[lld] 60ab8c8 - [lld][macho] Use reloc length correctly in hash computation (#165287)

[via llvm-commits]

Author: Ellis Hoag
Date: 2025-10-27T14:48:04-07:00
New Revision: 60ab8c89673a84a34e4245c5a590c45e22852f13

URL: https://github.com/llvm/llvm-project/commit/60ab8c89673a84a34e4245c5a590c45e22852f13
DIFF: https://github.com/llvm/llvm-project/commit/60ab8c89673a84a34e4245c5a590c45e22852f13.diff

LOG: [lld][macho] Use reloc length correctly in hash computation (#165287)

`Reloc::length` actually encodes the log2 of the length. Thanks @int3
for pointing this out in
https://github.com/llvm/llvm-project/issues/160894#issuecomment-3416250179.

This code computes hashes of relocations. With the correct length, the
hashes should more accurately represent the relocation. In my testing of
some large binaries, the compressed size change is negligable.

Added: 
    

Modified: 
    lld/MachO/BPSectionOrderer.cpp

Removed: 
    


################################################################################
diff  --git a/lld/MachO/BPSectionOrderer.cpp b/lld/MachO/BPSectionOrderer.cpp
index 1f07ea9caf5df..d50abc22fc6c1 100644
--- a/lld/MachO/BPSectionOrderer.cpp
+++ b/lld/MachO/BPSectionOrderer.cpp
@@ -61,12 +61,13 @@ struct BPOrdererMachO : lld::BPOrderer<BPOrdererMachO> {
 
     // Calculate relocation hashes
     for (const auto &r : sec.relocs) {
-      if (r.length == 0 || r.referent.isNull() || r.offset >= data.size())
+      uint32_t relocLength = 1 << r.length;
+      if (r.referent.isNull() || r.offset + relocLength > data.size())
         continue;
 
       uint64_t relocHash = getRelocHash(r, sectionToIdx);
       uint32_t start = (r.offset < windowSize) ? 0 : r.offset - windowSize + 1;
-      for (uint32_t i = start; i < r.offset + r.length; i++) {
+      for (uint32_t i = start; i < r.offset + relocLength; i++) {
         auto window = data.drop_front(i).take_front(windowSize);
         hashes.push_back(xxh3_64bits(window) ^ relocHash);
       }