[RFH] About dlltool --output-exp --add-indirect.

Pedro Alves pedro_alves@portugalmail.pt
Tue Oct 31 11:46:00 GMT 2006


I am looking at fixing the underscore usage in dlltool for arm-wince-pe,
but I see something I don't understand:

What is the --add-indirect option used for? I see that it puts the 
_imp_<symbol> on the export table,
but what is it that used for?

Here is a snippet of the dlltool.c:gen_exp_file, where --add-indirect is 
handled:

  /* Add to the output file a way of getting to the exported names
     without using the import library.  */
  if (add_indirect)
    {
      fprintf (f, "\t.section\t.rdata\n");
      for (i = 0, exp = d_exports; exp; i++, exp = exp->next)
    if (!exp->noname || show_allnames)
      {
        /* We use a single underscore for MS compatibility, and a
               double underscore for backward compatibility with old
               cygwin releases.  */
        if (create_compat_implib)
          fprintf (f, "\t%s\t__imp_%s\n", ASM_GLOBAL, exp->name);
        fprintf (f, "\t%s\t_imp__%s\n", ASM_GLOBAL, exp->name);
        if (create_compat_implib)
          fprintf (f, "__imp_%s:\n", exp->name);
        fprintf (f, "_imp__%s:\n", exp->name);
        fprintf (f, "\t%s\t%s\n", ASM_LONG, exp->name);
      }
    }

How can this be right? Since we are outputting assembly, isn't there an 
underscore missing in the left of all those _imp_ ?
In ld/pe-dll.c, if the target is underscored (cygwin/mingw), we use 
__imp_ by default, and add an ___imp_ alias
if compatibility with older cygwin releases is requested. From what I 
see with MSVC, __imp_ is indeed the correct
import prefix.
 From what I can find on the web, an exp file is a normal coff 
object/bfd with the only the .edata section of the image.

Anyone has an idea how to generate the equivalent of --add-indirect with 
MSFT's link.exe?
Also, does anyone use this option nowadays?

Oh, and --add-indirect docs on dlltool's manual has the funniest comment 
I could find on binutils.

<quoting>
--add-indirect
           Specifies that when dlltool is creating the exports file it 
should add a section which allows the exported  functions
           to be referenced without using the import library.  Whatever 
the hell that means!
</quoting>

Cheers,
Pedro Alves



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