linux-kernel - Re: [PATCH v9] kallsyms: Add self-test facility

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Message-ID: <CAMuHMdVUvPRvEvGNmB9WO0yg=w04g4q2_1hfOypqEnrYkFr6YQ@mail.gmail.com>
Date:   Fri, 16 Dec 2022 12:28:22 +0100
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     "Leizhen (ThunderTown)" <thunder.leizhen@...wei.com>
Cc:     Josh Poimboeuf <jpoimboe@...nel.org>,
        Jiri Kosina <jikos@...nel.org>,
        Miroslav Benes <mbenes@...e.cz>,
        Petr Mladek <pmladek@...e.com>,
        Joe Lawrence <joe.lawrence@...hat.com>,
        live-patching@...r.kernel.org, linux-kernel@...r.kernel.org,
        Masahiro Yamada <masahiroy@...nel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Jiri Olsa <jolsa@...nel.org>,
        Kees Cook <keescook@...omium.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Luis Chamberlain <mcgrof@...nel.org>,
        linux-modules@...r.kernel.org,
        Steven Rostedt <rostedt@...dmis.org>,
        Ingo Molnar <mingo@...hat.com>,
        David Laight <David.Laight@...lab.com>,
        linux-m68k <linux-m68k@...ts.linux-m68k.org>,
        "Jason A. Donenfeld" <Jason@...c4.com>
Subject: Re: [PATCH v9] kallsyms: Add self-test facility

Hi Zhen,

On Fri, Dec 16, 2022 at 10:43 AM Leizhen (ThunderTown)
<thunder.leizhen@...wei.com> wrote:
> On 2022/12/16 15:42, Leizhen (ThunderTown) wrote:
> > On 2022/12/15 22:51, Geert Uytterhoeven wrote:
> >> On 30f3bb09778de64 with your debug patch v2:
> > I've set up the qemu environment, and I'll try to solve it by tomorrow at the latest.
>
> It seems that the problem is still strcmp(). After I commented strcmp() in
> arch/m68k/include/asm/string.h, and force it to use the one in lib/string.c,
> it works well.

I can confirm that.

One difference is that the one in lib/string.c always return -1/0/1,
while the m68k version can return other negative or positive numbers.

However, adding:

       if (res < 0) return -1;
       if (res > 0) return 1;

to the m68k version doesn't make a difference.

Renaming the m68k version (changed to -1/0/1) to m68k_strcmp(), and
the generic version to lib_strcmp(), and adding a wrapper that calls
and compares both, shows that both functions do return the same value,
and the test succeeds.

Moving the m68k version inside lib/string.c makes the test pass, too.
So it must be related to the function being inline, and gcc making
(incorrect) assumptions...

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