<div dir="ltr">Hi Richard,<div><br></div><div>Can you say more about this part:</div><div><span style="font-family:arial,sans-serif;font-size:13px">> is to simply use a pipe between the parent and child to indicate when they're both ready.</span><br>
</div><div><span style="font-family:arial,sans-serif;font-size:13px"><br></span></div><div><span style="font-family:arial,sans-serif;font-size:13px">I think I assumed too much context with Greg -</span></div><div><span style="font-family:arial,sans-serif;font-size:13px"><br>
</span></div><div><span style="font-family:arial,sans-serif;font-size:13px">The exact scenario we're talking about is:</span></div><div><span style="font-family:arial,sans-serif;font-size:13px"><br></span></div><div><span style="font-family:arial,sans-serif;font-size:13px">1. Start up a process, going to be debugged, needs to be stopped at very-very start point (i.e. c/c++ library entry point). Debugger will pick it up from here.</span></div>
<div><span style="font-family:arial,sans-serif;font-size:13px"><br></span></div><div><span style="font-family:arial,sans-serif;font-size:13px">2. Apple's flow for this when debugging over debugserver on a local process is to start the exe up from lldb, in a mode that starts the process but keeps it in (essentially) a group-stop state at that first entry point. Then they have debugserver attach to that process.</span></div>
<div><span style="font-family:arial,sans-serif;font-size:13px"><br></span></div><div><span style="font-family:arial,sans-serif;font-size:13px">I could try to rewire that scenario for Linux/* (which I had originally considered and may eventually get back to that point) to have llgs configured and then have llgs launch the process, which would work right now. However, at the moment I'd like to see if I can not monkey around too much with the flow of starting a local llgs-debugged exe and just follow MacOSX's flow here.</span></div>
<div><br></div><div>Does your idea still fit into that context?</div><div><br></div><div>-Todd</div><div><br></div></div><div class="gmail_extra"><br><br><div class="gmail_quote">On Thu, Jul 24, 2014 at 12:46 PM, Richard Mitton <span dir="ltr"><<a href="mailto:richard@codersnotes.com" target="_blank">richard@codersnotes.com</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">A better way, rather than messing with signals, is to simply use a pipe between the parent and child to indicate when they're both ready.<span class="HOEnZb"><font color="#888888"><br>
<br>
Richard Mitton<br>
<a href="mailto:richard@codersnotes.com" target="_blank">richard@codersnotes.com</a></font></span><div class="HOEnZb"><div class="h5"><br>
<br>
On 07/24/2014 11:28 AM, Greg Clayton wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
On Jul 23, 2014, at 4:44 PM, Todd R. Fiala <<a href="mailto:todd.fiala@gmail.com" target="_blank">todd.fiala@gmail.com</a>> wrote:<br>
<br>
Hey Greg,<br>
<br>
I’m looking into implementing process start-up so I can just follow your flow of launching the exe, then connecting via llgs with reverse connect. I’d like to take a shot at getting Linux processes to start up in a “stopped at initial entry point” behavior rather than doing something different than MacOSX at this point.<br>
<br>
Linux PTRACE doesn’t provide this out of the box. There is an alternative that could work but is not reliable across Linux kernel versions: detaching from a PTRACE’d exe during a group-stop will leave it stopped. I think the initial startup signal I get with PTRACE may yield a group stop. If it’s not, I can immediately turn around and issue a stop, deliver that and get the real group stop. (Not 100% sure I could do that last part with guaranteed no-execution semantics at the entry point location). Unfortunately, the detach is not reliable everywhere I need this to run to keep the process in a stopped state at that point for handoff to llgs.<br>
What I could do instead, is fork, and have the child process self-send a SIGSTOP before doing the exec. And, on Linux (and maybe FreeBSD), when llgs attaches, it just needs to know that it has to wait for one exec signal before the process really starts. (I’m not sure if there is a shell mode for debugging with Linux - if there is, then we need to exec through the shell script too, I think — I don’t remember seeing that on the linux code path so it likely is buggy and/or unsupported at the moment). In any event, if I do this, I’m pretty sure I can guarantee that I can start a process in debug-ready mode with the caveat that there is an exec that has to be silently ignored when llgs attaches.<br>
<br>
How does that sound? Thoughts?<br>
</blockquote>
The idea sounds good, as you can just do:<br>
<br>
kill(getpid(), SIGSTOP)<br>
<br>
but you can run into problems with the foreground app in a terminal not being able to SIGSTOP itself and you might get some SIGTTOU or SIGTTIN signals.<br>
<br>
But do try it out. The ProcessLaunchInfo have:<br>
<br>
uint32_t<br>
GetResumeCount () const<br>
{<br>
return m_resume_count;<br>
}<br>
<br>
void<br>
SetResumeCount (uint32_t c)<br>
{<br>
m_resume_count = c;<br>
}<br>
<br>
<br>
So you just need to set this to 1 and it will continue past 1 exec without trying to read the dyld info for any execs before m_resume_count gets to zero.<br>
<br>
Greg<br>
<br>
<br>
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</blockquote>
<br>
<br>
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</div></div></blockquote></div><br><br clear="all"><div><br></div>-- <br><div dir="ltr"><table cellspacing="0" cellpadding="0" style="color:rgb(136,136,136);font-family:'Times New Roman'"><tbody><tr style="color:rgb(85,85,85);font-family:sans-serif;font-size:small">
<td nowrap style="border-top-style:solid;border-top-color:rgb(213,15,37);border-top-width:2px">Todd Fiala |</td><td nowrap style="border-top-style:solid;border-top-color:rgb(51,105,232);border-top-width:2px"> Software Engineer |</td>
<td nowrap style="border-top-style:solid;border-top-color:rgb(0,153,57);border-top-width:2px"> <a href="mailto:tfiala@google.com" style="color:rgb(17,85,204)" target="_blank"><span style="background-color:rgb(255,255,204);color:rgb(34,34,34);background-repeat:initial initial">tfiala@google.com</span></a> |</td>
<td nowrap style="border-top-style:solid;border-top-color:rgb(238,178,17);border-top-width:2px"><font color="#1155cc"> <a>650-943-3180</a></font></td></tr></tbody></table><br></div>
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