[PATCH] D122518: [scudo] Use template specialization on Quarantine to avoid zero-length array

[Dominic Chen via Phabricator via llvm-commits]

ddcc created this revision.
ddcc added reviewers: vitalybuka, eugenis, cryptoad, mcgrathr, hctim.
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ddcc requested review of this revision.
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Use a separate templated QuarantineBlocks class to avoid a zero-length array


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D122518

Files:
  compiler-rt/lib/scudo/standalone/secondary.h


Index: compiler-rt/lib/scudo/standalone/secondary.h
===================================================================
--- compiler-rt/lib/scudo/standalone/secondary.h
+++ compiler-rt/lib/scudo/standalone/secondary.h
@@ -176,12 +176,12 @@
           useMemoryTagging<Config>(Options)) {
         QuarantinePos =
             (QuarantinePos + 1) % Max(Config::SecondaryCacheQuarantineSize, 1u);
-        if (!Quarantine[QuarantinePos].CommitBase) {
-          Quarantine[QuarantinePos] = Entry;
+        if (!Quarantine.get(QuarantinePos)->CommitBase) {
+          *Quarantine.get(QuarantinePos) = Entry;
           return;
         }
-        CachedBlock PrevEntry = Quarantine[QuarantinePos];
-        Quarantine[QuarantinePos] = Entry;
+        CachedBlock PrevEntry = *Quarantine.get(QuarantinePos);
+        *Quarantine.get(QuarantinePos) = Entry;
         if (OldestTime == 0)
           OldestTime = Entry.Time;
         Entry = PrevEntry;
@@ -305,10 +305,10 @@
   void disableMemoryTagging() {
     ScopedLock L(Mutex);
     for (u32 I = 0; I != Config::SecondaryCacheQuarantineSize; ++I) {
-      if (Quarantine[I].CommitBase) {
-        unmap(reinterpret_cast<void *>(Quarantine[I].MapBase),
-              Quarantine[I].MapSize, UNMAP_ALL, &Quarantine[I].Data);
-        Quarantine[I].CommitBase = 0;
+      if (Quarantine.get(I)->CommitBase) {
+        unmap(reinterpret_cast<void *>(Quarantine.get(I)->MapBase),
+              Quarantine.get(I)->MapSize, UNMAP_ALL, &Quarantine.get(I)->Data);
+        Quarantine.get(I)->CommitBase = 0;
       }
     }
     const u32 MaxCount = atomic_load_relaxed(&MaxEntriesCount);
@@ -362,6 +362,18 @@
     u64 Time;
   };
 
+  // Template specialization to avoid producing zero-length array
+  template <size_t Size> class QuarantineBlocks {
+  public:
+    CachedBlock *get(uptr Idx) { return &Blocks[Idx]; }
+  private:
+    CachedBlock Blocks[Size];
+  };
+  template <> class QuarantineBlocks<0> {
+  public:
+    CachedBlock *get(uptr UNUSED Idx) { return nullptr; }
+  };
+
   void releaseIfOlderThan(CachedBlock &Entry, u64 Time) {
     if (!Entry.CommitBase || !Entry.Time)
       return;
@@ -380,7 +392,7 @@
       return;
     OldestTime = 0;
     for (uptr I = 0; I < Config::SecondaryCacheQuarantineSize; I++)
-      releaseIfOlderThan(Quarantine[I], Time);
+      releaseIfOlderThan(*Quarantine.get(I), Time);
     for (uptr I = 0; I < Config::SecondaryCacheEntriesArraySize; I++)
       releaseIfOlderThan(Entries[I], Time);
   }
@@ -395,7 +407,7 @@
   atomic_s32 ReleaseToOsIntervalMs = {};
 
   CachedBlock Entries[Config::SecondaryCacheEntriesArraySize] = {};
-  CachedBlock Quarantine[Config::SecondaryCacheQuarantineSize] = {};
+  QuarantineBlocks<Config::SecondaryCacheQuarantineSize> Quarantine = {};
 };
 
 template <typename Config> class MapAllocator {


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