COFF: Fix a bug of __imp_ symbol.

The change I made in r240620 was not correct. If a symbol foo is
defined, and if you use __imp_foo, __imp_foo symbol is automatically
defined as a pointer (not just an alias) to foo.

Now that we need to create a chunk for automatically-created symbols.
I defined LocalImportChunk class for them.

llvm-svn: 240622

Author: rui314

lld/COFF/Chunks.cpp

@@ -253,6 +253,10 @@ BaserelChunk::BaserelChunk(uint32_t Page, uint32_t *Begin, uint32_t *End) {
   }
 }
 
+void LocalImportChunk::writeTo(uint8_t *Buf) {
+  write32le(Buf + FileOff, Sym->getRVA());
+}
+
 void BaserelChunk::writeTo(uint8_t *Buf) {
   memcpy(Buf + FileOff, Data.data(), Data.size());
 }

lld/COFF/Chunks.h

@@ -211,6 +211,18 @@ class ImportThunkChunk : public Chunk {
   Defined *ImpSymbol;
 };
 
+// Windows-specific.
+// See comments for DefinedLocalImport class.
+class LocalImportChunk : public Chunk {
+public:
+  explicit LocalImportChunk(Defined *S) : Sym(S) {}
+  size_t getSize() const override { return 4; }
+  void writeTo(uint8_t *Buf) override;
+
+private:
+  Defined *Sym;
+};
+
 // Windows-specific.
 // This class represents a block in .reloc section.
 // See the PE/COFF spec 5.6 for details.

lld/COFF/SymbolTable.cpp

@@ -85,7 +85,9 @@ bool SymbolTable::reportRemainingUndefines() {
     // This odd rule is for compatibility with MSVC linker.
     if (Name.startswith("__imp_")) {
       if (Defined *Imp = find(Name.substr(strlen("__imp_")))) {
-        Sym->Body = Imp;
+        auto *S = new (Alloc) DefinedLocalImport(Name, Imp);
+        LocalImportChunks.push_back(S->getChunk());
+        Sym->Body = S;
         continue;
       }
     }

lld/COFF/SymbolTable.h

@@ -80,6 +80,9 @@ class SymbolTable {
   // Rename From -> To in the symbol table.
   std::error_code rename(StringRef From, StringRef To);
 
+  // A list of chunks which to be added to .rdata.
+  std::vector<Chunk *> LocalImportChunks;
+
 private:
   std::error_code resolve(SymbolBody *Body);
   std::error_code resolveLazy(StringRef Name);

lld/COFF/Symbols.h

@@ -49,6 +49,7 @@ class SymbolBody {
     DefinedAbsoluteKind,
     DefinedImportDataKind,
     DefinedImportThunkKind,
+    DefinedLocalImportKind,
     DefinedCommonKind,
     DefinedCOMDATKind,
     DefinedRegularKind,
@@ -315,6 +316,30 @@ class DefinedImportThunk : public Defined {
   ImportThunkChunk Data;
 };
 
+// If you have a symbol "__imp_foo" in your object file, a symbol name
+// "foo" becomes automatically available as a pointer to "__imp_foo".
+// This class is for such automatically-created symbols.
+// Yes, this is an odd feature. We didn't intend to implement that.
+// This is here just for compatibility with MSVC.
+class DefinedLocalImport : public Defined {
+public:
+  DefinedLocalImport(StringRef N, Defined *S)
+      : Defined(DefinedLocalImportKind), Name(N), Data(S) {}
+
+  static bool classof(const SymbolBody *S) {
+    return S->kind() == DefinedLocalImportKind;
+  }
+
+  StringRef getName() override { return Name; }
+  uint64_t getRVA() override { return Data.getRVA(); }
+  uint64_t getFileOff() override { return Data.getFileOff(); }
+  Chunk *getChunk() { return &Data; }
+
+private:
+  StringRef Name;
+  LocalImportChunk Data;
+};
+
 class DefinedBitcode : public Defined {
 public:
   DefinedBitcode(StringRef N, bool R)

lld/COFF/Writer.cpp

@@ -43,6 +43,7 @@ std::error_code Writer::write(StringRef OutputPath) {
   markLive();
   dedupCOMDATs();
   createSections();
+  createMiscChunks();
   createImportTables();
   createExportTable();
   if (Config->Relocatable)
@@ -169,6 +170,14 @@ void Writer::createSections() {
   }
 }
 
+void Writer::createMiscChunks() {
+  if (Symtab->LocalImportChunks.empty())
+    return;
+  OutputSection *Sec = createSection(".rdata");
+  for (Chunk *C : Symtab->LocalImportChunks)
+    Sec->addChunk(C);
+}
+
 // Create .idata section for the DLL-imported symbol table.
 // The format of this section is inherently Windows-specific.
 // IdataContents class abstracted away the details for us,

lld/COFF/Writer.h

@@ -81,6 +81,7 @@ class Writer {
   void markLive();
   void dedupCOMDATs();
   void createSections();
+  void createMiscChunks();
   void createImportTables();
   void createExportTable();
   void assignAddresses();

lld/test/COFF/locally-imported.test

@@ -1,7 +1,12 @@
 # RUN: yaml2obj < %s > %t.obj
 # RUN: lld -flavor link2 /out:%t.exe %t.obj
+# RUN: llvm-objdump -s %t.exe | FileCheck %s
 
-# The linker automatically removes __imp_ prefix if it helps to resolve all symbols.
+# CHECK:      Contents of section .text:
+# CHECK-NEXT: 1000 00200000
+
+# CHECK:      Contents of section .rdata:
+# CHECK-NEXT: 2000 04100000
 
 ---
 header:
@@ -11,7 +16,11 @@ sections:
   - Name:            .text
     Characteristics: [ IMAGE_SCN_CNT_CODE, IMAGE_SCN_MEM_EXECUTE, IMAGE_SCN_MEM_READ ]
     Alignment:       4
-    SectionData:     B82A000000C3
+    SectionData:     00000000
+    Relocations:
+      - VirtualAddress:  0
+        SymbolName:      __imp_mainCRTStartup
+        Type:            IMAGE_REL_AMD64_ADDR32NB
 symbols:
   - Name:            .text
     Value:           0
@@ -20,14 +29,14 @@ symbols:
     ComplexType:     IMAGE_SYM_DTYPE_NULL
     StorageClass:    IMAGE_SYM_CLASS_STATIC
     SectionDefinition:
-      Length:          6
-      NumberOfRelocations: 0
+      Length:          4
+      NumberOfRelocations: 1
       NumberOfLinenumbers: 0
       CheckSum:        0
       Number:          0
       Selection:       IMAGE_COMDAT_SELECT_ANY
   - Name:            mainCRTStartup
-    Value:           0
+    Value:           4
     SectionNumber:   1
     SimpleType:      IMAGE_SYM_TYPE_NULL
     ComplexType:     IMAGE_SYM_DTYPE_FUNCTION