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: <20180413184522.GD16308@e103592.cambridge.arm.com>
Date:   Fri, 13 Apr 2018 19:45:23 +0100
From:   Dave Martin <Dave.Martin@....com>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Russell King - ARM Linux <linux@...linux.org.uk>,
        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 11:23:36AM -0700, Linus Torvalds wrote:
> On Fri, Apr 13, 2018 at 10:54 AM, Russell King - ARM Linux
> <linux@...linux.org.uk> wrote:
> >
> > FPE_FLTINV means "floating point invalid operation".  Does it really
> > cover the case where hardware has failed, or is it intended to cover
> > the case where userspace did something wrong and asked for an invalid
> > operation from the FP hardware?
> 
> Note that the number of people who actually look at the si_code is
> approximately zero.
> 
> But the ones that _do_ check the si_code are certainly not going to
> check it against a new code that they don't know about.
> 
> I suspect that if you start searching for FLT_xyz occurrences in code,
> approximately 100% of them are from the kernel code that generates
> them, not from any actual users.
> 
> So I'd be very surprised if you can find *anybody* who cares about
> that exact value (with the possible exceptions of test-suites).
> 
> Sadly, google code-search is no more. It was useful for things like that.

I've found https://codesearch.debian.net/ useful for digging into this
kind of question, though it tends to throw up a lot of false positives.

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...

Cheers
---Dave