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<html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=ANSI_X3.4-1968" /><title>Chapter 6. KGDB Internals</title><meta name="generator" content="DocBook XSL Stylesheets V1.75.2" /><link rel="home" href="index.html" title="Using kgdb and the kgdb Internals" /><link rel="up" href="index.html" title="Using kgdb and the kgdb Internals" /><link rel="prev" href="ch05.html" title="Chapter 5. kgdb Test Suite" /><link rel="next" href="re01.html" title="kgdb_skipexception" /></head><body><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">Chapter 6. KGDB Internals</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="ch05.html">Prev</a> </td><th width="60%" align="center"> </th><td width="20%" align="right"> <a accesskey="n" href="re01.html">Next</a></td></tr></table><hr /></div><div class="chapter" title="Chapter 6. KGDB Internals"><div class="titlepage"><div><div><h2 class="title"><a id="CommonBackEndReq"></a>Chapter 6. KGDB Internals</h2></div></div></div><div class="toc"><p><b>Table of Contents</b></p><dl><dt><span class="sect1"><a href="ch06.html#kgdbArchitecture">Architecture Specifics</a></span></dt><dt><span class="sect1"><a href="ch06s02.html">kgdboc internals</a></span></dt></dl></div><div class="sect1" title="Architecture Specifics"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="kgdbArchitecture"></a>Architecture Specifics</h2></div></div></div><div class="toc"><dl><dt><span class="refentrytitle"><a href="re01.html"><span>kgdb_skipexception</span></a></span><span class="refpurpose"> —
(optional) exit kgdb_handle_exception early
</span></dt><dt><span class="refentrytitle"><a href="re02.html"><span>kgdb_post_primary_code</span></a></span><span class="refpurpose"> —
(optional) Save error vector/code numbers.
</span></dt><dt><span class="refentrytitle"><a href="re03.html"><span>kgdb_disable_hw_debug</span></a></span><span class="refpurpose"> —
(optional) Disable hardware debugging hook
</span></dt><dt><span class="refentrytitle"><a href="re04.html"><span>kgdb_breakpoint</span></a></span><span class="refpurpose"> —
compiled in breakpoint
</span></dt><dt><span class="refentrytitle"><a href="re05.html"><span>kgdb_arch_init</span></a></span><span class="refpurpose"> —
Perform any architecture specific initalization.
</span></dt><dt><span class="refentrytitle"><a href="re06.html"><span>kgdb_arch_exit</span></a></span><span class="refpurpose"> —
Perform any architecture specific uninitalization.
</span></dt><dt><span class="refentrytitle"><a href="re07.html"><span>pt_regs_to_gdb_regs</span></a></span><span class="refpurpose"> —
Convert ptrace regs to GDB regs
</span></dt><dt><span class="refentrytitle"><a href="re08.html"><span>sleeping_thread_to_gdb_regs</span></a></span><span class="refpurpose"> —
Convert ptrace regs to GDB regs
</span></dt><dt><span class="refentrytitle"><a href="re09.html"><span>gdb_regs_to_pt_regs</span></a></span><span class="refpurpose"> —
Convert GDB regs to ptrace regs.
</span></dt><dt><span class="refentrytitle"><a href="re10.html"><span>kgdb_arch_handle_exception</span></a></span><span class="refpurpose"> —
Handle architecture specific GDB packets.
</span></dt><dt><span class="refentrytitle"><a href="re11.html"><span>kgdb_roundup_cpus</span></a></span><span class="refpurpose"> —
Get other CPUs into a holding pattern
</span></dt><dt><span class="refentrytitle"><a href="re12.html"><span>struct kgdb_arch</span></a></span><span class="refpurpose"> —
Describe architecture specific values.
</span></dt><dt><span class="refentrytitle"><a href="re13.html"><span>struct kgdb_io</span></a></span><span class="refpurpose"> —
Describe the interface for an I/O driver to talk with KGDB.
