97 lines
3.6 KiB
ReStructuredText
97 lines
3.6 KiB
ReStructuredText
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====================
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Task Trace Internals
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====================
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Overview
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========
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.. image:: image/task-trace-internal.png
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The Task Trace is constructed by the following functions.
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NuttX kernel events collection
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------------------------------
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The kernel events are collected by ``sched_note_*()`` API calls embedded in NuttX kernel.
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- For task switch events
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- ``sched_note_start()``
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- ``sched_note_stop()``
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- ``sched_note_suspend()``
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- ``sched_note_resume()``
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- For system call events
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- ``sched_note_syscall_enter()``
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- ``sched_note_syscall_leave()``
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- For interrupt event
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- ``sched_note_irqhandler()``
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Filter logic (``nuttx/sched/sched_note.c``)
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-------------------------------------------
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- The ``sched_note_*()`` APIs are implemented here.
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- Filter the notes and pass them to noteram driver by ``sched_note_add()`` API.
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Noteram device driver (``nuttx/drivers/note/noteram_driver.c``)
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---------------------------------------------------------------
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- Accumurate incoming note records into the buffer.
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- Read the note records from the buffer by user requests.
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- The notes are recorded in the binary format of ``struct note_*_s``.
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- The detail function is described in :doc:`../reference/os/note`.
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Notectl device driver (``nuttx/drivers/note/notectl_driver.c``)
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---------------------------------------------------------------
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- ``/dev/notectl`` device driver.
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- Control the filter logic in ``sched_note.c`` by calling note filter APIs.
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- The detail function is described in :doc:`../reference/os/note`.
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"``trace``" Built-In Application (``apps/system/trace/trace.c``)
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----------------------------------------------------------------
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- ``trace`` Built-In Application to control the trace function interactively.
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- Read binary note records from ``/dev/note`` and convert into the ftrace text format which is acceptable by `"Trace Compass" <https://www.eclipse.org/tracecompass/>`_.
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- The command syntax is described in :doc:`tasktraceuser`.
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Getting the system call events
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==============================
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To get the system call events, two different methods are used for FLAT build and PROTECTED/KERNEL build.
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FLAT build
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----------
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In FLAT build, a system call is just a function call into the NuttX kernel.
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.. image:: image/syscall-flat-before.png
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To get the system call events, `wrapper function option <https://sourceware.org/binutils/docs/ld/Options.html#index-_002d_002dwrap_003dsymbol>`_ of the GNU Linker is used.
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The mksyscall tool is fixed to generate the system call wrapper which call system call enter/leave hook.
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The wrapper supersedes the system call function call of the NuttX binary by passing ``--wrap`` linker option to the build system.
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The wrapper calls the system call hooks before and after calling the real system call function.
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.. image:: image/syscall-flat-after.png
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PROTECTED/KERNEL build
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----------------------
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Different to FLAT build, in PROTECTED and KERNEL build, a system call is issued by an user space is handled as the following steps.
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#. System call issued by an application code is handled by the system call proxy (automatically generated by mksyscall).
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#. System call proxy issues the supervisor call instruction to enter into the kernel space.
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#. System call handler in the kernel space calls the system call stub (automatically generated by mksyscall).
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#. System call stub calls the API implementation in the NuttX kernel.
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.. image:: image/syscall-protected-before.png
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To get the system call events, the mksyscall tool is fixed to generate the system call wrapper which supersedes the system call function call in the system call stub.
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.. image:: image/syscall-protected-after.png
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