commit 82fe97e0578ebd0799761c3914753cd52692da1e
author Peter Collingbourne <peter@pcc.me.uk> Wed Apr 21 19:13:36 2021 -0700
committer Copybara-Service <copybara-worker@google.com> Sun May 09 19:08:58 2021 -0700
tree a76196e4b24ce60c47a21acb2d32a3402e06c2f2
parent d790cf4eae49b6e2c8ab9be448166c4126245374

scudo: Obtain tag from pointer instead of loading it from memory. NFCI.

Since we already have a tagged pointer available to us, we can just
extract the tag from it and avoid an LDG instruction.

Differential Revision: https://reviews.llvm.org/D101014

GitOrigin-RevId: e4fa0b307f7fe2c3db7442c719f643287f08eed4

combined.h

diff --git a/combined.h b/combined.h
index e778181..e621c87 100644
--- a/combined.h
+++ b/combined.h
@@ -518,6 +518,7 @@
     if (UNLIKELY(!isAligned(reinterpret_cast<uptr>(Ptr), MinAlignment)))
       reportMisalignedPointer(AllocatorAction::Deallocating, Ptr);
 
+    void *TaggedPtr = Ptr;
     Ptr = getHeaderTaggedPointer(Ptr);
 
     Chunk::UnpackedHeader Header;
@@ -543,7 +544,7 @@
         reportDeleteSizeMismatch(Ptr, DeleteSize, Size);
     }
 
-    quarantineOrDeallocateChunk(Options, Ptr, &Header, Size);
+    quarantineOrDeallocateChunk(Options, TaggedPtr, &Header, Size);
   }
 
   void *reallocate(void *OldPtr, uptr NewSize, uptr Alignment = MinAlignment) {
@@ -639,7 +640,7 @@
     void *NewPtr = allocate(NewSize, Chunk::Origin::Malloc, Alignment);
     if (LIKELY(NewPtr)) {
       memcpy(NewPtr, OldTaggedPtr, Min(NewSize, OldSize));
-      quarantineOrDeallocateChunk(Options, OldPtr, &OldHeader, OldSize);
+      quarantineOrDeallocateChunk(Options, OldTaggedPtr, &OldHeader, OldSize);
     }
     return NewPtr;
   }
@@ -1031,13 +1032,13 @@
            reinterpret_cast<uptr>(Ptr) - SizeOrUnusedBytes;
   }
 
-  void quarantineOrDeallocateChunk(Options Options, void *Ptr,
+  void quarantineOrDeallocateChunk(Options Options, void *TaggedPtr,
                                    Chunk::UnpackedHeader *Header, uptr Size) {
+    void *Ptr = getHeaderTaggedPointer(TaggedPtr);
     Chunk::UnpackedHeader NewHeader = *Header;
     if (UNLIKELY(useMemoryTagging<Params>(Options))) {
-      u8 PrevTag = 0;
+      u8 PrevTag = extractTag(reinterpret_cast<uptr>(TaggedPtr));
       if (NewHeader.ClassId) {
-        PrevTag = extractTag(loadTag(reinterpret_cast<uptr>(Ptr)));
         if (!TSDRegistry.getDisableMemInit()) {
           uptr TaggedBegin, TaggedEnd;
           const uptr OddEvenMask = computeOddEvenMaskForPointerMaybe(