COMDAT section PE

COMDAT section PE

[Tamar Christina]

Hi All,

I'm trying to create a few COMDAT sections using PE.

The documentation states that you can use a G type (group) with a comdat identifier on ELF,
but doesn't state anything for PE. I've looked at the source and found that starting my section with
.gnu.linkonce should work, but is this really the only way? I didn't want to have to change section names.

Does it drop the .gnu.linkonce afterwards?

Thanks,
Tamar

Re: COMDAT section PE

[Nick Clifton]

Hi Tamar,

> I'm trying to create a few COMDAT sections using PE.
> 
> The documentation states that you can use a G type (group) with a comdat identifier on ELF,
> but doesn't state anything for PE. I've looked at the source and found that starting my section with
> .gnu.linkonce should work, but is this really the only way? I didn't want to have to change section names.
> 
> Does it drop the .gnu.linkonce afterwards?

No.

I think that what you want is the .linkonce assembler pseudo-op:


  .linkonce [TYPE]
  ================

  Mark the current section so that the linker only includes a single copy
  of it.  This may be used to include the same section in several
  different object files, but ensure that the linker will only include it
  once in the final output file.  The `.linkonce' pseudo-op must be used
  for each instance of the section.  Duplicate sections are detected
  based on the section name, so it should be unique.

  This directive is only supported by a few object file formats; as of
  this writing, the only object file format which supports it is the
  Portable Executable format used on Windows NT.

  The TYPE argument is optional.  If specified, it must be one of the
  following strings.  For example:
     .linkonce same_size
   Not all types may be supported on all object file formats.

  `discard'
     Silently discard duplicate sections.  This is the default.

  `one_only'
     Warn if there are duplicate sections, but still keep only one copy.

  `same_size'
     Warn if any of the duplicates have different sizes.

  `same_contents'
     Warn if any of the duplicates do not have exactly the same
     contents.


Cheers
  Nick