Index: cmake/config-ix.cmake
===================================================================
--- cmake/config-ix.cmake
+++ cmake/config-ix.cmake
@@ -263,6 +263,7 @@
     ${MIPS32} ${MIPS64} ${PPC64})
 set(ALL_SAFESTACK_SUPPORTED_ARCH ${X86} ${X86_64} ${ARM64} ${MIPS32} ${MIPS64})
 set(ALL_CFI_SUPPORTED_ARCH ${X86} ${X86_64})
+set(ALL_ESAN_SUPPORTED_ARCH ${X86_64})
 
 if(APPLE)
   include(CompilerRTDarwinUtils)
@@ -495,6 +496,9 @@
   list_intersect(CFI_SUPPORTED_ARCH
     ALL_CFI_SUPPORTED_ARCH
     SANITIZER_COMMON_SUPPORTED_ARCH)
+  list_intersect(ESAN_SUPPORTED_ARCH
+    ALL_ESAN_SUPPORTED_ARCH
+    SANITIZER_COMMON_SUPPORTED_ARCH)
 else()
   # Architectures supported by compiler-rt libraries.
   filter_available_targets(BUILTIN_SUPPORTED_ARCH
@@ -517,6 +521,7 @@
   filter_available_targets(SAFESTACK_SUPPORTED_ARCH
     ${ALL_SAFESTACK_SUPPORTED_ARCH})
   filter_available_targets(CFI_SUPPORTED_ARCH ${ALL_CFI_SUPPORTED_ARCH})
+  filter_available_targets(ESAN_SUPPORTED_ARCH ${ALL_ESAN_SUPPORTED_ARCH})
 endif()
 
 if (MSVC)
@@ -624,3 +629,10 @@
 else()
   set(COMPILER_RT_HAS_CFI FALSE)
 endif()
+
+if (COMPILER_RT_HAS_SANITIZER_COMMON AND ESAN_SUPPORTED_ARCH AND
+    OS_NAME MATCHES "Linux")
+  set(COMPILER_RT_HAS_ESAN TRUE)
+else()
+  set(COMPILER_RT_HAS_ESAN FALSE)
+endif()
Index: lib/CMakeLists.txt
===================================================================
--- lib/CMakeLists.txt
+++ lib/CMakeLists.txt
@@ -48,4 +48,8 @@
   if(COMPILER_RT_HAS_CFI)
     add_subdirectory(cfi)
   endif()
+
+  if(COMPILER_RT_HAS_ESAN)
+    add_subdirectory(esan)
+  endif()
 endif()
Index: lib/esan/CMakeLists.txt
===================================================================
--- /dev/null
+++ lib/esan/CMakeLists.txt
@@ -0,0 +1,36 @@
+# Build for the EfficiencySanitizer runtime support library.
+
+add_custom_target(esan)
+
+set(ESAN_CFLAGS ${SANITIZER_COMMON_CFLAGS})
+append_rtti_flag(OFF ESAN_CFLAGS)
+set(ESAN_RTL_CFLAGS ${ESAN_CFLAGS})
+
+include_directories(..)
+
+set(ESAN_SOURCES
+  esan.cc
+  esan_interface.cc)
+
+foreach (arch ${ESAN_SUPPORTED_ARCH})
+  add_compiler_rt_runtime(clang_rt.esan
+    STATIC
+    ARCHS ${arch}
+    SOURCES ${ESAN_SOURCES}
+            $<TARGET_OBJECTS:RTInterception.${arch}>
+            $<TARGET_OBJECTS:RTSanitizerCommon.${arch}>
+            $<TARGET_OBJECTS:RTSanitizerCommonLibc.${arch}>
+    CFLAGS ${ESAN_RTL_CFLAGS})
+  add_sanitizer_rt_symbols(clang_rt.esan
+    ARCHS ${arch}
+    EXTRA esan.syms.extra)
+  add_dependencies(esan
+    clang_rt.esan-${arch}
+    clang_rt.esan-${arch}-symbols)
+endforeach()
+
+add_dependencies(compiler-rt esan)
+
+if (COMPILER_RT_INCLUDE_TESTS)
+  # TODO(bruening): add tests via add_subdirectory(tests)
+endif()
Index: lib/esan/esan.h
===================================================================
--- /dev/null
+++ lib/esan/esan.h
@@ -0,0 +1,48 @@
+//===-- esan.h --------------------------------------------------*- C++ -*-===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This file is a part of EfficiencySanitizer, a family of performance tuners.
+//
+// Main internal esan header file.
