eBPF hello world

hello_map.py

#!/usr/bin/python
from bcc import BPF
from time import sleep

# This outputs a count of how many times the clone and execve syscalls have been made
# showing the use of an eBPF map (called syscall). 

program = """
 BPF_HASH(syscall);

 int kprobe__sys_clone(void *ctx) {
     u64 counter = 0;
     u64 key = 56;
     u64 *p; 

     p = syscall.lookup(&key);

     // The verifier will reject access to a pointer if you don't check that it's non-null first
     // Try commenting out the if test (and its closing brace) if you want to see the verifier do its thing
     if (p != 0) {
         counter = *p;
     }

     counter++;
     syscall.update(&key, &counter);

     return 0;
 }

int kprobe__sys_execve(void *ctx) {
     u64 counter = 0;
     u64 key = 59;
     u64 *p; 

     p = syscall.lookup(&key);
     if (p != 0) {
         counter = *p;
     }

     counter++;
     syscall.update(&key, &counter);

     return 0;
 }
"""

b = BPF(text=program)
while True:
    sleep(2)
    line = ""
    for k, v in b["syscall"].items():
        line += "syscall {0}: {1}\t".format(k.value, v.value)
    print(line)

hello_world.py

#!/usr/bin/python
from bcc import BPF

prog = """
int hello(void *ctx) {
    bpf_trace_printk("Hello world\\n");
    return 0;
}
"""

b = BPF(text=prog)
clone = b.get_syscall_fnname("clone")
b.attach_kprobe(event=clone, fn_name="hello")
b.trace_print()

# This prints out a trace line every time the clone system call is called

# If you rename hello() to kprobe__sys_clone() you can delete the b.attach_kprobe() line, because bcc can work
# out what event to attach this to from the function name.

@rodolk a more portable way to do this is to use b.get_syscall_fnname("clone") - I've updated the gist to do that now

@lizrice Thank you for taking the time to explain me!