[LLVMdev] defining symbols with lld

[Michael Spencer]

On Thu, Aug 22, 2013 at 12:54 PM, Shankar Easwaran
<shankare at codeaurora.org>wrote:

> Hi Nick,
>
> I am planning to work on adding support for definining expressions for the
> Gnu flavor.
>
> Currently Gnu ld supports an option --defsym symbol=expression. The
> expression may be composed of other symbols.
> Any symbol that appears in the expression, gets its value from the output
> symbol value (address of the symbol in the output file).
>
> In addition the symbol only gets defined if and only if there is a
> relocation, that refers to the symbol.
>
> I was wondering how to accomplish this with lld. One thought that I had
> was to take list of  user defined symbols and the expressions associated
> with the symbols and evaluate at the time of writing the output file.
> The problem with that is
>
> a) if the expression uses a symbol thats not defined anywhere else except
> the defsym expression, the symbol would get garbage collected.
> b) Supporting linker scripts which create new symbols, will be an issue.
>
> What are your thoughts ?


Linker scripts have the same need. My idea for this was to allow atoms to
have an associated expression tree and would have references to all symbols
in that tree. The resolver wouldn't need any special handling for this, and
the backend would just need to evaluate the expression at the end.

- Michael Spencer
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.llvm.org/pipermail/llvm-dev/attachments/20130822/4be5759f/attachment.html>