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

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Date:   Thu, 2 Apr 2020 22:04:37 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Pavel Machek <pavel@...x.de>
Cc:     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

On Thu, Apr 02, 2020 at 09:53:24PM +0200, Pavel Machek wrote:
> 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?

Only if the structure has padding, and it is data to be sent to
userspace, or to be intrepreted in a way from userspace.

Good luck trying to write a checkpatch rule for that.

greg k-h