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From:   Geert Uytterhoeven <geert@linux-m68k.org>
Date:   Tue, 2 Nov 2021 08:56:06 +0100
Message-ID: <CAMuHMdW_0Q9oGfCqrdj9w=1n0CtTRZErZAeynToMQNrs--+oCg@mail.gmail.com>
Subject: Re: [PATCH] string: uninline memcpy_and_pad
To:     Guenter Roeck <linux@roeck-us.net>
Cc:     Andy Shevchenko <andy@kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Kees Cook <keescook@chromium.org>
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Hi Günter,

Thanks for your patch!

On Tue, Nov 2, 2021 at 5:30 AM Guenter Roeck <linux@roeck-us.net> wrote:
> When building m68k:allmodconfig, recent versions of gcc generate the
> following error if the length of UTS_RELEASE is less than 8 bytes.
>
> In function 'memcpy_and_pad',
>     inlined from 'nvmet_execute_disc_identify' at
>         drivers/nvme/target/discovery.c:268:2:
> arch/m68k/include/asm/string.h:72:25: error:
>         '__builtin_memcpy' reading 8 bytes from a region of size 7
>
> Discussions around the problem suggest that this only happens if an
> architecture does not provide strlen(), if -ffreestanding is provided as
> compiler option, and if CONFIG_FORTIFY_SOURCE=n. All of this is the case
> for m68k. The exact reasons are unknown, but seem to be related to the
> ability of the compiler to evaluate the return value of strlen() and
> the resulting execution flow in memcpy_and_pad(). It would be possible
> to work around the problem by using sizeof(UTS_RELEASE) instead of
> strlen(UTS_RELEASE), but that would only postpone the problem until the
> function is called in a similar way. Uninline memcpy_and_pad() instead
> to solve the problem for good.
>
> Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
> Cc: Geert Uytterhoeven <geert@linux-m68k.org>
> Signed-off-by: Guenter Roeck <linux@roeck-us.net>

Reviewed-by: Geert Uytterhoeven <geert@linux-m68k.org>

>  include/linux/string.h | 19 ++-----------------
>  lib/string.c           | 19 +++++++++++++++++++
>  2 files changed, 21 insertions(+), 17 deletions(-)

Given this now conflicts with commit cfecea6ead5f1588 ("lib/string:
Move helper functions out of string.c"). perhaps you should move this
to lib/string_helpers.c when respinning?

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-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