linux-kernel - Re: sigaltstack fun

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Message-Id: <20121203.215846.206188196607010695.davem@davemloft.net>
Date:	Mon, 03 Dec 2012 21:58:46 -0500 (EST)
From:	David Miller <davem@...emloft.net>
To:	viro@...IV.linux.org.uk
Cc:	torvalds@...ux-foundation.org, monstr@...str.eu,
	linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org
Subject: Re: sigaltstack fun

From: Al Viro <viro@...IV.linux.org.uk>
Date: Mon, 26 Nov 2012 05:10:02 +0000

> On Sun, Nov 18, 2012 at 10:27:24PM -0500, David Miller wrote:
>> > Cc: stable@...r.kernel.org
>> > Signed-off-by: Al Viro <viro@...iv.linux.org.uk>
>> 
>> Applied, thanks.
> 
> Hmm...  There's something odd going on with {rt_,}sigaction on sparc -
> we *do* have sa_restorer in struct sigaction and struct old_sigaction,
> but it's not used for anything whatsoever.  There's also a separately
> passed restorer pointer for rt_sigaction() and *that* is used instead,
> but not reported via *oact.
> 
> What's the reason for that weirdness?  I understand why we do that on
> alpha (we have no sa_restorer in struct sigaction we'd inherited from
> OSF/1), but sparc always had perfectly normal sigaction->sa_restorer
> field all along - even for old sigaction(2)...

I have no idea how things got this way.

In the old sigaction() we do use the sa_restorer, and for both RT and
non-RT sigaction, we do fill in the sa_restorer member for the old
sigaction returned.

This special 'restorer' argument overrides the sigaction one.

GLIBC wraps calls to this system call, see:

sysdeps/unix/sysv/linux/sparc/sparc32/sigaction.c
sysdeps/unix/sysv/linux/sparc/sparc64/sigaction.c

I wish I had more context and info, but I don't :-(
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