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<p>Hello Jussi,</p>
<p>from man 2 waitpid</p>
<p>The value of options is an OR of zero or more of the
following con‐<br>
stants:<br>
<br>
WNOHANG return immediately if no child has exited.<br>
</p>
<p>i do not exit the target process and waitpid returns to gambas
process.</p>
<p>With WNOHANG the gambas project (and also the c project) behaves
like there is no waitpid.</p>
<p>As a result is to break the target process and the Me.ret value
of <br>
</p>
<p>Me.ret = ptrace(PTRACE_PEEKDATA, Me.pid, Me.addr, Null) <br>
</p>
<br>
Me.ret = -1 which means ptrace exit with an error<br>
<br>
After that i cannot ptrace any more the target process.<br>
<br>
Thanks.<br>
<br>
<div class="moz-cite-prefix">On 06/09/2018 02:10 AM, Jussi Lahtinen
wrote:<br>
</div>
<blockquote type="cite"
cite="mid:CAFJMe7SRbDbmer9C6pz34PTGEU8_hdxa_RPW2_dm4YcFS4zhEg@mail.gmail.com">
<div dir="ltr">
<div>I'm not sure you need waitpid call at all, but if it is
needed for some side effects, then try to pass it as:</div>
<div>waitpid(Me.pid, Null, 1) ''IE WNOHANG</div>
<br>
<div><br>
</div>
<div>Jussi<br>
</div>
<div class="gmail_extra"><br>
<div class="gmail_quote">On Sat, Jun 9, 2018 at 1:57 AM, Jussi
Lahtinen <span dir="ltr"><<a
href="mailto:jussi.lahtinen@gmail.com" target="_blank"
moz-do-not-send="true">jussi.lahtinen@gmail.com</a>></span>
wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0
.8ex;border-left:1px #ccc solid;padding-left:1ex">
<div dir="ltr">
<div>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.</div>
<div><br>
</div>
<div>From the documentation:</div>
<div><i>"The <b>waitpid</b>() system call suspends
execution of the calling process until a child
specified by pid argument has changed state."</i></div>
<div><br>
</div>
<div>So this is what you observe as freezing.</div>
<div><br>
</div>
<div><i>"By default,
<b>waitpid</b>() waits only for terminated children,
but this behavior is modifiable via the options
argument, as described below."</i></div>
<div><i><br>
</i></div>
<div>Not sure what this means... maybe they meant to
write "... waitpid waits only for termination of the
children ...".</div>
<div>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.</div>
<span class="m_-2020266993320767296HOEnZb"><font
color="#888888">
<div><br>
</div>
<div><br>
</div>
<div>Jussi<br>
</div>
<div><br>
</div>
</font></span></div>
<div class="m_-2020266993320767296HOEnZb">
<div class="m_-2020266993320767296h5">
<div class="gmail_extra"><br>
<div class="gmail_quote">On Sat, Jun 9, 2018 at 1:22
AM, Demosthenes Koptsis <span dir="ltr"><<a
href="mailto:demosthenesk@gmail.com"
target="_blank" moz-do-not-send="true">demosthenesk@gmail.com</a>></span>
wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0
0 .8ex;border-left:1px #ccc
solid;padding-left:1ex"><span>On 06/09/2018
12:11 AM, Tobias Boege wrote:<br>
<blockquote class="gmail_quote"
style="margin:0 0 0 .8ex;border-left:1px
#ccc solid;padding-left:1ex">
On Fri, 08 Jun 2018, Demosthenes Koptsis
wrote:<br>
<blockquote class="gmail_quote"
style="margin:0 0 0 .8ex;border-left:1px
#ccc solid;padding-left:1ex">
Hello, i implemented a ptrace and waitpid
external functions in order to<br>
read/write a memory address of a process.<br>
<br>
i want to make a trainer for a game in
gambas and i created a small program<br>
that reads and writes to a memory process.<br>
<br>
The problem is that when i try to write to
memory it freezes at waitpid<br>
line.<br>
<br>
i attach the test program you have to 1)
open it as root 2) run a process<br>
you want to hack and get the pid 3) scan
memory with scanmem and locate an<br>
address you want to write. 4) run my test
program and see it freezes.<br>
<br>
Any help?<br>
<br>
</blockquote>
Does the same code work in a C program? It
seems like waitpid() is just what<br>
you need to do after PTRACE_ATTACH, but
anyway I'd say it's a good idea to<br>
develop the low-level bits in C first, so
that we're sure it's the translation<br>
to Gambas which is faulty, and not the
algorithm.<br>
<br>
Three other remarks:<br>
<br>
* I'm certainly not running a random
somebody's buggy program as root.<br>
Can't you spawn a child process
yourself and then use PTRACE_TRACEME<br>
for debugging purposes? That shouldn't
require root privileges.<br>
<br>
* You should also check return values of
system calls.<br>
<br>
* THIS MAILING LIST IS DEPRECATED. USE
THE NEW ONE: <a
href="https://lists.gambas-basic.org/listinfo/user"
rel="noreferrer" target="_blank"
moz-do-not-send="true">https://lists.gambas-basic.org<wbr>/listinfo/user</a><br>
<br>
Regards,<br>
Tobi<br>
<br>
</blockquote>
</span>
i also test it with c++ with codeblocks and it
also freezes at waitpid of WriteMemory function<br>
<br>
how i spawn a child process?
<div
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