[Gambas-user] external function freezes

[Jussi Lahtinen]

With exec or shell command, but I'm not sure that is what you want to do. I
think you want to attach to existing process.

>From the documentation:
*"The waitpid() system call suspends execution of the calling process until
a child specified by pid argument has changed state."*

So this is what you observe as freezing.

*"By default, waitpid() waits only for terminated children, but this
behavior is modifiable via the options argument, as described below."*

Not sure what this means... maybe they meant to write "... waitpid waits
only for termination of the children ...".
Are they required to be child processes or do attaching to process count as
child process? I don't know. If so, I don't think the options argument can
be zero in your case.


Jussi


On Sat, Jun 9, 2018 at 1:22 AM, Demosthenes Koptsis <demosthenesk at gmail.com>
wrote:

> On 06/09/2018 12:11 AM, Tobias Boege wrote:
>
>> On Fri, 08 Jun 2018, Demosthenes Koptsis wrote:
>>
>>> Hello, i implemented a ptrace and waitpid external functions in order to
>>> read/write a memory address of a process.
>>>
>>> i want to make a trainer for a game in gambas and i created a small
>>> program
>>> that reads and writes to a memory process.
>>>
>>> The problem is that when i try to write to memory it freezes at waitpid
>>> line.
>>>
>>> i attach the test program you have to 1) open it as root 2) run a process
>>> you want to hack and get the pid 3) scan memory with scanmem and locate
>>> an
>>> address you want to write. 4) run my test program and see it freezes.
>>>
>>> Any help?
>>>
>>> Does the same code work in a C program? It seems like waitpid() is just
>> what
>> you need to do after PTRACE_ATTACH, but anyway I'd say it's a good idea to
>> develop the low-level bits in C first, so that we're sure it's the
>> translation
>> to Gambas which is faulty, and not the algorithm.
>>
>> Three other remarks:
>>
>>    * I'm certainly not running a random somebody's buggy program as root.
>>      Can't you spawn a child process yourself and then use PTRACE_TRACEME
>>      for debugging purposes? That shouldn't require root privileges.
>>
>>    * You should also check return values of system calls.
>>
>>    * THIS MAILING LIST IS DEPRECATED. USE THE NEW ONE:
>> https://lists.gambas-basic.org/listinfo/user
>>
>> Regards,
>> Tobi
>>
>> i also test it with c++ with codeblocks and it also freezes at waitpid of
> WriteMemory function
>
> how i spawn a child process?
>
>
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