[PATCH] D86645: Fix an overflow issue at BackpatchWord

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stephan.yichao.zhao created this revision.
stephan.yichao.zhao added reviewers: tejohnson, vitalybuka.
Herald added subscribers: llvm-commits, dexonsmith.
Herald added a project: LLVM.
stephan.yichao.zhao requested review of this revision.

This happens when generating a huge file by LTO, for example, with -gmlt.
When BitNo is > 2^35, ByteNo is overflowed, and an incorrect output offset is overwritten.
This generates ill-formed bitcodes.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D86645

Files:
  llvm/include/llvm/Bitstream/BitstreamWriter.h


Index: llvm/include/llvm/Bitstream/BitstreamWriter.h
===================================================================
--- llvm/include/llvm/Bitstream/BitstreamWriter.h
+++ llvm/include/llvm/Bitstream/BitstreamWriter.h
@@ -103,7 +103,7 @@
   /// with the specified value.
   void BackpatchWord(uint64_t BitNo, unsigned NewWord) {
     using namespace llvm::support;
-    unsigned ByteNo = BitNo / 8;
+    uint64_t ByteNo = BitNo / 8;
     assert((!endian::readAtBitAlignment<uint32_t, little, unaligned>(
                &Out[ByteNo], BitNo & 7)) &&
            "Expected to be patching over 0-value placeholders");


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