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

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Date:   Fri, 17 May 2019 20:45:07 +0200
From:   Miguel Ojeda <miguel.ojeda.sandonis@...il.com>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     Ingo Molnar <mingo@...hat.com>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH] tracing: silence GCC 9 array bounds warning

Hi Steven,

On Fri, May 17, 2019 at 6:47 PM Steven Rostedt <rostedt@...dmis.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