Abseil LTS 20200923

What's New:
* `absl::StatusOr<T>` has been released. See our [blog
  post](https://abseil.io/blog/2020-091021-status) for more
  information.
* Abseil Flags reflection interfaces have been released.
* Abseil Flags memory usage has been significantly optimized.
* Abseil now supports a "hardened" build mode. This build mode enables
  runtime checks that guard against programming errors that may lead
  to security vulnerabilities.

Notable Fixes:
* Sanitizer dynamic annotations like `AnnotateRWLockCreate` that are
  also defined by the compiler sanitizer implementation are no longer
  also defined by Abseil.
* Sanitizer macros are now prefixed with `ABSL_` to avoid naming collisions.
* Sanitizer usage is now automatically detected and no longer requires
  macros like `ADDRESS_SANITIZER` to be defined on the command line.

Breaking Changes:
* Abseil no longer contains a `dynamic_annotations` library. Users
  using a supported build system (Bazel or CMake) are unaffected by
  this, but users manually specifying link libraries may get an error
  about a missing linker input.

Baseline: 7680a5f8efe32de4753baadbd63e74e59d95bac1
Cherry picks: None

1 files changed, 43 insertions, 24 deletions

diff --git a/absl/debugging/internal/stacktrace_config.h b/absl/debugging/internal/stacktrace_config.h
index d4e8480a..90af8528 100644
--- a/absl/debugging/internal/stacktrace_config.h
+++ b/absl/debugging/internal/stacktrace_config.h
@@ -28,43 +28,62 @@
 #define ABSL_STACKTRACE_INL_HEADER \
     "absl/debugging/internal/stacktrace_win32-inl.inc"
 
+#elif defined(__APPLE__)
+// Thread local support required for UnwindImpl.
+// Notes:
+// * Xcode's clang did not support `thread_local` until version 8, and
+//   even then not for all iOS < 9.0.
+// * Xcode 9.3 started disallowing `thread_local` for 32-bit iOS simulator
+//   targeting iOS 9.x.
+// * Xcode 10 moves the deployment target check for iOS < 9.0 to link time
+//   making __has_feature unreliable there.
+//
+// Otherwise, `__has_feature` is only supported by Clang so it has be inside
+// `defined(__APPLE__)` check.
+#if __has_feature(cxx_thread_local) && \
+    !(TARGET_OS_IPHONE && __IPHONE_OS_VERSION_MIN_REQUIRED < __IPHONE_9_0)
+#define ABSL_STACKTRACE_INL_HEADER \
+  "absl/debugging/internal/stacktrace_generic-inl.inc"
+#endif
+
 #elif defined(__linux__) && !defined(__ANDROID__)
 
-#if !defined(NO_FRAME_POINTER)
-# if defined(__i386__) || defined(__x86_64__)
+#if defined(NO_FRAME_POINTER) && \
+    (defined(__i386__) || defined(__x86_64__) || defined(__aarch64__))
+// Note: The libunwind-based implementation is not available to open-source
+// users.
 #define ABSL_STACKTRACE_INL_HEADER \
-    "absl/debugging/internal/stacktrace_x86-inl.inc"
-# elif defined(__ppc__) || defined(__PPC__)
-#define ABSL_STACKTRACE_INL_HEADER \
-    "absl/debugging/internal/stacktrace_powerpc-inl.inc"
-# elif defined(__aarch64__)
-#define ABSL_STACKTRACE_INL_HEADER \
-    "absl/debugging/internal/stacktrace_aarch64-inl.inc"
-# elif defined(__arm__)
+  "absl/debugging/internal/stacktrace_libunwind-inl.inc"
+#define STACKTRACE_USES_LIBUNWIND 1
+#elif defined(NO_FRAME_POINTER) && defined(__has_include)
+#if __has_include(<execinfo.h>)
 // Note: When using glibc this may require -funwind-tables to function properly.
 #define ABSL_STACKTRACE_INL_HEADER \
   "absl/debugging/internal/stacktrace_generic-inl.inc"
-# else
+#endif
+#elif defined(__i386__) || defined(__x86_64__)
 #define ABSL_STACKTRACE_INL_HEADER \
-   "absl/debugging/internal/stacktrace_unimplemented-inl.inc"
-# endif
-#else  // defined(NO_FRAME_POINTER)
-# if defined(__i386__) || defined(__x86_64__) || defined(__aarch64__)
+  "absl/debugging/internal/stacktrace_x86-inl.inc"
+#elif defined(__ppc__) || defined(__PPC__)
 #define ABSL_STACKTRACE_INL_HEADER \
-    "absl/debugging/internal/stacktrace_generic-inl.inc"
-# elif defined(__ppc__) || defined(__PPC__)
+  "absl/debugging/internal/stacktrace_powerpc-inl.inc"
+#elif defined(__aarch64__)
 #define ABSL_STACKTRACE_INL_HEADER \
-    "absl/debugging/internal/stacktrace_generic-inl.inc"
-# else
+  "absl/debugging/internal/stacktrace_aarch64-inl.inc"
+#elif defined(__has_include)
+#if __has_include(<execinfo.h>)
+// Note: When using glibc this may require -funwind-tables to function properly.
 #define ABSL_STACKTRACE_INL_HEADER \
-   "absl/debugging/internal/stacktrace_unimplemented-inl.inc"
-# endif
-#endif  // NO_FRAME_POINTER
+  "absl/debugging/internal/stacktrace_generic-inl.inc"
+#endif
+#endif
 
-#else
+#endif
+
+// Fallback to the empty implementation.
+#if !defined(ABSL_STACKTRACE_INL_HEADER)
 #define ABSL_STACKTRACE_INL_HEADER \
   "absl/debugging/internal/stacktrace_unimplemented-inl.inc"
-
 #endif
 
 #endif  // ABSL_DEBUGGING_INTERNAL_STACKTRACE_CONFIG_H_