+//
+// Ground rules:
+//   - C++ run-time should not be used (static CTORs, RTTI, exceptions, static
+//     function-scope locals)
+//   - All functions/classes/etc reside in namespace __esan, except for those
+//     declared in esan_interface.h.
+//   - Platform-specific files should be used instead of ifdefs (*).
+//   - No system headers included in header files (*).
+//   - Platform specific headres included only into platform-specific files (*).
+//
+//  (*) Except when inlining is critical for performance.
+//===----------------------------------------------------------------------===//
+
+#ifndef ESAN_H
+#define ESAN_H
+
+#include "sanitizer_common/sanitizer_common.h"
+#include "esan_interface.h"
+
+#define CALLERPC ((uptr)__builtin_return_address(0))
+
+namespace __esan {
+
+extern bool EsanIsInitialized;
+
+extern ToolType WhichTool;
+
+void initializeLibrary();
+int finalizeLibrary();
+void processMemAccess(uptr PC, uptr Addr, int Size, bool IsWrite);
+void processUnalignedAccess(uptr PC, uptr Addr, int Size, bool IsWrite);
+void processRangeAccess(uptr PC, uptr Addr, int Size, bool IsWrite);
+
+} // namespace __esan
+
+#endif // ESAN_H
Index: lib/esan/esan.cc
===================================================================
--- /dev/null
+++ lib/esan/esan.cc
@@ -0,0 +1,124 @@
+//===-- esan.cc ----------------------------------------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This file is a part of EfficiencySanitizer, a family of performance tuners.
+//
+// Main file (entry points) for the Esan run-time.
+//===----------------------------------------------------------------------===//
+
+#include "esan.h"
+#include "esan_interface.h"
+#include "sanitizer_common/sanitizer_common.h"
+#include "sanitizer_common/sanitizer_flag_parser.h"
+#include "sanitizer_common/sanitizer_flags.h"
+
+// See comment below.
+extern "C" {
+extern void __cxa_atexit(void (*function)(void));
+}
+
+namespace __esan {
+
+bool EsanIsInitialized;
+ToolType WhichTool;
+
+static const char *const EsanOpsEnv = "ESAN_OPTIONS";
+
+// We are combining multiple performance tuning tools under the umbrella of
+// one EfficiencySanitizer super-tool.  Most of our tools have very similar
+// memory access instrumentation, shadow memory mapping, libc interception,
+// etc., and there is typically more shared code than distinct code.
+//
+// We are not willing to dispatch on tool dynamically in our fastpath
+// instrumentation: thus, which tool to use is a static option selected
+// at compile time and passed to __esan_init().
+//
+// We are willing to pay the overhead of tool dispatch in the slowpath to more
+// easily share code.  We expect to only come here rarely.
+// If this becomes a performance hit, we can add separate interface
+// routines for each subtool (e.g., __esan_cache_frag_aligned_read_4).
+// But for libc interceptors, we'll have to do one of the following:
+// A) Add multiple-include support to sanitizer_common_interceptors.inc,
+//    instantiate it separately for each tool, and call the selected
+//    tool's intercept setup code.
+// B) Build separate static runtime libraries, one for each tool.
+// C) Completely split the tools into separate sanitizers.
+
+ALWAYS_INLINE USED void processMemAccess(uptr PC, uptr Addr, int Size,
+                                         bool IsWrite) {
+  VPrintf(4, "in esan::%s %p: %c %p %d\n", __FUNCTION__, PC,
+          IsWrite ? 'w' : 'r', Addr, Size);
+  // We expect common accesses to be inlined so we go for simplicity here:
+  processRangeAccess(PC, Addr, Size, IsWrite);
+}
+
+ALWAYS_INLINE USED void processUnalignedAccess(uptr PC, uptr Addr, int Size,
+                                               bool IsWrite) {
+  VPrintf(4, "in esan::%s %p: %c %p %d\n", __FUNCTION__, PC,
+          IsWrite ? 'w' : 'r', Addr, Size);
+  processRangeAccess(PC, Addr, Size, IsWrite);
+}
+
+void processRangeAccess(uptr PC, uptr Addr, int Size, bool IsWrite) {
+  VPrintf(3, "in esan::%s %p: %c %p %d\n", __FUNCTION__, PC,
+          IsWrite ? 'w' : 'r', Addr, Size);
+  if (WhichTool == ESAN_CacheFrag) {
+    // TODO(bruening): add shadow mapping and update shadow bits here.
+    // We'll move this to cache_frag.cc once we have something.
+  }
+}
+
+static void initializeFlags() {
+  // Once we add our own flags we'll parse them here.
+  // For now the common ones are sufficient.
