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

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Message-ID: <CAMuHMdU2fge6UJwKAKOAFqtsnhVyfX80g703TRUoPRK_aeuu-w@mail.gmail.com>
Date:   Thu, 15 Dec 2022 15:43:00 +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 Thu, Dec 15, 2022 at 2:58 PM Leizhen (ThunderTown)
<thunder.leizhen@...wei.com> wrote:
> On 2022/12/15 21:24, Geert Uytterhoeven wrote:
> > On Thu, Dec 15, 2022 at 1:34 PM Leizhen (ThunderTown)
> > <thunder.leizhen@...wei.com> wrote:
> >> On 2022/12/15 17:39, Geert Uytterhoeven wrote:
> >>> On Thu, Dec 15, 2022 at 10:16 AM Leizhen (ThunderTown)
> >>> <thunder.leizhen@...wei.com> wrote:
> >>>> On 2022/12/15 16:50, Geert Uytterhoeven wrote:
> >>>>> On Tue, Nov 15, 2022 at 9:41 AM Zhen Lei <thunder.leizhen@...wei.com> wrote:
> >>>>>> Added test cases for basic functions and performance of functions
> >>>>>> kallsyms_lookup_name(), kallsyms_on_each_symbol() and
> >>>>>> kallsyms_on_each_match_symbol(). It also calculates the compression rate
> >>>>>> of the kallsyms compression algorithm for the current symbol set.
> >>>>>>
> >>>>>> The basic functions test begins by testing a set of symbols whose address
> >>>>>> values are known. Then, traverse all symbol addresses and find the
> >>>>>> corresponding symbol name based on the address. It's impossible to
> >>>>>> determine whether these addresses are correct, but we can use the above
> >>>>>> three functions along with the addresses to test each other. Due to the
> >>>>>> traversal operation of kallsyms_on_each_symbol() is too slow, only 60
> >>>>>> symbols can be tested in one second, so let it test on average once
> >>>>>> every 128 symbols. The other two functions validate all symbols.
> >>>>>>
> >>>>>> If the basic functions test is passed, print only performance test
> >>>>>> results. If the test fails, print error information, but do not perform
> >>>>>> subsequent performance tests.
> >>>>>>
> >>>>>> Start self-test automatically after system startup if
> >>>>>> CONFIG_KALLSYMS_SELFTEST=y.
> >>>>>>
> >>>>>> Example of output content: (prefix 'kallsyms_selftest:' is omitted
> >>>>>>  start
> >>>>>>   ---------------------------------------------------------
> >>>>>>  | nr_symbols | compressed size | original size | ratio(%) |
> >>>>>>  |---------------------------------------------------------|
> >>>>>>  |     107543 |       1357912   |      2407433  |  56.40   |
> >>>>>>   ---------------------------------------------------------
> >>>>>>  kallsyms_lookup_name() looked up 107543 symbols
> >>>>>>  The time spent on each symbol is (ns): min=630, max=35295, avg=7353
> >>>>>>  kallsyms_on_each_symbol() traverse all: 11782628 ns
> >>>>>>  kallsyms_on_each_match_symbol() traverse all: 9261 ns
> >>>>>>  finish
> >>>>>>
> >>>>>> Signed-off-by: Zhen Lei <thunder.leizhen@...wei.com>
> >>>>>
> >>>>> Thanks for your patch, which is now commit 30f3bb09778de64e ("kallsyms:
> >>>>> Add self-test facility") in linus/master.
> >>>>>
> >>>>> I gave this a try on m68k (atari_defconfig + CONFIG_KALLSYMS_SELFTEST=y),
> >>>>> but it failed:
> >>>>>
> >>>>>     start
> >>>>>     kallsyms_lookup_name() for kallsyms_test_func_static failed:
> >>>>> addr=0, expect 60ab0
> >>>>>     kallsyms_lookup_name() for kallsyms_test_func failed: addr=0, expect 60ac0
> >>>>>     kallsyms_lookup_name() for kallsyms_test_func_weak failed: addr=0,
> >>>>> expect 60ac2
> >>>>>     kallsyms_lookup_name() for vmalloc failed: addr=0, expect c272a
> >>>>>     kallsyms_lookup_name() for vfree failed: addr=0, expect c2142
> >>>>>     kallsyms_on_each_match_symbol() for kallsyms_test_func_static
> >>>>> failed: count=0, addr=0, expect 60ab0
> >>>>>     kallsyms_on_each_match_symbol() for kallsyms_test_func failed:
> >>>>> count=0, addr=0, expect 60ac0
> >>>>>     kallsyms_on_each_match_symbol() for kallsyms_test_func_weak
> >>>>> failed: count=0, addr=0, expect 60ac2
> >>>>>     kallsyms_on_each_match_symbol() for vmalloc failed: count=0,
> >>>>> addr=0, expect c272a
> >>>>>     kallsyms_on_each_match_symbol() for vfree failed: count=0, addr=0,
> >>>>> expect c2142
> >>>>>     abort

> Oh, maybe you can "git reset --hard 30f3bb09778de64" and try again.
> 30f3bb09778de64 kallsyms: Add self-test facility
>
> But the latest kernel is OK on x86. So other patches are unlikely to
> affect this function.

On 30f3bb09778de64 it fails the same way:

    start
    kallsyms_lookup_name() for kallsyms_test_func_static failed:
addr=8dbc, expect 60308
    kallsyms_lookup_name() for kallsyms_test_func failed: addr=8dbc,
expect 60318
    kallsyms_lookup_name() for kallsyms_test_func_weak failed:
addr=8dbc, expect 6031a
    kallsyms_lookup_name() for vmalloc failed: addr=8dbc, expect bdc88
    kallsyms_lookup_name() for vfree failed: addr=8dbc, expect bd6de
    kallsyms_on_each_match_symbol() for kallsyms_test_func_static
failed: count=24890, addr=1ee870, expect 60308
    kallsyms_on_each_match_symbol() for kallsyms_test_func failed:
count=24890, addr=1ee870, expect 60318
    kallsyms_on_each_match_symbol() for kallsyms_test_func_weak
failed: count=24890, addr=1ee870, expect 6031a
    kallsyms_on_each_match_symbol() for vmalloc failed: count=24890,
addr=1ee870, expect bdc88
    kallsyms_on_each_match_symbol() for vfree failed: count=24890,
addr=1ee870, expect bd6de
    abort

> Is m68k big-endian?

Yes it is. And 32-bit values are aligned to only 2 bytes.

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