Re: SEC_NEVER_LOAD cleanup

[Dave Korn <dave dot korn dot cygwin at gmail dot com>]

    Hi Alan,

On 16/09/2010 01:03, Alan Modra wrote:
> This gets rid of SEC_NEVER_LOAD in ELF code, curing these failures:

> I spent quite a lot of time going through changes related to
> SEC_NEVER_LOAD.  Testcases in various bug reports behave reasonably
> after this patch, and I think the COFF support should work too but I'm
> less sure of this since I don't have any reason to use COFF/ECOFF/PE
> myself.

> bfd/
> 	* elf.c (bfd_elf_get_default_section_type): Don't test SEC_NEVER_LOAD.
> 	* elflink.c (elf_link_input_bfd): Likewise.
> ld/
> 	* ld.texinfo (NOLOAD): Do not erroneously state that contents will
> 	appear in output file.
> 	* ldlang.c (lang_add_section): Clear SEC_HAS_CONTENTS on noload
> 	unless SEC_COFF_SHARED_LIBRARY.
> 	(map_input_to_output_sections): Don't set SEC_HAS_CONTENTS for noload
> 	output sections.
> 	(lang_size_sections_1): Don't test SEC_NEVER_LOAD when deciding
> 	to update dot in region.  Ditto when setting SEC_ALLOC if dot
> 	advanced due to assignment.
> 	* ldwrite.c (build_link_order): Don't test SEC_NEVER_LOAD.

  This patch causes a failure building the cygwin dll:

> GNU ld (GNU Binutils) 2.20.51.20100916
> Creating library file: cygdll.a
> /gnu/binutils/git.repo/obj/ld/.libs/ld-new: BFD (GNU Binutils) 2.20.51.20100916
> assertion fail /gnu/binutils/git.repo/binutils/bfd/linker.c:2678
> /gnu/binutils/git.repo/obj/ld/.libs/ld-new: final link failed: Section has no contents

  Which appears to be from here:

> static bfd_boolean
> default_data_link_order (bfd *abfd,
> 			 struct bfd_link_info *info ATTRIBUTE_UNUSED,
> 			 asection *sec,
> 			 struct bfd_link_order *link_order)
> {
>   bfd_size_type size;
>   size_t fill_size;
>   bfd_byte *fill;
>   file_ptr loc;
>   bfd_boolean result;
> 
>   BFD_ASSERT ((sec->flags & SEC_HAS_CONTENTS) != 0);

  That's triggered by the ".gnu_debuglink_overlay" section.  It has flags =
512 - SEC_NEVER_LOAD is set and nothing else.  It's getting added to the link
via a bit of custom linker script in the cygwin dll build system that looks
like so:

>   .gnu_debuglink_overlay ALIGN(__section_alignment__) (NOLOAD):
>   {
>     BYTE(0)	/* c */
>     BYTE(0)	/* y */
>     BYTE(0)	/* g */
>     BYTE(0)	/* w */
>     BYTE(0)	/* i */
>     BYTE(0)	/* n */
>     BYTE(0)	/* 1 */
>     BYTE(0)	/* . */
>     BYTE(0)	/* d */
>     BYTE(0)	/* b */
>     BYTE(0)	/* g */
>     BYTE(0)	/* \0 */
>     LONG(0)	/* checksum */
>   }

  I think (haven't checked yet) that this looks like a consequence of the
ldlang.c changes.  Any thoughts on how to fix it?

    cheers,
      DaveK