android: crazy-linker: Fix 64-bit RELR relocation support.

When shifting a constant integer more than 32 bits, ensure
that it is a 64-bit constant, or chaos will ensue.

BUG=895194
R=pasko@chromium.org, agrieve@chromium.org, rmcilroy@chromium.org

Change-Id: I1fc334fc77b2f5f518b690936b60a0a7e0d78956
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1563997Reviewed-by: Egor Pasko <pasko@chromium.org>
Reviewed-by: Ross McIlroy <rmcilroy@chromium.org>
Commit-Queue: David Turner <digit@chromium.org>
Cr-Commit-Position: refs/heads/master@{#649849}

third_party/android_crazy_linker/src/src/crazy_linker_relr_relocations.cpp

@@ -4,6 +4,8 @@
 
 #include "crazy_linker_relr_relocations.h"
 
+#include <type_traits>
+
 namespace crazy {
 
 // Apply a single RELR relocation at virtual |offset| address, using
@@ -35,6 +37,12 @@ void RelrRelocations::Apply(size_t load_bias) {
       // An odd value corresponds to a bitmap of 31 or 63 words, based
       // on the CPU bitness / word_size.
       ELF::Addr offset = base;
+
+      // Right shift of signed integers has undefined behaviour before C++20.
+      static_assert(
+          std::is_unsigned<decltype(entry)>::value,
+          "The ELF::Relr type should be unsigned to avoid undefined behaviour");
+
       while (entry != 0) {
         entry >>= 1;
         if ((entry & 1) != 0)

third_party/android_crazy_linker/src/src/crazy_linker_relr_relocations_unittest.cpp

@@ -71,7 +71,7 @@ TEST(RelrRelocations, ApplyWithSimpleBitmaps) {
   ELF::Relr relr_table[kRelrSize] = {};
   for (size_t n = 0; n < kDataSize; ++n) {
     if ((n % 3) == 0)
-      relr_table[n / kBitsPerWord] |= (1 | (2 << (n % kBitsPerWord)));
+      relr_table[n / kBitsPerWord] |= 1U | (ELF::Relr(2) << (n % kBitsPerWord));
   }
   RelrRelocations relr;
   relr.SetAddress(reinterpret_cast<uintptr_t>(relr_table));