[scudo] Initial standalone skeleton check-in

[cryptoad]

Summary

This is the initial check-in for the Standalone version of Scudo.

The project is initially going to live in scudo/standalone then will
replace scudo. See http://lists.llvm.org/pipermail/llvm-dev/2019-January/129113.html
for details.

This initial CL is meant to lay out the project structure, of both
code & tests, providing a minimal amount of functionalities, namely
various definitions, some atomic helpers and an intrusive list.
(empty.cc is just here to have a compilation unit, but will go away
in the upcoming CLs).

Initial support is restricted to Linux i386 & x86_64 in make files
and will be extended once things land & work.

We will grow organically from here, adding functionalities in limited
amounts.

[krytarowski]

I have got a scudo support patch for NetBSD locally.. but the original tests are havily prepared against GNU malloc. This makes me uncertain whether scudo really works. Are there plans to make the tests more generic?

[cryptoad]

In D57412#1376046, @krytarowski wrote:

I have got a scudo support patch for NetBSD locally.. but the original tests are havily prepared against GNU malloc. This makes me uncertain whether scudo really works. Are there plans to make the tests more generic?

That should be the case for the unit-tests. The new way things are done will clearly separate the C/C++ wrappers.
I can add you on the standalone check-ins for you to chime in on the direction we are headed to.
All the development efforts so far has targeted Linux/Android/Fuchsia, and I unfortunately have no BSD knowledge, but we are definitely open to contributions.
Initial check-ins will be Linux specific though since it's my workstation and that's what I am testing things against.

I wouldn't pursue work on your side on the current non-standalone Scudo, as the standalone version will be better (more performant, smaller memory footprint, etc) on all fronts.

[krytarowski]

In D57412#1376056, @cryptoad wrote:

In D57412#1376046, @krytarowski wrote:

I have got a scudo support patch for NetBSD locally.. but the original tests are havily prepared against GNU malloc. This makes me uncertain whether scudo really works. Are there plans to make the tests more generic?

That should be the case for the unit-tests. The new way things are done will clearly separate the C/C++ wrappers.
I can add you on the standalone check-ins for you to chime in on the direction we are headed to.
All the development efforts so far has targeted Linux/Android/Fuchsia, and I unfortunately have no BSD knowledge, but we are definitely open to contributions.
Initial check-ins will be Linux specific though since it's my workstation and that's what I am testing things against.

I wouldn't pursue work on your side on the current non-standalone Scudo, as the standalone version will be better (more performant, smaller memory footprint, etc) on all fronts.

Please keep tests agnostic to system malloc implementation (as much as possible). I will rebase or rework my NetBSD support code and upstream. When I did the port I was unsure whether it even works, but the situation maybe improved since the introduction of Fuchsia.

[morehouse]

lib/scudo/standalone/atomic_helpers.h

54

necessarily*

64

Have we lost the memory_order checking that sanitizer_atomic_clang_x86.h does, or is this done in __atomic_load?

99

Can we simplify to return __atomic_exchange(&A->ValDoNotUse, &V, MO) instead?

lib/scudo/standalone/list.h

149

Any reason not to put a private: here?

lib/scudo/standalone/tests/CMakeLists.txt

37

Will this be uncommented eventually?

[cryptoad]

lib/scudo/standalone/atomic_helpers.h

64

I looked around (non-exhaustively) and found that it was checked by isValidOrderingForOp in Clang, so I figured it could go away.
Just checked gcc and it has checks in https://github.com/gcc-mirror/gcc/blob/master/gcc/builtins.c#L6434.
Let me know if you feel it's reasonable to not have them.

99

As far as I can tell __atomic_exchange has a void return type.
It's worth noting that __atomic_exchange_n returns type but it doesn't seem to be widely used (see libcxx's __c11_atomic_exchange for example).

lib/scudo/standalone/list.h

149

Good question, I think this was the case in the sanitizer_common code and I didn't question it.
I will check if that can actually be private.

lib/scudo/standalone/tests/CMakeLists.txt

37

It might, or not!
I'm not awesome at this CMake/lit thing and I feel it could come back and bit me if I remove it and forgot it was useful at some point.
But I'm Ok removing it.

[cryptoad]

• s/necessary/necessarily
• actually make the private members of the list class private

[cryptoad]

• remove commented RUNTIME ${SCUDO_TEST_RUNTIME} in tests CMake

[morehouse]

lib/scudo/standalone/atomic_helpers.h

64

In sanitizer_common, these are DCHECKs so not critical. And since we're just wrapping the builtins, I think we can delegate the checking to them.

99

Hm, right I see that now in the gcc documentation.

I was looking at this list, which might not be the right reference.

lib/scudo/standalone/tests/CMakeLists.txt

37

My guess is that you'll need it once you add some .cpp files. I'm fine either leaving the commented line or not.

[Eugene.Zelenko]

Build with -DLLVM_ENABLE_LIBCXX=ON is broken because:

clang-9: error: argument unused during compilation: '-stdlib=libc++' [-Werror,-Wunused-command-line-argument]

[cryptoad]

In D57412#1384504, @Eugene.Zelenko wrote:

Build with -DLLVM_ENABLE_LIBCXX=ON is broken because:

clang-9: error: argument unused during compilation: '-stdlib=libc++' [-Werror,-Wunused-command-line-argument]

Ack, I'll fix that.

