[Patch, LD]Fix GDB crash caused by discarding the grouped debug sections

[Terry Guo]

> -----Original Message-----
> From: Alan Modra [mailto:amodra@gmail.com]
> Sent: Sunday, January 11, 2015 12:15 PM
> To: Terry Guo
> Cc: binutils@sourceware.org
> Subject: Re: [Patch, LD]Fix GDB crash caused by discarding the grouped
> debug sections
> 
> On Wed, Jan 07, 2015 at 05:59:27PM +0800, Terry Guo wrote:
> > @@ -11971,6 +11971,48 @@ _bfd_elf_gc_mark (struct bfd_link_info *info,
> >    return ret;
> >  }
> >
> > +/* Scan and mark sections in a special or debug section group.  */
> > +
> > +static void
> > +_bfd_elf_gc_mark_debug_special_section_group (asection *grp)
> > +{
> > +  /* Point to first section of section group.  */
> > +  asection *ssec;
> > +  /* Used to iterate the section group.  */
> > +  asection *msec;
> > +
> > +  bfd_boolean is_special_grp = TRUE;
> > +  bfd_boolean is_debug_grp = TRUE;
> > +
> > +  /* First scan to see if group contains any section other than debug
> > +     and special section.  */
> > +  ssec = msec = elf_next_in_group (grp);
> > +  do
> > +    {
> > +      if ((msec->flags & SEC_DEBUGGING) == 0)
> > +	is_debug_grp = FALSE;
> > +
> > +      if ((msec->flags & (SEC_ALLOC | SEC_LOAD | SEC_RELOC)) != 0)
> > +	is_special_grp = FALSE;
> > +
> > +      msec = elf_next_in_group (msec);
> > +    }
> > +  while (msec != ssec);
> > +
> > +  /* If this is a pure debug section group or pure special section
group,
> > +     keep all sections in this group.  */
> > +  if (is_debug_grp || is_special_grp)
> > +    {
> > +      ssec = msec = elf_next_in_group (grp);
> 
> The above line isn't needed.
> 
> > +      do
> > +	{
> > +	  msec->gc_mark = 1;
> > +	  msec = elf_next_in_group (msec);
> > +	}
> > +      while (msec != ssec);
> > +    }
> > +}
> > +
> >  /* Keep debug and special sections.  */
> >
> >  bfd_boolean
> > @@ -12011,13 +12053,23 @@ _bfd_elf_gc_mark_extra_sections (struct
> bfd_link_info *info,
> >  	continue;
> >
> >        /* Keep debug and special sections like .comment when they are
> > -	 not part of a group, or when we have single-member groups.  */
> > +	 not part of a group, or when we have single-member groups.
> > +	 Also keep section group that contains just debug sections or
> > +	 special sections.  */
> >        for (isec = ibfd->sections; isec != NULL; isec = isec->next)
> > -	if ((elf_next_in_group (isec) == NULL
> > -	     || elf_next_in_group (isec) == isec)
> > -	    && ((isec->flags & SEC_DEBUGGING) != 0
> > -		|| (isec->flags & (SEC_ALLOC | SEC_LOAD | SEC_RELOC)) ==
> 0))
> > -	  isec->gc_mark = 1;
> > +	{
> > +	  if (isec->gc_mark)
> > +	    continue;
> > +	  else if ((isec->flags & SEC_DEBUGGING) != 0
> > +		   || (isec->flags & (SEC_ALLOC | SEC_LOAD | SEC_RELOC)) ==
> 0)
> > +	    {
> > +	      if ((elf_next_in_group (isec) == NULL
> > +		   || elf_next_in_group (isec) == isec))
> > +		isec->gc_mark = 1;
> > +	      else if ((isec->flags & SEC_GROUP) != 0)
> > +		_bfd_elf_gc_mark_debug_special_section_group (isec);
> > +	    }
> > +	}
> >
> >        if (! debug_frag_seen)
> >  	continue;
> 
> I think in most cases you will hit the SHT_GROUP section before member
> sections, so it is a waste of time checking for the
> elf_next_in_group (isec) == isec case.  Try this instead:
> 
>       for (isec = ibfd->sections; isec != NULL; isec = isec->next)
> 	{
> 	  if ((isec->flags & SEC_GROUP) != 0)
> 	    _bfd_elf_gc_mark_debug_special_section_group (isec);
> 	  else if (((isec->flags & SEC_DEBUGGING) != 0
> 		    || (isec->flags & (SEC_ALLOC | SEC_LOAD | SEC_RELOC))
> == 0)
> 		   && elf_next_in_group (isec) == NULL)
> 	    isec->gc_mark = 1;
> 	}
> 
> --
> Alan Modra
> Australia Development Lab, IBM

Thanks for the comments. Now I improved and tested the code per your
comments. Is this one OK?

BR,
Terry
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