Re: [Bug] DWARF-5 section names in PE/PEP and weak symbols

[Nick Clifton <nickc@redhat.com>]

Hi Achim,

   Please could you file a bug report for this problem here:

https://sourceware.org/bugzilla/enter_bug.cgi?product=binutils


> changed the behaviour of weak symbols in Cygwin.  The following test
> from gnulib that should fail.  In other words fputs should have a symbol
> value of 0x0 and the resulting executable should not be able to run
> since the Windows loader does not resolve weak symbols):
> 
> --8<--weak.c-------cut here---------------start------------->8---
> #include <stdio.h>
> #pragma weak fputs
> int main ()
> {
>    return (fputs == NULL);
> }
> --8<---------------cut here---------------end--------------->8---
> 
> $ gcc -o weak weak.c # w/ binutils 2.36.1
> $ ./weak ; echo $?
> ./weak: ./weak: cannot execute binary file
> 126
> 
> Instead, starting with the above commit, the test succeeds since fputs
> has the (expected) value from cygwin1.dll.  

So you are saying that because the linker script now includes specific
references to DWARF-5 debug sections, the fputs symbol is being pulled
in to the link from the cygwin1.dll and hence it is no longer undefined ?
That seems to be most strange.


> I've narrowed it down to just one of the new DWARF5 sections and
> removing them from the linker scripts restores the correct behaviour of
> weak symbols in Cygwin (I have no idea if that triggers problems
> elsewhere):

> +/* ===
>     .debug_loclists ${RELOCATING+BLOCK(__section_alignment__)} ${RELOCATING+(NOLOAD)} :
>     {
>       *(.debug_loclists)
>     }
> +=== */

Hmm, I suppose that the location lists will refer to real locations in
the code space, and so including the debug information could also pull
in the code itself.  But really you would only want to have the debug
information for code that is already part of the final link.  So maybe
the underlying problem is that the debug information has not been pruned
to match discarded code.

Quick question - if instead of deleting the references to the .debug_loclists
section you move them into the /DISCARD/ section earlier in the pe.se file,
does this also solve the problem.  (The point being that if the script
explitcitly discards this information we also have room to add a comment
explaining why.  Plus it will prevent future changes to the pe.sc file
from adding the section back in).  (Also the change would be needed in
the pep.sc file as well, obviously.  Plus the .zdebug_loclists section
would need similar treatment).

Cheers
   Nick