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

[Leizhen (ThunderTown)]

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@xxxxxxxxxx> wrote:
>> On 2022/12/15 17:39, Geert Uytterhoeven wrote:
>>> On Thu, Dec 15, 2022 at 10:16 AM Leizhen (ThunderTown)
>>> <thunder.leizhen@xxxxxxxxxx> wrote:
>>>> On 2022/12/15 16:50, Geert Uytterhoeven wrote:
>>>>> On Tue, Nov 15, 2022 at 9:41 AM Zhen Lei <thunder.leizhen@xxxxxxxxxx> 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@xxxxxxxxxx>
>>>>>
>>>>> 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@xxxxxxxxxxxxxx
> 
> 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