[lld] r192930 - Fill gap in .text with NOP.

[Sean Silva]

WIll this code realistically one ever have to deal with x86? Is there some
target flag you need to check?

-- Sean Silva


On Thu, Oct 17, 2013 at 6:45 PM, Rui Ueyama <ruiu at google.com> wrote:

> Author: ruiu
> Date: Thu Oct 17 17:45:16 2013
> New Revision: 192930
>
> URL: http://llvm.org/viewvc/llvm-project?rev=192930&view=rev
> Log:
> Fill gap in .text with NOP.
>
> Modified:
>     lld/trunk/lib/ReaderWriter/PECOFF/WriterPECOFF.cpp
>
> Modified: lld/trunk/lib/ReaderWriter/PECOFF/WriterPECOFF.cpp
> URL:
> http://llvm.org/viewvc/llvm-project/lld/trunk/lib/ReaderWriter/PECOFF/WriterPECOFF.cpp?rev=192930&r1=192929&r2=192930&view=diff
>
> ==============================================================================
> --- lld/trunk/lib/ReaderWriter/PECOFF/WriterPECOFF.cpp (original)
> +++ lld/trunk/lib/ReaderWriter/PECOFF/WriterPECOFF.cpp Thu Oct 17 17:45:16
> 2013
> @@ -585,6 +585,20 @@ void SectionHeaderTableChunk::write(uint
>  // \brief A TextSectionChunk represents a .text section.
>  class TextSectionChunk : public SectionChunk {
>  public:
> +  virtual void write(uint8_t *fileBuffer) {
> +    if (_atomLayouts.empty())
> +      return;
> +    // Fill the section with NOP (0x90) rather than NUL, so that the
> +    // disassembler will not interpret a garbage between atoms as the
> beginning
> +    // of multi-byte machine code. This does not change the behavior of
> +    // resulting binary but help debugging.
> +    uint8_t *start = fileBuffer + _atomLayouts.front()->_fileOffset;
> +    uint8_t *end = fileBuffer + _atomLayouts.back()->_fileOffset;
> +    memset(start, 0x90, end - start);
> +
> +    SectionChunk::write(fileBuffer);
> +  }
> +
>    TextSectionChunk(const File &linkedFile)
>        : SectionChunk(".text", characteristics) {
>      buildContents(linkedFile, [](const DefinedAtom *atom) {
>
>
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