[clang-tidy] Extend bugprone-sizeof-expression check to detect sizeof misuse in pointer arithmetic

Some programmers tend to forget that subtracting two pointers results in the
difference between them in number of elements of the pointee type instead of
bytes. This leads to codes such as `size_t size = (p - q) / sizeof(int)` where
`p` and `q` are of type `int*`. Or similarily, `if (p - q < buffer_size *
sizeof(int)) { ... }`. This patch extends `bugprone-sizeof-expression` to
detect such cases.

Differential Revision: https://reviews.llvm.org/D61422

llvm-svn: 360032

2 files changed, 84 insertions, 2 deletions

diff --git a/clang-tools-extra/clang-tidy/bugprone/SizeofExpressionCheck.cpp b/clang-tools-extra/clang-tidy/bugprone/SizeofExpressionCheck.cpp
index 959e0ae39b3..fb161957c5a 100644
--- a/clang-tools-extra/clang-tidy/bugprone/SizeofExpressionCheck.cpp
+++ b/clang-tools-extra/clang-tidy/bugprone/SizeofExpressionCheck.cpp
@@ -84,8 +84,11 @@ void SizeofExpressionCheck::registerMatchers(MatchFinder *Finder) {
   const auto IntegerCallExpr = expr(ignoringParenImpCasts(
       callExpr(anyOf(hasType(isInteger()), hasType(enumType())),
                unless(isInTemplateInstantiation()))));
-  const auto SizeOfExpr =
-      expr(anyOf(sizeOfExpr(has(type())), sizeOfExpr(has(expr()))));
+  const auto SizeOfExpr = expr(anyOf(
+      sizeOfExpr(
+          has(hasUnqualifiedDesugaredType(type().bind("sizeof-arg-type")))),
+      sizeOfExpr(has(expr(hasType(
+          hasUnqualifiedDesugaredType(type().bind("sizeof-arg-type"))))))));
   const auto SizeOfZero = expr(
       sizeOfExpr(has(ignoringParenImpCasts(expr(integerLiteral(equals(0)))))));
 
@@ -209,6 +212,36 @@ void SizeofExpressionCheck::registerMatchers(MatchFinder *Finder) {
                hasSizeOfDescendant(8, expr(SizeOfExpr, unless(SizeOfZero))))))))
           .bind("sizeof-sizeof-expr"),
       this);
+
+  // Detect sizeof in pointer aritmetic like: N * sizeof(S) == P1 - P2 or
+  // (P1 - P2) / sizeof(S) where P1 and P2 are pointers to type S.
+  const auto PtrDiffExpr = binaryOperator(
+      hasOperatorName("-"),
+      hasLHS(expr(hasType(hasUnqualifiedDesugaredType(pointerType(pointee(
+          hasUnqualifiedDesugaredType(type().bind("left-ptr-type")))))))),
+      hasRHS(expr(hasType(hasUnqualifiedDesugaredType(pointerType(pointee(
+          hasUnqualifiedDesugaredType(type().bind("right-ptr-type")))))))));
+
+  Finder->addMatcher(
+      binaryOperator(
+          anyOf(hasOperatorName("=="), hasOperatorName("!="),
+                hasOperatorName("<"), hasOperatorName("<="),
+                hasOperatorName(">"), hasOperatorName(">="),
+                hasOperatorName("+"), hasOperatorName("-")),
+          hasEitherOperand(expr(anyOf(
+              ignoringParenImpCasts(SizeOfExpr),
+              ignoringParenImpCasts(binaryOperator(
+                  hasOperatorName("*"),
+                  hasEitherOperand(ignoringParenImpCasts(SizeOfExpr))))))),
+          hasEitherOperand(ignoringParenImpCasts(PtrDiffExpr)))
+          .bind("sizeof-in-ptr-arithmetic-mul"),
+      this);
+
+  Finder->addMatcher(binaryOperator(hasOperatorName("/"),
+                                    hasLHS(ignoringParenImpCasts(PtrDiffExpr)),
+                                    hasRHS(ignoringParenImpCasts(SizeOfExpr)))
+                         .bind("sizeof-in-ptr-arithmetic-div"),
+                     this);
 }
 
