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

From: Geert Uytterhoeven
Date: Thu Dec 15 2022 - 08:25:17 EST

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

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.

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
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