path: root/lib
diff options
authorBernhard Kaindl <bk@suse.de>2008-01-30 13:34:11 +0100
committerIngo Molnar <mingo@elte.hu>2008-01-30 13:34:11 +0100
commitf212ec4b7b4d84290f12c9c0416cdea283bf5f40 (patch)
tree9beb7e5b87bac80410767fd3aacd93f92ecb0c04 /lib
parent6194ba6ff6ccf8d5c54c857600843c67aa82c407 (diff)
x86: early boot debugging via FireWire (ohci1394_dma=early)
This patch adds a new configuration option, which adds support for a new early_param which gets checked in arch/x86/kernel/setup_{32,64}.c:setup_arch() to decide wether OHCI-1394 FireWire controllers should be initialized and enabled for physical DMA access to allow remote debugging of early problems like issues ACPI or other subsystems which are executed very early. If the config option is not enabled, no code is changed, and if the boot paramenter is not given, no new code is executed, and independent of that, all new code is freed after boot, so the config option can be even enabled in standard, non-debug kernels. With specialized tools, it is then possible to get debugging information from machines which have no serial ports (notebooks) such as the printk buffer contents, or any data which can be referenced from global pointers, if it is stored below the 4GB limit and even memory dumps of of the physical RAM region below the 4GB limit can be taken without any cooperation from the CPU of the host, so the machine can be crashed early, it does not matter. In the extreme, even kernel debuggers can be accessed in this way. I wrote a small kgdb module and an accompanying gdb stub for FireWire which allows to gdb to talk to kgdb using remote remory reads and writes over FireWire. An version of the gdb stub fore FireWire is able to read all global data from a system which is running a a normal kernel without any kernel debugger, without any interruption or support of the system's CPU. That way, e.g. the task struct and so on can be read and even manipulated when the physical DMA access is granted. A HOWTO is included in this patch, in Documentation/debugging-via-ohci1394.txt and I've put a copy online at ftp://ftp.suse.de/private/bk/firewire/docs/debugging-via-ohci1394.txt It also has links to all the tools which are available to make use of it another copy of it is online at: ftp://ftp.suse.de/private/bk/firewire/kernel/ohci1394_dma_early-v2.diff Signed-Off-By: Bernhard Kaindl <bk@suse.de> Tested-By: Thomas Renninger <trenn@suse.de> Signed-off-by: Ingo Molnar <mingo@elte.hu> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Diffstat (limited to 'lib')
1 files changed, 28 insertions, 0 deletions
diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index aa56e631580..89f4035b526 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -586,5 +586,33 @@ config LATENCYTOP
Enable this option if you want to use the LatencyTOP tool
to find out which userspace is blocking on what kernel operations.
+ bool "Provide code for enabling DMA over FireWire early on boot"
+ depends on PCI && X86
+ help
+ If you want to debug problems which hang or crash the kernel early
+ on boot and the crashing machine has a FireWire port, you can use
+ this feature to remotely access the memory of the crashed machine
+ over FireWire. This employs remote DMA as part of the OHCI1394
+ specification which is now the standard for FireWire controllers.
+ With remote DMA, you can monitor the printk buffer remotely using
+ firescope and access all memory below 4GB using fireproxy from gdb.
+ Even controlling a kernel debugger is possible using remote DMA.
+ Usage:
+ If ohci1394_dma=early is used as boot parameter, it will initialize
+ all OHCI1394 controllers which are found in the PCI config space.
+ As all changes to the FireWire bus such as enabling and disabling
+ devices cause a bus reset and thereby disable remote DMA for all
+ devices, be sure to have the cable plugged and FireWire enabled on
+ the debugging host before booting the debug target for debugging.
+ This code (~1k) is freed after boot. By then, the firewire stack
+ in charge of the OHCI-1394 controllers should be used instead.
+ See Documentation/debugging-via-ohci1394.txt for more information.
source "samples/Kconfig"