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

Leizhen (ThunderTown)
2022-12-15T13:58:27Z

On 2022/12/15 21:24, Geert Uytterhoeven wrote:
> Hi Zhen,
>
> CC Jason
>
> On Thu, Dec 15, 2022 at 1:34 PM Leizhen (ThunderTown)
> <thunder.leizhen@huawei.com> wrote:
>> On 2022/12/15 17:39, Geert Uytterhoeven wrote:
>>> On Thu, Dec 15, 2022 at 10:16 AM Leizhen (ThunderTown)
>>> <thunder.leizhen@huawei.com> wrote:
>>>> On 2022/12/15 16:50, Geert Uytterhoeven wrote:
>>>>> On Tue, Nov 15, 2022 at 9:41 AM Zhen Lei <thunder.leizhen@huawei.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@huawei.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
>>>>>
>>>>> Given all addresses are zero, it looks like some required functionality
>>>>> or config option is missing.
>>>>>
>>>>> $ grep SYM .config
>>>>> CONFIG_KALLSYMS=y
>>>>> CONFIG_KALLSYMS_SELFTEST=y
>>>>> CONFIG_KALLSYMS_BASE_RELATIVE=y
>>>>> # CONFIG_ASYMMETRIC_KEY_TYPE is not set
>>>>> CONFIG_SYMBOLIC_ERRNAME=y
>>>>> # CONFIG_STRIP_ASM_SYMS is not set
>>>>> CONFIG_KALLSYMS_SELFTEST
>>>>>
>>>>> Do you have a clue?
>>>>
>>>> cat /proc/kallsyms | grep kallsyms_test_func
>>>> Let's see if the compiler-generated symbols have some special suffixes.
>>>
>>> Thanks, looks normal to me:
>>>
>>> atari:~# cat /proc/kallsyms | grep kallsyms_test_func
>>> 00060ab0 t kallsyms_test_func_static
>>> 00060ac0 T kallsyms_test_func
>>> 00060ac2 W kallsyms_test_func_weak
>>> atari:~#
>>
>> It's incredible. I don't have a m68k environment and I'm trying to build a qemu
>> environment. If you're in a hurry and willing, you can apply the debugging patch
>> in the attachment. I'd like to see what's wrong. Use "dmesg | grep tst" to collect
>> the output information.
>
> Still fails:
>
> tst: found kallsyms_test_func at index=12845
> tst: [12533] = kallsyms_test_func, seq=17370, offset=191223
> tst: [18800] = kallsyms_test_func, seq=23193, offset=259263
> tst: [21934] = kallsyms_test_func, seq=2527, offset=22331
> tst: [23501] = kallsyms_test_func, seq=11792, offset=126366
> tst: [24284] = kallsyms_test_func, seq=8427, offset=87395
> tst: [24676] = kallsyms_test_func, seq=21896, offset=243536
> tst: [24872] = kallsyms_test_func, seq=22571, offset=251856
> tst: [24970] = kallsyms_test_func, seq=23264, offset=260074
> tst: [25019] = kallsyms_test_func, seq=9003, offset=93752
> tst: [25043] = kallsyms_test_func, seq=14324, offset=155117
> tst: [25055] = kallsyms_test_func, seq=5942, offset=62266
> tst: [25061] = kallsyms_test_func, seq=14347, offset=155467
> tst: [25064] = kallsyms_test_func, seq=14350, offset=155512
> tst: [25066] = kallsyms_test_func, seq=14346, offset=155457
> tst: [25067] = kallsyms_test_func, seq=14354, offset=155565

- pr_warn("tst: [%d] = %s, seq=%d, offset=%d\n", mid, name, seq, off);
+ pr_warn("tst: [%d] = %s, seq=%d, offset=%d\n", mid, namebuf, seq, off);

Sorry, a variable in the debugging code is incorrectly written. 'name' should
be replaced with 'namebuf', then we can see which function the comparison is wrong.

>
> However, the binary search sequence looks very suspicious.
> After investigation, it turns out compare_symbol_name() and strcmp()
> always return positive numbers.
>
> Looks like commit 3bc753c06dd02a35 ("kbuild: treat char as always
> unsigned") is to blame.

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.

Is m68k big-endian?

>
> Changing:
>
> --- a/arch/m68k/include/asm/string.h
> +++ b/arch/m68k/include/asm/string.h
> @@ -42,7 +42,7 @@ static inline char *strncpy(char *dest, const
> char *src, size_t n)
> #define __HAVE_ARCH_STRCMP
> static inline int strcmp(const char *cs, const char *ct)
> {
> - char res;
> + signed char res;
>
> asm ("\n"
> "1: move.b (%0)+,%2\n" /* get *cs */
>
> fixes strcmp, but the test still fails:
>
> tst: kallsyms_lookup_names() is OK, name=kallsyms_test_func, i=0

i=0, i is impossible zero. Maybe kallsyms_lookup_names() always return success now.

> kallsyms_selftest: kallsyms_lookup_name() for
> kallsyms_test_func_static failed: addr=8e1c, expect 60cd4
> kallsyms_selftest: kallsyms_lookup_name() for kallsyms_test_func
> failed: addr=8e1c, expect 60ce4
> kallsyms_selftest: kallsyms_lookup_name() for
> kallsyms_test_func_weak failed: addr=8e1c, expect 60ce6
> kallsyms_selftest: kallsyms_lookup_name() for vmalloc failed:
> addr=8e1c, expect c2946
> kallsyms_selftest: kallsyms_lookup_name() for vfree failed:
> addr=8e1c, expect c235e
> kallsyms_selftest: kallsyms_on_each_match_symbol() for
> kallsyms_test_func_static failed: count=25068, addr=1f3d3c, expect
> 60cd4
> kallsyms_selftest: kallsyms_on_each_match_symbol() for
> kallsyms_test_func failed: count=25068, addr=1f3d3c, expect 60ce4
> kallsyms_selftest: kallsyms_on_each_match_symbol() for
> kallsyms_test_func_weak failed: count=25068, addr=1f3d3c, expect 60ce6
> kallsyms_selftest: kallsyms_on_each_match_symbol() for vmalloc
> failed: count=25068, addr=1f3d3c, expect c2946
> kallsyms_selftest: kallsyms_on_each_match_symbol() for vfree
> failed: count=25068, addr=1f3d3c, expect c235e
> kallsyms_selftest: abort
>
> Dropping -funsigned-char doesn't improve upon that...
>
> 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
>
> .
>

--
Regards,
Zhen Lei