Revert "[CFGuard] Add address-taken IAT tables and delay-load support"

This reverts commit ef4e971.

Author: aeubanks

lld/COFF/DLL.cpp

@@ -19,7 +19,6 @@
 
 #include "DLL.h"
 #include "Chunks.h"
-#include "SymbolTable.h"
 #include "llvm/Object/COFF.h"
 #include "llvm/Support/Endian.h"
 #include "llvm/Support/Path.h"
@@ -654,18 +653,9 @@ void DelayLoadContents::create(Defined *h) {
         auto *c = make<HintNameChunk>(extName, 0);
         names.push_back(make<LookupChunk>(c));
         hintNames.push_back(c);
-        // Add a syntentic symbol for this load thunk, using the "__imp_load"
-        // prefix, in case this thunk needs to be added to the list of valid
-        // call targets for Control Flow Guard.
-        StringRef symName = saver.save("__imp_load_" + extName);
-        s->loadThunkSym =
-            cast<DefinedSynthetic>(symtab->addSynthetic(symName, t));
       }
     }
     thunks.push_back(tm);
-    StringRef tmName =
-        saver.save("__tailMerge_" + syms[0]->getDLLName().lower());
-    symtab->addSynthetic(tmName, tm);
     // Terminate with null values.
     addresses.push_back(make<NullChunk>(8));
     names.push_back(make<NullChunk>(8));

lld/COFF/ICF.cpp

@@ -131,7 +131,7 @@ bool ICF::assocEquals(const SectionChunk *a, const SectionChunk *b) {
   auto considerForICF = [](const SectionChunk &assoc) {
     StringRef Name = assoc.getSectionName();
     return !(Name.startswith(".debug") || Name == ".gfids$y" ||
-             Name == ".giats$y" || Name == ".gljmp$y");
+             Name == ".gljmp$y");
   };
   auto ra = make_filter_range(a->children(), considerForICF);
   auto rb = make_filter_range(b->children(), considerForICF);

lld/COFF/InputFiles.cpp

@@ -280,8 +280,6 @@ SectionChunk *ObjFile::readSection(uint32_t sectionNumber,
     debugChunks.push_back(c);
   else if (name == ".gfids$y")
     guardFidChunks.push_back(c);
-  else if (name == ".giats$y")
-    guardIATChunks.push_back(c);
   else if (name == ".gljmp$y")
     guardLJmpChunks.push_back(c);
   else if (name == ".sxdata")

lld/COFF/InputFiles.h

@@ -144,7 +144,6 @@ class ObjFile : public InputFile {
   ArrayRef<SectionChunk *> getDebugChunks() { return debugChunks; }
   ArrayRef<SectionChunk *> getSXDataChunks() { return sxDataChunks; }
   ArrayRef<SectionChunk *> getGuardFidChunks() { return guardFidChunks; }
-  ArrayRef<SectionChunk *> getGuardIATChunks() { return guardIATChunks; }
   ArrayRef<SectionChunk *> getGuardLJmpChunks() { return guardLJmpChunks; }
   ArrayRef<Symbol *> getSymbols() { return symbols; }
 
@@ -284,11 +283,9 @@ class ObjFile : public InputFile {
   // 32-bit x86.
   std::vector<SectionChunk *> sxDataChunks;
 
-  // Chunks containing symbol table indices of address taken symbols, address
-  // taken IAT entries, and longjmp targets. These are not linked into the
-  // final binary when /guard:cf is set.
+  // Chunks containing symbol table indices of address taken symbols and longjmp
+  // targets.  These are not linked into the final binary when /guard:cf is set.
   std::vector<SectionChunk *> guardFidChunks;
-  std::vector<SectionChunk *> guardIATChunks;
   std::vector<SectionChunk *> guardLJmpChunks;
 
   // This vector contains a list of all symbols defined or referenced by this

lld/COFF/Symbols.h

@@ -343,13 +343,6 @@ class DefinedImportData : public Defined {
   uint16_t getOrdinal() { return file->hdr->OrdinalHint; }
 
   ImportFile *file;
-
-  // This is a pointer to the synthetic symbol associated with the load thunk
-  // for this symbol that will be called if the DLL is delay-loaded. This is
-  // needed for Control Flow Guard because if this DefinedImportData symbol is a
-  // valid call target, the corresponding load thunk must also be marked as a
-  // valid call target.
-  DefinedSynthetic *loadThunkSym;
 };
 
 // This class represents a symbol for a jump table entry which jumps

lld/COFF/Writer.cpp

@@ -227,9 +227,6 @@ class Writer {
   void markSymbolsForRVATable(ObjFile *file,
                               ArrayRef<SectionChunk *> symIdxChunks,
                               SymbolRVASet &tableSymbols);
-  void getSymbolsFromSections(ObjFile *file,
-                              ArrayRef<SectionChunk *> symIdxChunks,
-                              std::vector<Symbol *> &symbols);
   void maybeAddRVATable(SymbolRVASet tableSymbols, StringRef tableSym,
                         StringRef countSym);
   void setSectionPermissions();
@@ -608,9 +605,8 @@ void Writer::run() {
 
