Re: elf32-mips breaks binary compatibility

[Ralf Baechle <ralf@uni-koblenz.de>]

On Tue, Aug 17, 1999 at 06:16:25PM -0400, Ian Lance Taylor wrote:

>    It's impractical to tag old binaries, so therefore we have to tag new
>    ones.  So if Jakub goes and actually implements some Quickstart like
>    mechanism not both can use this tag at the same time.
> 
> OK.  I think we need to talk about this further if we plan to tag new
> binaries.  That would put us in the position of adding the new tag
> forever.  It would also mean that we could never support existing SGI
> MIPS/ELF shared libraries.  Certainly using DT_MIPS_TIME_STAMP is
> inappropriate if we are tagging new binaries.
> 
>    I think I have some better mechanism for the dynamic linker to detect
>    this problem without any tag at all.  I'll work on that tomorrow and
>    checkout if it's actually implementable.
> 
> That would be ideal.

I dumped above mentioned idea for something even simpler.  GNU binutils
reseverve two entries in the GOT.  Both old and new versions set 
got[1] = 0x80000000 to mark binaries build by GNU binutils.  We can
extend that and use another bit to mark new executables.  Detection then
is trivial like

  goodelf = ((got[1] & 0x80000000) == 0
             || (got[1] & 0xc0000000) == 0xc0000000);

  Ralf