Re: [PATCH v4 5/8] kallsyms: Add helper kallsyms_on_each_match_symbol()

Leizhen (ThunderTown)
2022-09-22T02:16:49Z

On 2022/9/21 23:30, Petr Mladek wrote:
> On Tue 2022-09-20 15:13:14, Zhen Lei wrote:
>> Function kallsyms_on_each_symbol() traverses all symbols and submits each
>> symbol to the hook 'fn' for judgment and processing. For some cases, the
>> hook actually only handles the matched symbol, such as livepatch.
>>
>> So that, we can first compress the name being looked up and then use
>> it for comparison when traversing 'kallsyms_names', this greatly reduces
>> the time consumed by traversing.
>>
>> The pseudo code of the test case is as follows:
>> static int tst_find(void *data, const char *name,
>> struct module *mod, unsigned long addr)
>> {
>> if (strcmp(name, "vmap") == 0)
>> *(unsigned long *)data = addr;
>> return 0;
>> }
>>
>> static int tst_match(void *data, unsigned long addr)
>> {
>> *(unsigned long *)data = addr;
>> return 0;
>> }
>>
>> start = sched_clock();
>> kallsyms_on_each_match_symbol(tst_match, "vmap", &addr);
>> end = sched_clock();
>>
>> start = sched_clock();
>> kallsyms_on_each_symbol(tst_find, &addr);
>> end = sched_clock();
>>
>> The test results are as follows (twice):
>> kallsyms_on_each_match_symbol: 557400, 583900
>> kallsyms_on_each_symbol : 16659500, 16113950
>>
>> kallsyms_on_each_match_symbol() consumes only 3.48% of
>> kallsyms_on_each_symbol()'s time.
>>
>> --- a/kernel/kallsyms.c
>> +++ b/kernel/kallsyms.c
>> @@ -305,6 +305,31 @@ int kallsyms_on_each_symbol(int (*fn)(void *, const char *, struct module *,
>> return 0;
>> }
>>
>> +int kallsyms_on_each_match_symbol(int (*fn)(void *, unsigned long),
>> + const char *name, void *data)
>> +{
>> + unsigned int i, off;
>> + int len, ret;
>> + char namebuf[KSYM_NAME_LEN];
>> +
>> + len = kallsyms_name_to_tokens(name, namebuf);
>> + for (i = 0, off = 0; len && i < kallsyms_num_syms; i++) {
>> + if ((i & 0xfff) == 0)
>> + cond_resched();
>> +
>> + if ((kallsyms_names[off] == len + 1) &&
>> + !memcmp(&kallsyms_names[off + 2], namebuf, len)) {
>> + ret = fn(data, kallsyms_sym_address(i));
>> + if (ret != 0)
>> + return ret;
>> + cond_resched();
>> + }
>> + off += kallsyms_names[off] + 1;
>
> Similar tricky code is used also in kallsyms_lookup_name(). Please,
> avoid code duplication and put this into a helper funtion.

Okay, I'll try it.

>
> Best Regards,
> Petr
>
>> + }
>> +
>> + return 0;
>> +}
>> +
>> static unsigned long get_symbol_pos(unsigned long addr,
>> unsigned long *symbolsize,
>> unsigned long *offset)
>> --
>> 2.25.1
> .
>

--
Regards,
Zhen Lei