[compiler-rt] 9d9a773 - [scudo] Temporariy dispatch region from `RegionBeg`

[Chia-hung Duan via llvm-commits]

Author: Chia-hung Duan
Date: 2023-04-11T22:42:03Z
New Revision: 9d9a7732e14d7d4c0db7b46d6ebe588e8f43b951

URL: https://github.com/llvm/llvm-project/commit/9d9a7732e14d7d4c0db7b46d6ebe588e8f43b951
DIFF: https://github.com/llvm/llvm-project/commit/9d9a7732e14d7d4c0db7b46d6ebe588e8f43b951.diff

LOG: [scudo] Temporariy dispatch region from `RegionBeg`

In general, a region is located from region base and has size
`RegionSize`. However, some platforms may not support mapping from
region base. Before we have each platform implements their specific
MemMap to handle the offset. Temporarily dispatch the region from
`RegionBeg` instead.

Reviewed By: cferris, fabio-d

Differential Revision: https://reviews.llvm.org/D147792

Added: 
    

Modified: 
    compiler-rt/lib/scudo/standalone/primary64.h

Removed: 
    


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diff  --git a/compiler-rt/lib/scudo/standalone/primary64.h b/compiler-rt/lib/scudo/standalone/primary64.h
index dad6d263a083d..4ea1ba367764f 100644
--- a/compiler-rt/lib/scudo/standalone/primary64.h
+++ b/compiler-rt/lib/scudo/standalone/primary64.h
@@ -747,8 +747,14 @@ template <typename Config> class SizeClassAllocator64 {
       }
       // TODO: Consider allocating MemMap in init().
       if (!Region->MemMap.isAllocated()) {
-        Region->MemMap = ReservedMemory.dispatch(
-            getRegionBaseByClassId(ClassId), RegionSize);
+        // TODO: Ideally, a region should reserve RegionSize because the memory
+        // between `RegionBeg` and region base is still belong to a region and
+        // it's just not used. In order to make it work on every platform (some
+        // of them don't support `remap()` across the unused range), dispatch
+        // from `RegionBeg` for now.
+        const uptr ReserveSize =
+            RegionSize - (RegionBeg - getRegionBaseByClassId(ClassId));
+        Region->MemMap = ReservedMemory.dispatch(RegionBeg, ReserveSize);
       }
       DCHECK(Region->MemMap.isAllocated());