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import os
import signal
import socket
import subprocess
import sys
import select
import ptrace.debugger
from ptrace.debugger import (
ProcessSignal,
ProcessExit,
NewProcessEvent,
)
# ----------------------------------------------------------------------
# Configuration
# ----------------------------------------------------------------------
# If scheduler does not provide input within this time (seconds),
# continue running the last chosen thread.
SCHED_TIMEOUT = 0
# ----------------------------------------------------------------------
# Scheduler (non-blocking)
# ----------------------------------------------------------------------
def schedule_next_nonblocking(sock, processes, current_proc):
timeout = SCHED_TIMEOUT if SCHED_TIMEOUT > 0 else 0
r, _, _ = select.select([sock], [], [], timeout)
if not r:
return current_proc # no input → continue with current
data = sock.recv(64)
if not data:
return current_proc
try:
tid = int(data.strip())
except ValueError:
print(f"Scheduler: invalid data {data!r}")
return current_proc
if tid in processes:
print(f"Scheduler picked TID {tid}")
return processes[tid]
print(f"Scheduler sent inactive TID {tid}, ignoring")
return current_proc
# ----------------------------------------------------------------------
# Main tracing logic
# ----------------------------------------------------------------------
def trace(pid, sched_socket_path):
debugger = ptrace.debugger.PtraceDebugger()
debugger.traceClone()
debugger.traceFork()
debugger.traceExec()
print(f"Attach process {pid}")
proc0 = debugger.addProcess(pid, False)
# ------------------------------------------------------------------
# Create scheduler socket
# ------------------------------------------------------------------
if os.path.exists(sched_socket_path):
os.unlink(sched_socket_path)
srv = socket.socket(socket.AF_UNIX, socket.SOCK_STREAM)
srv.bind(sched_socket_path)
srv.listen(1)
print(f"Waiting for scheduler connection on {sched_socket_path}")
conn, _ = srv.accept()
print("Scheduler connected")
# ------------------------------------------------------------------
# Prime the very first thread
# ------------------------------------------------------------------
current_proc = proc0
# Arm the first process: run until its first event/syscall
current_proc.syscall()
# Flag for ignoring the first clone
ignored_tid = None
first_clone_ignored = False
# ------------------------------------------------------------------
# Global event loop — always resume one tracee after every event
# ------------------------------------------------------------------
while debugger.list:
try:
event = debugger.waitSyscall()
# --------------------------------------------------------------
# New traced process (clone/fork/vfork)
# --------------------------------------------------------------
except NewProcessEvent as ev:
child = ev.process
parent = child.parent
child_tid = child.pid
if not first_clone_ignored:
# FIRST CLONE is ignored completely
first_clone_ignored = True
ignored_tid = child_tid
print(f"First clone: created TID {child_tid} — IGNORING it")
# Detach ignored child so it runs untraced
try:
child.detach()
except Exception:
pass
# Remove from debugger
debugger.deleteProcess(child)
# Resume parent so clone() completes
parent.syscall()
else:
# LATER CLONES ARE TRACED
print(f"New traced thread {child_tid} (parent {parent.pid})")
debugger.dict[child_tid] = child
# Arm both child and parent
child.syscall()
parent.syscall()
continue
# --------------------------------------------------------------
# When a process gets a non-SIGTRAP signal
# --------------------------------------------------------------
except ProcessSignal as ev:
ev.process.syscall(ev.signum)
continue
# --------------------------------------------------------------
# A traced thread died
# --------------------------------------------------------------
except ProcessExit as ev:
dead_proc = ev.process
tid = dead_proc.pid
print(f"TID {tid} exited (exitcode={ev.exitcode})")
try:
dead_proc.detach()
except Exception:
pass
debugger.deleteProcess(dead_proc)
# If the one that died was the current process, pick another
if debugger.list:
current_proc = debugger.list[0]
continue
# --------------------------------------------------------------
# NORMAL SYSCALL STOP
# --------------------------------------------------------------
proc = event.process
tid = proc.pid
if tid == ignored_tid:
# Should never happen (ignored child not traced)
print(f"WARNING: ignored TID {tid} hit a syscall-stop??")
else:
ip = proc.getInstrPointer()
print(f"TID {tid} syscall-stop at {hex(ip)}")
# Ensure all traced threads appear in debugger.dict
for p in debugger.list:
t = p.pid
if t not in debugger.dict:
debugger.dict[t] = p
# Ask scheduler which thread to run next
current_proc = schedule_next_nonblocking(conn, debugger.dict, proc)
if current_proc not in debugger.list:
# If scheduler picked a dead or detached thread, pick any alive one
current_proc = debugger.list[0]
# Resume chosen thread
current_proc.syscall()
conn.close()
srv.close()
debugger.quit()
# ----------------------------------------------------------------------
# Entry point
# ----------------------------------------------------------------------
def quoted(s: str) -> str:
return f'"{s}"'
if __name__ == "__main__":
env = os.environ.copy()
qemu = [
"qemu-x86_64",
"-g",
"12348",
"/nix/store/dmpq06y392i752zwhcna07kb2x5l58l5-memcached-static-x86_64-unknown-linux-musl-1.6.37/bin/memcached",
"-p",
"11211",
"-t",
"4",
"-vv"
]
sched_path = "/tmp/memcached_scheduler.sock"
proc = subprocess.Popen(qemu, env=env)
try:
trace(proc.pid, sched_path)
except Exception as e:
print(f"Got exception: {e}")
proc.kill()
exit(2)
exit(0)
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