[lld] r194754 - Move DOS stub data to PECOFFLinkingContext for /stub option.

[Sean Silva]

+  // DOS Stub. DOS stub is data located at the beginning of PE/COFF file.
+  // Windows loader do not really care about DOS stub contents, but it's
usually
+  // a small DOS program that prints out a message "This program requires
+  // Microsoft Windows." This feature was somewhat useful before Windows
95.
+  std::vector<uint8_t> _dosStub;
+  static const std::vector<uint8_t> _defaultDosStub;

Why on earth is this using a std::vector? (which adds a static
initializer!) Just use ArrayRef or even a const char array.

Also, do we really need to support this feature? Who uses /stub anymore?

-- Sean Silva


On Thu, Nov 14, 2013 at 6:54 PM, Rui Ueyama <ruiu at google.com> wrote:

> Author: ruiu
> Date: Thu Nov 14 17:54:24 2013
> New Revision: 194754
>
> URL: http://llvm.org/viewvc/llvm-project?rev=194754&view=rev
> Log:
> Move DOS stub data to PECOFFLinkingContext for /stub option.
>
> Modified:
>     lld/trunk/include/lld/ReaderWriter/PECOFFLinkingContext.h
>     lld/trunk/lib/ReaderWriter/PECOFF/PECOFFLinkingContext.cpp
>     lld/trunk/lib/ReaderWriter/PECOFF/WriterPECOFF.cpp
>
> Modified: lld/trunk/include/lld/ReaderWriter/PECOFFLinkingContext.h
> URL:
> http://llvm.org/viewvc/llvm-project/lld/trunk/include/lld/ReaderWriter/PECOFFLinkingContext.h?rev=194754&r1=194753&r2=194754&view=diff
>
> ==============================================================================
> --- lld/trunk/include/lld/ReaderWriter/PECOFFLinkingContext.h (original)
> +++ lld/trunk/include/lld/ReaderWriter/PECOFFLinkingContext.h Thu Nov 14
> 17:54:24 2013
> @@ -43,7 +43,7 @@ public:
>          _terminalServerAware(true), _dynamicBaseEnabled(true),
>          _createManifest(true), _embedManifest(false), _manifestId(1),
>          _manifestLevel("'asInvoker'"), _manifestUiAccess("'false'"),
> -        _imageType(ImageType::IMAGE_EXE) {
> +        _imageType(ImageType::IMAGE_EXE), _dosStub(_defaultDosStub) {
>      setDeadStripping(true);
>    }
>
> @@ -230,6 +230,10 @@ public:
>      return it == _sectionAttributeMask.end() ? 0 : it->second;
>    }
>
> +  const std::vector<uint8_t> &getDosStub() const {
> +    return _dosStub;
> +  }
> +
>    StringRef allocateString(StringRef ref) const {
>      char *x = _allocator.Allocate<char>(ref.size() + 1);
>      memcpy(x, ref.data(), ref.size());
> @@ -311,6 +315,13 @@ private:
>
>    // List of files that will be removed on destruction.
>    std::vector<std::unique_ptr<llvm::FileRemover> > _tempFiles;
> +
> +  // DOS Stub. DOS stub is data located at the beginning of PE/COFF file.
> +  // Windows loader do not really care about DOS stub contents, but it's
> usually
> +  // a small DOS program that prints out a message "This program requires
> +  // Microsoft Windows." This feature was somewhat useful before Windows
> 95.
> +  std::vector<uint8_t> _dosStub;
> +  static const std::vector<uint8_t> _defaultDosStub;
>  };
>
>  } // end namespace lld
>
> Modified: lld/trunk/lib/ReaderWriter/PECOFF/PECOFFLinkingContext.cpp
> URL:
> http://llvm.org/viewvc/llvm-project/lld/trunk/lib/ReaderWriter/PECOFF/PECOFFLinkingContext.cpp?rev=194754&r1=194753&r2=194754&view=diff
