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    <p>Well after many tries and search at Google i found that you
      cannot use waitpid more than once.</p>
    <p>i had to attach ptrace then call waitpid and the make all
      read/writes to memory and finaly detach ptrace.</p>
    <p>i attach a working example for test and try. You have to open and
      run it as root.<br>
    </p>
    <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>
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                    color="#888888">
                    <div><br>
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                    <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?
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