[cryptoad]

In D57412#1384504, @Eugene.Zelenko wrote:

Build with -DLLVM_ENABLE_LIBCXX=ON is broken because:

clang-9: error: argument unused during compilation: '-stdlib=libc++' [-Werror,-Wunused-command-line-argument]

What are your full cmake options? I can't seem to reproduce this with just -DLLVM_ENABLE_LIBCXX=ON

[cryptoad]

Repro'd the reported error with:

-DLLVM_ENABLE_LIBCXX=ON \
-DLLVM_ENABLE_LIBCXXABI=On \
-DCLANG_DEFAULT_CXX_STDLIB=libc++ \
-DCMAKE_CXX_FLAGS="-stdlib=libc++" \

Fix in D57757.

cmake/config-ix.cmake

set(ALL_PROFILE_SUPPORTED_ARCH ${X86} ${X86_64} ${ARM32} ${ARM64} ${PPC64}
     ${MIPS32} ${MIPS64} ${S390X})
 set(ALL_TSAN_SUPPORTED_ARCH ${X86_64} ${MIPS64} ${ARM64} ${PPC64})
 set(ALL_UBSAN_SUPPORTED_ARCH ${X86} ${X86_64} ${ARM32} ${ARM64}
     ${MIPS32} ${MIPS64} ${PPC64} ${S390X})
 set(ALL_SAFESTACK_SUPPORTED_ARCH ${X86} ${X86_64} ${ARM64} ${MIPS32} ${MIPS64})
 set(ALL_CFI_SUPPORTED_ARCH ${X86} ${X86_64} ${ARM32} ${ARM64} ${MIPS64})
 set(ALL_ESAN_SUPPORTED_ARCH ${X86_64} ${MIPS64})
 set(ALL_SCUDO_SUPPORTED_ARCH ${X86} ${X86_64} ${ARM32} ${ARM64} ${MIPS32} ${MIPS64} ${PPC64})
+set(ALL_SCUDO_STANDALONE_SUPPORTED_ARCH ${X86} ${X86_64})
 if(APPLE)
 set(ALL_XRAY_SUPPORTED_ARCH ${X86_64})
 else()
 set(ALL_XRAY_SUPPORTED_ARCH ${X86_64} ${ARM32} ${ARM64} ${MIPS32} ${MIPS64} powerpc64le)
 endif()
 set(ALL_SHADOWCALLSTACK_SUPPORTED_ARCH ${X86_64} ${ARM64})
 
 if(APPLE)
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)
   list_intersect(SCUDO_SUPPORTED_ARCH
     ALL_SCUDO_SUPPORTED_ARCH
     SANITIZER_COMMON_SUPPORTED_ARCH)
+  list_intersect(SCUDO_STANDALONE_SUPPORTED_ARCH
+    ALL_SCUDO_STANDALONE_SUPPORTED_ARCH
+    SANITIZER_COMMON_SUPPORTED_ARCH)
   list_intersect(FUZZER_SUPPORTED_ARCH
     ALL_FUZZER_SUPPORTED_ARCH
     SANITIZER_COMMON_SUPPORTED_ARCH)
   list_intersect(XRAY_SUPPORTED_ARCH
     ALL_XRAY_SUPPORTED_ARCH
     SANITIZER_COMMON_SUPPORTED_ARCH)
   list_intersect(SHADOWCALLSTACK_SUPPORTED_ARCH
     ALL_SHADOWCALLSTACK_SUPPORTED_ARCH
else()
   filter_available_targets(PROFILE_SUPPORTED_ARCH ${ALL_PROFILE_SUPPORTED_ARCH})
   filter_available_targets(TSAN_SUPPORTED_ARCH ${ALL_TSAN_SUPPORTED_ARCH})
   filter_available_targets(UBSAN_SUPPORTED_ARCH ${ALL_UBSAN_SUPPORTED_ARCH})
   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})
   filter_available_targets(SCUDO_SUPPORTED_ARCH ${ALL_SCUDO_SUPPORTED_ARCH})
+  filter_available_targets(SCUDO_STANDALONE_SUPPORTED_ARCH ${ALL_SCUDO_SUPPORTED_ARCH})
   filter_available_targets(XRAY_SUPPORTED_ARCH ${ALL_XRAY_SUPPORTED_ARCH})
   filter_available_targets(SHADOWCALLSTACK_SUPPORTED_ARCH
     ${ALL_SHADOWCALLSTACK_SUPPORTED_ARCH})
 endif()
 
 if (MSVC)
   # See if the DIA SDK is available and usable.
   set(MSVC_DIA_SDK_DIR "$ENV{VSINSTALLDIR}DIA SDK")

 
 if (COMPILER_RT_HAS_SANITIZER_COMMON AND ESAN_SUPPORTED_ARCH AND
     OS_NAME MATCHES "Linux|FreeBSD")
   set(COMPILER_RT_HAS_ESAN TRUE)
 else()
   set(COMPILER_RT_HAS_ESAN FALSE)
 endif()
 
+#TODO(kostyak): add back Android & Fuchsia when the code settles a bit.
+if (SCUDO_STANDALONE_SUPPORTED_ARCH AND OS_NAME MATCHES "Linux")
+  set(COMPILER_RT_HAS_SCUDO_STANDALONE TRUE)
+else()
+  set(COMPILER_RT_HAS_SCUDO_STANDALONE FALSE)
+endif()
+
 if (COMPILER_RT_HAS_SANITIZER_COMMON AND SCUDO_SUPPORTED_ARCH AND
     OS_NAME MATCHES "Linux|Android|Fuchsia")
   set(COMPILER_RT_HAS_SCUDO TRUE)
 else()
   set(COMPILER_RT_HAS_SCUDO FALSE)
 endif()
 
 if (COMPILER_RT_HAS_SANITIZER_COMMON AND XRAY_SUPPORTED_ARCH AND

lib/CMakeLists.txt

 
 function(compiler_rt_build_runtime runtime)
   string(TOUPPER ${runtime} runtime_uppercase)
   if(COMPILER_RT_HAS_${runtime_uppercase})
     add_subdirectory(${runtime})
     if(${runtime} STREQUAL tsan)
       add_subdirectory(tsan/dd)
     endif()
+    if(${runtime} STREQUAL scudo)
+      add_subdirectory(scudo/standalone)
+    endif()
   endif()
 endfunction()
 
 if(COMPILER_RT_BUILD_SANITIZERS)
   compiler_rt_build_runtime(interception)
 
   if(COMPILER_RT_HAS_SANITIZER_COMMON)
     add_subdirectory(stats)

