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Date:   Tue, 19 May 2020 18:14:18 +0200
From:   Christoph Hellwig <hch@lst.de>
To:     Linus Torvalds <torvalds@linux-foundation.org>
Cc:     Christoph Hellwig <hch@lst.de>,
        the arch/x86 maintainers <x86@kernel.org>,
        Alexei Starovoitov <ast@kernel.org>,
        Daniel Borkmann <daniel@iogearbox.net>,
        Masami Hiramatsu <mhiramat@kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        linux-parisc@vger.kernel.org,
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        Netdev <netdev@vger.kernel.org>, bpf@vger.kernel.org,
        Linux-MM <linux-mm@kvack.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 11/20] bpf: factor out a bpf_trace_copy_string helper
Message-ID: <20200519161418.GA26545@lst.de>
References: <20200519134449.1466624-1-hch@lst.de> <20200519134449.1466624-12-hch@lst.de> <CAHk-=wjm3HQy_awVX-WyF6KrSuE1pcFRaNX_XhiLKkBUFUZBtQ@mail.gmail.com>
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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@lst.de> 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..