Re: ptrace PT_CONTINUE
Re: ptrace PT_CONTINUE
- Subject: Re: ptrace PT_CONTINUE
- From: Aron-Zvi <email@hidden>
- Date: Thu, 9 Jul 2009 10:03:46 +0300
I'm trying to launch and trace a child process similar to what gdb does. i.e. gdb foo folowed by (gdb)run.
For the first step, I'd like to launch a child process, have it stop at its first instruction and then have it resume normal execution. The code I posted is supposed to do just that.
Ultimately, I'd like to control execution of the child process by reading / writing to it's memory and its thread's registers. I know ptrace() doesn't do any of that in OS X and that it must be done using the mach api, however, I thought a simple ptrace(PT_CONTINUE, ...) on a stopped, traced child process should work. I've seen references on the net of ptrace(PT_CONTINUE, ...) usage to continue a stopped process.
I'm sure you don't need to see this:
http://developer.apple.com/documentation/Darwin/Reference/Manpages/man2/ptrace.2.html
So what's the verdict? Can ptrace(PT_CONTINUE, ...) be used to continue a stopped, traced child process? If not, how do I go about it?
Aron-Zvi
On Thu, Jul 9, 2009 at 8:35 AM, Terry Lambert
<email@hidden> wrote:
You are expected to exec after the fork, not be tracing your own code. See the system_cmds project for the sc_usage source.
What are you really trying to do here?
-- Terry
On Jul 8, 2009, at 7:10 PM, Aron-Zvi wrote:
Hey guys,
I'm trying to get started with basic ptrace functionality with the following:
#include <sys/types.h>
#include <sys/ptrace.h>
#include <sys/wait.h>
#include <unistd.h>
#include <stdio.h>
#include <errno.h>
int main(int argc, char **argv)
{
int pid, status, ret;
if((pid = fork()) == 0)
{
ptrace(PT_TRACE_ME,0,0,0);
execl(argv[1],argv[1],0);
printf("exec failed\n");
}
else{
wait(&status);
if(WIFSTOPPED(status))
printf("child has stopped. child pid: %d\n", pid);
errno = 0;
ret = ptrace(PT_CONTINUE, pid, (caddr_t)1, 0);
printf("ret: %d\n", ret);
printf("errno: %s\n", strerror(errno));
}
}
>From my basic understanding, what the above should do is fork a child process which will stop at exec and cause the parent-tracing process to exit wait(). The parent process should then have the child process continue execution normally by calling ptrace() with PT_CONTINUE.
When I run the code, The child process is created, however, ptrace() with PT_CONTINUE seems to fail as the child process does not continue normal execution. ptrace's return value is 0 and errno is "Unknown error: 0".
Running output:
aronzvis-macbook:ptrace_test aronzvi$ ./ptrace ../voidinc
child has stopped. child pid: 37959
ret: 0
errno: Unknown error: 0
I'm running OS X 10.5.7 and building the code with the 10.5 SDK.
Your help is much appreciated,
Aron-Zvi
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