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* Add a migration warning to the update release system and the elf programs documentation pages. This is just to add a papertrail from where the documentation originate in case of error during the migration process. * Improve the building nuttx with app out of source tree * Add new guide pages * Building uclibc++ * Custom app directories * Debugging ELF loadable modules * Multiple NSH sessions * NSH network link management * RAM & ROM disks * Reading CAN messages * Remove device drivers with NSH
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84 lines
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==============================
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Debugging ELF Loadable Modules
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==============================
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.. warning::
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Migrated from:
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https://cwiki.apache.org/confluence/display/NUTTX/Debugging+ELF+Loadable+Modules
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Debugging ELF modules loaded in memory can be tricky because the load address
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in memory does not match the addresses in the ELF file. This challenge has long
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existed for debugging uClinux programs and Linux kernel modules; the same
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solution can be used with NuttX ELF files (and probably with NxFLAT modules as
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well). Below is a summary of one way to approach this:
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1. Get ELF Module Load Address
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==============================
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Put a change in ``nuttx/binfmt`` so that you print the address where the ELF
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text was loaded into memory.
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Turning on BINFMT debug (``CONFIG_DEBUG_BINFMT=y``) should give you the same
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information, although it may also provide more output than you really want.
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Alternatively, you could place a ``printf()`` at the beginning of your ``main()``
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function so that your ELF module can print its own load address. For example,
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the difference between the address of ``main()`` in your object file and the
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address of ``main()`` at run time reveals the actual load address.
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2. Make the ELF Module Wait for You
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===================================
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Insert an infinite loop in the ``main()`` routine of your ELF program. For
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example:
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.. code-block:: c
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volatile bool waitforme;
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int main (int arc, char **argv)
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{
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while (!waitforme);
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...
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When you start the ELF program, you will see where it was loaded in memory, and
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the ELF program will remain stuck in the infinite loop. It will continue to
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wait for ``waitforme`` to become true before proceeding.
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3. Start the Debugger
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=====================
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Start the debugger, connect to the GDB server, and halt the program. If your
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debugger is well-behaved, it should stop at the infinite loop in ``main()``.
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4. Load Offset Symbols
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======================
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Load symbols using the offset where the ELF module was loaded:
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.. code-block:: shell
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(gdb) add-symbol-file <myprogram> <load-address>
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Here, ``<myprogram>`` is your ELF file containing symbols, and
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``<load-address>`` is the address where the program text was actually loaded (as
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determined above). Single-step a couple of times and confirm that you are in the
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infinite loop.
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5. And Debug
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============
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Set ``waitforme`` to a non-zero value. Execution should exit the infinite loop,
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and now you can debug the ELF program loaded into RAM in the usual way.
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An Easier Way?
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==============
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There might be an alternative that allows you to step into the ELF module
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without modifying the code to include the ``waitforme`` loop. You could place a
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breakpoint on the OS function ``task_start()``. That function runs before your
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ELF program starts, so you should be able to single-step from the OS code
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directly into your loaded ELF application—no changes to the ELF application
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required.
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When you step into the application's ``main()``, you have the relocated address
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of ``main()`` and can use that address (see step #1) to compute the load offset.
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