[scudo] Add Android support

Summary:
This change adds Android support to the allocator (but doesn't yet enable it in
the cmake config), and should be the last fragment of the rewritten change
D31947.

Android has more memory constraints than other platforms, so the idea of a
unique context per thread would not have worked. The alternative chosen is to
allocate a set of contexts based on the number of cores on the machine, and
share those contexts within the threads. Contexts can be dynamically reassigned
to threads to prevent contention, based on a scheme suggested by @dvyuokv in
the initial review.

Additionally, given that Android doesn't support ELF TLS (only emutls for now),
we use the TSan TLS slot to make things faster: Scudo is mutually exclusive
with other sanitizers so this shouldn't cause any problem.

An additional change made here, is replacing `thread_local` by `THREADLOCAL`
and using the initial-exec thread model in the non-Android version to prevent
extraneous weak definition and checks on the relevant variables.

Reviewers: kcc, dvyukov, alekseyshl

Reviewed By: alekseyshl

Subscribers: srhines, mgorny, llvm-commits

Differential Revision: https://reviews.llvm.org/D32649

llvm-svn: 302300

1 files changed, 54 insertions, 0 deletions

diff --git a/compiler-rt/lib/scudo/scudo_tls_context_android.inc b/compiler-rt/lib/scudo/scudo_tls_context_android.inc
new file mode 100644
index 00000000000..f1951319d48
--- /dev/null
+++ b/compiler-rt/lib/scudo/scudo_tls_context_android.inc
@@ -0,0 +1,54 @@
+//===-- scudo_tls_context_android.inc ---------------------------*- C++ -*-===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+///
+/// Android specific base thread context definition.
+///
+//===----------------------------------------------------------------------===//
+
+#ifndef SCUDO_TLS_CONTEXT_ANDROID_INC_
+#define SCUDO_TLS_CONTEXT_ANDROID_INC_
+
+#ifndef SCUDO_TLS_H_
+# error "This file must be included inside scudo_tls.h."
+#endif  // SCUDO_TLS_H_
+
+#if SANITIZER_LINUX && SANITIZER_ANDROID
+
+struct ScudoThreadContextPlatform {
+  INLINE bool tryLock() {
+    if (Mutex.TryLock()) {
+      atomic_store_relaxed(&SlowLockPrecedence, 0);
+      return true;
+    }
+    if (atomic_load_relaxed(&SlowLockPrecedence) == 0)
+      atomic_store_relaxed(&SlowLockPrecedence, NanoTime());
+    return false;
+  }
+
+  INLINE void lock() {
+    Mutex.Lock();
+    atomic_store_relaxed(&SlowLockPrecedence, 0);
+  }
+
+  INLINE void unlock() {
+    Mutex.Unlock();
+  }
+
+  INLINE u64 getSlowLockPrecedence() {
+    return atomic_load_relaxed(&SlowLockPrecedence);
+  }
+
+ private:
+  StaticSpinMutex Mutex;
+  atomic_uint64_t SlowLockPrecedence;
+};
+
+#endif  // SANITIZER_LINUX && SANITIZER_ANDROID
+
+#endif  // SCUDO_TLS_CONTEXT_ANDROID_INC_