scudo: Adjust test to use correct check for primary allocations.

[pcc]

Summary

canAllocate() does not take into account the header size so it does
not return the right answer in borderline cases. There was already
code handling this correctly in isTaggedAllocation() so split it out
into a separate function and call it from the test.

Furthermore the test was incorrect when MTE is enabled because MTE
does not pattern fill primary allocations. Fix it.

[pcc]

Fix MTE issue

compiler-rt/lib/scudo/standalone/tests/combined_test.cpp

 #if SCUDO_ANDROID
   // Disable the debuggerd signal handler on Android, without this we can end
   // up spending a significant amount of time creating tombstones.
   signal(SIGSEGV, SIG_DFL);
 #endif
 }
 
 template <class AllocatorT>
-bool isTaggedAllocation(AllocatorT *Allocator, scudo::uptr Size,
-                        scudo::uptr Alignment) {
-  if (!Allocator->useMemoryTagging() ||
-      !scudo::systemDetectsMemoryTagFaultsTestOnly())
-    return false;
-
+bool isPrimaryAllocation(scudo::uptr Size, scudo::uptr Alignment) {
   const scudo::uptr MinAlignment = 1UL << SCUDO_MIN_ALIGNMENT_LOG;
   if (Alignment < MinAlignment)
     Alignment = MinAlignment;
   const scudo::uptr NeededSize =
       scudo::roundUpTo(Size, MinAlignment) +
       ((Alignment > MinAlignment) ? Alignment : scudo::Chunk::getHeaderSize());
   return AllocatorT::PrimaryT::canAllocate(NeededSize);
 }
 
 template <class AllocatorT>
+bool isTaggedAllocation(AllocatorT *Allocator, scudo::uptr Size,
+                        scudo::uptr Alignment) {
+  return Allocator->useMemoryTagging() &&
+         scudo::systemDetectsMemoryTagFaultsTestOnly() &&
+         isPrimaryAllocation<AllocatorT>(Size, Alignment);
+}
+
+template <class AllocatorT>
 void checkMemoryTaggingMaybe(AllocatorT *Allocator, void *P, scudo::uptr Size,
                              scudo::uptr Alignment) {
   if (!isTaggedAllocation(Allocator, Size, Alignment))
     return;
 
   Size = scudo::roundUpTo(Size, scudo::archMemoryTagGranuleSize());
   EXPECT_DEATH(
       {
for (scudo::uptr Delta = 0U; Delta <= 4U; Delta++) {
       for (scudo::uptr I = 0; I < Size; I++)
         ASSERT_EQ((reinterpret_cast<char *>(P))[I], 0);
       memset(P, 0xaa, Size);
       Allocator->deallocate(P, Origin, Size);
     }
   }
   Allocator->releaseToOS();
 
-  // Ensure that specifying PatternOrZeroFill returns a pattern-filled block in
-  // the primary allocator, and either pattern or zero filled block in the
-  // secondary.
+  // Ensure that specifying PatternOrZeroFill returns a pattern or zero filled
+  // block. The primary allocator only produces pattern filled blocks if MTE
+  // is disabled, so we only require pattern filled blocks in that case.
   Allocator->setFillContents(scudo::PatternOrZeroFill);
   for (scudo::uptr SizeLog = 0U; SizeLog <= 20U; SizeLog++) {
     for (scudo::uptr Delta = 0U; Delta <= 4U; Delta++) {
       const scudo::uptr Size = (1U << SizeLog) + Delta * 128U;
       void *P = Allocator->allocate(Size, Origin, 1U << MinAlignLog, false);
       EXPECT_NE(P, nullptr);
       for (scudo::uptr I = 0; I < Size; I++) {
         unsigned char V = (reinterpret_cast<unsigned char *>(P))[I];
-        if (AllocatorT::PrimaryT::canAllocate(Size))
+        if (isPrimaryAllocation<AllocatorT>(Size, 1U << MinAlignLog) &&
+            !Allocator->useMemoryTagging())
           ASSERT_EQ(V, scudo::PatternFillByte);
         else
           ASSERT_TRUE(V == scudo::PatternFillByte || V == 0);
       }
       memset(P, 0xaa, Size);
       Allocator->deallocate(P, Origin, Size);
     }
   }