+  FlagParser Parser;
+  SetCommonFlagsDefaults();
+  RegisterCommonFlags(&Parser);
+  Parser.ParseString(GetEnv(EsanOpsEnv));
+  InitializeCommonFlags();
+  if (Verbosity())
+    ReportUnrecognizedFlags();
+  if (common_flags()->help)
+    Parser.PrintFlagDescriptions();
+  __sanitizer_set_report_path(common_flags()->log_path);
+}
+
+void initializeLibrary() {
+  // We assume there is only one thread during init.
+  if (EsanIsInitialized)
+    return;
+  SanitizerToolName = "EfficiencySanitizer";
+  initializeFlags();
+
+  // Intercepting libc _exit or exit via COMMON_INTERCEPTOR_ON_EXIT only
+  // finalizes on an explicit exit call by the app.  To handle a normal
+  // exit we register an atexit handler.
+  ::__cxa_atexit((void (*)())finalizeLibrary);
+
+  VPrintf(1, "in esan::%s\n", __FUNCTION__);
+  if (WhichTool != ESAN_CacheFrag) {
+    Printf("ERROR: unknown tool %d requested\n", WhichTool);
+    Die();
+  }
+
+  EsanIsInitialized = true;
+}
+
+int finalizeLibrary() {
+  VPrintf(1, "in esan::%s\n", __FUNCTION__);
+  if (WhichTool == ESAN_CacheFrag) {
+    // FIXME NYI: we need to add sampling + callstack gathering and have a
+    // strategy for how to generate a final report.
+    // We'll move this to cache_frag.cc once we have something.
+    Report("%s is not finished: nothing yet to report\n", SanitizerToolName);
+  }
+  return 0;
+}
+
+} // namespace __esan
Index: lib/esan/esan.syms.extra
===================================================================
--- /dev/null
+++ lib/esan/esan.syms.extra
@@ -0,0 +1,3 @@
+__esan_init
+__esan_aligned*
+__esan_unaligned*
Index: lib/esan/esan_interface.h
===================================================================
--- /dev/null
+++ lib/esan/esan_interface.h
@@ -0,0 +1,64 @@
+//===-- esan_interface.h ----------------------------------------*- C++ -*-===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This file is a part of EfficiencySanitizer, a family of performance tuners.
+//
+// The functions declared in this header will be inserted by the instrumentation
+// module.
+// This header can be included by the instrumented program or by esan tests.
+//===----------------------------------------------------------------------===//
+
+#ifndef ESAN_INTERFACE_H
+#define ESAN_INTERFACE_H
+
+#include <sanitizer_common/sanitizer_internal_defs.h>
+
+// This header should NOT include any other headers.
+// All functions in this header are extern "C" and start with __esan_.
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+// This should be kept consistent with LLVM's EfficiencySanitizerOptions.
+typedef enum Type {
+  ESAN_CacheFrag = 0,
+} ToolType;
+
+// This function should be called at the very beginning of the process,
+// before any instrumented code is executed and before any call to malloc.
+SANITIZER_INTERFACE_ATTRIBUTE void __esan_init(ToolType Tool);
+
+SANITIZER_INTERFACE_ATTRIBUTE void __esan_aligned_read1(void *Addr);
+SANITIZER_INTERFACE_ATTRIBUTE void __esan_aligned_read2(void *Addr);
+SANITIZER_INTERFACE_ATTRIBUTE void __esan_aligned_read4(void *Addr);
+SANITIZER_INTERFACE_ATTRIBUTE void __esan_aligned_read8(void *Addr);
+SANITIZER_INTERFACE_ATTRIBUTE void __esan_aligned_read16(void *Addr);
+
+SANITIZER_INTERFACE_ATTRIBUTE void __esan_aligned_write1(void *Addr);
+SANITIZER_INTERFACE_ATTRIBUTE void __esan_aligned_write2(void *Addr);
+SANITIZER_INTERFACE_ATTRIBUTE void __esan_aligned_write4(void *Addr);
+SANITIZER_INTERFACE_ATTRIBUTE void __esan_aligned_write8(void *Addr);
+SANITIZER_INTERFACE_ATTRIBUTE void __esan_aligned_write16(void *Addr);
+
+SANITIZER_INTERFACE_ATTRIBUTE void __esan_unaligned_read2(const void *Addr);
+SANITIZER_INTERFACE_ATTRIBUTE void __esan_unaligned_read4(const void *Addr);
+SANITIZER_INTERFACE_ATTRIBUTE void __esan_unaligned_read8(const void *Addr);
+SANITIZER_INTERFACE_ATTRIBUTE void __esan_unaligned_read16(const void *Addr);
+
+SANITIZER_INTERFACE_ATTRIBUTE void __esan_unaligned_write2(const void *Addr);
+SANITIZER_INTERFACE_ATTRIBUTE void __esan_unaligned_write4(const void *Addr);
+SANITIZER_INTERFACE_ATTRIBUTE void __esan_unaligned_write8(const void *Addr);
+SANITIZER_INTERFACE_ATTRIBUTE void __esan_unaligned_write16(const void *Addr);
+
+#ifdef __cplusplus
+}  // extern "C"
+#endif
+
+#endif // ESAN_INTERFACE_H
Index: lib/esan/esan_interface.cc
===================================================================
--- /dev/null
+++ lib/esan/esan_interface.cc
@@ -0,0 +1,95 @@
+//===-- esan_interface.cc -------------------------------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This file is a part of EfficiencySanitizer, a family of performance tuners.
