[scudo] Fix EXPECT_DEATH tests

Put allocate/deallocate next to memory
access inside EXPECT_DEATH block.
This way we reduce probability that memory is not mapped
by unrelated code.

It's still not absolutely guaranty that mmap does not
happen so we repeat it few times to be sure.

Reviewed By: cryptoad

Differential Revision: https://reviews.llvm.org/D102886

Author: vitalybuka

compiler-rt/lib/scudo/standalone/tests/map_test.cpp

@@ -31,11 +31,19 @@ TEST(ScudoMapTest, MapNoAccessUnmap) {
 
 TEST(ScudoMapTest, MapUnmap) {
   const scudo::uptr Size = 4 * scudo::getPageSizeCached();
-  void *P = scudo::map(nullptr, Size, MappingName, 0, nullptr);
-  EXPECT_NE(P, nullptr);
-  memset(P, 0xaa, Size);
-  scudo::unmap(P, Size, 0, nullptr);
-  EXPECT_DEATH(memset(P, 0xbb, Size), "");
+  EXPECT_DEATH(
+      {
+        // Repeat few time to avoid missing crash if it's mmaped by unrelated
+        // code.
+        for (int i = 0; i < 10; ++i) {
+          void *P = scudo::map(nullptr, Size, MappingName, 0, nullptr);
+          if (!P)
+            continue;
+          scudo::unmap(P, Size, 0, nullptr);
+          memset(P, 0xbb, Size);
+        }
+      },
+      "");
 }
 
 TEST(ScudoMapTest, MapWithGuardUnmap) {

compiler-rt/lib/scudo/standalone/tests/secondary_test.cpp

@@ -39,9 +39,20 @@ template <typename Config> static void testSecondaryBasic(void) {
 // the test on arm32 until we can debug it further.
 #ifndef __arm__
   // If the Secondary can't cache that pointer, it will be unmapped.
-  if (!L->canCache(Size))
-    EXPECT_DEATH(memset(P, 'A', Size), "");
+  if (!L->canCache(Size)) {
+    EXPECT_DEATH(
+        {
+          // Repeat few time to avoid missing crash if it's mmaped by unrelated
+          // code.
+          for (int i = 0; i < 10; ++i) {
+            P = L->allocate(scudo::Options{}, Size);
+            L->deallocate(scudo::Options{}, P);
+            memset(P, 'A', Size);
+          }
+        },
+        "");
 #endif // __arm__
+  }
 
   const scudo::uptr Align = 1U << 16;
   P = L->allocate(scudo::Options{}, Size + Align, Align);