[PECOFF] A symbol with symbol with section number 0 and non-zero value represents a BSS atom.

llvm-svn: 187645

lld/lib/ReaderWriter/PECOFF/ReaderCOFF.cpp

@@ -161,6 +161,20 @@ private:
     // Filter non-defined atoms, and group defined atoms by its section.
     SectionToSymbolsT definedSymbols;
     for (const coff_symbol *sym : symbols) {
+      // A symbol with section number 0 and non-zero value represents an
+      // uninitialized data. I don't understand why there are two ways to define
+      // an uninitialized data symbol (.bss and this way), but that's how COFF
+      // works.
+      if (sym->SectionNumber == llvm::COFF::IMAGE_SYM_UNDEFINED &&
+          sym->Value > 0) {
+        StringRef name = _symbolName[sym];
+        uint32_t size = sym->Value;
+        auto *atom = new (_alloc) COFFBSSAtom(*this, name, sym, size, 0);
+        result.push_back(atom);
+        continue;
+      }
+
+      // Skip if it's not for defined atom.
       if (sym->SectionNumber == llvm::COFF::IMAGE_SYM_ABSOLUTE ||
           sym->SectionNumber == llvm::COFF::IMAGE_SYM_UNDEFINED)
         continue;

lld/test/pecoff/Inputs/bss-undef.obj.yaml

@@ -0,0 +1,43 @@
+---
+header:
+  Machine:         IMAGE_FILE_MACHINE_I386
+  Characteristics: [  ]
+sections:
+  - Name:            .text
+    Characteristics: [ IMAGE_SCN_CNT_CODE, IMAGE_SCN_MEM_EXECUTE, IMAGE_SCN_MEM_READ ]
+    Alignment:       4
+    SectionData:     ""
+  - Name:            .data
+    Characteristics: [ IMAGE_SCN_CNT_INITIALIZED_DATA, IMAGE_SCN_MEM_READ, IMAGE_SCN_MEM_WRITE ]
+    Alignment:       4
+    SectionData:     03000000
+symbols:
+  - Name:            .text
+    Value:           0
+    SectionNumber:   1
+    SimpleType:      IMAGE_SYM_TYPE_NULL
+    ComplexType:     IMAGE_SYM_DTYPE_NULL
+    StorageClass:    IMAGE_SYM_CLASS_STATIC
+    NumberOfAuxSymbols: 1
+    AuxiliaryData:   000000000000000000000000000000000000
+  - Name:            .data
+    Value:           0
+    SectionNumber:   2
+    SimpleType:      IMAGE_SYM_TYPE_NULL
+    ComplexType:     IMAGE_SYM_DTYPE_NULL
+    StorageClass:    IMAGE_SYM_CLASS_STATIC
+    NumberOfAuxSymbols: 1
+    AuxiliaryData:   040000000000000000000000000000000000
+  - Name:            _bssdata1
+    Value:           4
+    SectionNumber:   0
+    SimpleType:      IMAGE_SYM_TYPE_NULL
+    ComplexType:     IMAGE_SYM_DTYPE_NULL
+    StorageClass:    IMAGE_SYM_CLASS_EXTERNAL
+  - Name:            _bssdata2
+    Value:           4
+    SectionNumber:   0
+    SimpleType:      IMAGE_SYM_TYPE_NULL
+    ComplexType:     IMAGE_SYM_DTYPE_NULL
+    StorageClass:    IMAGE_SYM_CLASS_EXTERNAL
+...

lld/test/pecoff/bss-undef.test

@@ -0,0 +1,22 @@
+# RUN: yaml2obj %p/Inputs/bss-undef.obj.yaml > %t.obj
+#
+# RUN: lld -flavor link /out:%t /subsystem:console /force -- %t.obj \
+# RUN:    && llvm-readobj -sections %t | FileCheck %s
+
+CHECK:       Section {
+CHECK:         Number: 2
+CHECK-NEXT:    Name: .bss
+CHECK-NEXT:    VirtualSize: 0x0
+CHECK-NEXT:    VirtualAddress: 0x2000
+CHECK-NEXT:    RawDataSize: 512
+CHECK-NEXT:    PointerToRawData: 0x0
+CHECK-NEXT:    PointerToRelocations: 0x0
+CHECK-NEXT:    PointerToLineNumbers: 0x0
+CHECK-NEXT:    RelocationCount: 0
+CHECK-NEXT:    LineNumberCount: 0
+CHECK-NEXT:    Characteristics [
+CHECK-NEXT:      IMAGE_SCN_CNT_UNINITIALIZED_DATA
+CHECK-NEXT:      IMAGE_SCN_MEM_READ
+CHECK-NEXT:      IMAGE_SCN_MEM_WRITE
+CHECK-NEXT:    ]
+CHECK-NEXT:  }