stdlib: add a secret key for hashing

Author: gribozavr

stdlib/public/SwiftShims/GlobalObjects.h

@@ -39,6 +39,14 @@ struct _SwiftEmptyArrayStorage {
 extern SWIFT_RUNTIME_STDLIB_INTERFACE
 struct _SwiftEmptyArrayStorage _swiftEmptyArrayStorage;
 
+struct _SwiftHashingSecretKey {
+  __swift_uint64_t key0;
+  __swift_uint64_t key1;
+};
+
+extern SWIFT_RUNTIME_STDLIB_INTERFACE
+struct _SwiftHashingSecretKey _swift_stdlib_Hashing_secretKey;
+
 extern SWIFT_RUNTIME_STDLIB_INTERFACE
 __swift_uint64_t _swift_stdlib_HashingDetail_fixedSeedOverride;
 

stdlib/public/core/Hashing.swift

@@ -23,6 +23,27 @@
 
 import SwiftShims
 
+public // @testable
+struct _Hashing {
+  // FIXME(ABI): make this an actual public API.
+  public // SPI
+  static var secretKey: (UInt64, UInt64) {
+    get {
+      // The variable itself is defined in C++ code so that it is initialized
+      // during static construction.  Almost every Swift program uses hash
+      // tables, so initializing the secret key during the startup seems to be
+      // the right trade-off.
+      return (
+        _swift_stdlib_Hashing_secretKey.key0,
+        _swift_stdlib_Hashing_secretKey.key1)
+    }
+    set {
+      (_swift_stdlib_Hashing_secretKey.key0,
+       _swift_stdlib_Hashing_secretKey.key1) = newValue
+    }
+  }
+}
+
 public // @testable
 struct _HashingDetail {
 

stdlib/public/stubs/GlobalObjects.cpp

@@ -18,6 +18,8 @@
 
 #include "../SwiftShims/GlobalObjects.h"
 #include "swift/Runtime/Metadata.h"
+#include "swift/Runtime/Debug.h"
+#include <stdlib.h>
 
 namespace swift {
 // FIXME(ABI): does this declaration need SWIFT_RUNTIME_STDLIB_INTERFACE?
@@ -39,6 +41,32 @@ swift::_SwiftEmptyArrayStorage swift::_swiftEmptyArrayStorage = {
   }
 };
 
+static __swift_uint64_t randomUInt64() {
+#if defined(__APPLE__)
+  return static_cast<__swift_uint64_t>(arc4random()) |
+         (static_cast<__swift_uint64_t>(arc4random()) << 32);
+#else
+  auto devUrandom = fopen("/dev/urandom", "r");
+  if (!devUrandom) {
+    swift::fatalError(/* flags = */ 0, "Opening \"/dev/urandom\" failed");
+  }
+  uint64_t result;
+  if (fread(&result, sizeof(result), 1, devUrandom) != 1) {
+    swift::fatalError(/* flags = */ 0, "Reading from \"/dev/urandom\" failed");
+  }
+  if (fclose(devUrandom)) {
+    swift::fatalError(/* flags = */ 0, "Closing \"/dev/urandom\" failed");
+  }
+  return result;
+#endif
+}
+
+SWIFT_ALLOWED_RUNTIME_GLOBAL_CTOR_BEGIN
+swift::_SwiftHashingSecretKey swift::_swift_stdlib_Hashing_secretKey = {
+  randomUInt64(), randomUInt64()
+};
+SWIFT_ALLOWED_RUNTIME_GLOBAL_CTOR_END
+
 __swift_uint64_t swift::_swift_stdlib_HashingDetail_fixedSeedOverride = 0;
 
 namespace llvm { namespace hashing { namespace detail {