Date: Thu, 16 Mar 2017 11:57:40 -0700 From: Mark Millard <markmi@dsl-only.net> To: Andrew Gierth <andrew@tao11.riddles.org.uk> Cc: Michal Meloun <melounmichal@gmail.com>, Sylvain Garrigues <sylvain@sylvaingarrigues.com>, freebsd-arm <freebsd-arm@freebsd.org>, mmel@freebsd.org Subject: Re: Is CPUTYPE=cortex-A7 supposed to work? Message-ID: <B605332C-6945-4C59-9E6F-D0A24EAC4FCD@dsl-only.net> In-Reply-To: <87lgs52kke.fsf@news-spur.riddles.org.uk> References: <871suc3nv8.fsf@news-spur.riddles.org.uk> <CANCZdfq4EwH%2B_9FVNai8s6Y-gdTjHJ8dNkJwSrnF%2BSAkdwvYdg@mail.gmail.com> <8737ely05c.fsf@news-spur.riddles.org.uk> <CANCZdfpftVHaPahTOP0vxB-FR%2BKtpqY9JMJr=F2DGifD0fhKMQ@mail.gmail.com> <87wpbxw3yd.fsf@news-spur.riddles.org.uk> <79EBD44B-2C2D-4394-A90C-DF494A049F20@dsl-only.net> <E6BC9F77-F65B-4918-9E22-3BFECA268E30@sylvaingarrigues.com> <674facba-68cd-8ce1-887a-1ef3c51520bc@freebsd.org> <ED8405B6-1150-4A9C-AD93-5C74306FB361@sylvaingarrigues.com> <67504df9-9452-3ad3-b3b0-01d1a03727cc@freebsd.org> <87lgs52kke.fsf@news-spur.riddles.org.uk>
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On 2017-Mar-16, at 11:09 AM, Andrew Gierth <andrew at = tao11.riddles.org.uk> wrote: >>>>>> "Michal" =3D=3D Michal Meloun <melounmichal@gmail.com> writes: >=20 > Michal> Is this enough to confirm that the FPU instructions in a = signal > Michal> handler is not used so frequently? >=20 > Actually what it confirms is that it's rare for applications to use > signal delivery heavily. Just a side note in this area: buildworld buildkernel (e.g., -j 4) makes heavy SIGCHLD signal usage overall but seems to survive relative to these VFP/NEON issues. I've not looked into why but may be the processes receiving the signals make no use of NEON for integer activity (and has no floating point code?). > Emacs is a notorious exception to this, since it has used SIGIO since > time immemorial to have incoming keystrokes interrupt terminal = redisplay > (important on slow serial terminals, oh the nostalgia) and it kept the > same basic design when moving to X, so it now gets SIGIO on X events, > resulting in hundreds of signal deliveries just from moving the mouse > past its window. To say that this is not normal application behaviour > would be a massive understatement. >=20 > The problem manifests in git clone despite the fact that signal = delivery > is infrequent there simply because it spends so much of its time > executing the vectorized SHA1 block update; again, normal applications > don't do this kind of thing, and are likely to use the VFP/NEON > registers too transiently for there to be a significant chance of > detectable corruption. Even most crypto apps wouldn't often take a > signal delivery while running crypto code. >=20 > As an example, I happen to be very familiar with PostgreSQL, which by > normal standards (as opposed to Emacs standards) is a fairly heavy = user > of signals, and I don't think I could come up with a reliable > demonstration of it being affected by this bug (except maybe by using > SSL client connections). What I _would_ expect is that pgsql running = on > affected systems would experience a very slow rate of subtle data > corruption problems, which might or might not ever be noticed. >=20 > --=20 > Andrew. =3D=3D=3D Mark Millard markmi at dsl-only.net
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