[llvm] dd56bec - [CAS] Fix alignment error from MappedFileRegionArena (#159128)

[via llvm-commits]

Author: Steven Wu
Date: 2025-09-16T11:36:52-07:00
New Revision: dd56becdbc31cce16973172f0a447207ddf67861

URL: https://github.com/llvm/llvm-project/commit/dd56becdbc31cce16973172f0a447207ddf67861
DIFF: https://github.com/llvm/llvm-project/commit/dd56becdbc31cce16973172f0a447207ddf67861.diff

LOG: [CAS] Fix alignment error from MappedFileRegionArena (#159128)

Fix a bug that when an alignment error can happen when reading a slice
of file from existing MappedFileRegionArena.

Added: 
    

Modified: 
    llvm/lib/CAS/MappedFileRegionArena.cpp

Removed: 
    


################################################################################
diff  --git a/llvm/lib/CAS/MappedFileRegionArena.cpp b/llvm/lib/CAS/MappedFileRegionArena.cpp
index 2deb87d7adecf..472843d78af6e 100644
--- a/llvm/lib/CAS/MappedFileRegionArena.cpp
+++ b/llvm/lib/CAS/MappedFileRegionArena.cpp
@@ -216,17 +216,18 @@ Expected<MappedFileRegionArena> MappedFileRegionArena::create(
     if (!Size)
       return Size.takeError();
 
-    Header *H = reinterpret_cast<Header *>(HeaderContent.data());
-    if (H->HeaderOffset != HeaderOffset)
+    Header H;
+    memcpy(&H, HeaderContent.data(), sizeof(H));
+    if (H.HeaderOffset != HeaderOffset)
       return createStringError(
           std::make_error_code(std::errc::invalid_argument),
           "specified header offset (" + utostr(HeaderOffset) +
-              ") does not match existing config (" + utostr(H->HeaderOffset) +
+              ") does not match existing config (" + utostr(H.HeaderOffset) +
               ")");
 
     // If the capacity doesn't match, use the existing capacity instead.
-    if (H->Capacity != Capacity)
-      Capacity = H->Capacity;
+    if (H.Capacity != Capacity)
+      Capacity = H.Capacity;
   }
 
   // If the size is smaller than capacity, we need to resize the file.