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Date: Mon, 13 Apr 2015 18:21:41 -0700
From: Andy Lutomirski <luto@kernel.org>
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To: Richard Weinberger <richard@nod.at>, linux-arch@vger.kernel.org
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Subject: Re: Remove execution domain support
References: <1428785283-20501-1-git-send-email-richard@nod.at>
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On 04/11/2015 01:47 PM, Richard Weinberger wrote:
> A long time ago there was the idea to support different ABIs on Linux
> Such that someone could use for example SCO UNIX binaries on Linux
> without emulation. While the linux-abi project existed mostly as
> out-of-tree patch it's core component, execution domains,
> went mainline. An execution domain allows to specify mappings between
> different ABIs, these mappings consist of signal, error, socket type,
> socket options and addess familiy mappings.
> Mainline has only support for signal mappings.
> The signal mapping happens in the architecutre specific signal code.
> Some archs support it, some not, most of them copy&pasted from i386.
>
> While the mapping support is incomplete we have two in-kernel users of
> execution domains.
>
> 1. RISC OS personality on ARM.
> The Kconfig help message states that this feature is very experimental
> and it is likely that it never worked as expected.
> Russel is fine with the removal.
>
> 2. ia32 support on ia64.
> This is a left over from:
> commit 32974ad4907cdde6c9de612cd1b2ee0568fb9409 ([IA64] Remove COMPAT_IA32 support)
> It registers a dummy Linux/x86 execdomain to make calls to
> personality(PER_LINUX32) faster as the execution domain core code
> would try to load a module.
>
> As both users can be removed there is no user left and we can remove
> execution domains support at all from the kernel.
> The removal will make architecutre specific signal handling easier
> and there is no need to keep execuction domains as this feature is
> obviously incomplete and abandoned.

I like this.

FWIW, we recently removed restart_block from thread_info, so I'm not too 
worried about fallout from removing another field.

--Andy
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