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.

This only effects kernel compared with CONFIG_LTO_CLANG.

Signed-off-by: Song Liu <song@kernel.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

On Mon, 29 Jul 2024 17:54:33 -0700
Song Liu <song@kernel.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@kernel/kprobes.c may also fail with this change.

Thanks,

> This only effects kernel compared with CONFIG_LTO_CLANG.
> 
> Signed-off-by: Song Liu <song@kernel.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@kernel.org>

Hi Masami,

> On Jul 30, 2024, at 6:04 AM, Masami Hiramatsu <mhiramat@kernel.org> wrote:
> 
> On Mon, 29 Jul 2024 17:54:33 -0700
> Song Liu <song@kernel.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@kernel/kprobes.c may also fail with this change.
> 

Thanks for catching this! I will fix this in the next version. 

Song