linux-kernel - Re: [m68k:master 1174/1174] arch/m68k/include/asm/string.h:72:25: warning: '__builtin_memcpy' forming offset 8 is out of the bounds [0, 7]

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Message-ID: <CAMuHMdUuwudbk15GUPPxL+-Gt4zhhSomk-wMAHeTOkoaDOCUAA@mail.gmail.com>
Date:   Tue, 5 Mar 2019 08:49:35 +0100
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Finn Thain <fthain@...egraphics.com.au>
Cc:     kbuild test robot <lkp@...el.com>, kbuild-all@...org,
        linux-m68k <linux-m68k@...ts.linux-m68k.org>,
        Arnd Bergmann <arnd@...db.de>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [m68k:master 1174/1174] arch/m68k/include/asm/string.h:72:25:
 warning: '__builtin_memcpy' forming offset 8 is out of the bounds [0, 7]

Hi Finn,

On Tue, Mar 5, 2019 at 3:58 AM Finn Thain <fthain@...egraphics.com.au> wrote:
> On Tue, 5 Mar 2019, Finn Thain wrote:
> > Looks bogus to me.
> >
> > If you change memcpy to __builtin_memcpy, then we avoid the macro and the
> > warning changes to,
> >
> > ./include/linux/string.h:456:3: warning: '__builtin_memcpy' forming offset [7, 8] is out of the bounds [0, 6] [-Warray-bounds]
> >    __builtin_memcpy(dest, src, dest_len);
> >
> > The compiler has nothing to complain about here. dest is known to be
> > id->fr and dest_len is known to be sizeof(id->fr).
> >
> > The error message indicates that gcc has applied the bounds [0, 6] to dest
> > when in fact those are the bounds for src.
> >
>
> My mistake. GCC is right, it seems memcpy will read past the end of
> "5.0.0+".

But only if the else branch is taken, which is not the case.

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds