[compiler-rt] [scudo] Make guard pages optional in the secondary (PR #125960)

[Christopher Ferris via llvm-commits]

================
@@ -243,6 +289,64 @@ TEST(ScudoSecondaryTest, AllocatorWithReleaseThreadsRace) {
     T.join();
 }
 
+TEST(ScudoSecondaryTest, AllocatorWithReleaseThreadsRace) {
+  testAllocatorWithReleaseThreadsRace<TestNoCacheConfig>();
+  testAllocatorWithReleaseThreadsRace<TestNoCacheNoGuardPageConfig>();
+}
+
+template <typename Config>
+void testGetMappedSize(scudo::uptr Size, scudo::uptr *mapped,
+                       scudo::uptr *guard_page_size) {
+  AllocatorInfoType<Config> Info;
+
+  scudo::uptr Stats[scudo::StatCount] = {};
+  Info.GlobalStats.get(Stats);
+  *mapped = Stats[scudo::StatMapped];
+  Stats[scudo::StatMapped] = 0;
+
+  // Make sure the allocation is aligned to a page boundary so that the checks
+  // in the tests can avoid problems due to allocations having different
+  // alignments.
+  void *Ptr = Info.Allocator->allocate(Info.Options, Size, PageSize);
+  EXPECT_NE(Ptr, nullptr);
+
+  Info.GlobalStats.get(Stats);
+  EXPECT_GE(Stats[scudo::StatMapped], *mapped);
+  *mapped = Stats[scudo::StatMapped] - *mapped;
+
+  Info.Allocator->deallocate(Info.Options, Ptr);
+
+  *guard_page_size = Info.Allocator->getGuardPageSize();
+}
+
+TEST(ScudoSecondaryTest, VerifyGuardPageOption) {
+  static scudo::uptr AllocSize = 1000 * PageSize;
+
+  // Verify that a config with guard pages enabled:
+  //  - Non-zero sized guard page
+  //  - Mapped in at least the size of the allocation plus 2 * guard page size
+  scudo::uptr guard_mapped = 0;
+  scudo::uptr guard_page_size = 0;
+  testGetMappedSize<TestNoCacheConfig>(AllocSize, &guard_mapped,
+                                       &guard_page_size);
+  EXPECT_GT(guard_page_size, 0U);
+  EXPECT_GE(guard_mapped, AllocSize + 2 * guard_page_size);
+
+  // Verify that a config with guard pages disabled:
+  //  - Zero sized guard page
+  //  - The total mapped in is greater than the allocation size
----------------
cferris1000 wrote:

As of now, you are guaranteed to have one extra page as long as the allocation is aligned to a page and the total size is aligned to a page. I didn't add a specific check for this because I was worried it would make the test too brittle. I envision this test as more of a simple, is the option actually working.

https://github.com/llvm/llvm-project/pull/125960