lldb on Linux leaves inferior stopped at breakpoint even after detaching

[godlygeek]

Given this C++11 program in a file called test.cpp:

#include <thread>
#include <vector>

#include <unistd.h>

void getpid_eventually()
{
    sleep(2);
    getpid();
}

int main()
{
    std::vector<std::thread> threads;
    for (int i = 0; i < 5; ++i) {
        threads.emplace_back(getpid_eventually);
    }
    for (auto& thread: threads) {
        thread.join();
    }
}

Compiled with g++ -std=c++11 test.cpp -lpthread -o test

This lldb command line consistently results in the inferior process remaining in a stopped state even after lldb has detached and exited:

./test & sleep 1; lldb --batch -o "br set -b getpid -C 'breakpoint disable' -C 'thread list'"  -o "continue" -p $! 

That is, run the executable in the background, sleep 1 second (until threads have been spawned and are blocked in sleep), and then attach to it in batch mode, set a breakpoint with commands, and continue.

The full output is:

(lldb) process attach --pid 16532                                                                                                                                                                                                     [35/6718]
Process 16532 stopped
* thread #1, name = 'test', stop reason = signal SIGSTOP
    frame #0: 0x00007fe7a656b017 libpthread.so.0`pthread_join + 167
libpthread.so.0`pthread_join:
->  0x7fe7a656b017 <+167>: cmpl   $0x0, (%rdi)
    0x7fe7a656b01a <+170>: jne    0x7fe7a656b00e            ; <+158>
    0x7fe7a656b01c <+172>: movl   %r8d, %edi
    0x7fe7a656b01f <+175>: callq  0x7fe7a65704a0            ; __pthread_disable_asynccancel
  thread #2, name = 'test', stop reason = signal SIGSTOP
    frame #0: 0x00007fe7a5a399fd libc.so.6`__nanosleep + 45
libc.so.6`__nanosleep:
->  0x7fe7a5a399fd <+45>: movq   (%rsp), %rdi
    0x7fe7a5a39a01 <+49>: movq   %rax, %rdx
    0x7fe7a5a39a04 <+52>: callq  0x7fe7a5a80890            ; __libc_disable_asynccancel
    0x7fe7a5a39a09 <+57>: movq   %rdx, %rax
  thread #3, name = 'test', stop reason = signal SIGSTOP
    frame #0: 0x00007fe7a5a399fd libc.so.6`__nanosleep + 45
libc.so.6`__nanosleep:
->  0x7fe7a5a399fd <+45>: movq   (%rsp), %rdi
    0x7fe7a5a39a01 <+49>: movq   %rax, %rdx
    0x7fe7a5a39a04 <+52>: callq  0x7fe7a5a80890            ; __libc_disable_asynccancel
    0x7fe7a5a39a09 <+57>: movq   %rdx, %rax
  thread #4, name = 'test', stop reason = signal SIGSTOP
    frame #0: 0x00007fe7a5a399fd libc.so.6`__nanosleep + 45
libc.so.6`__nanosleep:
->  0x7fe7a5a399fd <+45>: movq   (%rsp), %rdi
    0x7fe7a5a39a01 <+49>: movq   %rax, %rdx
    0x7fe7a5a39a04 <+52>: callq  0x7fe7a5a80890            ; __libc_disable_asynccancel
    0x7fe7a5a39a09 <+57>: movq   %rdx, %rax
  thread #5, name = 'test', stop reason = signal SIGSTOP
    frame #0: 0x00007fe7a5a399fd libc.so.6`__nanosleep + 45
libc.so.6`__nanosleep:
->  0x7fe7a5a399fd <+45>: movq   (%rsp), %rdi
    0x7fe7a5a39a01 <+49>: movq   %rax, %rdx
    0x7fe7a5a39a04 <+52>: callq  0x7fe7a5a80890            ; __libc_disable_asynccancel
    0x7fe7a5a39a09 <+57>: movq   %rdx, %rax
  thread #6, name = 'test', stop reason = signal SIGSTOP
    frame #0: 0x00007fe7a5a399fd libc.so.6`__nanosleep + 45
