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Date: Sun, 15 Apr 2018 14:12:06 +0100
From: Russell King - ARM Linux <linux@armlinux.org.uk>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Dave Martin <Dave.Martin@arm.com>,
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Subject: Re: sparc/ppc/arm compat siginfo ABI regressions: sending SIGFPE via
 kill() returns wrong values in si_pid and si_uid
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On Fri, Apr 13, 2018 at 12:53:49PM -0700, Linus Torvalds wrote:
> On Fri, Apr 13, 2018 at 11:45 AM, Dave Martin <Dave.Martin@arm.com> wrote:
> >
> > Most uses I've seen do nothing more than use the FPE_xyz value to
> > format diagnostic messages while dying.  I struggled to find code that
> > made a meaningful functional decision based on the value, though that's
> > not proof...
> 
> Yeah. I've seen code that cares about SIGFPE deeply, but it's almost
> invariably about some emulated environment (eg Java VM, or CPU
> emulation).
> 
> And the siginfo data is basically never good enough for those
> environments anyway on its own, so they will go and look at the actual
> instruction that caused the fault and the register state instead,
> because they need *all* the information.
> 
> The cases that use si_code are the ones that just trapped signals in
> order to give a more helpful abort message.
> 
> So I could certainly imagine that si_code is actually used by somebody
> who then decides to actuall act differently on it, but aside from
> perhaps printing out a different message, it sounds far-fetched.

Okay, in that case let's just use FPE_FLTINV.  That makes the patch
easily back-portable for stable kernels.

-- 
RMK's Patch system: http://www.armlinux.org.uk/developer/patches/
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