Merge IAT and ILT.

Previously, LLD-produced executables had IAT (Import Address Table) and
ILT (Import Lookup Table) as separate chunks of data, although their
contents are identical. My interpretation of the COFF spec when I wrote
the COFF linker is that they need to be separate tables even though they
are the same.

But Peter found that the Windows loader is fine with executables in
which IAT and ILT are merged. This is a patch to merge IAT and ILT.
I confirmed that an lld-link self-hosted with this patch works fine.

Fixes https://bugs.llvm.org/show_bug.cgi?id=33064

Differential Revision: https://reviews.llvm.org/D33326

llvm-svn: 303374

lld/COFF/DLL.cpp

@@ -100,13 +100,17 @@ public:
 
   void writeTo(uint8_t *Buf) const override {
     auto *E = (coff_import_directory_table_entry *)(Buf + OutputSectionOff);
-    E->ImportLookupTableRVA = LookupTab->getRVA();
     E->NameRVA = DLLName->getRVA();
+
+    // The import descriptor table contains two pointers to
+    // the tables describing dllimported symbols. But the
+    // Windows loader actually uses only one. So we create
+    // only one table and set both fields to its address.
+    E->ImportLookupTableRVA = AddressTab->getRVA();
     E->ImportAddressTableRVA = AddressTab->getRVA();
   }
 
   Chunk *DLLName;
-  Chunk *LookupTab;
   Chunk *AddressTab;
 };
 
@@ -388,7 +392,6 @@ std::vector<Chunk *> IdataContents::getChunks() {
   // Add each type in the correct order.
   std::vector<Chunk *> V;
   V.insert(V.end(), Dirs.begin(), Dirs.end());
-  V.insert(V.end(), Lookups.begin(), Lookups.end());
   V.insert(V.end(), Addresses.begin(), Addresses.end());
   V.insert(V.end(), Hints.begin(), Hints.end());
   V.insert(V.end(), DLLNames.begin(), DLLNames.end());
@@ -404,21 +407,18 @@ void IdataContents::create() {
     // we need to create HintName chunks to store the names.
     // If they don't (if they are import-by-ordinals), we store only
     // ordinal values to the table.
-    size_t Base = Lookups.size();
+    size_t Base = Addresses.size();
     for (DefinedImportData *S : Syms) {
       uint16_t Ord = S->getOrdinal();
       if (S->getExternalName().empty()) {
-        Lookups.push_back(make<OrdinalOnlyChunk>(Ord));
         Addresses.push_back(make<OrdinalOnlyChunk>(Ord));
         continue;
       }
       auto *C = make<HintNameChunk>(S->getExternalName(), Ord);
-      Lookups.push_back(make<LookupChunk>(C));
       Addresses.push_back(make<LookupChunk>(C));
       Hints.push_back(C);
     }
     // Terminate with null values.
-    Lookups.push_back(make<NullChunk>(ptrSize()));
     Addresses.push_back(make<NullChunk>(ptrSize()));
 
     for (int I = 0, E = Syms.size(); I < E; ++I)
@@ -427,7 +427,6 @@ void IdataContents::create() {
     // Create the import table header.
     DLLNames.push_back(make<StringChunk>(Syms[0]->getDLLName()));
     auto *Dir = make<ImportDirectoryChunk>(DLLNames.back());
-    Dir->LookupTab = Lookups[Base];
     Dir->AddressTab = Addresses[Base];
     Dirs.push_back(Dir);
   }

lld/COFF/DLL.h

@@ -36,7 +36,6 @@ private:
 
   std::vector<DefinedImportData *> Imports;
   std::vector<Chunk *> Dirs;
-  std::vector<Chunk *> Lookups;
   std::vector<Chunk *> Addresses;
   std::vector<Chunk *> Hints;
   std::vector<Chunk *> DLLNames;

lld/test/COFF/armnt-imports.test

@@ -6,7 +6,7 @@
 # CHECK: Import {
 # CHECK:   Name: library.dll
 # CHECK:   ImportLookupTableRVA: 0x2028
-# CHECK:   ImportAddressTableRVA: 0x2030
+# CHECK:   ImportAddressTableRVA: 0x2028
 # CHECK:   Symbol: function (0)
 # CHECK: }
 

lld/test/COFF/hello32.test

@@ -77,7 +77,7 @@ HEADER-NEXT:     LoadConfigTableRVA: 0x0
 HEADER-NEXT:     LoadConfigTableSize: 0x0
 HEADER-NEXT:     BoundImportRVA: 0x0
 HEADER-NEXT:     BoundImportSize: 0x0
-HEADER-NEXT:     IATRVA: 0x3034
+HEADER-NEXT:     IATRVA: 0x3028
 HEADER-NEXT:     IATSize: 0xC
 HEADER-NEXT:     DelayImportDescriptorRVA: 0x0
 HEADER-NEXT:     DelayImportDescriptorSize: 0x0
@@ -113,7 +113,7 @@ IMPORTS: AddressSize: 32bit
 IMPORTS: Import {
 IMPORTS:   Name: std32.dll
 IMPORTS:   ImportLookupTableRVA: 0x3028
-IMPORTS:   ImportAddressTableRVA: 0x3034
+IMPORTS:   ImportAddressTableRVA: 0x3028
 IMPORTS:   Symbol: ExitProcess (0)
 IMPORTS:   Symbol: MessageBoxA (1)
 IMPORTS: }

lld/test/COFF/imports.test

@@ -21,14 +21,14 @@ TEXT-NEXT: callq   60
 TEXT-NEXT: movl    $0, %ecx
 TEXT-NEXT: callq   18
 TEXT-NEXT: callq   29
-TEXT:      jmpq    *4098(%rip)
-TEXT:      jmpq    *4090(%rip)
-TEXT:      jmpq    *4082(%rip)
+TEXT:      jmpq    *4066(%rip)
+TEXT:      jmpq    *4058(%rip)
+TEXT:      jmpq    *4050(%rip)
 
 IMPORT:      Import {
 IMPORT-NEXT:   Name: std64.dll
 IMPORT-NEXT:   ImportLookupTableRVA: 0x3028
-IMPORT-NEXT:   ImportAddressTableRVA: 0x3048
+IMPORT-NEXT:   ImportAddressTableRVA: 0x3028
 IMPORT-NEXT:   Symbol: ExitProcess (0)
 IMPORT-NEXT:   Symbol:  (50)
 IMPORT-NEXT:   Symbol: MessageBoxA (1)