[GWP-ASan] Add thread ID to PRNG seed.

[hctim]

Summary

Adds thread ID to PRNG seed for increased entropy. In particular, this allows
multiple runs in quick succession that will have different PRNG seeds, allowing
for better demos/testing.

[hctim]

• Removed unneccessary static cast.

[kcc]

LGTM

compiler-rt/lib/gwp_asan/guarded_pool_allocator.h

public:
   // Dumps an error report (including allocation and deallocation stack traces).
   // An optional error may be provided if the caller knows what the error is
   // ahead of time. This is primarily a helper function to locate the static
   // singleton pointer and call the internal version of this function. This
   // method is never thread safe, and should only be called when fatal errors
   // occur.
   static void reportError(uintptr_t AccessPtr, Error E = Error::UNKNOWN);
 
+  // Get the current thread ID, or kInvalidThreadID if failure. Note: This
+  // implementation is platform-specific.
+  static uint64_t getThreadID();
+
 private:
   static constexpr size_t kInvalidSlotID = SIZE_MAX;
 
   // These functions anonymously map memory or change the permissions of mapped
   // memory into this process in a platform-specific way. Pointer and size
   // arguments are expected to be page-aligned. These functions will never
   // return on error, instead electing to kill the calling process on failure.
   // Note that memory is initially mapped inaccessible. In order for RW
   // mappings, call mapMemory() followed by markReadWrite() on the returned
   // pointer.
   void *mapMemory(size_t Size) const;
   void markReadWrite(void *Ptr, size_t Size) const;
   void markInaccessible(void *Ptr, size_t Size) const;
 
-  // Get the current thread ID, or kInvalidThreadID if failure. Note: This
-  // implementation is platform-specific.
-  static uint64_t getThreadID();
-
   // Get the page size from the platform-specific implementation. Only needs to
   // be called once, and the result should be cached in PageSize in this class.
   static size_t getPlatformPageSize();
 
   // Install the SIGSEGV crash handler for printing use-after-free and heap-
   // buffer-{under|over}flow exceptions. This is platform specific as even
   // though POSIX and Windows both support registering handlers through
   // signal(), we have to use platform-specific signal handlers to obtain the

compiler-rt/lib/gwp_asan/random.cpp

 //===-- random.cpp ----------------------------------------------*- 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 "gwp_asan/random.h"
+#include "gwp_asan/guarded_pool_allocator.h"
 
 #include <time.h>
 
 namespace gwp_asan {
 uint32_t getRandomUnsigned32() {
-  thread_local uint32_t RandomState = static_cast<uint64_t>(time(nullptr));
+  thread_local uint32_t RandomState = static_cast<uint64_t>(
+      time(nullptr) + GuardedPoolAllocator::getThreadID());
   RandomState ^= RandomState << 13;
   RandomState ^= RandomState >> 17;
   RandomState ^= RandomState << 5;
   return RandomState;
 }
 } // namespace gwp_asan