Messages in this thread | | | Date | Sun, 17 Feb 2002 15:56:15 +0100 | From | Juan Cespedes <> | Subject | ptrace() bug |
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Hi,
I am the author of "ltrace" and unfortunatelly it does not work in 2.4 kernels, due to a bug in the kernel. Unfortunately, I don't know when did this behaviour started and what could have caused it...
Summary: if I use ptrace() witth a process that does fork(), and after the fork I modify with PTRACE_POKETEXT some of the code in the parent, the same modification is observed in the child.
I need to modify the .text in order to introduce breakpoints, but with this bug ltrace does not work with any process which forks.
The attached little program shows the bug: the child should not see the content of "sync" modified after it is alive.
Thanks for your help,
-- .+'''+. .+'''+. .+'''+. .+'''+. .+'' Juan Cespedes / \ / \ cespedes@debian.org .+' `+...+' `+...+' `+...+' `+...+' #include <stdio.h> #include <unistd.h> #include <sys/types.h> #include <sys/wait.h> #include <sys/ptrace.h> #include <signal.h>
void traced_process(void) { if (ptrace(PTRACE_TRACEME, 0, 0, 0) < 0) exit(1); kill(getpid(), SIGCONT); if (fork()) { sleep(2); /* printf("parent: *sync=%d\n", *(unsigned char*)sync); */ } else { printf("child is alive (*sync=%d)\n", *(unsigned char*)sync); sleep(1); printf("child: *sync=%d\n", *(unsigned char*)sync); } exit(0); }
int main(void) { pid_t pid; int status; int i=0;
pid = fork(); if (!pid) traced_process();
while(1) { if (wait(&status)==-1) { break; } printf("ptrace(PTRACE_POKETEXT, %d, sync, %d)...\n", pid, ++i); ptrace(PTRACE_POKETEXT, pid, sync, i); ptrace(PTRACE_SYSCALL, pid, 0, 0); } exit(0); }
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