Messages in this thread | | | Subject | 2.4.x, can't ptrace a task created with clone() ? | From | Daniel Barlow <> | Date | Wed, 15 Jan 2003 16:34:58 +0000 |
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Tested with 4.2.20 and 2.4.21-pre3, after PTRACE_ATTACHing to a process I created with clone(), wait() returns ECHILD . strace of the parent shows
clone(child_stack=0x80599a8, flags=CLONE_VM) = 1292 rt_sigprocmask(SIG_BLOCK, [CHLD], [], 8) = 0 rt_sigaction(SIGCHLD, NULL, {SIG_DFL}, 8) = 0 rt_sigprocmask(SIG_SETMASK, [], NULL, 8) = 0 nanosleep({5, 0}, {5, 0}) = 0 ptrace(PTRACE_ATTACH, 1292, 0, 0) = 0 --- SIGCHLD (Child exited) --- wait4(-1, 0xbffffbf0, 0, NULL) = -1 ECHILD (No child processes) write(2, "waitpid: No child processes\n", 28) = 28
If I replace the clone in my test program with a fork, everything works as I expected. Is this a bug, or are my expectations at fault? if the latter, how _do_ I attach to one of my cloned children?
Here's the test program I've been using:
#include <sched.h> #include <sys/ptrace.h> #include <linux/user.h> #include <stdio.h> #include <unistd.h> #include <sys/types.h> #include <sys/wait.h>
void child(void *d) { int foo; fprintf(stderr,"child stack is somewhere around 0x%x\n",&foo); while(1){ fprintf(stderr, "still here\n"); sleep(3); } }
main() { pid_t kid; int waitr; struct user_regs_struct regs;
kid=clone(child,SIGSTKSZ*8+malloc(SIGSTKSZ*8), CLONE_VM ,0); /* kid=fork(); */ if(kid<0) perror("clone"); if(kid==0) child(0); sleep(5); if(kid>0) { if(ptrace(PTRACE_ATTACH,kid,0,0)) perror("PTRACE_ATTACH"); if(wait(&waitr)==-1) { perror("waitpid"); exit(1); } if(ptrace(PTRACE_GETREGS,kid,0,®s)) perror("PTRACE_GETREGS"); fprintf(stderr,"child stack pointer is 0x%x\n",regs.esp); if(ptrace(PTRACE_DETACH,kid,0,0)) perror("PTRACE_DETACH"); kill(kid,15); } }
libc 2.3.1, in case that makes a difference. Let me know if there's anything else you wanted to ask
-dan
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