>
> ==============================================================================
> --- lld/trunk/lib/ReaderWriter/PECOFF/PECOFFLinkingContext.cpp (original)
> +++ lld/trunk/lib/ReaderWriter/PECOFF/PECOFFLinkingContext.cpp Thu Nov 14
> 17:54:24 2013
> @@ -29,6 +29,13 @@
>
>  namespace lld {
>
> +namespace {
> +uint8_t DefaultDosStub[128] = {'M', 'Z'};
> +};
> +
> +const std::vector<uint8_t> PECOFFLinkingContext::_defaultDosStub(
> +    DefaultDosStub, DefaultDosStub + sizeof(DefaultDosStub));
> +
>  bool PECOFFLinkingContext::validateImpl(raw_ostream &diagnostics) {
>    if (_stackReserve < _stackCommit) {
>      diagnostics << "Invalid stack size: reserve size must be equal to or "
>
> Modified: lld/trunk/lib/ReaderWriter/PECOFF/WriterPECOFF.cpp
> URL:
> http://llvm.org/viewvc/llvm-project/lld/trunk/lib/ReaderWriter/PECOFF/WriterPECOFF.cpp?rev=194754&r1=194753&r2=194754&view=diff
>
> ==============================================================================
> --- lld/trunk/lib/ReaderWriter/PECOFF/WriterPECOFF.cpp (original)
> +++ lld/trunk/lib/ReaderWriter/PECOFF/WriterPECOFF.cpp Thu Nov 14 17:54:24
> 2013
> @@ -106,29 +106,19 @@ public:
>  /// of PE/COFF files.
>  class DOSStubChunk : public HeaderChunk {
>  public:
> -  DOSStubChunk() : HeaderChunk() {
> -    // Make the DOS stub occupy the first 128 bytes of an exe. Technically
> -    // this can be as small as 64 bytes, but GNU binutil's objdump cannot
> -    // parse such irregular header.
> -    _size = 128;
> -
> -    // A DOS stub is usually a small valid DOS program that prints out a
> message
> -    // "This program requires Microsoft Windows" to help user who
> accidentally
> -    // run a Windows executable on DOS. That's not a technical
> requirement, so
> -    // we don't bother to emit such code, at least for now. We simply
> fill the
> -    // DOS stub with null bytes.
> -    std::memset(&_dosHeader, 0, sizeof(_dosHeader));
> -
> -    _dosHeader.Magic = 'M' | ('Z' << 8);
> -    _dosHeader.AddressOfNewExeHeader = _size;
> +  DOSStubChunk(const PECOFFLinkingContext &ctx)
> +      : HeaderChunk(), _dosStub(ctx.getDosStub()) {
> +    auto *header = reinterpret_cast<llvm::object::dos_header
> *>(&_dosStub[0]);
> +    header->AddressOfNewExeHeader = _dosStub.size();
> +    _size = _dosStub.size();
>    }
>
>    virtual void write(uint8_t *fileBuffer) {
> -    std::memcpy(fileBuffer, &_dosHeader, sizeof(_dosHeader));
> +    std::memcpy(fileBuffer, &_dosStub[0], _dosStub.size());
>    }
>
>  private:
> -  llvm::object::dos_header _dosHeader;
> +  std::vector<uint8_t> _dosStub;
>  };
>
>  /// A PEHeaderChunk represents PE header including COFF header.
> @@ -810,7 +800,7 @@ public:
>    // Create all chunks that consist of the output file.
>    void build(const File &linkedFile) {
>      // Create file chunks and add them to the list.
> -    auto *dosStub = new DOSStubChunk();
> +    auto *dosStub = new DOSStubChunk(_PECOFFLinkingContext);
>      auto *peHeader = new PEHeaderChunk(_PECOFFLinkingContext);
>      auto *dataDirectory = new DataDirectoryChunk(linkedFile);
>      auto *sectionTable = new SectionHeaderTableChunk();
>
>
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