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Re: [PATCH, RFC] MIPS: Implement the getcontext API

To: Brian Foster <brian.foster@innova-card.com>
Subject: Re: [PATCH, RFC] MIPS: Implement the getcontext API
From: Daniel Jacobowitz <dan@debian.org>
Date: Wed, 4 Mar 2009 07:17:32 -0500
Cc: David Daney <ddaney@caviumnetworks.com>, "Maciej W. Rozycki" <macro@codesourcery.com>, Ralf Baechle <ralf@linux-mips.org>, linux-mips@linux-mips.org, libc-ports@sourceware.org, "Maciej W. Rozycki" <macro@linux-mips.org>
In-reply-to: <200903040919.29294.brian.foster@innova-card.com>
Original-recipient: rfc822;linux-mips@linux-mips.org
References: <alpine.DEB.1.10.0902282326580.4064@tp.orcam.me.uk> <49AD6139.60209@caviumnetworks.com> <200903040919.29294.brian.foster@innova-card.com>
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On Wed, Mar 04, 2009 at 09:19:28AM +0100, Brian Foster wrote:
>  moving the signal trampoline to a vdso (which
>  is(? was?) called, maybe misleadingly, ‘vsyscall’,
>  on other architectures) is the obvious solution to
>  that part of the puzzle.  and yes, it is possible
>  to maintain the ABI; the signal trampoline is still
>  also put on the stack, and modulo XI, would work if
>  used — the trampoline-on-stack is simply not used
>  if there is a vdso with the signal trampoline.

That won't quite retain the ABI: you need to make sure everyone
locates it by using the stack pointer instead of the return pc.
Fortunately, GCC uses the return PC only for instruction matching
today.  I have a vague memory it used to use the stack pointer but
this was more reliable.

They don't necessarily have to go into the vdso; other architectures
have moved them off the stack directly to glibc.

-- 
Daniel Jacobowitz
CodeSourcery

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