[lld] r326943 - Revert "Write a hash of the executable into the PE timestamp fields."

[Zachary Turner via llvm-commits]

Author: zturner
Date: Wed Mar  7 13:22:10 2018
New Revision: 326943

URL: http://llvm.org/viewvc/llvm-project?rev=326943&view=rev
Log:
Revert "Write a hash of the executable into the PE timestamp fields."

This is breaking a couple of tests, so I'm reverting temporarily
until I can get everything resolved properly.

Modified:
    lld/trunk/COFF/Writer.cpp

Modified: lld/trunk/COFF/Writer.cpp
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/COFF/Writer.cpp?rev=326943&r1=326942&r2=326943&view=diff
==============================================================================
--- lld/trunk/COFF/Writer.cpp (original)
+++ lld/trunk/COFF/Writer.cpp Wed Mar  7 13:22:10 2018
@@ -28,7 +28,6 @@
 #include "llvm/Support/Parallel.h"
 #include "llvm/Support/Path.h"
 #include "llvm/Support/RandomNumberGenerator.h"
-#include "llvm/Support/xxhash.h"
 #include <algorithm>
 #include <cstdio>
 #include <map>
@@ -72,18 +71,11 @@ public:
       uint64_t Offs = OS->getFileOff() + (Record->getRVA() - OS->getRVA());
       D->PointerToRawData = Offs;
 
-      TimeDateStamps.push_back(&D->TimeDateStamp);
       ++D;
     }
   }
 
-  void setTimeDateStamp(uint32_t TimeDateStamp) {
-    for (support::ulittle32_t *TDS : TimeDateStamps)
-      *TDS = TimeDateStamp;
-  }
-
 private:
-  mutable std::vector<support::ulittle32_t *> TimeDateStamps;
   const std::vector<Chunk *> &Records;
 };
 
@@ -165,7 +157,7 @@ private:
   RVATableChunk *GuardFidsTable = nullptr;
   RVATableChunk *SEHTable = nullptr;
 
-  DebugDirectoryChunk *DebugDirectory = nullptr;
+  Chunk *DebugDirectory = nullptr;
   std::vector<Chunk *> DebugRecords;
   CVDebugRecordChunk *BuildId = nullptr;
   Optional<codeview::DebugInfo> PreviousBuildId;
@@ -1034,50 +1026,22 @@ void Writer::writeSections() {
 }
 
 void Writer::writeBuildId() {
-  // There are two important parts to the build ID.
-  // 1) If building with debug info, the COFF debug directory contains a
-  //    timestamp as well as a Guid and Age of the PDB.
-  // 2) In all cases, the PE COFF file header also contains a timestamp.
-  // For reproducibility, instead of a timestamp we want to use a hash of the
-  // binary, however when building with debug info the hash needs to take into
-  // account the debug info, since it's possible to add blank lines to a file
-  // which causes the debug info to change but not the generated code.
-  //
-  // To handle this, we first set the Guid and Age in the debug directory (but
-  // only if we're doing a debug build).  Then, we hash the binary (thus causing
-  // the hash to change if only the debug info changes, since the Age will be
-  // different).  Finally, we write that hash into the debug directory (if
-  // present) as well as the COFF file header (always).
-  if (Config->Debug) {
-    assert(BuildId && "BuildId is not set!");
-    if (PreviousBuildId.hasValue()) {
-      *BuildId->BuildId = *PreviousBuildId;
-      BuildId->BuildId->PDB70.Age = BuildId->BuildId->PDB70.Age + 1;
-    } else {
-      BuildId->BuildId->Signature.CVSignature = OMF::Signature::PDB70;
-      BuildId->BuildId->PDB70.Age = 1;
-      llvm::getRandomBytes(BuildId->BuildId->PDB70.Signature, 16);
-    }
-  }
-
-  // At this point the only fields in the COFF file which remain unset are the
-  // "timestamp" in the COFF file header, and the ones in the coff debug
-  // directory.  Now we can hash the file and write that hash to the various
-  // timestamp fields in the file.
-  StringRef OutputFileData(
-      reinterpret_cast<const char *>(Buffer->getBufferStart()),
-      Buffer->getBufferSize());
+  // If we're not writing a build id (e.g. because /debug is not specified),
+  // then just return;
+  if (!Config->Debug)
+    return;
 
-  uint32_t Hash = static_cast<uint32_t>(xxHash64(OutputFileData));
+  assert(BuildId && "BuildId is not set!");
 
-  if (DebugDirectory)
-    DebugDirectory->setTimeDateStamp(Hash);
+  if (PreviousBuildId.hasValue()) {
+    *BuildId->BuildId = *PreviousBuildId;
+    BuildId->BuildId->PDB70.Age = BuildId->BuildId->PDB70.Age + 1;
+    return;
+  }
 
-  uint8_t *Buf = Buffer->getBufferStart();
-  Buf += DOSStubSize + sizeof(PEMagic);
-  object::coff_file_header *CoffHeader =
-      reinterpret_cast<coff_file_header *>(Buf);
-  CoffHeader->TimeDateStamp = Hash;
+  BuildId->BuildId->Signature.CVSignature = OMF::Signature::PDB70;
+  BuildId->BuildId->PDB70.Age = 1;
+  llvm::getRandomBytes(BuildId->BuildId->PDB70.Signature, 16);
 }
 
 // Sort .pdata section contents according to PE/COFF spec 5.5.