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Hans J. Koch authored and Greg Kroah-Hartman committed Aug 5, 2010
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2 changes: 1 addition & 1 deletion [refs]
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---
refs/heads/master: c513b67e68787eceafeede32bcd0edbee45c0006
refs/heads/master: 5685ad5b29934e09dd9746f8553066f8288d4dff
71 changes: 71 additions & 0 deletions trunk/Documentation/ABI/testing/debugfs-kmemtrace
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What: /sys/kernel/debug/kmemtrace/
Date: July 2008
Contact: Eduard - Gabriel Munteanu <eduard.munteanu@linux360.ro>
Description:

In kmemtrace-enabled kernels, the following files are created:

/sys/kernel/debug/kmemtrace/
cpu<n> (0400) Per-CPU tracing data, see below. (binary)
total_overruns (0400) Total number of bytes which were dropped from
cpu<n> files because of full buffer condition,
non-binary. (text)
abi_version (0400) Kernel's kmemtrace ABI version. (text)

Each per-CPU file should be read according to the relay interface. That is,
the reader should set affinity to that specific CPU and, as currently done by
the userspace application (though there are other methods), use poll() with
an infinite timeout before every read(). Otherwise, erroneous data may be
read. The binary data has the following _core_ format:

Event ID (1 byte) Unsigned integer, one of:
0 - represents an allocation (KMEMTRACE_EVENT_ALLOC)
1 - represents a freeing of previously allocated memory
(KMEMTRACE_EVENT_FREE)
Type ID (1 byte) Unsigned integer, one of:
0 - this is a kmalloc() / kfree()
1 - this is a kmem_cache_alloc() / kmem_cache_free()
2 - this is a __get_free_pages() et al.
Event size (2 bytes) Unsigned integer representing the
size of this event. Used to extend
kmemtrace. Discard the bytes you
don't know about.
Sequence number (4 bytes) Signed integer used to reorder data
logged on SMP machines. Wraparound
must be taken into account, although
it is unlikely.
Caller address (8 bytes) Return address to the caller.
Pointer to mem (8 bytes) Pointer to target memory area. Can be
NULL, but not all such calls might be
recorded.

In case of KMEMTRACE_EVENT_ALLOC events, the next fields follow:

Requested bytes (8 bytes) Total number of requested bytes,
unsigned, must not be zero.
Allocated bytes (8 bytes) Total number of actually allocated
bytes, unsigned, must not be lower
than requested bytes.
Requested flags (4 bytes) GFP flags supplied by the caller.
Target CPU (4 bytes) Signed integer, valid for event id 1.
If equal to -1, target CPU is the same
as origin CPU, but the reverse might
not be true.

The data is made available in the same endianness the machine has.

Other event ids and type ids may be defined and added. Other fields may be
added by increasing event size, but see below for details.
Every modification to the ABI, including new id definitions, are followed
by bumping the ABI version by one.

Adding new data to the packet (features) is done at the end of the mandatory
data:
Feature size (2 byte)
Feature ID (1 byte)
Feature data (Feature size - 3 bytes)


