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

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Date:   Wed, 21 Sep 2022 10:00:07 +0200
From:   Petr Mladek <pmladek@...e.com>
To:     Zhen Lei <thunder.leizhen@...wei.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 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?

> 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);

		} while (p2);

Best Regards,
Petr