Re: [PATCH v5] libbpf: kprobe.multi: Filter with available_filter_functions

[Jackie Liu <liu.yun@linux.dev>]

在 2023/5/26 17:53, Jiri Olsa 写道:
> On Fri, May 26, 2023 at 10:10:47AM +0800, Jackie Liu wrote:
> 
> SNIP
> 
>> -resolve_kprobe_multi_cb(unsigned long long sym_addr, char sym_type,
>> -			const char *sym_name, void *ctx)
>> +kallsyms_resolve_kprobe_multi_cb(unsigned long long sym_addr, char sym_type,
>> +				 const char *sym_name, void *ctx)
>>   {
>>   	struct kprobe_multi_resolve *res = ctx;
>>   	int err;
>> @@ -10431,8 +10438,8 @@ resolve_kprobe_multi_cb(unsigned long long sym_addr, char sym_type,
>>   	if (!glob_match(sym_name, res->pattern))
>>   		return 0;
>>   
>> -	err = libbpf_ensure_mem((void **) &res->addrs, &res->cap, sizeof(unsigned long),
>> -				res->cnt + 1);
>> +	err = libbpf_ensure_mem((void **) &res->addrs, &res->cap,
>> +				sizeof(unsigned long), res->cnt + 1);
> 
> hum, looks like this is just formatting change, AFAICS we don't need that
> 
>>   	if (err)
>>   		return err;
>>   
>> @@ -10440,6 +10447,75 @@ resolve_kprobe_multi_cb(unsigned long long sym_addr, char sym_type,
>>   	return 0;
>>   }
>>   
> 
> SNIP
> 
>> +
>> +static void kprobe_multi_resolve_free(struct kprobe_multi_resolve *res)
>> +{
>> +	while (res->syms && res->cnt)
>> +		free((char *)res->syms[--res->cnt]);
>> +
>> +	free(res->syms);
>> +	free(res->addrs);
> 
> we should set cnt and cap to zero for the fallback sake

It is necessary to set cap to 0, cnt is already 0, if syms exists.

> 
>> +}
>> +
>>   struct bpf_link *
>>   bpf_program__attach_kprobe_multi_opts(const struct bpf_program *prog,
>>   				      const char *pattern,
>> @@ -10476,13 +10552,20 @@ bpf_program__attach_kprobe_multi_opts(const struct bpf_program *prog,
>>   		return libbpf_err_ptr(-EINVAL);
>>   
>>   	if (pattern) {
>> -		err = libbpf_kallsyms_parse(resolve_kprobe_multi_cb, &res);
>> -		if (err)
>> -			goto error;
>> +		err = libbpf_available_kprobes_parse(ftrace_resolve_kprobe_multi_cb,
>> +						     &res);
>> +		if (err) {
>> +			/* fallback to kallsyms */
> 
> we need to call kprobe_multi_resolve_free in here and set
> cnt/cap to zero in kprobe_multi_resolve_free

Yes.

> 
> jirka
> 
>> +			err = libbpf_kallsyms_parse(kallsyms_resolve_kprobe_multi_cb,
>> +						    &res);
>> +			if (err)
>> +				goto error;
>> +		}
>>   		if (!res.cnt) {
>>   			err = -ENOENT;
>>   			goto error;
>>   		}
>> +		syms = res.syms;
>>   		addrs = res.addrs;
>>   		cnt = res.cnt;
>>   	}
>> @@ -10511,12 +10594,12 @@ bpf_program__attach_kprobe_multi_opts(const struct bpf_program *prog,
>>   		goto error;
>>   	}
>>   	link->fd = link_fd;
>> -	free(res.addrs);
>> +	kprobe_multi_resolve_free(&res);
>>   	return link;
>>   
>>   error:
>>   	free(link);
>> -	free(res.addrs);
>> +	kprobe_multi_resolve_free(&res);
>>   	return libbpf_err_ptr(err);
>>   }
>>   
>> -- 
>> 2.25.1
>>