[Bug win32/18027] dwarf2 debug info after rebasing DLLs unusable

["corinna at vinschen dot de" <sourceware-bugzilla@sourceware.org>]

https://sourceware.org/bugzilla/show_bug.cgi?id=18027

--- Comment #20 from Corinna Vinschen <corinna at vinschen dot de> ---
(In reply to Nick Clifton from comment #19)
> (In reply to Corinna Vinschen from comment #18)
> 
> > what do you think about Tom's idea in comment 14?
> 
> To be honest, I do not get what Tom is suggesting. :-(  What is that
> coffread.c should be detecting and then doing ?

That's what GDB would be able to do if the extra section with
the original address is available.  There would be an offset
between original address and rebased address which could be taken
into account.

> > Would it be possible to add something like that?
> > Maybe like I suggest in comment 16?
> 
> It certainly should be possible for the linker to add an extra section. 
> There is already a precedence for this, for example when it creates the
> .reloc section.
> 
> In fact it may even be possible to create the section and its contents using
> the
> default linker script, so that there is no need to change the linker at all.
> For example adding (untested):
> 
>   .debug_pe_defaddr 0 { .long DLLMain }

Aha, nice. That should ideally be the load address of the DLL, so I tried
this with the Cygwin DLL which provides its own linker script, and I came up
with:

  .debug_pe_defaddr ALIGN(__section_alignment__) (NOLOAD) :
    {
      QUAD (__image_base__)
    }

which appears to work.

> Cheers
>   Nick
> 
> PS.  I assume that the rebase program cannot update the addresses in the
> debug information itself ?

Rebasing is actually not performed by some code we have under control.
Rather, we're calling a function Rebase64(), which is part of Windows itself.
Given that Windows has no idea what Dwarf-2 is, it doesn't even touch these
sections.

> PPS. Would the __pei386_runtime_relocator symbol be of any use in addressing
> this problem ?

I have no idea.  How so?


Thanks,
Corinna

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