lib/scudo/standalone/CMakeLists.txt

+add_compiler_rt_component(scudo_standalone)
+
+include_directories(../..)
+
+set(SCUDO_CFLAGS)
+
+list(APPEND SCUDO_CFLAGS
+  -Wall
+  -Werror
+  -nostdinc++)
+
+append_list_if(COMPILER_RT_HAS_FFREESTANDING_FLAG -ffreestanding SCUDO_CFLAGS)
+
+append_list_if(COMPILER_RT_HAS_FVISIBILITY_HIDDEN_FLAG -fvisibility=hidden SCUDO_CFLAGS)
+
+if(COMPILER_RT_DEBUG)
+  list(APPEND SCUDO_CFLAGS -O0)
+else()
+  list(APPEND SCUDO_CFLAGS -O3)
+endif()
+
+set(SCUDO_LINK_FLAGS)
+
+list(APPEND SCUDO_LINK_FLAGS -Wl,-z,defs,-z,now,-z,relro)
+
+append_list_if(COMPILER_RT_HAS_NODEFAULTLIBS_FLAG -nodefaultlibs SCUDO_LINK_FLAGS)
+
+if(ANDROID)
+# Put the shared library in the global group. For more details, see
+# android-changes-for-ndk-developers.md#changes-to-library-search-order
+  append_list_if(COMPILER_RT_HAS_Z_GLOBAL -Wl,-z,global SCUDO_LINK_FLAGS)
+endif()
+
+set(SCUDO_SOURCES empty.cc)
+
+set(SCUDO_HEADERS
+  platform.h
+  internal_defs.h
+  atomic_helpers.h
+  list.h)
+
+if(COMPILER_RT_HAS_SCUDO_STANDALONE)
+  add_compiler_rt_runtime(clang_rt.scudo_standalone
+    STATIC
+    ARCHS ${SCUDO_SUPPORTED_ARCH}
+    SOURCES ${SCUDO_SOURCES}
+    ADDITIONAL_HEADERS ${SCUDO_HEADERS}
+    CFLAGS ${SCUDO_CFLAGS}
+    PARENT_TARGET scudo_standalone)
+
+  if(COMPILER_RT_INCLUDE_TESTS)
+    add_subdirectory(tests)
+  endif()
+endif()

lib/scudo/standalone/atomic_helpers.h

+//===-- atomic_helpers.h ----------------------------------------*- C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef SCUDO_ATOMIC_H_
+#define SCUDO_ATOMIC_H_
+
+#include "internal_defs.h"
+
+namespace scudo {
+
+enum memory_order {
+  memory_order_relaxed = 0,
+  memory_order_consume = 1,
+  memory_order_acquire = 2,
+  memory_order_release = 3,
+  memory_order_acq_rel = 4,
+  memory_order_seq_cst = 5
+};
+COMPILER_CHECK(memory_order_relaxed == __ATOMIC_RELAXED);
+COMPILER_CHECK(memory_order_consume == __ATOMIC_CONSUME);
+COMPILER_CHECK(memory_order_acquire == __ATOMIC_ACQUIRE);
+COMPILER_CHECK(memory_order_release == __ATOMIC_RELEASE);
+COMPILER_CHECK(memory_order_acq_rel == __ATOMIC_ACQ_REL);
+COMPILER_CHECK(memory_order_seq_cst == __ATOMIC_SEQ_CST);
+
+struct atomic_u8 {
+  typedef u8 Type;
+  volatile Type ValDoNotUse;
+};
+
+struct atomic_u16 {
+  typedef u16 Type;
+  volatile Type ValDoNotUse;
+};
+
+struct atomic_s32 {
+  typedef s32 Type;
+  volatile Type ValDoNotUse;
+};
+
+struct atomic_u32 {
+  typedef u32 Type;
+  volatile Type ValDoNotUse;
+};
+
+struct atomic_u64 {
+  typedef u64 Type;
+  // On 32-bit platforms u64 is not necessarily aligned on 8 bytes.
+  volatile ALIGNED(8) Type ValDoNotUse;
+};
+
+struct atomic_uptr {
+  typedef uptr Type;
+  volatile Type ValDoNotUse;
+};
+
+template <typename T>
+INLINE typename T::Type atomic_load(const volatile T *A, memory_order MO) {
+  DCHECK(!(reinterpret_cast<uptr>(A) % sizeof(*A)));
+  typename T::Type V;
+  __atomic_load(&A->ValDoNotUse, &V, MO);
+  return V;
+}
+
+template <typename T>
+INLINE void atomic_store(volatile T *A, typename T::Type V, memory_order MO) {
+  DCHECK(!(reinterpret_cast<uptr>(A) % sizeof(*A)));
+  __atomic_store(&A->ValDoNotUse, &V, MO);
+}
+
+INLINE void atomic_thread_fence(memory_order) { __sync_synchronize(); }
+
+template <typename T>
+INLINE typename T::Type atomic_fetch_add(volatile T *A, typename T::Type V,
+                                         memory_order MO) {
+  DCHECK(!(reinterpret_cast<uptr>(A) % sizeof(*A)));
+  return __atomic_fetch_add(&A->ValDoNotUse, V, MO);
+}
+
+template <typename T>
+INLINE typename T::Type atomic_fetch_sub(volatile T *A, typename T::Type V,
+                                         memory_order MO) {
+  DCHECK(!(reinterpret_cast<uptr>(A) % sizeof(*A)));
+  return __atomic_fetch_sub(&A->ValDoNotUse, V, MO);
+}
+
+template <typename T>
+INLINE typename T::Type atomic_exchange(volatile T *A, typename T::Type V,
+                                        memory_order MO) {
+  DCHECK(!(reinterpret_cast<uptr>(A) % sizeof(*A)));
+  typename T::Type R;
+  __atomic_exchange(&A->ValDoNotUse, &V, &R, MO);
+  return R;
+}
+
+template <typename T>
+INLINE bool atomic_compare_exchange_strong(volatile T *A, typename T::Type *Cmp,
+                                           typename T::Type Xchg,
+                                           memory_order MO) {
+  return __atomic_compare_exchange(&A->ValDoNotUse, Cmp, &Xchg, false, MO,
+                                   __ATOMIC_RELAXED);
+}
+
+template <typename T>
+INLINE bool atomic_compare_exchange_weak(volatile T *A, typename T::Type *Cmp,
+                                         typename T::Type Xchg,
+                                         memory_order MO) {
+  return __atomic_compare_exchange(&A->ValDoNotUse, Cmp, &Xchg, true, MO,
+                                   __ATOMIC_RELAXED);
+}
+
+// Clutter-reducing helpers.
+
+template <typename T>
+INLINE typename T::Type atomic_load_relaxed(const volatile T *A) {
+  return atomic_load(A, memory_order_relaxed);
+}
+
+template <typename T>
+INLINE void atomic_store_relaxed(volatile T *A, typename T::Type V) {
+  atomic_store(A, V, memory_order_relaxed);
+}
+
+} // namespace scudo
+
+#endif // SCUDO_ATOMIC_H_

