linux-kernel - Re: [PATCH] x86: Remove a.out support

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Date:   Mon, 4 Apr 2022 12:03:37 +0100 (BST)
From:   "Maciej W. Rozycki" <macro@...am.me.uk>
To:     Kees Cook <keescook@...omium.org>
cc:     James Jones <linux@...innocuous.com>, bp@...en8.de, x86@...nel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] x86: Remove a.out support

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).

  Maciej