[llvm-objcopy] [COFF] Fix handling of aux symbols for big objects

The aux symbols were stored in an opaque std::vector<uint8_t>,
with contents interpreted according to the rest of the symbol.

All aux symbol types but one fit in 18 bytes (sizeof(coff_symbol16)),
and if written to a bigobj, two extra padding bytes are written (as
sizeof(coff_symbol32) is 20). In the storage agnostic intermediate
representation, store the aux symbols as a series of coff_symbol16
sized opaque blobs. (In practice, all such aux symbols only consist
of one aux symbol, so this is more flexible than what reality needs.)

The special case is the file aux symbols, which are written in
potentially more than one aux symbol slot, without any padding,
as one single long string. This can't be stored in the same opaque
vector of fixed sized aux symbol entries. The file aux symbols will
occupy a different number of aux symbol slots depending on the type
of output object file. As nothing in the intermediate process needs
to have accurate raw symbol indices, updating that is moved into the
writer class.

Differential Revision: https://reviews.llvm.org/D57009

llvm-svn: 351947

1 files changed, 37 insertions, 12 deletions

diff --git a/llvm/tools/llvm-objcopy/COFF/Writer.cpp b/llvm/tools/llvm-objcopy/COFF/Writer.cpp
index db897e2ff33..6e69c597217 100644
--- a/llvm/tools/llvm-objcopy/COFF/Writer.cpp
+++ b/llvm/tools/llvm-objcopy/COFF/Writer.cpp
@@ -55,7 +55,8 @@ Error COFFWriter::finalizeSymbolContents() {
       if (Sym.Sym.NumberOfAuxSymbols == 1 &&
           Sym.Sym.StorageClass == IMAGE_SYM_CLASS_STATIC) {
         coff_aux_section_definition *SD =
-            reinterpret_cast<coff_aux_section_definition *>(Sym.AuxData.data());
+            reinterpret_cast<coff_aux_section_definition *>(
+                Sym.AuxData[0].Opaque);
         uint32_t SDSectionNumber;
         if (Sym.AssociativeComdatTargetSectionId == 0) {
           // Not a comdat associative section; just set the Number field to
@@ -79,7 +80,7 @@ Error COFFWriter::finalizeSymbolContents() {
     // we want to set. Only >= 1 would be required, but only == 1 makes sense.
     if (Sym.WeakTargetSymbolId && Sym.Sym.NumberOfAuxSymbols == 1) {
       coff_aux_weak_external *WE =
-          reinterpret_cast<coff_aux_weak_external *>(Sym.AuxData.data());
+          reinterpret_cast<coff_aux_weak_external *>(Sym.AuxData[0].Opaque);
       const Symbol *Target = Obj.findSymbol(*Sym.WeakTargetSymbolId);
       if (Target == nullptr)
         return createStringError(object_error::invalid_symbol_index,
@@ -141,13 +142,26 @@ size_t COFFWriter::finalizeStringTable() {
 
 template <class SymbolTy>
 std::pair<size_t, size_t> COFFWriter::finalizeSymbolTable() {
-  size_t SymTabSize = Obj.getSymbols().size() * sizeof(SymbolTy);
-  for (const auto &S : Obj.getSymbols())
-    SymTabSize += S.AuxData.size();
-  return std::make_pair(SymTabSize, sizeof(SymbolTy));
+  size_t RawSymIndex = 0;
+  for (auto &S : Obj.getMutableSymbols()) {
+    // Symbols normally have NumberOfAuxSymbols set correctly all the time.
+    // For file symbols, we need to know the output file's symbol size to be
+    // able to calculate the number of slots it occupies.
+    if (!S.AuxFile.empty())
+      S.Sym.NumberOfAuxSymbols =
+          alignTo(S.AuxFile.size(), sizeof(SymbolTy)) / sizeof(SymbolTy);
+    S.RawIndex = RawSymIndex;
+    RawSymIndex += 1 + S.Sym.NumberOfAuxSymbols;
+  }
+  return std::make_pair(RawSymIndex * sizeof(SymbolTy), sizeof(SymbolTy));
 }
 
 Error COFFWriter::finalize(bool IsBigObj) {
+  size_t SymTabSize, SymbolSize;
+  std::tie(SymTabSize, SymbolSize) = IsBigObj
+                                         ? finalizeSymbolTable<coff_symbol32>()
+                                         : finalizeSymbolTable<coff_symbol16>();
+
   if (Error E = finalizeRelocTargets())
     return E;
   if (Error E = finalizeSymbolContents())
@@ -199,10 +213,6 @@ Error COFFWriter::finalize(bool IsBigObj) {
   }
 
   size_t StrTabSize = finalizeStringTable();
-  size_t SymTabSize, SymbolSize;
-  std::tie(SymTabSize, SymbolSize) = IsBigObj
-                                         ? finalizeSymbolTable<coff_symbol32>()
-                                         : finalizeSymbolTable<coff_symbol16>();
 
   size_t PointerToSymbolTable = FileSize;
   // StrTabSize <= 4 is the size of an empty string table, only consisting
@@ -312,8 +322,23 @@ template <class SymbolTy> void COFFWriter::writeSymbolStringTables() {
     copySymbol<SymbolTy, coff_symbol32>(*reinterpret_cast<SymbolTy *>(Ptr),
                                         S.Sym);
     Ptr += sizeof(SymbolTy);
-    std::copy(S.AuxData.begin(), S.AuxData.end(), Ptr);
-    Ptr += S.AuxData.size();
+    if (!S.AuxFile.empty()) {
+      // For file symbols, just write the string into the aux symbol slots,
+      // assuming that the unwritten parts are initialized to zero in the memory
+      // mapped file.
+      std::copy(S.AuxFile.begin(), S.AuxFile.end(), Ptr);
+      Ptr += S.Sym.NumberOfAuxSymbols * sizeof(SymbolTy);
+    } else {
+      // For other auxillary symbols, write their opaque payload into one symbol
+      // table slot each. For big object files, the symbols are larger than the
+      // opaque auxillary symbol struct and we leave padding at the end of each
+      // entry.
+      for (const AuxSymbol &AuxSym : S.AuxData) {
+        ArrayRef<uint8_t> Ref = AuxSym.getRef();
+        std::copy(Ref.begin(), Ref.end(), Ptr);
+        Ptr += sizeof(SymbolTy);
+      }
+    }
   }
   if (StrTabBuilder.getSize() > 4 || !Obj.IsPE) {
     // Always write a string table in object files, even an empty one.