[PATCH] Fix --as-needed for MIPS.

[David Daney <ddaney at avtrex dot com>]

As noted in these threads:

http://sourceware.org/ml/binutils/2005-07/msg00476.html
http://sourceware.org/ml/binutils/2005-07/msg00490.html

ld --as-needed seems to be broken for my mipsel-linux cross tool chain.

Quoting from the e-mail threads:

<quote>

It seems that the linker thinks that any shared object that references 
the magic _gp_disp symbol actually provides it. Since all mips objects 
reference _gp_disp, ld thinks that all shared objects are required to 
resolve all the other _gp_disp references. This causes all shared 
objects specified with --as-needed to be deemed needed and get a 
DT_NEEDED entry.

The linker automagically resolves _gp_disp so this symbol should not 
cause a shared library to be needed.

I hope that makes at least a little sense.

I suspect that the problem is mips specific as _gp_disp handling is mips 
specific.

And:

Here is my current plan:

$ mipsel-linux-readelf -s -D -W 
/usr/local/mipsel-linux-3.4.3/lib/libc-2.3.3.so | grep SECTION
131 324: 0019bfb0 0 SECTION GLOBAL DEFAULT ABS _gp_disp


This seems to be where ld thinks that _gp_disp is defined by shared objects.

I can detect this special case in _bfd_mips_elf_add_symbol_hook() and 
cause it to be ignored, thus solving the problem.

Does this seem like a reasonable course of action?

I am not sure how that dynamic symbol got into the shared objects in the 
first place. I suppose if the proper solution was to not put it there in 
the first place, I could fix that and rebuild the world. But that would 
be much more work.

</quote>

The attached patch seems to correct the problem.

Tested with a cross build running on i686-pc-linux configured as:

../src/configure  --target=mipsel-linux 
--prefix=/usr/local/mipsel-linux-3.4.3 
--with-sysroot=/usr/local/mipsel-linux-3.4.3

make -k check with no regressions.

2005-07-29  David Daney  <ddaney@avtrex.com>

	* elfxx-mips.c (_bfd_mips_elf_add_symbol_hook):  Ignore _gp_disp
	if it is not in the *UND* section.

O.K. to commit?

David Daney
Index: elfxx-mips.c
===================================================================
RCS file: /cvs/src/src/bfd/elfxx-mips.c,v
retrieving revision 1.146
diff -c -p -r1.146 elfxx-mips.c
*** elfxx-mips.c	8 Jul 2005 06:20:05 -0000	1.146
--- elfxx-mips.c	29 Jul 2005 04:03:03 -0000
*************** _bfd_mips_elf_add_symbol_hook (bfd *abfd
*** 5414,5419 ****
--- 5414,5430 ----
        return TRUE;
      }
  
+   /* Shared objects may have a dynamic symbol '_gp_disp' defined as
+      a SECTION *ABS*.  This causes ld to think it can resolve _gp_disp
+      by setting a DT_NEEDED for the shared object.  Since _gp_disp is
+      a magic symbol resolved by the linker, we ignore this bogus definition
+      of _gp_disp. */
+   if ((strcmp (*namep, "_gp_disp") == 0) && !bfd_is_und_section (*secp))
+     {
+       *namep = NULL;
+       return TRUE;
+     }
+ 
    switch (sym->st_shndx)
      {
      case SHN_COMMON: