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Date:   Mon, 4 Apr 2022 11:18:42 -0700
From:   Kees Cook <keescook@chromium.org>
To:     David Laight <David.Laight@aculab.com>
Cc:     "'Maciej W. Rozycki'" <macro@orcam.me.uk>,
        James Jones <linux@theinnocuous.com>,
        "bp@alien8.de" <bp@alien8.de>, "x86@kernel.org" <x86@kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] x86: Remove a.out support
Message-ID: <202204041117.0CD04EB@keescook>
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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