Re: [patch] sys_modify_ldt extension (default_ldt)

[Christoph Hellwig <hch@ns.caldera.de>]

Hi Joerg,

In article <m158sRu-0009RiC@hydrops.han.de> you wrote:
> Hi,
>
> I am trying to integrate binfmt_xout.c into kernel 2.4 as part of the 
> linux-abi project (formerly known as iBCS). For old Xenix 286 binaries the 
> lcall7 gate needs to part of the LDT.
>
> In kernels 2.0 sys_modify_ldt(0,...) used to return the default_ldt (with 
> lcall7 gate) if there were no segments set up. This behaviour changed in 
> kernels 2.2 . As a result of a discussion with Linus, David Bruce wrote a 
> patch for binfmt_xout.c tweaking with gdt and current->tss.ldt to get the
> address of default_ldt. This patch does not work any more with kernels 2.4
> as tss vanished from task_struct. 
>
> I do see 4 ways to cope with this problem:
>
> a) extend sys_modify_ldt with a function to retrieve the default_ldt. I did 
>    this for testing (see attached diff for arch/i386/kernel/ldt.c ).

Looks sane to me.

> b) do some work an Davids patch but this is kind of magic for me :-)
>    (see attached default_ldt patch)
>
> c) loose the option to compile binfmt_xout (and the rest of linux-abi) as 
>    module and simply use the symbol default_ldt. I dint't try that.

As the linux-abi maintainer I do not think that's a good idea..

> d) Forget about those old fashioned 286 binaries. This option will make some
>    linux users feel sad, as they run these progs for their daily business.

If possible at all I'll vote for having 286 support.

I'll integrate the patch into the linux-abi tree if you also send me the
other changes (mostly binfmt_xout.c changes I suppose).

	Christoph

-- 
Of course it doesn't work. We've performed a software upgrade.