Re: [PATCHv2 bpf-next 1/6] kprobes: Add new KPROBE_FLAG_ON_FUNC_ENTRY kprobe flag

[Masami Hiramatsu (Google) <mhiramat@kernel.org>]

Hi Jiri,

On Thu, 11 Aug 2022 11:15:21 +0200
Jiri Olsa <jolsa@kernel.org> wrote:

> Adding KPROBE_FLAG_ON_FUNC_ENTRY kprobe flag to indicate that
> attach address is on function entry. This is used in following
> changes in get_func_ip helper to return correct function address.

Sorry about late reply.

> 
> Signed-off-by: Jiri Olsa <jolsa@kernel.org>
> ---
>  include/linux/kprobes.h | 1 +
>  kernel/kprobes.c        | 6 +++++-
>  2 files changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/include/linux/kprobes.h b/include/linux/kprobes.h
> index 55041d2f884d..a0b92be98984 100644
> --- a/include/linux/kprobes.h
> +++ b/include/linux/kprobes.h
> @@ -103,6 +103,7 @@ struct kprobe {
>  				   * this flag is only for optimized_kprobe.
>  				   */
>  #define KPROBE_FLAG_FTRACE	8 /* probe is using ftrace */
> +#define KPROBE_FLAG_ON_FUNC_ENTRY	16 /* probe is on the function entry */
>  
>  /* Has this kprobe gone ? */
>  static inline bool kprobe_gone(struct kprobe *p)
> diff --git a/kernel/kprobes.c b/kernel/kprobes.c
> index f214f8c088ed..a6b1b5c49d92 100644
> --- a/kernel/kprobes.c
> +++ b/kernel/kprobes.c
> @@ -1605,9 +1605,10 @@ int register_kprobe(struct kprobe *p)
>  	struct kprobe *old_p;
>  	struct module *probed_mod;
>  	kprobe_opcode_t *addr;
> +	bool on_func_entry;
>  
>  	/* Adjust probe address from symbol */
> -	addr = kprobe_addr(p);
> +	addr = _kprobe_addr(p->addr, p->symbol_name, p->offset, &on_func_entry);

Hmm, OK. And I think now we can remove kprobe_addr() itself. It is still
used in register_kretprobe() but that is redundant.

Anyway, this patch itself looks good to me.

Acked-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>

Thank you!

>  	if (IS_ERR(addr))
>  		return PTR_ERR(addr);
>  	p->addr = addr;
> @@ -1627,6 +1628,9 @@ int register_kprobe(struct kprobe *p)
>  
>  	mutex_lock(&kprobe_mutex);
>  
> +	if (on_func_entry)
> +		p->flags |= KPROBE_FLAG_ON_FUNC_ENTRY;
> +
>  	old_p = get_kprobe(p->addr);
>  	if (old_p) {
>  		/* Since this may unoptimize 'old_p', locking 'text_mutex'. */
> -- 
> 2.37.1
> 


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