[Tracing] Use BCC tools to do dynamic tracing in Linux user space

Here is a very simple example of using BCC to trace a program and get the data from the function's argument.

A Simple Test Code in C: "test.c"

#include <stdio.h>

// student structure
struct student {
  char id[15];
  char firstname[64];
  char lastname[64];
  float points;
};
// function declaration
void getDetail(struct student *);
void displayDetail(struct student *);

int main(void) {
  // student structure variable
  struct student std[1];
  // get student detail
  getDetail(std);
  // display student detail
  displayDetail(std);
  return 0;
}

// function definition
void getDetail(struct student *ptr) {
  int i;
  for (i = 0; i < 1; i++) {
    printf("Enter detail of student #%d\n", (i + 1));
    printf("Enter ID: ");
    scanf("%s", ptr->id);
    printf("Enter first name: ");
    scanf("%s", ptr->firstname);
    printf("Enter last name: ");
    scanf("%s", ptr->lastname);
    printf("Enter Points: ");
    scanf("%f", &ptr->points);
    // update pointer to point at next element
    // of the array std
    ptr++;
  }
}

void displayDetail(struct student *ptr) {
  int i;
  for (i = 0; i < 1; i++) {
    printf("\nDetail of student #%d\n", (i + 1));
    // display result via ptr variable
    printf("\nResult via ptr\n");
    printf("ID: %s\n", ptr->id);
    printf("First Name: %s\n", ptr->firstname);
    printf("Last Name: %s\n", ptr->lastname);
    printf("Points: %f\n", ptr->points);
    // update pointer to point at next element
    // of the array std
    ptr++;
  }
}

The simple BCC example code: "mytrace.py"
It will get and print out the string of firstname when it runs

from __future__ import print_function
from bcc import BPF
from time import strftime
import argparse


# load BPF program
bpf_text = """
#include <uapi/linux/ptrace.h>
#include <linux/sched.h>
struct str_t {
    u64 pid;
    char str[80];
};

// student structure
struct student {
  char id[15];
  char firstname[64];
  char lastname[64];
  float points;
};

BPF_PERF_OUTPUT(events);
int printret(struct pt_regs *ctx) {
    struct str_t data  = {};
    char comm[TASK_COMM_LEN] = {};
    u32 pid;
    if (!PT_REGS_RC(ctx))
        return 0;
    pid = bpf_get_current_pid_tgid();
    data.pid = pid;
    bpf_probe_read(&data.str, sizeof(data.str),
        ((struct student *)PT_REGS_RC(ctx))->firstname);
    bpf_get_current_comm(&comm, sizeof(comm));
    events.perf_submit(ctx,&data,sizeof(data));
    return 0;
};
"""

b = BPF(text=bpf_text)
b.attach_uprobe(name="<...your test binary file location...>/test",
        sym="displayDetail", fn_name="printret")

# header
print("%-9s %-6s %s" % ("TIME", "PID", "ARGUMENT"))

def print_event(cpu, data, size):
    event = b["events"].event(data)
    print("%-9s %-6d %s" % (strftime("%H:%M:%S"), event.pid,
                            event.str.decode('utf-8', 'replace')))

b["events"].open_perf_buffer(print_event)
while 1:
    try:
        b.perf_buffer_poll()
    except KeyboardInterrupt:
        exit()

Here is the steps:

$ sudo python mytrace.py

# open another terminal
$ gcc -o test test.c
$ ./test
Enter detail of student #1
Enter ID: 1234
Enter first name: Danny
Enter last name: Liu
Enter Points: 100

Detail of student #1

Result via ptr
ID: 1234
First Name: Danny
Last Name: Liu
Points: 100.000000

Then you will see the tracing message in your previous terminal as follows:
(print out the first name from function's argument)

$ sudo python mytrace.py
TIME      PID    ARGUMENT
17:01:32  7265   Danny

[Tracing] Dynamic tracing in Linux using uprobe and kprobe

This post is based on the following articles to trace again by myself. Through this process, I can get a deeper impression of the user-space tracing using uprobe.
https://opensource.com/article/17/7/dynamic-tracing-linux-user-and-kernel-space
http://www.brendangregg.com/perf.html

[Darknet][Python] Support using Numpy array as image input instead of image path in Darknet Python API

When I dealt with Darknet's detect function in Python, I found that there is only one way for accepting an image file path as the argument, which is convenient for inferencing images from files.  But, it is not very well for images from video files or cameras.
Due to this reason, I dig out some solutions already on the Internet, and modify as follows: