Re: [OT] Pseudo module name in kallsyms (Re: [PATCH V3 03/13] kprobes: Add symbols for kprobe insn pages)

[Adrian Hunter]

On 3/03/20 12:47 pm, Masami Hiramatsu wrote:
> Hi,
> 
> On Mon, 2 Mar 2020 15:43:07 +0100
> Jiri Olsa <jolsa@xxxxxxxxxx> wrote:
> 
>> On Sat, Feb 29, 2020 at 06:49:13PM -0500, Steven Rostedt wrote:
>>> On Sat, 29 Feb 2020 13:49:47 +0900
>>> Masami Hiramatsu <mhiramat@xxxxxxxxxx> wrote:
>>>
>>>> On Fri, 28 Feb 2020 18:20:04 +0100
>>>> Jiri Olsa <jolsa@xxxxxxxxxx> wrote:
>>>>
>>>>>> BTW, it seems to pretend to be a module, but is there no concern of
>>>>>> confusing users? Shouldn't it be [*kprobes] so that it is non-exist
>>>>>> module name?  
>>>>>
>>>>> note we already have bpf symbols as [bpf] module  
>>>>
>>>> Yeah, and this series adds [kprobe(s)] and [ftrace] too.
>>>> I simply concern that the those module names implicitly become
>>>> special word (rule) and embedded in the code. If such module names
>>>> are not exposed to users, it is OK (but I hope to have some comments).
>>>> However, it is under /proc, which means users can notice it.
>>>
>>> I share Masami's concerns. It would be good to have something
>>> differentiate local functions that are not modules. That's one way I
>>> look to see if something is a module or built in, is to see if kallsyms
>>> has it as a [].
>>>
>>> Perhaps prepend with: '&' ?
> 
> Yeah, '*' may not good from the filename point of view.
> 
>>
>> that would break some of the perf code.. IMO Arnaldo's explanation
>> makes sense and we could keep it as it is
> 
>  From the in-kernel API/coding point of view,
> 
> +static int get_ksymbol_kprobe(struct kallsym_iter *iter)
> +{
> +	strlcpy(iter->module_name, "kprobe", MODULE_NAME_LEN);
> +	iter->exported = 0;
> +	return kprobe_get_kallsym(iter->pos - iter->pos_bpf_end,
> +				  &iter->value, &iter->type,
> +				  iter->name) < 0 ? 0 : 1;
>  }
> 
> This clearly shows that is a iter->module_name.
> 
> And also, if someone make a module names "kprobes.ko", it will also
> have [kprobes] in kallsyms. That is also confusing.

If special characters are a problem, modules also do not start with '-' or
'_', so would "_kprobes" and "_ftrace" be acceptable to everyone?