linux-kernel - Re: [PATCH] proc: fix proc-self-map-files selftest for arm

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Message-ID: <20181011220009.GF2401@uranus.lan>
Date:   Fri, 12 Oct 2018 01:00:09 +0300
From:   Cyrill Gorcunov <gorcunov@...il.com>
To:     Alexey Dobriyan <adobriyan@...il.com>
Cc:     Rafael David Tinoco <rafael.tinoco@...aro.org>,
        linux-kselftest@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-kernel@...r.kernel.org, akpm@...ux-foundation.org,
        shuah@...nel.org
Subject: Re: [PATCH] proc: fix proc-self-map-files selftest for arm

On Fri, Oct 12, 2018 at 12:30:06AM +0300, Alexey Dobriyan wrote:
> On Fri, Oct 12, 2018 at 12:02:56AM +0300, Cyrill Gorcunov wrote:
> > On Thu, Oct 11, 2018 at 11:56:01PM +0300, Alexey Dobriyan wrote:
> > > 
> > > As the comment in the beginning says this test is specifically for addresss 0.
> > > Maybe it should be ifdeffed with __arm__ then.
> > 
> > Is there some other reason than allocating non-mergable VMA?
> 
> IIRC the reason is to test address 0 as it is effectively banned
> for userspace so if it will be broken, it will be broken silently
> for a long time.

This is rather a side effect of the test because the primary reason
was to check procfs numbers conversion, right? Don't get me wrong,
I don't mind about __arm__ define or similar, this is fine for
one architecture, but if there comes more we will get a number
of #ifdefs which is unrelated to procfs numeric routines at all.

> As for "unmergeable" libc here doesn't map /dev/zero. I know how to
> avoid even theoretical breakage by creating binaries by hand but it
> will be probably too much.

Sure.