Re: [PATCH] tracing: silence GCC 9 array bounds warning

From: Miguel Ojeda <miguel.ojeda.sandonis@gmail.com>
To: Steven Rostedt <rostedt@goodmis.org>
Cc: Ingo Molnar <mingo@redhat.com>,
	linux-kernel <linux-kernel@vger.kernel.org>,
	Linus Torvalds <torvalds@linux-foundation.org>
Subject: Re: [PATCH] tracing: silence GCC 9 array bounds warning
Date: Fri, 17 May 2019 20:45:07 +0200	[thread overview]
Message-ID: <CANiq72=Wr-u1S8bxV07zPSV8vaXGVqYkTULKQADXfXXEZ0cmxQ@mail.gmail.com> (raw)
In-Reply-To: <20190517124715.3d82bdbe@oasis.local.home>

Hi Steven,

On Fri, May 17, 2019 at 6:47 PM Steven Rostedt <rostedt@goodmis.org> wrote:
>
> Hi Miguel,
>
> Linus mentioned this too.
>
>  https://lore.kernel.org/lkml/CAHk-=wihYB8w__YQjgYjYZsVniu5CtkTcFycmCGdqVg8GUje7g@mail.gmail.com/T/#u

Ah, I didn't see that. We were discussing here [1] backporting to 4.19
some cleanups we did for GCC 9 a few months ago, so I was testing that
Linus' master was still clean a few hours ago. When I found that
couple of warnings I quickly made a patch before I forgot. I should
probably have added RFC :-)

[1] https://lore.kernel.org/lkml/CANiq72=fsL5m2_e+bNovFCHy3=YVf53EKGtGE_sWvsAD=ONHuQ@mail.gmail.com/

> Setting the LAT_FMT isn't something a function called "reset" should do.

I added the surrounding code heuristically since it was in a single
block with the comment above and since it was repeated in both places,
but I had no idea on the semantics. :-)

> > +     memset((char *)(iter) + offsetof(struct trace_iterator,
>
> Why (char *)? Please use (void *).

We are adding a byte-sized offset, so char * is the one that makes
sense. Doing it with void * works, although it is a GNU extension. But
as you prefer :-)

Cheers,
Miguel