Tom> IMO this is just a longstanding hole in GDB. Green threads exist, Tom> so it would be good for GDB to have a way to inspect them.
I took a stab at implementing this recently. It's still very rough but it's good enough to discuss whether it's something I should try to polish. For testing the proof of concept, I used vireo, a simple user-space thread setup based on makecontext. https://github.com/geofft/vireo I've appended the Python code that teaches gdb how to find vireo threads. It's incomplete, as in, if you re-'run', it will fail. Here's what a session looks like: (gdb) cont Continuing. [New Vireo Thread 1] [New Vireo Thread 2] send 0 from 0 to 1 Thread 1 "pingpong" hit Breakpoint 2, pingpong () at examples/pingpong.c:27 27 int i = vireo_recv(&who); (gdb) info thread Id Target Id Frame * 1 Thread 0x7ffff7cb2b80 (LWP 42208) "pingpong" pingpong () at examples/pingpong.c:27 2 Vireo Thread 1 "pingpong" pingpong () at examples/pingpong.c:27 3 Vireo Thread 2 "pingpong" pingpong () at examples/pingpong.c:27 (gdb) thread 3 [Switching to thread 3 (Vireo Thread 2)] #0 pingpong () at examples/pingpong.c:27 27 int i = vireo_recv(&who); (gdb) bt #0 pingpong () at examples/pingpong.c:27 #1 0x00007ffff7d329c0 in ?? () from /lib64/libc.so.6 #2 0x00007ffff7fc20e0 in ?? () from /home/tromey/gdb/vireo/examples/../libvireo.so #3 0x0000000000000000 in ?? () I realize now, writing this, that the approach to underlying threads should be improved. These need to be tracked more actively, so that breakpoint stops can report the corresponding green thread. You can see above that this isn't done. Also I think the "Frame" info is wrong right now. Anyway, the basic idea is to let Python tell gdb about the existence of green threads, and let gdb mostly treat them identically to OS threads. Under the hood, things like 'continue' will use the underlying OS thread. You can play with this if you want. It's on 'submit/green-threads' on my github. Be warned that I rebase a lot. Some things to work out: - Exactly how should the 'underlying thread' concept work? Hooking into the inferior's scheduler seems slow, and also like it could present a chicken/egg problem. Maybe it needs a "green thread provider" object so that on a stop we can query that to see if the green thread corresponding to an OS thread is already known. - Do we need a special hook to stop unwinding per-green-thread. You may not want to allow unwinding through the scheduler. Tom import gdb thread_map = {} main_thread = None # From glibc/sysdeps/unix/sysv/linux/x86/sys/ucontext.h x8664_regs = [ 'r8', 'r9', 'r10', 'r11', 'r12', 'r13', 'r14', 'r15', 'rdi', 'rsi', 'rbp', 'rbx', 'rdx', 'rax', 'rcx', 'rsp', 'rip', 'efl', 'csgsfs', 'err', 'trapno', 'oldmask', 'cr2' ] def vireo_current(): return int(gdb.parse_and_eval('curenv')) + 1 class VireoGreenThread: def __init__(self, tid): self.tid = tid def _get_state(self): return gdb.parse_and_eval('envs')[self.tid]['state'] def fetch(self, reg): """Fetch REG from memory.""" global x8664_regs global thread_map thread = thread[self.tid] state = self._get_state() gregs = state['uc_mcontext']['gregs'] for i in range(0, len(x8664_regs)): if reg is None or reg == x8664_regs[i]: thread.write_register(x8664_regs[i], gregs[i]) def store(self, reg): global x8664_regs global thread_map thread = thread[self.tid] state = self._get_state() gregs = state['uc_mcontext']['gregs'] for i in range(0, len(x8664_regs)): if reg is None or reg == x8664_regs[i]: gregs[i] = thread.read_register(x8664_regs[i]) def name(self): return "Vireo Thread " + str(self.tid) def underlying_thread(self): if vireo_current() == self.tid: global main_thread return main_thread return None class VFinish(gdb.FinishBreakpoint): def stop(self): tid = int(self.return_value) + 1 global thread_map thread_map[tid] = gdb.create_green_thread(tid, VireoGreenThread(tid)) return False class VCreate(gdb.Breakpoint): def stop(self): VFinish(gdb.newest_frame(), True) return False class VExit(gdb.Breakpoint): def stop(self): global main_thread if main_thread is None: main_thread = gdb.selected_thread() global thread_map tid = vireo_current() if tid in thread_map: thread_map[tid].set_exited() del thread_map[tid] VCreate('vireo_create', internal=True) VExit('vireo_exit', internal=True)
