[analyzer] Suppress warnings coming out of macros defined in sys/queue.h

Suppress the warning by just not emitting the report. The sink node
would get generated, which is fine since we did reach a bad state.

Motivation

Due to the way code is structured in some of these macros, we do not
reason correctly about it and report false positives. Specifically, the
following loop reports a use-after-free. Because of the way the code is
structured inside of the macro, the analyzer assumes that the list can
have cycles, so you end up with use-after-free in the loop, that is
safely deleting elements of the list. (The user does not have a way to
teach the analyzer about shape of data structures.)

SLIST_FOREACH_SAFE(item, &ctx->example_list, example_le, tmpitem) {
			if (item->index == 3) { // if you remove each time, no complaints
				assert((&ctx->example_list)->slh_first == item);
				SLIST_REMOVE(&ctx->example_list, item, example_s, example_le);
				free(item);
			}
		}

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@172883 91177308-0d34-0410-b5e6-96231b3b80d8

include/clang/StaticAnalyzer/Core/BugReporter/BugReporter.h

@@ -457,6 +457,11 @@ public:
 
   void Register(BugType *BT);
 
+  /// \brief Suppress reports that might lead to known false positives.
+  ///
+  /// Currently this suppresses reports based on locations of bugs.
+  bool suppressReport(BugReport *R);
+
   /// \brief Add the given report to the set of reports tracked by BugReporter.
   ///
   /// The reports are usually generated by the checkers. Further, they are

lib/StaticAnalyzer/Core/BugReporter.cpp

@@ -2137,7 +2137,32 @@ void BugReporter::Register(BugType *BT) {
   BugTypes = F.add(BugTypes, BT);
 }
 
+bool BugReporter::suppressReport(BugReport *R) {
+  const Stmt *S = R->getStmt();
+  if (!S)
+    return false;
+
+  // Here we suppress false positives coming from system macros. This list is
+  // based on known issues.
+
+  // Skip reports within the sys/queue.h macros as we do not have the ability to
+  // reason about data structure shapes.
+  SourceManager &SM = getSourceManager();
+  SourceLocation Loc = S->getLocStart();
+  while (Loc.isMacroID()) {
+    if (SM.isInSystemMacro(Loc) &&
+       (SM.getFilename(SM.getSpellingLoc(Loc)).endswith("sys/queue.h")))
+      return true;
+    Loc = SM.getSpellingLoc(Loc);
+  }
+
+  return false;
+}
+
 void BugReporter::emitReport(BugReport* R) {
+  if (suppressReport(R))
+    return;
+
   // Compute the bug report's hash to determine its equivalence class.
   llvm::FoldingSetNodeID ID;
   R->Profile(ID);

test/Analysis/diagnostics/false-positive-suppression.c

@@ -0,0 +1,23 @@
+// RUN: %clang_cc1 -analyze -analyzer-checker=core,unix -verify %s
+// expected-no-diagnostics
+
+#include "include/sys/queue.h"
+
+typedef __typeof(sizeof(int)) size_t;
+void *malloc(size_t);
+
+int radar12491259() {
+    int *p = malloc(12);
+    FREE_POINTER(p);
+    FREE_POINTER(p); // no-warning: we are suppressing errors coming from sys/queue macros.
+    return 0;
+}
+
+#define MYMACRO(p) FREE_POINTER(p)
+
+int radar12491259_inside_macro() {
+    int *p = malloc(12);
+    MYMACRO(p);
+    MYMACRO(p); // no-warning: we are suppressing errors coming from sys/queue macros.
+    return 0;
+}

test/Analysis/diagnostics/include/sys/queue.h

@@ -0,0 +1,5 @@
+#pragma clang system_header
+
+void free(void *);
+#define FREE_POINTER(x) free(x)
+