linux-kernel - Re: sparc/ppc/arm compat siginfo ABI regressions: sending SIGFPE via kill() returns wrong values in si_pid and si

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Message-ID: <20180415131206.GR16141@n2100.armlinux.org.uk>
Date:   Sun, 15 Apr 2018 14:12:06 +0100
From:   Russell King - ARM Linux <linux@...linux.org.uk>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Dave Martin <Dave.Martin@....com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "Dmitry V. Levin" <ldv@...linux.org>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        sparclinux <sparclinux@...r.kernel.org>,
        ppc-dev <linuxppc-dev@...ts.ozlabs.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>
Subject: Re: sparc/ppc/arm compat siginfo ABI regressions: sending SIGFPE via
 kill() returns wrong values in si_pid and si_uid

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@....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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