lib/scudo/standalone/empty.cc

+//===-- empty.cc ------------------------------------------------*- C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "atomic_helpers.h"
+#include "list.h"

lib/scudo/standalone/internal_defs.h

+//===-- internal_defs.h -----------------------------------------*- C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef SCUDO_INTERNAL_DEFS_H_
+#define SCUDO_INTERNAL_DEFS_H_
+
+#include "platform.h"
+
+#ifndef SCUDO_DEBUG
+#define SCUDO_DEBUG 0
+#endif
+
+#define ARRAY_SIZE(a) (sizeof(a) / sizeof((a)[0]))
+
+// String related macros.
+
+#define STRINGIFY_(S) #S
+#define STRINGIFY(S) STRINGIFY_(S)
+#define CONCATENATE_(S, C) S##C
+#define CONCATENATE(S, C) CONCATENATE_(S, C)
+
+// Attributes & builtins related macros.
+
+#define INTERFACE __attribute__((visibility("default")))
+#define WEAK __attribute__((weak))
+#define INLINE inline
+#define ALWAYS_INLINE inline __attribute__((always_inline))
+#define ALIAS(x) __attribute__((alias(x)))
+#define ALIGNED(x) __attribute__((aligned(x)))
+#define FORMAT(f, a) __attribute__((format(printf, f, a)))
+#define NOINLINE __attribute__((noinline))
+#define NORETURN __attribute__((noreturn))
+#define THREADLOCAL __thread
+#define LIKELY(x) __builtin_expect(!!(x), 1)
+#define UNLIKELY(x) __builtin_expect(!!(x), 0)
+#if defined(__i386__) || defined(__x86_64__)
+// __builtin_prefetch(x) generates prefetchnt0 on x86
+#define PREFETCH(x) __asm__("prefetchnta (%0)" : : "r"(x))
+#else
+#define PREFETCH(x) __builtin_prefetch(x)
+#endif
+#define UNUSED __attribute__((unused))
+#define USED __attribute__((used))
+#define NOEXCEPT noexcept
+
+namespace scudo {
+
+typedef unsigned long uptr;
+typedef signed long sptr;
+typedef unsigned char u8;
+typedef unsigned short u16;
+typedef unsigned int u32;
+typedef unsigned long long u64;
+typedef signed char s8;
+typedef signed short s16;
+typedef signed int s32;
+typedef signed long long s64;
+
+// Various integer constants.
+
+#undef __INT64_C
+#undef __UINT64_C
+#undef UINTPTR_MAX
+#if SCUDO_WORDSIZE == 64U
+#define __INT64_C(c) c##L
+#define __UINT64_C(c) c##UL
+#define UINTPTR_MAX (18446744073709551615UL)
+#else
+#define __INT64_C(c) c##LL
+#define __UINT64_C(c) c##ULL
+#define UINTPTR_MAX (4294967295U)
+#endif // SCUDO_WORDSIZE == 64U
+#undef INT32_MIN
+#define INT32_MIN (-2147483647 - 1)
+#undef INT32_MAX
+#define INT32_MAX (2147483647)
+#undef UINT32_MAX
+#define UINT32_MAX (4294967295U)
+#undef INT64_MIN
+#define INT64_MIN (-__INT64_C(9223372036854775807) - 1)
+#undef INT64_MAX
+#define INT64_MAX (__INT64_C(9223372036854775807))
+#undef UINT64_MAX
+#define UINT64_MAX (__UINT64_C(18446744073709551615))
+
+enum LinkerInitialized { LINKER_INITIALIZED = 0 };
+
+// Various CHECK related macros.
+
+#define COMPILER_CHECK(Pred) static_assert(Pred, "")
+
+// TODO(kostyak): implement at a later check-in.
+#define CHECK_IMPL(c1, op, c2)                                                 \
+  do {                                                                         \
+  } while (false)
+
+#define CHECK(a) CHECK_IMPL((a), !=, 0)
+#define CHECK_EQ(a, b) CHECK_IMPL((a), ==, (b))
+#define CHECK_NE(a, b) CHECK_IMPL((a), !=, (b))
+#define CHECK_LT(a, b) CHECK_IMPL((a), <, (b))
+#define CHECK_LE(a, b) CHECK_IMPL((a), <=, (b))
+#define CHECK_GT(a, b) CHECK_IMPL((a), >, (b))
+#define CHECK_GE(a, b) CHECK_IMPL((a), >=, (b))
+
+#if SCUDO_DEBUG
+#define DCHECK(a) CHECK(a)
+#define DCHECK_EQ(a, b) CHECK_EQ(a, b)
+#define DCHECK_NE(a, b) CHECK_NE(a, b)
+#define DCHECK_LT(a, b) CHECK_LT(a, b)
+#define DCHECK_LE(a, b) CHECK_LE(a, b)
+#define DCHECK_GT(a, b) CHECK_GT(a, b)
+#define DCHECK_GE(a, b) CHECK_GE(a, b)
+#else
+#define DCHECK(a)
+#define DCHECK_EQ(a, b)
+#define DCHECK_NE(a, b)
+#define DCHECK_LT(a, b)
+#define DCHECK_LE(a, b)
+#define DCHECK_GT(a, b)
+#define DCHECK_GE(a, b)
+#endif
+
+// TODO(kostyak): implement at a later check-in.
+#define UNREACHABLE(msg)                                                       \
+  do {                                                                         \
+  } while (false)
+
+} // namespace scudo
+
+#endif // SCUDO_INTERNAL_DEFS_H_

