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

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Message-ID: <f1eaedb1-fc3e-cd0e-e63a-6e3caa9e015e@huawei.com>
Date:   Wed, 21 Sep 2022 16:31:04 +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 16:00, 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.

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

-- 
Regards,
  Zhen Lei