+//
+//===----------------------------------------------------------------------===//
+
+#include "esan_interface.h"
+#include "esan.h"
+#include "sanitizer_common/sanitizer_internal_defs.h"
+
+using namespace __esan; // NOLINT
+
+void __esan_init(ToolType Tool) {
+  WhichTool = Tool;
+  initializeLibrary();
+}
+
+void __esan_aligned_read1(void *Addr) {
+  processMemAccess(CALLERPC, (uptr)Addr, 1, false);
+}
+
+void __esan_aligned_read2(void *Addr) {
+  processMemAccess(CALLERPC, (uptr)Addr, 2, false);
+}
+
+void __esan_aligned_read4(void *Addr) {
+  processMemAccess(CALLERPC, (uptr)Addr, 4, false);
+}
+
+void __esan_aligned_read8(void *Addr) {
+  processMemAccess(CALLERPC, (uptr)Addr, 8, false);
+}
+
+void __esan_aligned_read16(void *Addr) {
+  processMemAccess(CALLERPC, (uptr)Addr, 16, false);
+}
+
+void __esan_aligned_write1(void *Addr) {
+  processMemAccess(CALLERPC, (uptr)Addr, 1, true);
+}
+
+void __esan_aligned_write2(void *Addr) {
+  processMemAccess(CALLERPC, (uptr)Addr, 2, true);
+}
+
+void __esan_aligned_write4(void *Addr) {
+  processMemAccess(CALLERPC, (uptr)Addr, 4, true);
+}
+
+void __esan_aligned_write8(void *Addr) {
+  processMemAccess(CALLERPC, (uptr)Addr, 8, true);
+}
+
+void __esan_aligned_write16(void *Addr) {
+  processMemAccess(CALLERPC, (uptr)Addr, 16, true);
+}
+
+void __esan_unaligned_read2(const void *Addr) {
+  processUnalignedAccess(CALLERPC, (uptr)Addr, 2, false);
+}
+
+void __esan_unaligned_read4(const void *Addr) {
+  processUnalignedAccess(CALLERPC, (uptr)Addr, 4, false);
+}
+
+void __esan_unaligned_read8(const void *Addr) {
+  processUnalignedAccess(CALLERPC, (uptr)Addr, 8, false);
+}
+
+void __esan_unaligned_read16(const void *Addr) {
+  processUnalignedAccess(CALLERPC, (uptr)Addr, 16, false);
+}
+
+void __esan_unaligned_write2(const void *Addr) {
+  processUnalignedAccess(CALLERPC, (uptr)Addr, 2, true);
+}
+
+void __esan_unaligned_write4(const void *Addr) {
+  processUnalignedAccess(CALLERPC, (uptr)Addr, 4, true);
+}
+
+void __esan_unaligned_write8(const void *Addr) {
+  processUnalignedAccess(CALLERPC, (uptr)Addr, 8, true);
+}
+
+void __esan_unaligned_write16(const void *Addr) {
+  processUnalignedAccess(CALLERPC, (uptr)Addr, 16, true);
+}
Index: lib/sanitizer_common/sanitizer_common_interceptors.inc
===================================================================
--- lib/sanitizer_common/sanitizer_common_interceptors.inc
+++ lib/sanitizer_common/sanitizer_common_interceptors.inc
@@ -30,6 +30,9 @@
 //   COMMON_INTERCEPTOR_SET_PTHREAD_NAME
 //   COMMON_INTERCEPTOR_HANDLE_RECVMSG
 //   COMMON_INTERCEPTOR_NOTHING_IS_INITIALIZED
+//
+// COMMON_INTERCEPTOR_ON_EXIT is only called if the app explicitly calls exit(),
+// not on a normal exit.
 //===----------------------------------------------------------------------===//
 
 #include "interception/interception.h"