lib/scudo/standalone/list.h

+//===-- list.h --------------------------------------------------*- C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef SCUDO_LIST_H_
+#define SCUDO_LIST_H_
+
+#include "internal_defs.h"
+
+namespace scudo {
+
+// Intrusive POD singly-linked list.
+// An object with all zero fields should represent a valid empty list. clear()
+// should be called on all non-zero-initialized objects before using.
+template <class Item> struct IntrusiveList {
+  friend class Iterator;
+
+  void clear() {
+    First = Last = nullptr;
+    Size = 0;
+  }
+
+  bool empty() const { return Size == 0; }
+  uptr size() const { return Size; }
+
+  void push_back(Item *X) {
+    if (empty()) {
+      X->Next = nullptr;
+      First = Last = X;
+      Size = 1;
+    } else {
+      X->Next = nullptr;
+      Last->Next = X;
+      Last = X;
+      Size++;
+    }
+  }
+
+  void push_front(Item *X) {
+    if (empty()) {
+      X->Next = nullptr;
+      First = Last = X;
+      Size = 1;
+    } else {
+      X->Next = First;
+      First = X;
+      Size++;
+    }
+  }
+
+  void pop_front() {
+    DCHECK(!empty());
+    First = First->Next;
+    if (!First)
+      Last = nullptr;
+    Size--;
+  }
+
+  void extract(Item *Prev, Item *X) {
+    DCHECK(!empty());
+    DCHECK_NE(Prev, nullptr);
+    DCHECK_NE(X, nullptr);
+    DCHECK_EQ(Prev->Next, X);
+    Prev->Next = X->Next;
+    if (Last == X)
+      Last = Prev;
+    Size--;
+  }
+
+  Item *front() { return First; }
+  const Item *front() const { return First; }
+  Item *back() { return Last; }
+  const Item *back() const { return Last; }
+
+  void append_front(IntrusiveList<Item> *L) {
+    DCHECK_NE(this, L);
+    if (L->empty())
+      return;
+    if (empty()) {
+      *this = *L;
+    } else if (!L->empty()) {
+      L->Last->Next = First;
+      First = L->First;
+      Size += L->size();
+    }
+    L->clear();
+  }
+
+  void append_back(IntrusiveList<Item> *L) {
+    DCHECK_NE(this, L);
+    if (L->empty())
+      return;
+    if (empty()) {
+      *this = *L;
+    } else {
+      Last->Next = L->First;
+      Last = L->Last;
+      Size += L->size();
+    }
+    L->clear();
+  }
+
+  void checkConsistency() {
+    if (Size == 0) {
+      CHECK_EQ(First, 0);
+      CHECK_EQ(Last, 0);
+    } else {
+      uptr count = 0;
+      for (Item *i = First;; i = i->Next) {
+        count++;
+        if (i == Last)
+          break;
+      }
+      CHECK_EQ(size(), count);
+      CHECK_EQ(Last->Next, 0);
+    }
+  }
+
+  template <class ItemT> class IteratorBase {
+  public:
+    explicit IteratorBase(ItemT *CurrentItem) : Current(CurrentItem) {}
+    IteratorBase &operator++() {
+      Current = Current->Next;
+      return *this;
+    }
+    bool operator!=(IteratorBase Other) const {
+      return Current != Other.Current;
+    }
+    ItemT &operator*() { return *Current; }
+
+  private:
+    ItemT *Current;
+  };
+
+  typedef IteratorBase<Item> Iterator;
+  typedef IteratorBase<const Item> ConstIterator;
+
+  Iterator begin() { return Iterator(First); }
+  Iterator end() { return Iterator(nullptr); }
+
+  ConstIterator begin() const { return ConstIterator(First); }
+  ConstIterator end() const { return ConstIterator(nullptr); }
+
+private:
+  uptr Size;
+  Item *First;
+  Item *Last;
+};
+
+} // namespace scudo
+
+#endif // SCUDO_LIST_H_

lib/scudo/standalone/platform.h

+//===-- platform.h ----------------------------------------------*- C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef SCUDO_PLATFORM_H_
+#define SCUDO_PLATFORM_H_
+
+#if defined(__linux__)
+#define SCUDO_LINUX 1
+#else
+#define SCUDO_LINUX 0
+#endif
+
+#if defined(__ANDROID__)
+#define SCUDO_ANDROID 1
+#else
+#define SCUDO_ANDROID 0
+#endif
+
+#if defined(__Fuchsia__)
+#define SCUDO_FUCHSIA 1
+#else
+#define SCUDO_FUCHSIA 0
+#endif
+
+#if __LP64__
+#define SCUDO_WORDSIZE 64U
+#else
+#define SCUDO_WORDSIZE 32U
+#endif
+
+#if SCUDO_WORDSIZE == 64U
+#define FIRST_32_SECOND_64(a, b) (b)
+#else
+#define FIRST_32_SECOND_64(a, b) (a)
+#endif
+
+#ifndef SCUDO_CAN_USE_PRIMARY64
+#define SCUDO_CAN_USE_PRIMARY64 (SCUDO_WORDSIZE == 64U)
+#endif
+
+#ifndef SCUDO_MIN_ALIGNMENT_LOG
+// We force malloc-type functions to be aligned to std::max_align_t, but there
+// is no reason why the minimum alignment for all other functions can't be 8
+// bytes. Except obviously for applications making incorrect assumptions.
+// TODO(kostyak): define SCUDO_MIN_ALIGNMENT_LOG 3
+#define SCUDO_MIN_ALIGNMENT_LOG FIRST_32_SECOND_64(3, 4)
+#endif
+
+#if defined(__aarch64__)
+#define SCUDO_MMAP_RANGE_SIZE FIRST_32_SECOND_64(1ULL << 32, 1ULL << 48)
+#else
+#define SCUDO_MMAP_RANGE_SIZE FIRST_32_SECOND_64(1ULL << 32, 1ULL << 47)
+#endif
+
+// Older gcc have issues aligning to a constexpr, and require an integer.
+// See https://gcc.gnu.org/bugzilla/show_bug.cgi?id=56859 among others.
+#if defined(__powerpc__) || defined(__powerpc64__)
+#define SCUDO_CACHE_LINE_SIZE 128
+#else
+#define SCUDO_CACHE_LINE_SIZE 64
+#endif
+
+#define SCUDO_POINTER_FORMAT_LENGTH FIRST_32_SECOND_64(8, 12)
+
+#endif // SCUDO_PLATFORM_H_

