[PATCH] D91827: EXPERIMENTAL sign-extend addresses in CompactRingBuffer

[Evgenii Stepanov via Phabricator via llvm-commits]

eugenis created this revision.
eugenis added reviewers: ro, vitalybuka.
Herald added a project: Sanitizers.
Herald added a subscriber: Sanitizers.
eugenis requested review of this revision.

Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D91827

Files:
  compiler-rt/lib/sanitizer_common/sanitizer_ring_buffer.h


Index: compiler-rt/lib/sanitizer_common/sanitizer_ring_buffer.h
===================================================================
--- compiler-rt/lib/sanitizer_common/sanitizer_ring_buffer.h
+++ compiler-rt/lib/sanitizer_common/sanitizer_ring_buffer.h
@@ -86,10 +86,13 @@
   // Lower bytes store the address of the next buffer element.
   static constexpr int kPageSizeBits = 12;
   static constexpr int kSizeShift = 56;
+  static constexpr int kSizeBits = 64 - kSizeShift;
   static constexpr uptr kNextMask = (1ULL << kSizeShift) - 1;
 
   uptr GetStorageSize() const { return (long_ >> kSizeShift) << kPageSizeBits; }
 
+  static uptr SignExtend(uptr x) { return ((sptr)x) << kSizeBits >> kSizeBits; }
+
   void Init(void *storage, uptr size) {
     CHECK_EQ(sizeof(CompactRingBuffer<T>), sizeof(void *));
     CHECK(IsPowerOfTwo(size));
@@ -97,12 +100,14 @@
     CHECK_LE(size, 128 << kPageSizeBits);
     CHECK_EQ(size % 4096, 0);
     CHECK_EQ(size % sizeof(T), 0);
-    CHECK_EQ((uptr)storage % (size * 2), 0);
-    long_ = (uptr)storage | ((size >> kPageSizeBits) << kSizeShift);
+    uptr st = (uptr)storage;
+    CHECK_EQ(st % (size * 2), 0);
+    CHECK_EQ(st, SignExtend(st & kNextMask));
+    long_ = (st & kNextMask) | ((size >> kPageSizeBits) << kSizeShift);
   }
 
   void SetNext(const T *next) {
-    long_ = (long_ & ~kNextMask) | (uptr)next;
+    long_ = (long_ & ~kNextMask) | ((uptr)next & kNextMask);
   }
 
  public:
@@ -119,7 +124,7 @@
     SetNext((const T *)storage + Idx);
   }
 
-  T *Next() const { return (T *)(long_ & kNextMask); }
+  T *Next() const { return (T *)(SignExtend(long_ & kNextMask)); }
 
   void *StartOfStorage() const {
     return (void *)((uptr)Next() & ~(GetStorageSize() - 1));


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