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From: Al Viro <viro@ZenIV.linux.org.uk>
Subject: Re: [PATCH] ARC: uaccess: get_user to zero out dest in cause of fault
Date: Sun, 21 Aug 2016 02:40:30 +0100
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To: "H. Peter Anvin" <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>, Jakub Jelinek <jakub@redhat.com>, Vineet Gupta <Vineet.Gupta1@synopsys.com>, "linux-arch@vger.kernel.org" <linux-arch@vger.kernel.org>, Linux Kernel Mailing List <linux-kernel@vger.kernel.org>, Ingo Molnar <mingo@redhat.com>

On Sat, Aug 20, 2016 at 06:09:15PM -0700, H. Peter Anvin wrote:

> >Sorry for the bogus noise. I don't know why I was so convinced setjmp
> >needed special gcc semantics.
> >
> >             Linus
> 
> I think the specific name setjmp() is magic in gcc.

It is; attribute equivalent is returns_twice.  I wonder if "explicitly
clobber everything if we got false" + asm volatile to prevent reordering
would suffice for our purposes, but that's really a question for gcc
folks...