lib/scudo/standalone/tests/CMakeLists.txt

+include_directories(..)
+
+add_custom_target(ScudoUnitTests)
+set_target_properties(ScudoUnitTests PROPERTIES
+  FOLDER "Compiler-RT Tests")
+
+set(SCUDO_UNITTEST_CFLAGS
+  ${COMPILER_RT_UNITTEST_CFLAGS}
+  ${COMPILER_RT_GTEST_CFLAGS}
+  -I${COMPILER_RT_SOURCE_DIR}/include
+  -I${COMPILER_RT_SOURCE_DIR}/lib
+  -I${COMPILER_RT_SOURCE_DIR}/lib/scudo/standalone
+  -DGTEST_HAS_RTTI=0)
+
+set(SCUDO_TEST_ARCH ${SCUDO_SUPPORTED_ARCH})
+
+# gtests requires c++
+set(LINK_FLAGS -lstdc++ -pthread)
+
+set(TEST_HEADERS)
+foreach (header ${SCUDO_HEADERS})
+  list(APPEND TEST_HEADERS ${CMAKE_CURRENT_SOURCE_DIR}/../${header})
+endforeach()
+
+# add_scudo_unittest(<name>
+#                   SOURCES <sources list>
+#                   HEADERS <extra headers list>)
+macro(add_scudo_unittest testname)
+  cmake_parse_arguments(TEST "" "" "SOURCES;HEADERS" ${ARGN})
+  if(COMPILER_RT_HAS_SCUDO_STANDALONE)
+    foreach(arch ${SCUDO_TEST_ARCH})
+      set(ScudoUnitTestsObjects)
+      generate_compiler_rt_tests(ScudoUnitTestsObjects ScudoUnitTests
+        "${testname}-${arch}-Test" ${arch}
+        SOURCES ${TEST_SOURCES} ${COMPILER_RT_GTEST_SOURCE} 
+        COMPILE_DEPS ${TEST_HEADERS}
+        DEPS gtest scudo_standalone
+        CFLAGS ${SCUDO_UNITTEST_CFLAGS}
+        LINK_FLAGS ${LINK_FLAGS})
+    endforeach()
+  endif()
+endmacro()
+
+set(SCUDO_UNIT_TEST_SOURCES
+  atomic_test.cc
+  list_test.cc
+  scudo_unit_test_main.cc)
+
+add_scudo_unittest(ScudoUnitTest
+  SOURCES ${SCUDO_UNIT_TEST_SOURCES})

