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

From: "Måns Rullgård" <mans@mansr.com>
To: Arnd Bergmann <arnd@arndb.de>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
	Matt Turner <mattst88@gmail.com>, Borislav Petkov <bp@alien8.de>,
	Alan Cox <gnomes@lxorguk.ukuu.org.uk>,
	Matthew Wilcox <willy@infradead.org>,
	Jann Horn <jannh@google.com>, Al Viro <viro@zeniv.linux.org.uk>,
	Thomas Gleixner <tglx@linutronix.de>,
	kernel list <linux-kernel@vger.kernel.org>,
	linux-fsdevel <linux-fsdevel@vger.kernel.org>,
	"the arch\/x86 maintainers" <x86@kernel.org>,
	Linux API <linux-api@vger.kernel.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	Richard Weinberger <richard@nod.at>,
	Anton Ivanov <anton.ivanov@cambridgegreys.com>,
	linux-alpha <linux-alpha@vger.kernel.org>,
	linux-m68k <linux-m68k@lists.linux-m68k.org>
Subject: Re: [PATCH] x86: Deprecate a.out support
Date: Mon, 11 Mar 2019 22:06:19 +0000	[thread overview]
Message-ID: <yw1xwol52hic.fsf@mansr.com> (raw)
In-Reply-To: <CAK8P3a031d9mSOxVmCAGcrbdaCE8N3R4e2Smtxp-Z+cautTAvg@mail.gmail.com> (Arnd Bergmann's message of "Mon, 11 Mar 2019 22:34:26 +0100")

Arnd Bergmann <arnd@arndb.de> writes:

> On Mon, Mar 11, 2019 at 8:47 PM Måns Rullgård <mans@mansr.com> wrote:
>> Linus Torvalds <torvalds@linux-foundation.org> writes:
>> > On Mon, Mar 11, 2019 at 11:08 AM Måns Rullgård <mans@mansr.com> wrote:
>> >>
>> >> The latest version I have is 5.1, and that uses ECOFF.
>> >
>> > ECOFF _is_ a.out as far as Linux is concerned.
>> >
>> > So Linux basically treats ECOFF as "regular a.out with just some
>> > header extensions".
>> >
>> > We don't have any specific support for ECOFF.
>> >
>> > I _think_. Again, it's been years and years.
>>
>> Right, which is why killing a.out entirely would have the unfortunate
>> effect of also removing the OSF/1 compatibility on Alpha.
>>
>> If we are to support Alpha as an architecture at all, it makes sense to
>> support the things people actually use it for.
>>
>> Now, personally I can live without it.  I just don't like to see
>> features removed without due consideration.
>
> The main historic use case I've heard of was running Netscape
> Navigator on Alpha Linux, before there was an open source version.
> Doing this today to connect to the open internet is probably
> a bit pointless, but there may be other use cases.

Once upon a time, I used it to run Matlab.

> Looking at the system call table in the kernel
> (arch/alpha/kernel/syscalls/syscall.tbl), we seem to support a
> specific subset that was required for a set of applications, and
> not much more. Old system calls (osf_old_open, osf_execve,
> osf_old_sigaction) are listed but not implemented, and the same
> is true for most of the later calls (osf_fuser, osf_sigsendset,
> osf_waitid, osf_signal, ...), just the ones in the middle are there.
> This would also indicate that it never really worked as a
> general-purpose emulation layer but was only there for a specific
> set of applications.

It works for many applications, though I did have to add a few syscalls
myself (yes, I sent patches).

> Another data point I have is that osf1 emulation was broken
> between linux-4.13 and linux-4.16 without anyone noticing, see
> 47669fb6b595 ("alpha: osf_sys.c: fix put_tv32 regression").

That's interesting, but it doesn't mean nobody is using it.  I tend to
run the LTS branches and switch to a new one only once it seems to have
settled a bit, so when 4.16 was released, I was probably still running
4.9.  I don't think I'm the only one using this strategy.

-- 
Måns Rullgård