linux-kernel - Re: [PATCH v4 2/8] scripts/kallsyms: ensure that all possible combinations are compressed

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Message-ID: <43492a06-6506-7cbf-100e-883a5f54a3df@huawei.com>
Date:   Wed, 21 Sep 2022 20:46:43 +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 2/8] scripts/kallsyms: ensure that all possible
 combinations are compressed



On 2022/9/21 16:31, Leizhen (ThunderTown) wrote:
> 
> 
> On 2022/9/21 16:00, Petr Mladek wrote:
>> On Tue 2022-09-20 15:13:11, Zhen Lei wrote:
>>> For a symbol, there may be more than one place that can be merged. For
>>> example: nfs_fs_proc_net_init, there are two "f"+"s_" combinations.
>>> And we're only compressing the first combination at the moment.
>>
>> Really?
> 
> Yes, there are about 200 such functions.
> 
>>
>>> diff --git a/scripts/kallsyms.c b/scripts/kallsyms.c
>>> index 8caccc8f4a23703..3319d9f38d7a5f2 100644
>>> --- a/scripts/kallsyms.c
>>> +++ b/scripts/kallsyms.c
>>> @@ -553,7 +553,7 @@ static void compress_symbols(const unsigned char *str, int idx)
>>>  	unsigned char *p1, *p2;
>>>  
>>>  	for (i = 0; i < table_cnt; i++) {
>>> -
>>> +retry:
>>>  		len = table[i]->len;
>>>  		p1 = table[i]->sym;
>>>  
>>> @@ -585,6 +585,9 @@ static void compress_symbols(const unsigned char *str, int idx)
>>>  
>>>  		/* increase the counts for this symbol's new tokens */
>>>  		learn_symbol(table[i]->sym, len);
>>> +
>>> +		/* May be more than one place that can be merged, try again */
>>> +		goto retry;
>>>  	}
>>>  }
>>
>> My understanding is that the code already tries to find the same
>> token several times. Here are the important parts of the existing
>> code:
>>
>> static void compress_symbols(const unsigned char *str, int idx)
>> {
>>
>> 		p2 = find_token(p1, len, str);
>>
>> 		do {
>> 			/* replace the found token with idx */
>> 			*p2 = idx;
>> 			[...]
>>
>> 			/* find the token on the symbol */
>> 			p2 = find_token(p1, size, str);
> 
> Oh, yes, it retries. Let me reanalyze it. However, the problem is
> real, and there may be a problem somewhere in the loop.

Hi, Petr:
  Thanks. I found that it's my fault. The first round skip the type
character. But the next round will incorrectly skip one character,
so for nfs_fs_proc_net_init, the next round start from s, and using
            ^
the proposed "unsigned char type" in your next reply should solve
the problem. Thank you very much.

-	for (i = 0; i < len - 1; i++)
+	for (i = sym_start_idx; i < len - 1; i++)

> 
>>
>> 		} while (p2);
>>
>> Best Regards,
>> Petr
>> .
>>
> 

-- 
Regards,
  Zhen Lei