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 +1,35 @@
+# Build for the EfficiencySanitizer runtime support library.
+
+add_custom_target(esan)
+
+set(ESAN_RTL_CFLAGS ${SANITIZER_COMMON_CFLAGS})
+append_rtti_flag(OFF ESAN_RTL_CFLAGS)
+
+include_directories(..)
+
+set(ESAN_SOURCES
+  esan.cpp
+  esan_interface.cpp)
+
+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 +1,44 @@
+//===-- 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_internal.h.
+//   - Platform-specific files should be used instead of ifdefs (*).
+//   - No system headers included in header files (*).
+//   - Platform specific headers 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_internal.h"
+
+namespace __esan {
+
+extern bool EsanIsInitialized;
+
+extern ToolType WhichTool;
+
+void initializeLibrary(ToolType Tool);
+int finalizeLibrary();
+void processRangeAccess(uptr PC, uptr Addr, int Size, bool IsWrite);
+
+} // namespace __esan
+
+#endif // ESAN_H
Index: lib/esan/esan.cpp
===================================================================
--- /dev/null
+++ lib/esan/esan.cpp
@@ -0,0 +1,112 @@
+//===-- esan.cpp ----------------------------------------------------------===//
+//
+//                     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_internal.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 EsanOptsEnv[] = "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_load_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.
+
+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.cpp 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(EsanOptsEnv));
+  InitializeCommonFlags();
+  if (Verbosity())
+    ReportUnrecognizedFlags();
+  if (common_flags()->help)
+    Parser.PrintFlagDescriptions();
+  __sanitizer_set_report_path(common_flags()->log_path);
+}
+
+void initializeLibrary(ToolType Tool) {
+  // We assume there is only one thread during init.
+  if (EsanIsInitialized) {
+    CHECK(Tool == WhichTool);
+    return;
+  }
+  WhichTool = Tool;
+  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.cpp 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.cpp
===================================================================
--- /dev/null
+++ lib/esan/esan_interface.cpp
@@ -0,0 +1,106 @@
+//===-- esan_interface.cpp ------------------------------------------------===//
+//
+//                     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_internal.h"
+#include "esan.h"
+#include "sanitizer_common/sanitizer_internal_defs.h"
+
+using namespace __esan; // NOLINT
+
+// The instrumentation passes ToolType as a 32-bit integer.
+// Here we guard against some arch with a non-32-bit int.
+static_assert(sizeof(ToolType) == sizeof(u32), "enum type is not 32 bits");
+
+void __esan_init(ToolType Tool) {
+  initializeLibrary(Tool);
+}
+
+void __esan_aligned_load1(void *Addr) {
+  processRangeAccess(GET_CALLER_PC(), (uptr)Addr, 1, false);
+}
+
+void __esan_aligned_load2(void *Addr) {
+  processRangeAccess(GET_CALLER_PC(), (uptr)Addr, 2, false);
+}
+
+void __esan_aligned_load4(void *Addr) {
+  processRangeAccess(GET_CALLER_PC(), (uptr)Addr, 4, false);
+}
+
+void __esan_aligned_load8(void *Addr) {
+  processRangeAccess(GET_CALLER_PC(), (uptr)Addr, 8, false);
+}
+
+void __esan_aligned_load16(void *Addr) {
+  processRangeAccess(GET_CALLER_PC(), (uptr)Addr, 16, false);
+}
+
+void __esan_aligned_store1(void *Addr) {
+  processRangeAccess(GET_CALLER_PC(), (uptr)Addr, 1, true);
+}
+
+void __esan_aligned_store2(void *Addr) {
+  processRangeAccess(GET_CALLER_PC(), (uptr)Addr, 2, true);
+}
+
+void __esan_aligned_store4(void *Addr) {
+  processRangeAccess(GET_CALLER_PC(), (uptr)Addr, 4, true);
+}
+
+void __esan_aligned_store8(void *Addr) {
+  processRangeAccess(GET_CALLER_PC(), (uptr)Addr, 8, true);
+}
+
+void __esan_aligned_store16(void *Addr) {
+  processRangeAccess(GET_CALLER_PC(), (uptr)Addr, 16, true);
+}
+
+void __esan_unaligned_load2(void *Addr) {
+  processRangeAccess(GET_CALLER_PC(), (uptr)Addr, 2, false);
+}
+
+void __esan_unaligned_load4(void *Addr) {
+  processRangeAccess(GET_CALLER_PC(), (uptr)Addr, 4, false);
+}
+
+void __esan_unaligned_load8(void *Addr) {
+  processRangeAccess(GET_CALLER_PC(), (uptr)Addr, 8, false);
+}
+
+void __esan_unaligned_load16(void *Addr) {
+  processRangeAccess(GET_CALLER_PC(), (uptr)Addr, 16, false);
+}
+
+void __esan_unaligned_store2(void *Addr) {
+  processRangeAccess(GET_CALLER_PC(), (uptr)Addr, 2, true);
+}
+
+void __esan_unaligned_store4(void *Addr) {
+  processRangeAccess(GET_CALLER_PC(), (uptr)Addr, 4, true);
+}
+
+void __esan_unaligned_store8(void *Addr) {
+  processRangeAccess(GET_CALLER_PC(), (uptr)Addr, 8, true);
+}
+
+void __esan_unaligned_store16(void *Addr) {
+  processRangeAccess(GET_CALLER_PC(), (uptr)Addr, 16, true);
+}
+
+void __esan_unusual_load(void *Addr, uptr Size) {
+  processRangeAccess(GET_CALLER_PC(), (uptr)Addr, Size, false);
+}
+
+void __esan_unusual_store(void *Addr, uptr Size) {
+  processRangeAccess(GET_CALLER_PC(), (uptr)Addr, Size, true);
+}
Index: lib/esan/esan_interface_internal.h
===================================================================
--- /dev/null
+++ lib/esan/esan_interface_internal.h
@@ -0,0 +1,73 @@
+//===-- esan_interface_internal.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.
