[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

4 files changed, 58 insertions, 0 deletions

diff --git a/include/clang/StaticAnalyzer/Core/BugReporter/BugReporter.h b/include/clang/StaticAnalyzer/Core/BugReporter/BugReporter.h
index 7a87e47f74..74579b7b4c 100644
--- a/include/clang/StaticAnalyzer/Core/BugReporter/BugReporter.h
+++ b/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
diff --git a/lib/StaticAnalyzer/Core/BugReporter.cpp b/lib/StaticAnalyzer/Core/BugReporter.cpp
index 8e6bc69cc4..d64aa39feb 100644
--- a/lib/StaticAnalyzer/Core/BugReporter.cpp
+++ b/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);
diff --git a/test/Analysis/diagnostics/false-positive-suppression.c b/test/Analysis/diagnostics/false-positive-suppression.c
new file mode 100644
index 0000000000..420a573380
--- /dev/null
+++ b/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;
+}
diff --git a/test/Analysis/diagnostics/include/sys/queue.h b/test/Analysis/diagnostics/include/sys/queue.h
new file mode 100644
index 0000000000..e5698ed443
--- /dev/null
+++ b/test/Analysis/diagnostics/include/sys/queue.h
@@ -0,0 +1,5 @@
+#pragma clang system_header
+
+void free(void *);
+#define FREE_POINTER(x) free(x)
+