lib/scudo/standalone/tests/atomic_test.cc

+//===-- atomic_test.cc ------------------------------------------*- C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "scudo/standalone/atomic_helpers.h"
+#include "gtest/gtest.h"
+
+namespace scudo {
+
+template <typename T> struct ValAndMagic {
+  typename T::Type Magic0;
+  T A;
+  typename T::Type Magic1;
+
+  static ValAndMagic<T> *Sink;
+};
+
+template <typename T> ValAndMagic<T> *ValAndMagic<T>::Sink;
+
+template <typename T, memory_order LoadMO, memory_order StoreMO>
+void checkStoreLoad() {
+  typedef typename T::Type Type;
+  ValAndMagic<T> Val;
+  // Prevent the compiler from scalarizing the struct.
+  ValAndMagic<T>::Sink = &Val;
+  // Ensure that surrounding memory is not overwritten.
+  Val.Magic0 = Val.Magic1 = (Type)-3;
+  for (u64 I = 0; I < 100; I++) {
+    // Generate A value that occupies all bytes of the variable.
+    u64 V = I;
+    V |= V << 8;
+    V |= V << 16;
+    V |= V << 32;
+    Val.A.ValDoNotUse = (Type)V;
+    EXPECT_EQ(atomic_load(&Val.A, LoadMO), (Type)V);
+    Val.A.ValDoNotUse = (Type)-1;
+    atomic_store(&Val.A, (Type)V, StoreMO);
+    EXPECT_EQ(Val.A.ValDoNotUse, (Type)V);
+  }
+  EXPECT_EQ(Val.Magic0, (Type)-3);
+  EXPECT_EQ(Val.Magic1, (Type)-3);
+}
+
+TEST(ScudoStandalone, AtomicStoreLoad) {
+  checkStoreLoad<atomic_u8, memory_order_relaxed, memory_order_relaxed>();
+  checkStoreLoad<atomic_u8, memory_order_consume, memory_order_relaxed>();
+  checkStoreLoad<atomic_u8, memory_order_acquire, memory_order_relaxed>();
+  checkStoreLoad<atomic_u8, memory_order_relaxed, memory_order_release>();
+  checkStoreLoad<atomic_u8, memory_order_seq_cst, memory_order_seq_cst>();
+
+  checkStoreLoad<atomic_u16, memory_order_relaxed, memory_order_relaxed>();
+  checkStoreLoad<atomic_u16, memory_order_consume, memory_order_relaxed>();
+  checkStoreLoad<atomic_u16, memory_order_acquire, memory_order_relaxed>();
+  checkStoreLoad<atomic_u16, memory_order_relaxed, memory_order_release>();
+  checkStoreLoad<atomic_u16, memory_order_seq_cst, memory_order_seq_cst>();
+
+  checkStoreLoad<atomic_u32, memory_order_relaxed, memory_order_relaxed>();
+  checkStoreLoad<atomic_u32, memory_order_consume, memory_order_relaxed>();
+  checkStoreLoad<atomic_u32, memory_order_acquire, memory_order_relaxed>();
+  checkStoreLoad<atomic_u32, memory_order_relaxed, memory_order_release>();
+  checkStoreLoad<atomic_u32, memory_order_seq_cst, memory_order_seq_cst>();
+
+  checkStoreLoad<atomic_u64, memory_order_relaxed, memory_order_relaxed>();
+  checkStoreLoad<atomic_u64, memory_order_consume, memory_order_relaxed>();
+  checkStoreLoad<atomic_u64, memory_order_acquire, memory_order_relaxed>();
+  checkStoreLoad<atomic_u64, memory_order_relaxed, memory_order_release>();
+  checkStoreLoad<atomic_u64, memory_order_seq_cst, memory_order_seq_cst>();
+
+  checkStoreLoad<atomic_uptr, memory_order_relaxed, memory_order_relaxed>();
+  checkStoreLoad<atomic_uptr, memory_order_consume, memory_order_relaxed>();
+  checkStoreLoad<atomic_uptr, memory_order_acquire, memory_order_relaxed>();
+  checkStoreLoad<atomic_uptr, memory_order_relaxed, memory_order_release>();
+  checkStoreLoad<atomic_uptr, memory_order_seq_cst, memory_order_seq_cst>();
+}
+
+template <typename T> void checkAtomicCompareExchange() {
+  typedef typename T::Type Type;
+  {
+    Type OldVal = 42;
+    Type NewVal = 24;
+    Type V = OldVal;
+    EXPECT_TRUE(atomic_compare_exchange_strong(
+        reinterpret_cast<T *>(&V), &OldVal, NewVal, memory_order_relaxed));
+    EXPECT_FALSE(atomic_compare_exchange_strong(
+        reinterpret_cast<T *>(&V), &OldVal, NewVal, memory_order_relaxed));
+    EXPECT_EQ(NewVal, OldVal);
+  }
+  {
+    Type OldVal = 42;
+    Type NewVal = 24;
+    Type V = OldVal;
+    EXPECT_TRUE(atomic_compare_exchange_weak(reinterpret_cast<T *>(&V), &OldVal,
+                                             NewVal, memory_order_relaxed));
+    EXPECT_FALSE(atomic_compare_exchange_weak(
+        reinterpret_cast<T *>(&V), &OldVal, NewVal, memory_order_relaxed));
+    EXPECT_EQ(NewVal, OldVal);
+  }
+}
+
+TEST(ScudoStandalone, AtomicCompareExchangeTest) {
+  checkAtomicCompareExchange<atomic_u8>();
+  checkAtomicCompareExchange<atomic_u16>();
+  checkAtomicCompareExchange<atomic_u32>();
+  checkAtomicCompareExchange<atomic_u64>();
+  checkAtomicCompareExchange<atomic_uptr>();
+}
+
+} // namespace scudo

