On Fri, 2 Aug 2024 14:08:35 -0700
Song Liu <song@xxxxxxxxxx> wrote:
> Use the new kallsyms APIs that matches symbols name with .XXX
> 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 compile with CONFIG_LTO_CLANG.
>
> Signed-off-by: Song Liu <song@xxxxxxxxxx>
> ---
> kernel/kprobes.c | 6 +++++-
> kernel/trace/trace_kprobe.c | 11 ++++++++++-
> 2 files changed, 15 insertions(+), 2 deletions(-)
>
> diff --git a/kernel/kprobes.c b/kernel/kprobes.c
> index e85de37d9e1e..99102283b076 100644
> --- a/kernel/kprobes.c
> +++ b/kernel/kprobes.c
> @@ -70,7 +70,11 @@ static DEFINE_PER_CPU(struct kprobe *, kprobe_instance);
> kprobe_opcode_t * __weak kprobe_lookup_name(const char *name,
> unsigned int __unused)
> {
> - return ((kprobe_opcode_t *)(kallsyms_lookup_name(name)));
> + unsigned long addr = kallsyms_lookup_name(name);
> +
> + if (IS_ENABLED(CONFIG_LTO_CLANG) && !addr)
> + addr = kallsyms_lookup_name_without_suffix(name);
> + return ((kprobe_opcode_t *)(addr));
> }
>
> /*
> diff --git a/kernel/trace/trace_kprobe.c b/kernel/trace/trace_kprobe.c
> index 61a6da808203..d2ad0c561c83 100644
> --- a/kernel/trace/trace_kprobe.c
> +++ b/kernel/trace/trace_kprobe.c
> @@ -203,6 +203,10 @@ unsigned long trace_kprobe_address(struct trace_kprobe *tk)
> if (tk->symbol) {
> addr = (unsigned long)
> kallsyms_lookup_name(trace_kprobe_symbol(tk));
> +
> + if (IS_ENABLED(CONFIG_LTO_CLANG) && !addr)
> + addr = kallsyms_lookup_name_without_suffix(trace_kprobe_symbol(tk));
> +
So you do the lookup twice if this is enabled?
Why not just use "kallsyms_lookup_name_without_suffix()" the entire time,
and it should work just the same as "kallsyms_lookup_name()" if it's not
needed?
> if (addr)
> addr += tk->rp.kp.offset;
> } else {
> @@ -766,8 +770,13 @@ 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_without_suffix(
> + count_symbols, func_name, &ctx.count);
Same here.
-- Steve
> + }
> + }
>
> module_kallsyms_on_each_symbol(mod, count_mod_symbols, &ctx);
>
