[Runtime] [Darwin] Add code to trigger the external backtracer.

When a Swift program crashes, we should catch the crash and execute the
external backtracer.

rdar://105391747

Author: al45tair

include/swift/Runtime/Backtrace.h

@@ -0,0 +1,117 @@
+//===--- Backtrace.cpp - Swift crash catching and backtracing support ---- ===//
+//
+// This source file is part of the Swift.org open source project
+//
+// Copyright (c) 2022 Apple Inc. and the Swift project authors
+// Licensed under Apache License v2.0 with Runtime Library Exception
+//
+// See https://swift.org/LICENSE.txt for license information
+// See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
+//
+//===----------------------------------------------------------------------===//
+//
+// Definitions relating to backtracing.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef SWIFT_RUNTIME_BACKTRACE_H
+#define SWIFT_RUNTIME_BACKTRACE_H
+
+#include "swift/Runtime/Config.h"
+
+#include "swift/shims/Visibility.h"
+#include "swift/shims/_SwiftBacktracing.h"
+
+#include <inttypes.h>
+
+#ifdef __cplusplus
+namespace swift {
+namespace runtime {
+namespace backtrace {
+#endif
+
+#ifdef _WIN32
+typedef wchar_t ArgChar;
+typedef DWORD ErrorCode;
+#else
+typedef char ArgChar;
+typedef int ErrorCode;
+#endif
+
+SWIFT_RUNTIME_STDLIB_INTERNAL ErrorCode _swift_installCrashHandler();
+
+SWIFT_RUNTIME_STDLIB_INTERNAL bool _swift_spawnBacktracer(const ArgChar * const *argv);
+
+enum class UnwindAlgorithm {
+  Auto = 0,
+  Fast = 1,
+  Precise = 2
+};
+
+enum class OnOffTty {
+  Off = 0,
+  On = 1,
+  TTY = 2
+};
+
+enum class Preset {
+  Auto = -1,
+  Friendly = 0,
+  Medium = 1,
+  Full = 2
+};
+
+enum class ThreadsToShow {
+  Preset = -1,
+  All = 0,
+  Crashed = 1
+};
+
+enum class RegistersToShow {
+  Preset = -1,
+  None = 0,
+  All = 1,
+  Crashed = 2
+};
+
+enum class ImagesToShow {
+  Preset = -1,
+  None = 0,
+  All = 1,
+  Mentioned = 2
+};
+
+enum class SanitizePaths {
+  Preset = -1,
+  Off = 0,
+  On = 1
+};
+
+struct BacktraceSettings {
+  UnwindAlgorithm  algorithm;
+  OnOffTty         enabled;
+  bool             demangle;
+  OnOffTty         interactive;
+  OnOffTty         color;
+  unsigned         timeout;
+  ThreadsToShow    threads;
+  RegistersToShow  registers;
+  ImagesToShow     images;
+  unsigned         limit;
+  unsigned         top;
+  SanitizePaths    sanitize;
+  Preset           preset;
+  const char      *swiftBacktracePath;
+};
+
+SWIFT_RUNTIME_STDLIB_INTERNAL BacktraceSettings _swift_backtraceSettings;
+
+SWIFT_RUNTIME_STDLIB_SPI SWIFT_CC(swift) bool _swift_isThunkFunction(const char *mangledName);
+
+#ifdef __cplusplus
+} // namespace backtrace
+} // namespace runtime
+} // namespace swift
+#endif
+
+#endif // SWIFT_RUNTIME_BACKTRACE_H

include/swift/Runtime/Config.h

@@ -481,6 +481,34 @@ swift_auth_code(T value, unsigned extra) {
 #endif
 }
 
+/// Does this platform support backtrace-on-crash?
+#ifdef __APPLE__
+#  include <TargetConditionals.h>
+#  if TARGET_OS_OSX
+#    define SWIFT_BACKTRACE_ON_CRASH_SUPPORTED 1
+#    define SWIFT_BACKTRACE_SECTION "__DATA,swift5_backtrace"
+#  else
+#    define SWIFT_BACKTRACE_ON_CRASH_SUPPORTED 0
+#  endif
+#elif defined(_WIN32)
+#  define SWIFT_BACKTRACE_ON_CRASH_SUPPORTED 0
+#  define SWIFT_BACKTRACE_SECTION ".sw5bckt"
+#elif defined(__linux__)
+#  define SWIFT_BACKTRACE_ON_CRASH_SUPPORTED 0
+#  define SWIFT_BACKTRACE_SECTION "swift5_backtrace"
+#else
+#  define SWIFT_BACKTRACE_ON_CRASH_SUPPORTED 0
+#endif
+
+/// What is the system page size?
+#if defined(__APPLE__) && defined(__arm64__)
+  // Apple Silicon systems use a 16KB page size
+  #define SWIFT_PAGE_SIZE 16384
+#else
+  // Everything else uses 4KB pages
+  #define SWIFT_PAGE_SIZE 4096
+#endif
+
 #endif
 
 #endif // SWIFT_RUNTIME_CONFIG_H