   createImportTables();
   createSections();
-  appendImportThunks();
-  // Import thunks must be added before the Control Flow Guard tables are added.
   createMiscChunks();
+  appendImportThunks();
   createExportTable();
   mergeSections();
   removeUnusedSections();
@@ -1622,8 +1618,6 @@ static void markSymbolsWithRelocations(ObjFile *file,
 // table.
 void Writer::createGuardCFTables() {
   SymbolRVASet addressTakenSyms;
-  SymbolRVASet giatsRVASet;
-  std::vector<Symbol *> giatsSymbols;
   SymbolRVASet longJmpTargets;
   for (ObjFile *file : ObjFile::instances) {
     // If the object was compiled with /guard:cf, the address taken symbols
@@ -1633,8 +1627,6 @@ void Writer::createGuardCFTables() {
     // possibly address-taken.
     if (file->hasGuardCF()) {
       markSymbolsForRVATable(file, file->getGuardFidChunks(), addressTakenSyms);
-      markSymbolsForRVATable(file, file->getGuardIATChunks(), giatsRVASet);
-      getSymbolsFromSections(file, file->getGuardIATChunks(), giatsSymbols);
       markSymbolsForRVATable(file, file->getGuardLJmpChunks(), longJmpTargets);
     } else {
       markSymbolsWithRelocations(file, addressTakenSyms);
@@ -1649,16 +1641,6 @@ void Writer::createGuardCFTables() {
   for (Export &e : config->exports)
     maybeAddAddressTakenFunction(addressTakenSyms, e.sym);
 
-  // For each entry in the .giats table, check if it has a corresponding load
-  // thunk (e.g. because the DLL that defines it will be delay-loaded) and, if
-  // so, add the load thunk to the address taken (.gfids) table.
-  for (Symbol *s : giatsSymbols) {
-    if (auto *di = dyn_cast<DefinedImportData>(s)) {
-      if (di->loadThunkSym)
-        addSymbolToRVASet(addressTakenSyms, di->loadThunkSym);
-    }
-  }
-
   // Ensure sections referenced in the gfid table are 16-byte aligned.
   for (const ChunkAndOffset &c : addressTakenSyms)
     if (c.inputChunk->getAlignment() < 16)
@@ -1667,10 +1649,6 @@ void Writer::createGuardCFTables() {
   maybeAddRVATable(std::move(addressTakenSyms), "__guard_fids_table",
                    "__guard_fids_count");
 
-  // Add the Guard Address Taken IAT Entry Table (.giats).
-  maybeAddRVATable(std::move(giatsRVASet), "__guard_iat_table",
-                   "__guard_iat_count");
-
   // Add the longjmp target table unless the user told us not to.
   if (config->guardCF == GuardCFLevel::Full)
     maybeAddRVATable(std::move(longJmpTargets), "__guard_longjmp_table",
@@ -1687,11 +1665,11 @@ void Writer::createGuardCFTables() {
 }
 
 // Take a list of input sections containing symbol table indices and add those
-// symbols to a vector. The challenge is that symbol RVAs are not known and
+// symbols to an RVA table. The challenge is that symbol RVAs are not known and
 // depend on the table size, so we can't directly build a set of integers.
-void Writer::getSymbolsFromSections(ObjFile *file,
+void Writer::markSymbolsForRVATable(ObjFile *file,
                                     ArrayRef<SectionChunk *> symIdxChunks,
-                                    std::vector<Symbol *> &symbols) {
+                                    SymbolRVASet &tableSymbols) {
   for (SectionChunk *c : symIdxChunks) {
     // Skip sections discarded by linker GC. This comes up when a .gfids section
     // is associated with something like a vtable and the vtable is discarded.
@@ -1709,7 +1687,7 @@ void Writer::getSymbolsFromSections(ObjFile *file,
     }
 
     // Read each symbol table index and check if that symbol was included in the
-    // final link. If so, add it to the vector of symbols.
+    // final link. If so, add it to the table symbol set.
     ArrayRef<ulittle32_t> symIndices(
         reinterpret_cast<const ulittle32_t *>(data.data()), data.size() / 4);
     ArrayRef<Symbol *> objSymbols = file->getSymbols();
@@ -1721,24 +1699,12 @@ void Writer::getSymbolsFromSections(ObjFile *file,
       }
       if (Symbol *s = objSymbols[symIndex]) {
         if (s->isLive())
-          symbols.push_back(cast<Symbol>(s));
+          addSymbolToRVASet(tableSymbols, cast<Defined>(s));
       }
     }
   }
 }
 
-// Take a list of input sections containing symbol table indices and add those
-// symbols to an RVA table.
-void Writer::markSymbolsForRVATable(ObjFile *file,
-                                    ArrayRef<SectionChunk *> symIdxChunks,
-                                    SymbolRVASet &tableSymbols) {
-  std::vector<Symbol *> syms;
-  getSymbolsFromSections(file, symIdxChunks, syms);
-
-  for (Symbol *s : syms)
-    addSymbolToRVASet(tableSymbols, cast<Defined>(s));
-}
-
 // Replace the absolute table symbol with a synthetic symbol pointing to
 // tableChunk so that we can emit base relocations for it and resolve section
 // relative relocations.

lld/test/COFF/giats.s

@@ -215,7 +215,6 @@ class MCObjectFileInfo {
   MCSection *XDataSection = nullptr;
   MCSection *SXDataSection = nullptr;
   MCSection *GFIDsSection = nullptr;
-  MCSection *GIATsSection = nullptr;
   MCSection *GLJMPSection = nullptr;
 
   // XCOFF specific sections
@@ -399,7 +398,6 @@ class MCObjectFileInfo {
   MCSection *getXDataSection() const { return XDataSection; }
   MCSection *getSXDataSection() const { return SXDataSection; }
   MCSection *getGFIDsSection() const { return GFIDsSection; }
-  MCSection *getGIATsSection() const { return GIATsSection; }
   MCSection *getGLJMPSection() const { return GLJMPSection; }
 
   // XCOFF specific sections