[compiler-rt] [scudo] [MTE] resize stack depot for allocation ring buffer (PR #74515)

[Florian Mayer via llvm-commits]

================
@@ -62,47 +63,103 @@ class StackDepot {
   // This is achieved by re-checking the hash of the stack trace before
   // returning the trace.
 
-#if SCUDO_SMALL_STACK_DEPOT
-  static const uptr TabBits = 4;
-#else
-  static const uptr TabBits = 16;
-#endif
-  static const uptr TabSize = 1 << TabBits;
-  static const uptr TabMask = TabSize - 1;
-  atomic_u32 Tab[TabSize] = {};
-
-#if SCUDO_SMALL_STACK_DEPOT
-  static const uptr RingBits = 4;
-#else
-  static const uptr RingBits = 19;
-#endif
-  static const uptr RingSize = 1 << RingBits;
-  static const uptr RingMask = RingSize - 1;
-  atomic_u64 Ring[RingSize] = {};
+  uptr RingSize = 0;
+  uptr RingMask = 0;
+  uptr TabMask = 0;
+  // This is immediately followed by RingSize atomic_u64 and
+  // (TabMask + 1) atomic_u32.
+
+  atomic_u64 *Ring(char *RawStackDepot) {
+    return reinterpret_cast<atomic_u64 *>(RawStackDepot + sizeof(StackDepot));
+  }
+
+  atomic_u32 *Tab(char *RawStackDepot) {
+    return reinterpret_cast<atomic_u32 *>(RawStackDepot + sizeof(StackDepot) +
+                                          sizeof(atomic_u64) * RingSize);
+  }
+
+  const atomic_u64 *Ring(const char *RawStackDepot) const {
+    return reinterpret_cast<const atomic_u64 *>(RawStackDepot +
+                                                sizeof(StackDepot));
+  }
+
+  const atomic_u32 *Tab(const char *RawStackDepot) const {
+    return reinterpret_cast<const atomic_u32 *>(
+        RawStackDepot + sizeof(StackDepot) + sizeof(atomic_u64) * RingSize);
+  }
 
 public:
+  void init(uptr RingSz, uptr TabSz) {
+    DCHECK(isPowerOfTwo(RingSz));
+    DCHECK(isPowerOfTwo(TabSz));
----------------
fmayer wrote:

No, the other checks are different. They are used in `getErrorInfo` and are done on the buffer we get from debuggerd, not directly from the object initialized from here.

https://github.com/llvm/llvm-project/pull/74515