Re: [PATCH 11/20] bpf: factor out a bpf_trace_copy_string helper

[Christoph Hellwig]

On Tue, May 19, 2020 at 09:07:55AM -0700, Linus Torvalds wrote:
> On Tue, May 19, 2020 at 6:45 AM Christoph Hellwig <hch@xxxxxx> wrote:
> >
> > +       switch (fmt_ptype) {
> > +       case 's':
> > +#ifdef CONFIG_ARCH_HAS_NON_OVERLAPPING_ADDRESS_SPACE
> > +               strncpy_from_unsafe(buf, unsafe_ptr, bufsz);
> > +               break;
> > +#endif
> > +       case 'k':
> > +               strncpy_from_kernel_nofault(buf, unsafe_ptr, bufsz);
> > +               break;
> 
> That 's' case needs a "fallthrough;" for the overlapping case,
> methinks. Otherwise you'll get warnings.

I don't think we need it as the case of

	case 'a':
	case 'b':
		do_stuff();
		break;

has always been fine even with the fallthough warnings.  And the
rest of the stuff gets removed by cpp..