libc.so.6`__nanosleep:
->  0x7fe7a5a399fd <+45>: movq   (%rsp), %rdi
    0x7fe7a5a39a01 <+49>: movq   %rax, %rdx
    0x7fe7a5a39a04 <+52>: callq  0x7fe7a5a80890            ; __libc_disable_asynccancel
    0x7fe7a5a39a09 <+57>: movq   %rdx, %rax
Executable module set to "/home/mwoznisk/sandbox/lldb_breakpoint_after_detach/test".
Architecture set to: x86_64-unknown-linux-gnu.
(lldb) breakpoint set -b getpid -C 'breakpoint disable' -C 'thread list'
Breakpoint 1: 2 locations.
(lldb) continue
(lldb)  breakpoint disable
All breakpoints disabled. (1 breakpoints)
(lldb)  thread list
Process 16532 stopped
* thread #1: tid = 16532, 0x00007fe7a656b017 libpthread.so.0`pthread_join + 167, name = 'test'
  thread #2: tid = 16534, 0x00007fe7a5a3a9a0 libc.so.6`getpid, name = 'test', stop reason = breakpoint 1.
  thread #3: tid = 16535, 0x00007fe7a5a3a9a0 libc.so.6`getpid, name = 'test', stop reason = breakpoint 1.
  thread #4: tid = 16536, 0x00007fe7a5a3a9a0 libc.so.6`getpid, name = 'test', stop reason = breakpoint 1.
  thread #5: tid = 16537, 0x00007fe7a5a3a9a0 libc.so.6`getpid, name = 'test', stop reason = breakpoint 1.
  thread #6: tid = 16538, 0x00007fe7a5a3a9a0 libc.so.6`getpid, name = 'test', stop reason = breakpoint 1.
Process 16532 resuming
Process 16532 stopped
* thread #2, name = 'test', stop reason = breakpoint 1.
    frame #0: 0x00007fe7a5a3a9a0 libc.so.6`getpid
libc.so.6`getpid:
->  0x7fe7a5a3a9a0 <+0>:  movl   %fs:0x2d4, %edx
    0x7fe7a5a3a9a8 <+8>:  cmpl   $0x0, %edx
    0x7fe7a5a3a9ab <+11>: movl   %edx, %eax
    0x7fe7a5a3a9ad <+13>: jle    0x7fe7a5a3a9b1            ; <+17>
  thread #3, name = 'test', stop reason = breakpoint 1.
    frame #0: 0x00007fe7a5a3a9a0 libc.so.6`getpid
libc.so.6`getpid:
->  0x7fe7a5a3a9a0 <+0>:  movl   %fs:0x2d4, %edx
    0x7fe7a5a3a9a8 <+8>:  cmpl   $0x0, %edx
    0x7fe7a5a3a9ab <+11>: movl   %edx, %eax
    0x7fe7a5a3a9ad <+13>: jle    0x7fe7a5a3a9b1            ; <+17>
  thread #4, name = 'test', stop reason = breakpoint 1.
    frame #0: 0x00007fe7a5a3a9a0 libc.so.6`getpid
libc.so.6`getpid:
->  0x7fe7a5a3a9a0 <+0>:  movl   %fs:0x2d4, %edx
    0x7fe7a5a3a9a8 <+8>:  cmpl   $0x0, %edx
    0x7fe7a5a3a9ab <+11>: movl   %edx, %eax
    0x7fe7a5a3a9ad <+13>: jle    0x7fe7a5a3a9b1            ; <+17>
  thread #5, name = 'test', stop reason = breakpoint 1.
    frame #0: 0x00007fe7a5a3a9a0 libc.so.6`getpid
libc.so.6`getpid:
->  0x7fe7a5a3a9a0 <+0>:  movl   %fs:0x2d4, %edx
    0x7fe7a5a3a9a8 <+8>:  cmpl   $0x0, %edx
    0x7fe7a5a3a9ab <+11>: movl   %edx, %eax
    0x7fe7a5a3a9ad <+13>: jle    0x7fe7a5a3a9b1            ; <+17>
  thread #6, name = 'test', stop reason = breakpoint 1.
    frame #0: 0x00007fe7a5a3a9a0 libc.so.6`getpid
libc.so.6`getpid:
->  0x7fe7a5a3a9a0 <+0>:  movl   %fs:0x2d4, %edx
    0x7fe7a5a3a9a8 <+8>:  cmpl   $0x0, %edx
    0x7fe7a5a3a9ab <+11>: movl   %edx, %eax
    0x7fe7a5a3a9ad <+13>: jle    0x7fe7a5a3a9b1            ; <+17>
[2]  + suspended (signal)  ./test

After which, listing the jobs in my zsh shell shows:

[2]  + suspended (signal)  ./test

until I foreground it or prod it with a SIGCONT.

This reproduces on Linux in lldb 10.0.0, lldb 15.0.4, and in a debug build of main.

[llvmbot]

@llvm/issue-subscribers-lldb