[lld] r187645 - [PECOFF] A symbol with symbol with section number 0 and non-zero value represents a BSS atom.

[Shankar Easwaran]

Isnt this supposed to be meant for common symbols ?

On 8/2/2013 12:25 AM, Rui Ueyama wrote:
> Author: ruiu
> Date: Fri Aug  2 00:25:31 2013
> New Revision: 187645
>
> URL: http://llvm.org/viewvc/llvm-project?rev=187645&view=rev
> Log:
> [PECOFF] A symbol with symbol with section number 0 and non-zero value represents a BSS atom.
>
> Added:
>      lld/trunk/test/pecoff/Inputs/bss-undef.obj.yaml
>      lld/trunk/test/pecoff/bss-undef.test
> Modified:
>      lld/trunk/lib/ReaderWriter/PECOFF/ReaderCOFF.cpp
>
> Modified: lld/trunk/lib/ReaderWriter/PECOFF/ReaderCOFF.cpp
> URL: http://llvm.org/viewvc/llvm-project/lld/trunk/lib/ReaderWriter/PECOFF/ReaderCOFF.cpp?rev=187645&r1=187644&r2=187645&view=diff
> ==============================================================================
> --- lld/trunk/lib/ReaderWriter/PECOFF/ReaderCOFF.cpp (original)
> +++ lld/trunk/lib/ReaderWriter/PECOFF/ReaderCOFF.cpp Fri Aug  2 00:25:31 2013
> @@ -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;
>
> Added: lld/trunk/test/pecoff/Inputs/bss-undef.obj.yaml
> URL: http://llvm.org/viewvc/llvm-project/lld/trunk/test/pecoff/Inputs/bss-undef.obj.yaml?rev=187645&view=auto
> ==============================================================================
> --- lld/trunk/test/pecoff/Inputs/bss-undef.obj.yaml (added)
> +++ lld/trunk/test/pecoff/Inputs/bss-undef.obj.yaml Fri Aug  2 00:25:31 2013
> @@ -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
> +...
>
> Added: lld/trunk/test/pecoff/bss-undef.test
> URL: http://llvm.org/viewvc/llvm-project/lld/trunk/test/pecoff/bss-undef.test?rev=187645&view=auto
> ==============================================================================
> --- lld/trunk/test/pecoff/bss-undef.test (added)
> +++ lld/trunk/test/pecoff/bss-undef.test Fri Aug  2 00:25:31 2013
> @@ -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:  }
>
>
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