[COFF] Add /Brepro and /TIMESTAMP options.

Previously we would always write a hash of the binary into the
PE file, for reproducible builds.  This breaks AppCompat, which
is a feature of Windows that relies on the timestamp in the PE
header being set to a real value (or at the very least, a value
that satisfies certain properties).

To address this, we put the old behavior of writing the hash
behind the /Brepro flag, which mimics MSVC linker behavior.  We
also match MSVC default behavior, which is to write an actual
timestamp to the PE header.  Finally, we add the /TIMESTAMP
option (an lld extension) so that the user can specify the exact
value to be used in case he/she manually constructs a value which
is both reproducible and satisfies AppCompat.

Differential Revision: https://reviews.llvm.org/D46966

llvm-svn: 332613

1 files changed, 5 insertions, 3 deletions

diff --git a/lld/COFF/Writer.cpp b/lld/COFF/Writer.cpp
index b14cbb47dc7..b38bef80ef6 100644
--- a/lld/COFF/Writer.cpp
+++ b/lld/COFF/Writer.cpp
@@ -1192,16 +1192,18 @@ void Writer::writeBuildId() {
       reinterpret_cast<const char *>(Buffer->getBufferStart()),
       Buffer->getBufferSize());
 
-  uint32_t Hash = static_cast<uint32_t>(xxHash64(OutputFileData));
+  uint32_t Timestamp = Config->Timestamp;
+  if (Config->Repro)
+    Timestamp = static_cast<uint32_t>(xxHash64(OutputFileData));
 
   if (DebugDirectory)
-    DebugDirectory->setTimeDateStamp(Hash);
+    DebugDirectory->setTimeDateStamp(Timestamp);
 
   uint8_t *Buf = Buffer->getBufferStart();
   Buf += DOSStubSize + sizeof(PEMagic);
   object::coff_file_header *CoffHeader =
       reinterpret_cast<coff_file_header *>(Buf);
-  CoffHeader->TimeDateStamp = Hash;
+  CoffHeader->TimeDateStamp = Timestamp;
 }
 
 // Sort .pdata section contents according to PE/COFF spec 5.5.