Re: [PATCH] x86: Remove a.out support

Kees Cook
2022-04-04T21:50:11Z

On Mon, Apr 04, 2022 at 05:07:11PM +0000, David Laight wrote:
> From: Maciej W. Rozycki
> > Sent: 04 April 2022 12:04
> >
> > On Sat, 2 Apr 2022, Kees Cook wrote:
> >
> > > > Chiming in late as I'm scanning outstanding mailing list traffic: if this
> > > >is as you say all statically linked stuff, then converting from a.out to
> > > >ELF might be as easy as:
> > > >
> > > >$ objcopy -I a.out-i386-linux -O elf32-i386 a.out-binary elf-binary
> > >
> > > Based on my research (and the wrapper I ended up writing), I don't think
> > > this is sufficient because entry point handling is different between ELF
> > > and a.out (specifically the stack layout and initial sp register value).
> >
> > Fair enough. I guess the exact value of %esp doesn't matter that much
> > (why would it?), but the arguments and environment may well be structured
> > differently (and indeed based on a glance over binfmt_aout.c there's extra
> > indirection involved compared to the ELF i386 psABI).
>
> You could write a custom 'elf interpreter'.
> Hacking at those isn't for the faint-hearted :-)

A thread on LWN pointed to:
https://github.com/siegfriedpammer/run-aout
which appears to be a much more complete a.out wrapper.

--
Kees Cook