From bcd35a8ec11ea000d6a6fc31becc549eb5c25a30 Mon Sep 17 00:00:00 2001
From: Anna Zaks <ganna@apple.com>
Date: Fri, 11 Nov 2016 23:22:44 +0000
Subject: [PATCH] [tsan][clang] Introduce a function attribute to disable TSan
 checking at run time

This introduces a function annotation that disables TSan checking for the
function at run time. The benefit over attribute((no_sanitize("thread")))
is that the accesses within the callees will also be suppressed.

The motivation for this attribute is a guarantee given by the objective C
language that the calls to the reference count decrement and object
deallocation will be synchronized. To model this properly, we would need to
intercept all ref count decrement calls (which are very common in ObjC due
to use of ARC) and also every single message send. Instead, we propose to
just ignore all accesses made from within dealloc at run time. The main
downside is that this still does not introduce any synchronization, which
means we might still report false positives if the code that relies on this
synchronization is not executed from within dealloc. However, we have not
seen this in practice so far and think these cases will be very rare.

(This problem is similar in nature to https://reviews.llvm.org/D21609;
unfortunately, the same solution does not apply here.)

Differential Revision: https://reviews.llvm.org/D25857

llvm-svn: 286672
---
 clang/lib/CodeGen/CodeGenFunction.cpp              | 14 +++++++++
 .../sanitize-thread-no-checking-at-run-time.m      | 34 ++++++++++++++++++++++
 2 files changed, 48 insertions(+)
 create mode 100644 clang/test/CodeGen/sanitize-thread-no-checking-at-run-time.m

diff --git a/clang/lib/CodeGen/CodeGenFunction.cpp b/clang/lib/CodeGen/CodeGenFunction.cpp
index aac8f0a..b2243bc 100644
--- a/clang/lib/CodeGen/CodeGenFunction.cpp
+++ b/clang/lib/CodeGen/CodeGenFunction.cpp
@@ -731,6 +731,20 @@ void CodeGenFunction::StartFunction(GlobalDecl GD,
   if (SanOpts.has(SanitizerKind::SafeStack))
     Fn->addFnAttr(llvm::Attribute::SafeStack);
 
+  // Ignore TSan memory acesses from within ObjC/ObjC++ dealloc, initialize,
+  // .cxx_destruct and all of their calees at run time.
+  if (SanOpts.has(SanitizerKind::Thread)) {
+    if (const auto *OMD = dyn_cast_or_null<ObjCMethodDecl>(D)) {
+      IdentifierInfo *II = OMD->getSelector().getIdentifierInfoForSlot(0);
+      if (OMD->getMethodFamily() == OMF_dealloc ||
+          OMD->getMethodFamily() == OMF_initialize ||
+          (OMD->getSelector().isUnarySelector() && II->isStr(".cxx_destruct"))) {
+        Fn->addFnAttr("sanitize_thread_no_checking_at_run_time");
+        Fn->removeFnAttr(llvm::Attribute::SanitizeThread);
+      }
+    }
+  }
+
   // Apply xray attributes to the function (as a string, for now)
   if (D && ShouldXRayInstrumentFunction()) {
     if (const auto *XRayAttr = D->getAttr<XRayInstrumentAttr>()) {
diff --git a/clang/test/CodeGen/sanitize-thread-no-checking-at-run-time.m b/clang/test/CodeGen/sanitize-thread-no-checking-at-run-time.m
new file mode 100644
index 0000000..fade1e3
--- /dev/null
+++ b/clang/test/CodeGen/sanitize-thread-no-checking-at-run-time.m
@@ -0,0 +1,34 @@
+// RUN: %clang_cc1 -triple x86_64-apple-darwin -x objective-c++ -emit-llvm -o - %s | FileCheck -check-prefix=WITHOUT %s
+// RUN: %clang_cc1 -triple x86_64-apple-darwin -x objective-c++ -emit-llvm -o - %s -fsanitize=thread | FileCheck -check-prefix=TSAN %s
+
+__attribute__((objc_root_class))
+@interface NSObject
+- (void)dealloc;
+@end
+
+class NeedCleanup {
+public:
+  ~NeedCleanup() __attribute__((no_sanitize("thread"))) {}
+};
+
+@interface MyObject : NSObject {
+  NeedCleanup v;
+};
++ (void) initialize;
+- (void) dealloc;
+@end
+
+@implementation MyObject
++ (void)initialize {
+}
+- (void)dealloc {
+  [super dealloc];
+}
+@end
+
+// WITHOUT-NOT: "sanitize_thread_no_checking_at_run_time"
+
+// TSAN: initialize{{.*}}) [[ATTR:#[0-9]+]]
+// TSAN: dealloc{{.*}}) [[ATTR:#[0-9]+]]
+// TSAN: cxx_destruct{{.*}}) [[ATTR:#[0-9]+]]
+// TSAN: attributes [[ATTR]] = { nounwind {{.*}} "sanitize_thread_no_checking_at_run_time" {{.*}} }
-- 
2.7.4