kgdb: documentation fixes
Minor cleanups to kgdb docs. Signed-off-by: Jason Wessel <jason.wessel@windriver.com> Signed-off-by: Ingo Molnar <mingo@elte.hu>
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Jason Wessel
Ingo Molnar
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@ -152,9 +152,10 @@
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<para>
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The kgdboc driver was originally an abbreviation meant to stand for
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"kgdb over console". Kgdboc is designed to work with a single
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serial port as example, and it was meant to cover the circumstance
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serial port. It was meant to cover the circumstance
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where you wanted to use a serial console as your primary console as
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well as using it to perform kernel debugging.
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well as using it to perform kernel debugging. Of course you can
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also use kgdboc without assigning a console to the same port.
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</para>
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<sect2 id="UsingKgdboc">
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<title>Using kgdboc</title>
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@ -195,37 +196,6 @@
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unmodified gdb to do the debugging.
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</para>
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</sect2>
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<sect2 id="kgdbocDesign">
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<title>kgdboc internals</title>
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<para>
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The kgdboc driver is actually a very thin driver that relies on the
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underlying low level to the hardware driver having "polling hooks"
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which the to which the tty driver is attached. In the initial
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implementation of kgdboc it the serial_core was changed to expose a
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low level uart hook for doing polled mode reading and writing of a
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single character while in an atomic context. When kgdb makes an I/O
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request to the debugger, kgdboc invokes a call back in the serial
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core which in turn uses the call back in the uart driver. It is
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certainly possible to extend kgdboc to work with non-uart based
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consoles in the future.
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</para>
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<para>
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When using kgdboc with a uart, the uart driver must implement two callbacks in the <constant>struct uart_ops</constant>. Example from drivers/8250.c:<programlisting>
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#ifdef CONFIG_CONSOLE_POLL
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.poll_get_char = serial8250_get_poll_char,
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.poll_put_char = serial8250_put_poll_char,
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#endif
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</programlisting>
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Any implementation specifics around creating a polling driver use the
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<constant>#ifdef CONFIG_CONSOLE_POLL</constant>, as shown above.
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Keep in mind that polling hooks have to be implemented in such a way
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that they can be called from an atomic context and have to restore
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the state of the uart chip on return such that the system can return
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to normal when the debugger detaches. You need to be very careful
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with any kind of lock you consider, because failing here is most
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going to mean pressing the reset button.
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</para>
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</sect2>
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</sect1>
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<sect1 id="kgdbcon">
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<title>Kernel parameter: kgdbcon</title>
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@ -327,6 +297,8 @@
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</para>
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</chapter>
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<chapter id="CommonBackEndReq">
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<title>KGDB Internals</title>
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<sect1 id="kgdbArchitecture">
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<title>Architecture Specifics</title>
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<para>
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Kgdb is organized into three basic components:
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@ -365,18 +337,23 @@
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</listitem>
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<listitem><para>kgdb I/O driver</para>
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<para>
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Each kgdb I/O driver has to provide an configuration
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initialization, and cleanup handler for when it
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unloads/unconfigures. Any given kgdb I/O driver has to operate
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very closely with the hardware and must do it in such a way that
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does not enable interrupts or change other parts of the system
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context without completely restoring them. Every kgdb I/O
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driver must provide a read and write character interface. The
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kgdb core will repeatedly "poll" a kgdb I/O driver for characters
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when it needs input. The I/O driver is expected to return
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immediately if there is no data available. Doing so allows for
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the future possibility to touch watch dog hardware in such a way
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as to have a target system not reset when these are enabled.
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Each kgdb I/O driver has to provide an implemenation for the following:
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<itemizedlist>
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<listitem><para>configuration via builtin or module</para></listitem>
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<listitem><para>dynamic configuration and kgdb hook registration calls</para></listitem>
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<listitem><para>read and write character interface</para></listitem>
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<listitem><para>A cleanup handler for unconfiguring from the kgdb core</para></listitem>
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<listitem><para>(optional) Early debug methodology</para></listitem>
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</itemizedlist>
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Any given kgdb I/O driver has to operate very closely with the
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hardware and must do it in such a way that does not enable
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interrupts or change other parts of the system context without
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completely restoring them. The kgdb core will repeatedly "poll"
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a kgdb I/O driver for characters when it needs input. The I/O
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driver is expected to return immediately if there is no data
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available. Doing so allows for the future possibility to touch
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watch dog hardware in such a way as to have a target system not
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reset when these are enabled.
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</para>
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</listitem>
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</orderedlist>
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@ -419,6 +396,38 @@
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does not need to provide a specific implementation.
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</para>
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!Iinclude/linux/kgdb.h
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</sect1>
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<sect1 id="kgdbocDesign">
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<title>kgdboc internals</title>
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<para>
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The kgdboc driver is actually a very thin driver that relies on the
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underlying low level to the hardware driver having "polling hooks"
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which the to which the tty driver is attached. In the initial
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implementation of kgdboc it the serial_core was changed to expose a
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low level uart hook for doing polled mode reading and writing of a
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single character while in an atomic context. When kgdb makes an I/O
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request to the debugger, kgdboc invokes a call back in the serial
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core which in turn uses the call back in the uart driver. It is
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certainly possible to extend kgdboc to work with non-uart based
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consoles in the future.
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</para>
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<para>
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When using kgdboc with a uart, the uart driver must implement two callbacks in the <constant>struct uart_ops</constant>. Example from drivers/8250.c:<programlisting>
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#ifdef CONFIG_CONSOLE_POLL
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.poll_get_char = serial8250_get_poll_char,
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.poll_put_char = serial8250_put_poll_char,
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#endif
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</programlisting>
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Any implementation specifics around creating a polling driver use the
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<constant>#ifdef CONFIG_CONSOLE_POLL</constant>, as shown above.
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Keep in mind that polling hooks have to be implemented in such a way
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that they can be called from an atomic context and have to restore
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the state of the uart chip on return such that the system can return
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to normal when the debugger detaches. You need to be very careful
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with any kind of lock you consider, because failing here is most
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going to mean pressing the reset button.
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</para>
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</sect1>
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</chapter>
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<chapter id="credits">
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<title>Credits</title>
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@ -427,8 +436,11 @@
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<orderedlist>
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<listitem><para>Amit Kale<email>amitkale@linsyssoft.com</email></para></listitem>
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<listitem><para>Tom Rini<email>trini@kernel.crashing.org</email></para></listitem>
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<listitem><para>Jason Wessel<email>jason.wessel@windriver.com</email></para></listitem>
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</orderedlist>
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In March 2008 this document was completely rewritten by:
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<itemizedlist>
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<listitem><para>Jason Wessel<email>jason.wessel@windriver.com</email></para></listitem>
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</itemizedlist>
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</para>
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</chapter>
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</book>
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