</span></dt></dl></div><p>
Kgdb is organized into three basic components:
</p><div class="orderedlist"><ol class="orderedlist" type="1"><li class="listitem"><p>kgdb core</p><p>
The kgdb core is found in kernel/kgdb.c. It contains:
</p><div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem"><p>All the logic to implement the gdb serial protocol</p></li><li class="listitem"><p>A generic OS exception handler which includes sync'ing the processors into a stopped state on an multi cpu system.</p></li><li class="listitem"><p>The API to talk to the kgdb I/O drivers</p></li><li class="listitem"><p>The API to make calls to the arch specific kgdb implementation</p></li><li class="listitem"><p>The logic to perform safe memory reads and writes to memory while using the debugger</p></li><li class="listitem"><p>A full implementation for software breakpoints unless overridden by the arch</p></li></ul></div><p>
</p></li><li class="listitem"><p>kgdb arch specific implementation</p><p>
This implementation is generally found in arch/*/kernel/kgdb.c.
As an example, arch/x86/kernel/kgdb.c contains the specifics to
implement HW breakpoint as well as the initialization to
dynamically register and unregister for the trap handlers on
this architecture. The arch specific portion implements:
</p><div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem"><p>contains an arch specific trap catcher which
invokes kgdb_handle_exception() to start kgdb about doing its
work</p></li><li class="listitem"><p>translation to and from gdb specific packet format to pt_regs</p></li><li class="listitem"><p>Registration and unregistration of architecture specific trap hooks</p></li><li class="listitem"><p>Any special exception handling and cleanup</p></li><li class="listitem"><p>NMI exception handling and cleanup</p></li><li class="listitem"><p>(optional)HW breakpoints</p></li></ul></div><p>
</p></li><li class="listitem"><p>kgdb I/O driver</p><p>
Each kgdb I/O driver has to provide an implemenation for the following:
</p><div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem"><p>configuration via builtin or module</p></li><li class="listitem"><p>dynamic configuration and kgdb hook registration calls</p></li><li class="listitem"><p>read and write character interface</p></li><li class="listitem"><p>A cleanup handler for unconfiguring from the kgdb core</p></li><li class="listitem"><p>(optional) Early debug methodology</p></li></ul></div><p>
Any given kgdb I/O driver has to operate very closely with the
hardware and must do it in such a way that does not enable
interrupts or change other parts of the system context without
completely restoring them. The kgdb core will repeatedly "poll"
a kgdb I/O driver for characters when it needs input. The I/O
driver is expected to return immediately if there is no data
available. Doing so allows for the future possibility to touch
watch dog hardware in such a way as to have a target system not
reset when these are enabled.
</p></li></ol></div><p>
</p><p>
If you are intent on adding kgdb architecture specific support
for a new architecture, the architecture should define
<code class="constant">HAVE_ARCH_KGDB</code> in the architecture specific
Kconfig file. This will enable kgdb for the architecture, and
at that point you must create an architecture specific kgdb
implementation.
</p><p>
There are a few flags which must be set on every architecture in
their <asm/kgdb.h> file. These are:
</p><div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem"><p>
NUMREGBYTES: The size in bytes of all of the registers, so
that we can ensure they will all fit into a packet.
</p><p>
BUFMAX: The size in bytes of the buffer GDB will read into.
This must be larger than NUMREGBYTES.
</p><p>
CACHE_FLUSH_IS_SAFE: Set to 1 if it is always safe to call
flush_cache_range or flush_icache_range. On some architectures,
these functions may not be safe to call on SMP since we keep other
CPUs in a holding pattern.
</p></li></ul></div><p>
</p><p>
There are also the following functions for the common backend,
found in kernel/kgdb.c, that must be supplied by the
architecture-specific backend unless marked as (optional), in
which case a default function maybe used if the architecture
does not need to provide a specific implementation.
</p></div></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="ch05.html">Prev</a> </td><td width="20%" align="center"> </td><td width="40%" align="right"> <a accesskey="n" href="re01.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">Chapter 5. kgdb Test Suite </td><td width="20%" align="center"><a accesskey="h" href="index.html">Home</a></td><td width="40%" align="right" valign="top"> <span>kgdb_skipexception</span></td></tr></table></div></body></html>
