BindExpr(CE, LCtx, result);
-      }
 
+      // The byte after the last byte copied is the return value.
+      state = state->BindExpr(CE, LCtx, lastElement);
     } else {
       // All other copies return the destination buffer.
       // (Well, bcopy() has a void return type, but this won't hurt.)

clang/test/Analysis/bstring.cpp

@@ -1,8 +1,35 @@
 // RUN: %clang_analyze_cc1 -analyzer-checker=core,unix.cstring,alpha.unix.cstring,debug.ExprInspection -analyzer-store=region -verify %s
+// RUN: %clang_analyze_cc1 -DUSE_BUILTINS -analyzer-checker=core,unix.cstring,alpha.unix.cstring,debug.ExprInspection -analyzer-store=region -verify %s
+// RUN: %clang_analyze_cc1 -DVARIANT -analyzer-checker=core,unix.cstring,alpha.unix.cstring,debug.ExprInspection -analyzer-store=region -verify %s
+// RUN: %clang_analyze_cc1 -DUSE_BUILTINS -DVARIANT -analyzer-checker=core,unix.cstring,alpha.unix.cstring,debug.ExprInspection -analyzer-store=region -verify %s
 
 #include "Inputs/system-header-simulator-cxx.h"
 #include "Inputs/system-header-simulator-for-malloc.h"
 
+// This provides us with four possible mempcpy() definitions.
+// See also comments in bstring.c.
+
+#ifdef USE_BUILTINS
+#define BUILTIN(f) __builtin_##f
+#else /* USE_BUILTINS */
+#define BUILTIN(f) f
+#endif /* USE_BUILTINS */
+
+#ifdef VARIANT
+
+#define __mempcpy_chk BUILTIN(__mempcpy_chk)
+void *__mempcpy_chk(void *__restrict__ s1, const void *__restrict__ s2,
+                    size_t n, size_t destlen);
+
+#define mempcpy(a,b,c) __mempcpy_chk(a,b,c,(size_t)-1)
+
+#else /* VARIANT */
+
+#define mempcpy BUILTIN(mempcpy)
+void *mempcpy(void *__restrict__ s1, const void *__restrict__ s2, size_t n);
+
+#endif /* VARIANT */
+
 void clang_analyzer_eval(int);
 
 int *testStdCopyInvalidatesBuffer(std::vector<int> v) {
@@ -36,3 +63,17 @@ int *testStdCopyBackwardInvalidatesBuffer(std::vector<int> v) {
 
   return buf;
 }
+
+namespace pr34460 {
+short a;
+class b {
+  int c;
+  long g;
+  void d() {
+    int e = c;
+    f += e;
+    mempcpy(f, &a, g);
+  }
+  unsigned *f;
+};
+}

clang/test/Analysis/casts.c

@@ -123,3 +123,29 @@ void locAsIntegerCasts(void *p) {
   int x = (int) p;
   clang_analyzer_eval(++x < 10); // no-crash // expected-warning{{UNKNOWN}}
 }
+
+void multiDimensionalArrayPointerCasts() {
+  static int x[10][10];
+  int *y1 = &(x[3][5]);
+  char *z = ((char *) y1) + 2;
+  int *y2 = (int *)(z - 2);
+  int *y3 = ((int *)x) + 35; // This is offset for [3][5].
+
+  clang_analyzer_eval(y1 == y2); // expected-warning{{TRUE}}
+
+  // FIXME: should be FALSE (i.e. equal pointers).
+  clang_analyzer_eval(y1 - y2); // expected-warning{{UNKNOWN}}
+  // FIXME: should be TRUE (i.e. same symbol).
+  clang_analyzer_eval(*y1 == *y2); // expected-warning{{UNKNOWN}}
+
+  clang_analyzer_eval(*((char *)y1) == *((char *) y2)); // expected-warning{{TRUE}}
+
+  clang_analyzer_eval(y1 == y3); // expected-warning{{TRUE}}
+
+  // FIXME: should be FALSE (i.e. equal pointers).
+  clang_analyzer_eval(y1 - y3); // expected-warning{{UNKNOWN}}
+  // FIXME: should be TRUE (i.e. same symbol).
+  clang_analyzer_eval(*y1 == *y3); // expected-warning{{UNKNOWN}}
+
+  clang_analyzer_eval(*((char *)y1) == *((char *) y3)); // expected-warning{{TRUE}}
+}