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POHow does GDB know about threads
 

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  1. POHow does GDB know about threads
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    <p>I am trying to understand more deeply how GDB knows about threads.</p> <ul> <li>How is it able to tell which one is the current thread ?</li> <li>How does it know all the context information relative to each thread ?</li> </ul> <p>My question aims at how it works internally in GDB, I do not have any problem debugging threads, it is all really about GDB's internals.</p> <p>I found the <a href="http://www.sourceware.org/gdb/onlinedocs/gdbint.html" rel="nofollow noreferrer">GDB internals documentation</a>, but the threads part is empty as for now.<br> All my other research lead me to question about debugging multi-threaded programs and I cannot seem to dig the precise information I am looking for.</p> <p>Edit :</p> <p>So far it seems that GDB intercepts signals (thanks to ptrace?) and finds out when threads are created. But I would like to know more precisely how it is actually done.</p> <p>I also have a particular architecture that comes with a GDB that was configured with --enable-threads=single. That GDB is however able to list the current threads. How is this possible ?</p> <p>Every knowledge, useful links or documentations are welcomed.</p> <p>Thanks.</p> <hr> <p><strong>Update March 5 '14</strong></p> <p>I have looked into the libthread_db and found out that GDB allows providing a custom built library to debug threads (see <a href="https://sourceware.org/gdb/onlinedocs/gdb/Threads.html" rel="nofollow noreferrer">doc</a> for information) </p> <p>I have tried to do that and am able to provide gdb information about my thread (ID, start function, stack and such) by implementing the <code>td_thr_get_info</code> function defined in <code>gdb/common/gdb_thread_db.h</code>.</p> <p>Still i am not able to give gdb any information about the context of my threads and still looking for any clue on that issue.</p> <p>Thanks.</p> <p>PS: <a href="https://stackoverflow.com/questions/19972568/teaching-gdb-to-understand-micro-threads-from-core-files#comment33599283_19972568">This question</a> seem to address the same questions but has unfortunately no directions too.</p>
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    1. COFYI, I am working in a Linux environment, but I'd like to keep the information as much generic as possible.
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    2. COWhat do you mean by "current" thread? I would imagine the thread creating routines are intercepted, so GDB finds out about stack and other properties from certain memory locations in the process memory (heap).
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      1. USPatrik Beck
    3. COYes, I came across such assertions during my researchs although I am looking for more precision in how this is actually done in GDB. Studying its source code gives information, but it is quite a wild jungle. I also edited the question to focus more on the problem I am facing.
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