linux-kernel - Re: [PATCH 4.19 105/116] bpf: Explicitly memset the bpf

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Message-ID: <20200402195324.GB8077@duo.ucw.cz>
Date:   Thu, 2 Apr 2020 21:53:24 +0200
From:   Pavel Machek <pavel@...x.de>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Pavel Machek <pavel@...x.de>, linux-kernel@...r.kernel.org,
        stable@...r.kernel.org,
        Maciej Żenczykowski <maze@...gle.com>,
        John Stultz <john.stultz@...aro.org>,
        Alexander Potapenko <glider@...gle.com>,
        Alistair Delva <adelva@...gle.com>,
        Daniel Borkmann <daniel@...earbox.net>,
        Yonghong Song <yhs@...com>
Subject: Re: [PATCH 4.19 105/116] bpf: Explicitly memset the bpf_attr
 structure

Hi!

> > Should we fix gcc, instead?
> 
> Also, this is allowed in the C standard, and both clang and gcc
> sometimes emit code that does not clear padding in structures.  Changing
> the compiler to not do this would be wonderful, but we still have to
> live with this for the next 10 years as those older compilers age-out.

I agree C standard allows this. It allows to even worse stuff.

I was just surprised that gcc does that.. and that I did not know
about this trap. I was probably telling people to do = {} for
structure init...

Should we get "= {}" warning for checkpatch?

Is it fair to replace "= {}" with memset() as soon as it is returned
to userland, without testing that gcc "miscompiles" this particular
example?

Best regards,
								Pavel
-- 
DENX Software Engineering GmbH,      Managing Director: Wolfgang Denk
HRB 165235 Munich, Office: Kirchenstr.5, D-82194 Groebenzell, Germany

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