linux-kernel - Re: [PATCH v4 5/8] kallsyms: Add helper kallsyms_on_each_match

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Date:   Thu, 22 Sep 2022 10:16:43 +0800
From:   "Leizhen (ThunderTown)" <thunder.leizhen@...wei.com>
To:     Petr Mladek <pmladek@...e.com>
CC:     Josh Poimboeuf <jpoimboe@...nel.org>,
        Jiri Kosina <jikos@...nel.org>,
        Miroslav Benes <mbenes@...e.cz>,
        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>
Subject: Re: [PATCH v4 5/8] kallsyms: Add helper
 kallsyms_on_each_match_symbol()



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