 void SizeofExpressionCheck::check(const MatchFinder::MatchResult &Result) {
@@ -275,6 +308,26 @@ void SizeofExpressionCheck::check(const MatchFinder::MatchResult &Result) {
   } else if (const auto *E =
                  Result.Nodes.getNodeAs<Expr>("sizeof-multiply-sizeof")) {
     diag(E->getBeginLoc(), "suspicious 'sizeof' by 'sizeof' multiplication");
+  } else if (const auto *E =
+                 Result.Nodes.getNodeAs<Expr>("sizeof-in-ptr-arithmetic-mul")) {
+    const auto *LPtrTy = Result.Nodes.getNodeAs<Type>("left-ptr-type");
+    const auto *RPtrTy = Result.Nodes.getNodeAs<Type>("right-ptr-type");
+    const auto *SizeofArgTy = Result.Nodes.getNodeAs<Type>("sizeof-arg-type");
+
+    if ((LPtrTy == RPtrTy) && (LPtrTy == SizeofArgTy)) {
+      diag(E->getBeginLoc(), "suspicious usage of 'sizeof(...)' in "
+                              "pointer arithmetic");
+    }
+  } else if (const auto *E =
+                 Result.Nodes.getNodeAs<Expr>("sizeof-in-ptr-arithmetic-div")) {
+    const auto *LPtrTy = Result.Nodes.getNodeAs<Type>("left-ptr-type");
+    const auto *RPtrTy = Result.Nodes.getNodeAs<Type>("right-ptr-type");
+    const auto *SizeofArgTy = Result.Nodes.getNodeAs<Type>("sizeof-arg-type");
+
+    if ((LPtrTy == RPtrTy) && (LPtrTy == SizeofArgTy)) {
+      diag(E->getBeginLoc(), "suspicious usage of 'sizeof(...)' in "
+                              "pointer arithmetic");
+    }
   }
 }
 
diff --git a/clang-tools-extra/test/clang-tidy/bugprone-sizeof-expression.cpp b/clang-tools-extra/test/clang-tidy/bugprone-sizeof-expression.cpp
index 683ad083007..57b73ea4dc9 100644
--- a/clang-tools-extra/test/clang-tidy/bugprone-sizeof-expression.cpp
+++ b/clang-tools-extra/test/clang-tidy/bugprone-sizeof-expression.cpp
@@ -231,6 +231,35 @@ int Test5() {
   return sum;
 }
 
+int Test6() {
+  int sum = 0;
+
+  struct S A = AsStruct(), B = AsStruct();
+  struct S *P = &A, *Q = &B;
+  sum += sizeof(struct S) == P - Q;
+  // CHECK-MESSAGES: :[[@LINE-1]]:10: warning: suspicious usage of 'sizeof(...)' in pointer arithmetic
+  sum += 5 * sizeof(S) != P - Q;
+  // CHECK-MESSAGES: :[[@LINE-1]]:10: warning: suspicious usage of 'sizeof(...)' in pointer arithmetic
+  sum += sizeof(S) < P - Q;
+  // CHECK-MESSAGES: :[[@LINE-1]]:10: warning: suspicious usage of 'sizeof(...)' in pointer arithmetic
+  sum += 5 * sizeof(S) <= P - Q;
+  // CHECK-MESSAGES: :[[@LINE-1]]:10: warning: suspicious usage of 'sizeof(...)' in pointer arithmetic
+  sum += 5 * sizeof(*P) >= P - Q;
+  // CHECK-MESSAGES: :[[@LINE-1]]:10: warning: suspicious usage of 'sizeof(...)' in pointer arithmetic
+  sum += Q - P > 3 * sizeof(*P);
+  // CHECK-MESSAGES: :[[@LINE-1]]:10: warning: suspicious usage of 'sizeof(...)' in pointer arithmetic
+  sum += sizeof(S) + (P - Q);
+  // CHECK-MESSAGES: :[[@LINE-1]]:10: warning: suspicious usage of 'sizeof(...)' in pointer arithmetic
+  sum += 5 * sizeof(S) - (P - Q);
+  // CHECK-MESSAGES: :[[@LINE-1]]:10: warning: suspicious usage of 'sizeof(...)' in pointer arithmetic
+  sum += (P - Q) / sizeof(S);
+  // CHECK-MESSAGES: :[[@LINE-1]]:10: warning: suspicious usage of 'sizeof(...)' in pointer arithmetic
+  sum += (P - Q) / sizeof(*Q);
+  // CHECK-MESSAGES: :[[@LINE-1]]:10: warning: suspicious usage of 'sizeof(...)' in pointer arithmetic
+
+  return sum;
+}
+
 int ValidExpressions() {
   int A[] = {1, 2, 3, 4};
   static const char str[] = "hello";