+//
+// Calls to the functions declared in this header will be inserted by
+// the instrumentation module.
+//===----------------------------------------------------------------------===//
+
+#ifndef ESAN_INTERFACE_INTERNAL_H
+#define ESAN_INTERFACE_INTERNAL_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_None = 0,
+  ESAN_CacheFrag,
+} 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);
+
+// The instrumentation module will insert a call to one of these routines prior
+// to each load and store instruction for which we do not have "fastpath"
+// inlined instrumentation.  These calls constitute the "slowpath" for our
+// tools.  We have separate routines for each type of memory access to enable
+// targeted optimization.
+SANITIZER_INTERFACE_ATTRIBUTE void __esan_aligned_load1(void *Addr);
+SANITIZER_INTERFACE_ATTRIBUTE void __esan_aligned_load2(void *Addr);
+SANITIZER_INTERFACE_ATTRIBUTE void __esan_aligned_load4(void *Addr);
+SANITIZER_INTERFACE_ATTRIBUTE void __esan_aligned_load8(void *Addr);
+SANITIZER_INTERFACE_ATTRIBUTE void __esan_aligned_load16(void *Addr);
+
+SANITIZER_INTERFACE_ATTRIBUTE void __esan_aligned_store1(void *Addr);
+SANITIZER_INTERFACE_ATTRIBUTE void __esan_aligned_store2(void *Addr);
+SANITIZER_INTERFACE_ATTRIBUTE void __esan_aligned_store4(void *Addr);
+SANITIZER_INTERFACE_ATTRIBUTE void __esan_aligned_store8(void *Addr);
+SANITIZER_INTERFACE_ATTRIBUTE void __esan_aligned_store16(void *Addr);
+
+SANITIZER_INTERFACE_ATTRIBUTE void __esan_unaligned_load2(void *Addr);
+SANITIZER_INTERFACE_ATTRIBUTE void __esan_unaligned_load4(void *Addr);
+SANITIZER_INTERFACE_ATTRIBUTE void __esan_unaligned_load8(void *Addr);
+SANITIZER_INTERFACE_ATTRIBUTE void __esan_unaligned_load16(void *Addr);
+
+SANITIZER_INTERFACE_ATTRIBUTE void __esan_unaligned_store2(void *Addr);
+SANITIZER_INTERFACE_ATTRIBUTE void __esan_unaligned_store4(void *Addr);
+SANITIZER_INTERFACE_ATTRIBUTE void __esan_unaligned_store8(void *Addr);
+SANITIZER_INTERFACE_ATTRIBUTE void __esan_unaligned_store16(void *Addr);
+
+// These cover unusually-sized accesses.
