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

5 files changed, 14 insertions, 16 deletions

diff --git a/lld/COFF/DLL.cpp b/lld/COFF/DLL.cpp
index d76410b6747..3ac14e4ea2b 100644
--- a/lld/COFF/DLL.cpp
+++ b/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);
   }
diff --git a/lld/COFF/DLL.h b/lld/COFF/DLL.h
index ad312789edf..939771b3290 100644
--- a/lld/COFF/DLL.h
+++ b/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;
diff --git a/lld/test/COFF/armnt-imports.test b/lld/test/COFF/armnt-imports.test
index 519886eb0c0..f0aaebd3f29 100644
--- a/lld/test/COFF/armnt-imports.test
+++ b/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: }
 
diff --git a/lld/test/COFF/hello32.test b/lld/test/COFF/hello32.test
index b7bc887d46e..e6117b990da 100644
--- a/lld/test/COFF/hello32.test
+++ b/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: }
diff --git a/lld/test/COFF/imports.test b/lld/test/COFF/imports.test
index 584c24eb1b7..4df6d492ff2 100644
--- a/lld/test/COFF/imports.test
+++ b/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)