lib/scudo/standalone/tests/list_test.cc

+//===-- list_test.cc --------------------------------------------*- C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "scudo/standalone/list.h"
+#include "gtest/gtest.h"
+
+struct ListItem {
+  ListItem *Next;
+};
+
+typedef scudo::IntrusiveList<ListItem> List;
+
+static List StaticList;
+
+static void setList(List *L, ListItem *X = nullptr, ListItem *Y = nullptr,
+                    ListItem *Z = nullptr) {
+  L->clear();
+  if (X)
+    L->push_back(X);
+  if (Y)
+    L->push_back(Y);
+  if (Z)
+    L->push_back(Z);
+}
+
+static void checkList(List *L, ListItem *I1, ListItem *I2 = nullptr,
+                      ListItem *I3 = nullptr, ListItem *I4 = nullptr,
+                      ListItem *I5 = nullptr, ListItem *I6 = nullptr) {
+  if (I1) {
+    EXPECT_EQ(L->front(), I1);
+    L->pop_front();
+  }
+  if (I2) {
+    EXPECT_EQ(L->front(), I2);
+    L->pop_front();
+  }
+  if (I3) {
+    EXPECT_EQ(L->front(), I3);
+    L->pop_front();
+  }
+  if (I4) {
+    EXPECT_EQ(L->front(), I4);
+    L->pop_front();
+  }
+  if (I5) {
+    EXPECT_EQ(L->front(), I5);
+    L->pop_front();
+  }
+  if (I6) {
+    EXPECT_EQ(L->front(), I6);
+    L->pop_front();
+  }
+  EXPECT_TRUE(L->empty());
+}
+
+TEST(ScudoSandalone, IntrusiveList) {
+  ListItem Items[6];
+  EXPECT_EQ(StaticList.size(), 0U);
+
+  List L;
+  L.clear();
+
+  ListItem *X = &Items[0];
+  ListItem *Y = &Items[1];
+  ListItem *Z = &Items[2];
+  ListItem *A = &Items[3];
+  ListItem *B = &Items[4];
+  ListItem *C = &Items[5];
+
+  EXPECT_EQ(L.size(), 0U);
+  L.push_back(X);
+  EXPECT_EQ(L.size(), 1U);
+  EXPECT_EQ(L.back(), X);
+  EXPECT_EQ(L.front(), X);
+  L.pop_front();
+  EXPECT_TRUE(L.empty());
+  L.checkConsistency();
+
+  L.push_front(X);
+  EXPECT_EQ(L.size(), 1U);
+  EXPECT_EQ(L.back(), X);
+  EXPECT_EQ(L.front(), X);
+  L.pop_front();
+  EXPECT_TRUE(L.empty());
+  L.checkConsistency();
+
+  L.push_front(X);
+  L.push_front(Y);
+  L.push_front(Z);
+  EXPECT_EQ(L.size(), 3U);
+  EXPECT_EQ(L.front(), Z);
+  EXPECT_EQ(L.back(), X);
+  L.checkConsistency();
+
+  L.pop_front();
+  EXPECT_EQ(L.size(), 2U);
+  EXPECT_EQ(L.front(), Y);
+  EXPECT_EQ(L.back(), X);
+  L.pop_front();
+  L.pop_front();
+  EXPECT_TRUE(L.empty());
+  L.checkConsistency();
+
+  L.push_back(X);
+  L.push_back(Y);
+  L.push_back(Z);
+  EXPECT_EQ(L.size(), 3U);
+  EXPECT_EQ(L.front(), X);
+  EXPECT_EQ(L.back(), Z);
+  L.checkConsistency();
+
+  L.pop_front();
+  EXPECT_EQ(L.size(), 2U);
+  EXPECT_EQ(L.front(), Y);
+  EXPECT_EQ(L.back(), Z);
+  L.pop_front();
+  L.pop_front();
+  EXPECT_TRUE(L.empty());
+  L.checkConsistency();
+
+  L.push_back(X);
+  L.push_back(Y);
+  L.push_back(Z);
+  L.extract(X, Y);
+  EXPECT_EQ(L.size(), 2U);
+  EXPECT_EQ(L.front(), X);
+  EXPECT_EQ(L.back(), Z);
+  L.checkConsistency();
+  L.extract(X, Z);
+  EXPECT_EQ(L.size(), 1U);
+  EXPECT_EQ(L.front(), X);
+  EXPECT_EQ(L.back(), X);
+  L.checkConsistency();
+  L.pop_front();
+  EXPECT_TRUE(L.empty());
+
+  List L1, L2;
+  L1.clear();
+  L2.clear();
+
+  L1.append_front(&L2);
+  EXPECT_TRUE(L1.empty());
+  EXPECT_TRUE(L2.empty());
+
+  L1.append_back(&L2);
+  EXPECT_TRUE(L1.empty());
+  EXPECT_TRUE(L2.empty());
+
+  setList(&L1, X);
+  checkList(&L1, X);
+
+  setList(&L1, X, Y, Z);
+  setList(&L2, A, B, C);
+  L1.append_back(&L2);
+  checkList(&L1, X, Y, Z, A, B, C);
+  EXPECT_TRUE(L2.empty());
+
+  setList(&L1, X, Y);
+  setList(&L2);
+  L1.append_front(&L2);
+  checkList(&L1, X, Y);
+  EXPECT_TRUE(L2.empty());
+}
+
+TEST(ScudoStandalone, IntrusiveListAppendEmpty) {
+  ListItem I;
+  List L;
+  L.clear();
+  L.push_back(&I);
+  List L2;
+  L2.clear();
+  L.append_back(&L2);
+  EXPECT_EQ(L.back(), &I);
+  EXPECT_EQ(L.front(), &I);
+  EXPECT_EQ(L.size(), 1U);
+  L.append_front(&L2);
+  EXPECT_EQ(L.back(), &I);
+  EXPECT_EQ(L.front(), &I);
+  EXPECT_EQ(L.size(), 1U);
+}

lib/scudo/standalone/tests/scudo_unit_test_main.cc

+//===-- scudo_unit_test_main.cc ---------------------------------*- C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "gtest/gtest.h"
+
+int main(int argc, char **argv) {
+  testing::InitGoogleTest(&argc, argv);
+  return RUN_ALL_TESTS();
+}

test/scudo/CMakeLists.txt

foreach(arch ${SCUDO_TEST_ARCH})
   set(CONFIG_NAME ${ARCH_UPPER_CASE}${OS_NAME}Config)
 
   configure_lit_site_cfg(
     ${CMAKE_CURRENT_SOURCE_DIR}/lit.site.cfg.in
     ${CMAKE_CURRENT_BINARY_DIR}/${CONFIG_NAME}/lit.site.cfg)
   list(APPEND SCUDO_TESTSUITES ${CMAKE_CURRENT_BINARY_DIR}/${CONFIG_NAME})
 endforeach()
 
+add_subdirectory(standalone)
+
 add_lit_testsuite(check-scudo "Running the Scudo Hardened Allocator tests"
   ${SCUDO_TESTSUITES}
   DEPENDS ${SCUDO_TEST_DEPS})
 set_target_properties(check-scudo PROPERTIES FOLDER "Compiler-RT Misc")

test/scudo/standalone/CMakeLists.txt

+if(COMPILER_RT_INCLUDE_TESTS AND COMPILER_RT_HAS_SCUDO_STANDALONE)
+  configure_lit_site_cfg(
+    ${CMAKE_CURRENT_SOURCE_DIR}/unit/lit.site.cfg.in
+    ${CMAKE_CURRENT_BINARY_DIR}/unit/lit.site.cfg)
+  list(APPEND SCUDO_STANDALONE_TEST_DEPS ScudoUnitTests)
+  list(APPEND SCUDO_STANDALONE_TESTSUITES ${CMAKE_CURRENT_BINARY_DIR}/unit)
+endif()
+
+add_lit_testsuite(check-scudo_standalone
+  "Running Scudo Standalone tests"
+  ${SCUDO_STANDALONE_TESTSUITES}
+  DEPENDS ${SCUDO_STANDALONE_TEST_DEPS})
+
+set_target_properties(check-scudo_standalone
+  PROPERTIES FOLDER "Compiler-RT Tests")

test/scudo/standalone/unit/lit.site.cfg.in

+@LIT_SITE_CFG_IN_HEADER@
+
+# Load common config for all compiler-rt unit tests.
+lit_config.load_config(config, "@COMPILER_RT_BINARY_DIR@/unittests/lit.common.unit.configured")
+
+# Setup config name.
+config.name = 'ScudoStandalone-Unit'
+
+# Setup test source and exec root.
+# For unit tests, we define it as build directory with unit tests.
+config.test_exec_root = "@COMPILER_RT_BINARY_DIR@/lib/scudo/standalone/tests"
+config.test_source_root = config.test_exec_root