+SANITIZER_INTERFACE_ATTRIBUTE void __esan_unusual_load(void *Addr, uptr Size);
+SANITIZER_INTERFACE_ATTRIBUTE void __esan_unusual_store(void *Addr, uptr Size);
+
+#ifdef __cplusplus
+}  // extern "C"
+#endif
+
+#endif // ESAN_INTERFACE_INTERNAL_H
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"
Index: test/CMakeLists.txt
===================================================================
--- test/CMakeLists.txt
+++ test/CMakeLists.txt
@@ -70,6 +70,9 @@
   if(COMPILER_RT_HAS_SAFESTACK)
     add_subdirectory(safestack)
   endif()
+  if(COMPILER_RT_HAS_ESAN)
+    add_subdirectory(esan)
+  endif()
 endif()
 
 if(COMPILER_RT_STANDALONE_BUILD)
Index: test/esan/CMakeLists.txt
===================================================================
--- /dev/null
+++ test/esan/CMakeLists.txt
@@ -0,0 +1,32 @@
+set(ESAN_TEST_DEPS ${SANITIZER_COMMON_LIT_TEST_DEPS})
+if(NOT COMPILER_RT_STANDALONE_BUILD)
+  list(APPEND ESAN_TEST_DEPS esan)
+endif()
+
+set(ESAN_TESTSUITES)
+
+set(ESAN_TEST_ARCH ${ESAN_SUPPORTED_ARCH})
+
+set(ESAN_LIT_SOURCE_DIR ${CMAKE_CURRENT_SOURCE_DIR})
+
+foreach(arch ${ESAN_TEST_ARCH})
+  set(ESAN_TEST_TARGET_ARCH ${arch})
+  string(TOLOWER "-${arch}" ESAN_TEST_CONFIG_SUFFIX)
+  get_target_flags_for_arch(${arch} ESAN_TEST_TARGET_CFLAGS)
+  string(REPLACE ";" " " ESAN_TEST_TARGET_CFLAGS "${ESAN_TEST_TARGET_CFLAGS}")
+
+  string(TOUPPER ${arch} ARCH_UPPER_CASE)
+  set(CONFIG_NAME ${ARCH_UPPER_CASE}Config)
+
+  configure_lit_site_cfg(
+    ${CMAKE_CURRENT_SOURCE_DIR}/lit.site.cfg.in
+    ${CMAKE_CURRENT_BINARY_DIR}/${CONFIG_NAME}/lit.site.cfg)
+  list(APPEND ESAN_TESTSUITES ${CMAKE_CURRENT_BINARY_DIR}/${CONFIG_NAME})
+endforeach()
+
+# TODO(bruening): add Unit/ tests as well
+
+add_lit_testsuite(check-esan "Running EfficiencySanitizer tests"
+  ${ESAN_TESTSUITES}
+  DEPENDS ${ESAN_TEST_DEPS})
+set_target_properties(check-esan PROPERTIES FOLDER "Esan tests")
Index: test/esan/TestCases/verbose-simple.c
===================================================================
--- /dev/null
+++ test/esan/TestCases/verbose-simple.c
@@ -0,0 +1,11 @@
+// RUN: %clang_esan_frag -O0 %s -o %t 2>&1
+// RUN: %env_esan_opts=verbosity=1 %run %t 2>&1 | FileCheck %s
+
+#include <stdlib.h>
+#include <string.h>
+int main(int argc, char **argv) {
+  // CHECK:      in esan::initializeLibrary
+  // CHECK-NEXT: in esan::finalizeLibrary
+  // CHECK-NEXT: {{.*}}EfficiencySanitizer is not finished: nothing yet to report
+  return 0;
+}
Index: test/esan/lit.cfg
===================================================================
--- /dev/null
+++ test/esan/lit.cfg
@@ -0,0 +1,32 @@
+# -*- Python -*-
+
+import os
+
+# Setup config name.
+config.name = 'EfficiencySanitizer' + config.name_suffix
+
+# Setup source root.
+config.test_source_root = os.path.dirname(__file__)
+
+# Setup default compiler flags used with -fsanitize=efficiency option.
+base_cflags = ([config.target_cflags] + config.debug_info_flags)
+base_cxxflags = config.cxx_mode_flags + base_cflags
+
+frag_cflags = (["-fsanitize=efficiency-cache-frag"] + base_cflags)
+
+def build_invocation(compile_flags):
+  return " " + " ".join([config.clang] + compile_flags) + " "
+
+config.substitutions.append( ("%clang_esan_frag ",
+                              build_invocation(frag_cflags)) )
+
+default_esan_opts = ''
+config.substitutions.append(('%env_esan_opts=',
+                             'env ESAN_OPTIONS=' + default_esan_opts))
+
+# Default test suffixes.
+config.suffixes = ['.c', '.cpp']
+
+# EfficiencySanitizer tests are currently supported on Linux x86-64 only.
+if config.host_os not in ['Linux'] or config.target_arch != 'x86_64':
+  config.unsupported = True
Index: test/esan/lit.site.cfg.in
===================================================================
--- /dev/null
+++ test/esan/lit.site.cfg.in
@@ -0,0 +1,14 @@
+## Autogenerated by LLVM/Clang configuration.
+# Do not edit!
+
+# Tool-specific config options.
+config.name_suffix = "@ESAN_TEST_CONFIG_SUFFIX@"
+config.esan_lit_source_dir = "@ESAN_LIT_SOURCE_DIR@"
+config.target_cflags = "@ESAN_TEST_TARGET_CFLAGS@"
+config.target_arch = "@ESAN_TEST_TARGET_ARCH@"
+
+# Load common config for all compiler-rt lit tests.
+lit_config.load_config(config, "@COMPILER_RT_BINARY_DIR@/test/lit.common.configured")
+
+# Load tool-specific config that would do the real work.
+lit_config.load_config(config, "@ESAN_LIT_SOURCE_DIR@/lit.cfg")