Add some logging in ASAN builds

Summary:
- Log whether slab poisoning is enabled or disabled
- Log if an allocation class size is not a multiple of 8 and may lead to poisoning/unpoisoning imprecision

Reviewed By: AlnisM

Differential Revision: D109388859

fbshipit-source-id: e9d7f4e129b06880abce449a00b46fb0fbf6f181

Author: rlyerly

cachelib/allocator/memory/AllocationClass.cpp

@@ -91,6 +91,15 @@ void AllocationClass::checkState() const {
         fmt::format("Current allocation slab {} is not in allocated slabs list",
                     fmt::ptr(currSlab_)));
   }
+
+  if (slabAlloc_.isAsanPoisoningEnabled() && (allocationSize_ % 8 != 0)) {
+    XLOGF(WARN,
+          "Slab ASAN poisoning is enabled but allocation class {} has size {}, "
+          "which is not a multiple of 8; freed-allocation poisoning will be "
+          "imprecise at allocation boundaries.",
+          classId_,
+          allocationSize_);
+  }
 }
 
 // TODO(stuclar): Add poolId to the metadata to be serialized when cache shuts

cachelib/allocator/memory/SlabAllocator.cpp

@@ -81,6 +81,16 @@ void SlabAllocator::checkState() const {
   }
 }
 
+void SlabAllocator::logAsanPoisoningStatus() const {
+#if FOLLY_SANITIZE_ADDRESS
+  if (asanPoisoningEnabled_) {
+    XLOG(INFO, "CacheLib slab ASAN poisoning is ENABLED");
+  } else {
+    XLOG(INFO, "CacheLib slab ASAN poisoning is DISABLED");
+  }
+#endif
+}
+
 SlabAllocator::~SlabAllocator() {
   stopMemoryLocker();
 
@@ -153,6 +163,8 @@ SlabAllocator::SlabAllocator(void* memoryStart,
   XDCHECK(nextSlabAllocation_ != nullptr);
   XDCHECK_EQ(reinterpret_cast<uintptr_t>(nextSlabAllocation_),
              reinterpret_cast<uintptr_t>(slabMemoryStart_));
+
+  logAsanPoisoningStatus();
 }
 
 SlabAllocator::SlabAllocator(const serialization::SlabAllocatorObject& object,
@@ -251,6 +263,8 @@ SlabAllocator::SlabAllocator(const serialization::SlabAllocatorObject& object,
   asanPoisonMemoryRegion(memoryStart_,
                          reinterpret_cast<const uint8_t*>(slabMemoryStart_) -
                              reinterpret_cast<const uint8_t*>(memoryStart_));
+
+  logAsanPoisoningStatus();
 }
 
 void SlabAllocator::lockMemoryAsync() noexcept {

cachelib/allocator/memory/SlabAllocator.h

@@ -380,6 +380,9 @@ class SlabAllocator {
   // @throw std::invalid_argument if the state is invalid.
   void checkState() const;
 
+  // Logs whether slab ASAN poisoning is active. No-op in non-ASAN builds.
+  void logAsanPoisoningStatus() const;
+
   // returns first byte after the end of memory region we own.
   const Slab* getSlabMemoryEnd() const noexcept {
     return reinterpret_cast<Slab*>(reinterpret_cast<uint8_t*>(memoryStart_) +