Re: [PATCH 01/64] media: omap3isp: Extract struct group for memcpy() region

Nick Desaulniers
2021-07-30T17:08:21Z

On Fri, Jul 30, 2021 at 9:44 AM Kees Cook <keescook@chromium.org> wrote:
>
> On Fri, Jul 30, 2021 at 12:00:54PM +0300, Dan Carpenter wrote:
> > On Fri, Jul 30, 2021 at 10:38:45AM +0200, David Sterba wrote:
> > > Then is explicit memset the only reliable way accross all compiler
> > > flavors and supported versions?
> > >
> >
> > The = { } initializer works. It's only when you start partially
> > initializing the struct that it doesn't initialize holes.
>
> No, partial works. It's when you _fully_ initialize the struct where the
> padding doesn't get initialized. *sob*

I'm pretty sure that this has more to do with whether or not the
compiler applies SROA then observes uses of the individual members or
not.

>
> struct foo {
> u8 flag;
> /* padding */
> void *ptr;
> };
>
> These are fine:
>
> struct foo ok1 = { };
> struct foo ok2 = { .flag = 7 };
> struct foo ok3 = { .ptr = NULL };
>
> This is not:
>
> struct foo bad = { .flag = 7, .ptr = NULL };
>
> (But, of course, it depends on padding size, compiler version, and
> architecture. i.e. things remain unreliable.)
>
> --

--
Thanks,
~Nick Desaulniers