stack protector: use AT_RANDOM

Populate the stack canaries from the kernel supplied
AT_RANDOM value, which doesn't involve any system calls.
This is slightly faster (6 fewer syscalls) and avoids
unnecessarily reading /dev/urandom, which depletes entropy.

Bug: 7959813

Change-Id: If2b43100a2a9929666df3de56b6139fed969e0f1

1 files changed, 3 insertions, 13 deletions

diff --git a/tests/stack_protector_test.cpp b/tests/stack_protector_test.cpp
index 9cf3c38ab..ca90deac1 100644
--- a/tests/stack_protector_test.cpp
+++ b/tests/stack_protector_test.cpp
@@ -56,13 +56,7 @@ struct stack_protector_checker {
 
     // Duplicate tid. gettid(2) bug? Seeing this would be very upsetting.
     ASSERT_TRUE(tids.find(tid) == tids.end());
-#ifdef __GLIBC__
-    // glibc uses the same guard for every thread. bionic uses a different guard for each one.
-#else
-    // Duplicate guard. Our bug. Note this is potentially flaky; we _could_ get the
-    // same guard for two threads, but it should be vanishingly unlikely.
-    ASSERT_TRUE(guards.find(guard) == guards.end());
-#endif
+
     // Uninitialized guard. Our bug. Note this is potentially flaky; we _could_ get
     // four random zero bytes, but it should be vanishingly unlikely.
     ASSERT_NE(guard, 0U);
@@ -78,7 +72,7 @@ static void* ThreadGuardHelper(void* arg) {
   return NULL;
 }
 
-TEST(stack_protector, guard_per_thread) {
+TEST(stack_protector, same_guard_per_thread) {
   stack_protector_checker checker;
   size_t thread_count = 10;
   for (size_t i = 0; i < thread_count; ++i) {
@@ -90,12 +84,8 @@ TEST(stack_protector, guard_per_thread) {
   }
   ASSERT_EQ(thread_count, checker.tids.size());
 
-  // glibc uses the same guard for every thread. bionic uses a different guard for each one.
-#ifdef __BIONIC__
-  ASSERT_EQ(thread_count, checker.guards.size());
-#else
+  // bionic x86 and glibc uses the same guard for every thread.
   ASSERT_EQ(1U, checker.guards.size());
-#endif
 }
 
 #endif