linux-kernel - Re: [PATCH 3/3] tracing/kprobes: Use APIs that matches symbols with .llvm.<hash> suffix

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Message-Id: <20240730220417.33bd5f0d75c3742c413136d1@kernel.org>
Date: Tue, 30 Jul 2024 22:04:17 +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 3/3] tracing/kprobes: Use APIs that matches symbols with
 .llvm.<hash> suffix

On Mon, 29 Jul 2024 17:54:33 -0700
Song Liu <song@...nel.org> wrote:

> Use the new kallsyms APIs that matches symbols name with .llvm.<hash>
> suffix. This allows userspace tools to get kprobes on the expected
> function name, while the actual symbol has a .llvm.<hash> suffix.
> 

_kprobe_addr@...nel/kprobes.c may also fail with this change.

Thanks,

> This only effects kernel compared with CONFIG_LTO_CLANG.
> 
> Signed-off-by: Song Liu <song@...nel.org>
> ---
>  kernel/trace/trace_kprobe.c | 10 ++++++++--
>  1 file changed, 8 insertions(+), 2 deletions(-)
> 
> diff --git a/kernel/trace/trace_kprobe.c b/kernel/trace/trace_kprobe.c
> index 61a6da808203..c319382c1a09 100644
> --- a/kernel/trace/trace_kprobe.c
> +++ b/kernel/trace/trace_kprobe.c
> @@ -202,7 +202,8 @@ unsigned long trace_kprobe_address(struct trace_kprobe *tk)
>  
>  	if (tk->symbol) {
>  		addr = (unsigned long)
> -			kallsyms_lookup_name(trace_kprobe_symbol(tk));
> +			kallsyms_lookup_name_or_prefix(trace_kprobe_symbol(tk));
> +
>  		if (addr)
>  			addr += tk->rp.kp.offset;
>  	} else {
> @@ -766,8 +767,13 @@ static unsigned int number_of_same_symbols(const char *mod, const char *func_nam
>  {
>  	struct sym_count_ctx ctx = { .count = 0, .name = func_name };
>  
> -	if (!mod)
> +	if (!mod) {
>  		kallsyms_on_each_match_symbol(count_symbols, func_name, &ctx.count);
> +		if (IS_ENABLED(CONFIG_LTO_CLANG) && !ctx.count) {
> +			kallsyms_on_each_match_symbol_or_prefix(
> +				count_symbols, func_name, &ctx.count);
> +		}
> +	}
>  
>  	module_kallsyms_on_each_symbol(mod, count_mod_symbols, &ctx);
>  
> -- 
> 2.43.0
> 


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