[LLVMdev] LLD AbsoluteAtoms

Nick Kledzik kledzik at apple.com
Mon Oct 15 10:01:28 PDT 2012

On Oct 15, 2012, at 8:08 AM, Sidney Manning wrote:
> I think that absolute atoms will need something similar to, "contentType" added.
> SHN_ABS symbols can have different types, STT_OBJECT, STT_FILE and maybe others.  In order for the writer to tell it must have a way to reach back and ask the atom what type of symbols caused it to be created.  To that end I added a contentType method to AbsoluteAtom and sprinkled changes around to make this work.
Tell me more about the semantics of STT_FILE.  The goal is not just to pass through ELF-isms.  The goal is to define a really good model and translate each object format into that model.  A web search for STT_FILE gives:

> Conventionally, the symbol's name gives the name of the source file associated with the object file. A file symbol has STB_LOCAL binding and its section index is SHN_ABS. This symbol, if present, precedes the other STB_LOCAL symbols for the file. Symbol index 1 of the SHT_SYMTAB is an STT_FILE symbol representing the file itself. Conventionally, this symbols is followed by the files STT_SECTION symbols, and any global symbols that have been reduced to locals.

This sounds like these symbols are not really about absolute address (e.g. ROM), but a way to sneak meta data (like source file name) into the object file. 

> What do the V1 suffixes mean in the Native code?  I had to add a new Attributes array to for the Absolute atoms and simply used, NCS_AttributesArrayV2 following the lead of NCS_ReferencesArrayV[12]

The V1 is for for when the file format is eventually stable and we need to support new features.  We are not there yet.  


More information about the llvm-dev mailing list