Is CPUTYPE=cortex-A7 supposed to work?

[Mark Millard]

On 2017-Mar-16, at 11:09 AM, Andrew Gierth <andrew at tao11.riddles.org.uk> wrote:

>>>>>> "Michal" == Michal Meloun <melounmichal at gmail.com> writes:
> 
> Michal> Is this enough to confirm that the FPU instructions in a signal
> Michal> handler is not used so frequently?
> 
> 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.
> 
> 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.
> 
> 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.
> 
> -- 
> Andrew.

===
Mark Millard
markmi at dsl-only.net