Users:
kmemtrace-user - git://repo.or.cz/kmemtrace-user.git

108 changes: 8 additions & 100 deletions trunk/Documentation/DocBook/kgdb.tmpl
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Expand Up @@ -199,33 +199,10 @@
may be configured as a kernel built-in or a kernel loadable module.
You can only make use of <constant>kgdbwait</constant> and early
debugging if you build kgdboc into the kernel as a built-in.
<para>Optionally you can elect to activate kms (Kernel Mode
Setting) integration. When you use kms with kgdboc and you have a
video driver that has atomic mode setting hooks, it is possible to
enter the debugger on the graphics console. When the kernel
execution is resumed, the previous graphics mode will be restored.
This integration can serve as a useful tool to aid in diagnosing
crashes or doing analysis of memory with kdb while allowing the
full graphics console applications to run.
</para>
</para>
<sect2 id="kgdbocArgs">
<title>kgdboc arguments</title>
<para>Usage: <constant>kgdboc=[kms][[,]kbd][[,]serial_device][,baud]</constant></para>
<para>The order listed above must be observed if you use any of the
optional configurations together.
</para>
<para>Abbreviations:
<itemizedlist>
<listitem><para>kms = Kernel Mode Setting</para></listitem>
<listitem><para>kbd = Keyboard</para></listitem>
</itemizedlist>
</para>
<para>You can configure kgdboc to use the keyboard, and or a serial
device depending on if you are using kdb and or kgdb, in one of the
following scenarios. The order listed above must be observed if
you use any of the optional configurations together. Using kms +
only gdb is generally not a useful combination.</para>
<para>Usage: <constant>kgdboc=[kbd][[,]serial_device][,baud]</constant></para>
<sect3 id="kgdbocArgs1">
<title>Using loadable module or built-in</title>
<para>
Expand All @@ -235,7 +212,7 @@
<listitem>
<para>As a kernel loadable module:</para>
<para>Use the command: <constant>modprobe kgdboc kgdboc=&lt;tty-device&gt;,[baud]</constant></para>
<para>Here are two examples of how you might format the kgdboc
<para>Here are two examples of how you might formate the kgdboc
string. The first is for an x86 target using the first serial port.
The second example is for the ARM Versatile AB using the second
serial port.
Expand Down Expand Up @@ -263,9 +240,6 @@
</sect3>
<sect3 id="kgdbocArgs3">
<title>More examples</title>
<para>You can configure kgdboc to use the keyboard, and or a serial
device depending on if you are using kdb and or kgdb, in one of the
following scenarios.</para>
<para>You can configure kgdboc to use the keyboard, and or a serial device
depending on if you are using kdb and or kgdb, in one of the
following scenarios.
Expand All @@ -281,12 +255,6 @@
<listitem><para>kdb with a keyboard</para>
<para><constant>kgdboc=kbd</constant></para>
</listitem>
<listitem><para>kdb with kernel mode setting</para>
<para><constant>kgdboc=kms,kbd</constant></para>
</listitem>
<listitem><para>kdb with kernel mode setting and kgdb over a serial port</para>
<para><constant>kgdboc=kms,kbd,ttyS0,115200</constant></para>
</listitem>
</orderedlist>
</para>
</sect3>
Expand Down Expand Up @@ -669,8 +637,6 @@ Task Addr Pid Parent [*] cpu State Thread Command
<listitem><para>The logic to perform safe memory reads and writes to memory while using the debugger</para></listitem>
<listitem><para>A full implementation for software breakpoints unless overridden by the arch</para></listitem>
<listitem><para>The API to invoke either the kdb or kgdb frontend to the debug core.</para></listitem>
<listitem><para>The structures and callback API for atomic kernel mode setting.</para>
<para>NOTE: kgdboc is where the kms callbacks are invoked.</para></listitem>
</itemizedlist>
</para>
</listitem>
Expand Down Expand Up @@ -781,17 +747,18 @@ Task Addr Pid Parent [*] cpu State Thread Command
</sect1>
<sect1 id="kgdbocDesign">
<title>kgdboc internals</title>
<sect2>
<title>kgdboc and uarts</title>
<para>
The kgdboc driver is actually a very thin driver that relies on the
underlying low level to the hardware driver having "polling hooks"
which the to which the tty driver is attached. In the initial
implementation of kgdboc it the serial_core was changed to expose a
low level UART hook for doing polled mode reading and writing of a
single character while in an atomic context. When kgdb makes an I/O
request to the debugger, kgdboc invokes a callback in the serial
core which in turn uses the callback in the UART driver.</para>
request to the debugger, kgdboc invokes a call back in the serial
core which in turn uses the call back in the UART driver. It is
certainly possible to extend kgdboc to work with non-UART based
consoles in the future.
</para>
<para>
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>
#ifdef CONFIG_CONSOLE_POLL
Expand All @@ -805,68 +772,9 @@ Task Addr Pid Parent [*] cpu State Thread Command
that they can be called from an atomic context and have to restore
the state of the UART chip on return such that the system can return
to normal when the debugger detaches. You need to be very careful
with any kind of lock you consider, because failing here is most likely
with any kind of lock you consider, because failing here is most
going to mean pressing the reset button.
</para>
</sect2>
<sect2 id="kgdbocKbd">
<title>kgdboc and keyboards</title>
<para>The kgdboc driver contains logic to configure communications
with an attached keyboard. The keyboard infrastructure is only
compiled into the kernel when CONFIG_KDB_KEYBOARD=y is set in the
kernel configuration.</para>
<para>The core polled keyboard driver driver for PS/2 type keyboards
is in drivers/char/kdb_keyboard.c. This driver is hooked into the
debug core when kgdboc populates the callback in the array
called <constant>kdb_poll_funcs[]</constant>. The
kdb_get_kbd_char() is the top-level function which polls hardware
for single character input.
</para>
</sect2>
<sect2 id="kgdbocKms">
<title>kgdboc and kms</title>
<para>The kgdboc driver contains logic to request the graphics
display to switch to a text context when you are using
"kgdboc=kms,kbd", provided that you have a video driver which has a
frame buffer console and atomic kernel mode setting support.</para>
<para>
Every time the kernel
debugger is entered it calls kgdboc_pre_exp_handler() which in turn
calls con_debug_enter() in the virtual console layer. On resuming kernel
execution, the kernel debugger calls kgdboc_post_exp_handler() which
in turn calls con_debug_leave().</para>
<para>Any video driver that wants to be compatible with the kernel
debugger and the atomic kms callbacks must implement the
mode_set_base_atomic, fb_debug_enter and fb_debug_leave operations.
For the fb_debug_enter and fb_debug_leave the option exists to use
the generic drm fb helper functions or implement something custom for
the hardware. The following example shows the initialization of the
.mode_set_base_atomic operation in
drivers/gpu/drm/i915/intel_display.c:
<informalexample>
<programlisting>
static const struct drm_crtc_helper_funcs intel_helper_funcs = {
[...]
.mode_set_base_atomic = intel_pipe_set_base_atomic,
[...]
};
</programlisting>
</informalexample>
</para>
<para>Here is an example of how the i915 driver initializes the fb_debug_enter and fb_debug_leave functions to use the generic drm helpers in
drivers/gpu/drm/i915/intel_fb.c:
<informalexample>
<programlisting>
static struct fb_ops intelfb_ops = {
[...]
.fb_debug_enter = drm_fb_helper_debug_enter,
.fb_debug_leave = drm_fb_helper_debug_leave,
[...]
};
</programlisting>
</informalexample>
</para>
</sect2>
</sect1>
</chapter>
<chapter id="credits">
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<param name="callout.graphics">0</param>
<!-- <param name="paper.type">A4</param> -->
<param name="generate.section.toc.level">2</param>
<param name="use.id.as.filename">1</param>
</stylesheet>
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