linux-kernel - Re: [PATCH v2 2/3] kallsyms: Add APIs to match symbol without .XXXX suffix.

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Message-Id: <20240805224544.e0a4277dff4ac41d867c6bc1@kernel.org>
Date: Mon, 5 Aug 2024 22:45:44 +0900
From: Masami Hiramatsu (Google) <mhiramat@...nel.org>
To: Song Liu <song@...nel.org>
Cc: live-patching@...r.kernel.org, linux-kernel@...r.kernel.org,
 linux-trace-kernel@...r.kernel.org, jpoimboe@...nel.org, jikos@...nel.org,
 mbenes@...e.cz, pmladek@...e.com, joe.lawrence@...hat.com,
 nathan@...nel.org, morbo@...gle.com, justinstitt@...gle.com,
 mcgrof@...nel.org, thunder.leizhen@...wei.com, kees@...nel.org,
 kernel-team@...a.com, mmaurer@...gle.com, samitolvanen@...gle.com,
 mhiramat@...nel.org, rostedt@...dmis.org
Subject: Re: [PATCH v2 2/3] kallsyms: Add APIs to match symbol without .XXXX
 suffix.

On Fri,  2 Aug 2024 14:08:34 -0700
Song Liu <song@...nel.org> wrote:

> With CONFIG_LTO_CLANG=y, the compiler may add suffix to function names
> to avoid duplication. This causes confusion with users of kallsyms.
> On one hand, users like livepatch are required to match the symbols
> exactly. On the other hand, users like kprobe would like to match to
> original function names.
> 
> Solve this by splitting kallsyms APIs. Specifically, existing APIs now
> should match the symbols exactly. Add two APIs that match only the part
> without .XXXX suffix. Specifically, the following two APIs are added.
> 
> 1. kallsyms_lookup_name_without_suffix()
> 2. kallsyms_on_each_match_symbol_without_suffix()
> 
> These APIs will be used by kprobe.
> 
> Also cleanup some code and update kallsyms_selftests accordingly.
> 
> Signed-off-by: Song Liu <song@...nel.org>

Looks good to me, but I have a nitpick. 

> --- a/kernel/kallsyms.c
> +++ b/kernel/kallsyms.c
> @@ -164,30 +164,27 @@ static void cleanup_symbol_name(char *s)
>  {
>  	char *res;
>  
> -	if (!IS_ENABLED(CONFIG_LTO_CLANG))
> -		return;
> -
>  	/*
>  	 * LLVM appends various suffixes for local functions and variables that
>  	 * must be promoted to global scope as part of LTO.  This can break
>  	 * hooking of static functions with kprobes. '.' is not a valid
> -	 * character in an identifier in C. Suffixes only in LLVM LTO observed:
> -	 * - foo.llvm.[0-9a-f]+
> +	 * character in an identifier in C, so we can just remove the
> +	 * suffix.
>  	 */
> -	res = strstr(s, ".llvm.");
> +	res = strstr(s, ".");

nit: "strchr(s, '.')" ?

Anyway,

Reviewed-by: Masami Hiramatsu (Google) <mhiramat@...nel.org>

Thank you,

-- 
Masami Hiramatsu (Google) <mhiramat@...nel.org>