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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 /arch
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 'arch')
-rw-r--r--arch/x86/kernel/setup_32.c11
-rw-r--r--arch/x86/kernel/setup_64.c11
2 files changed, 22 insertions, 0 deletions
diff --git a/arch/x86/kernel/setup_32.c b/arch/x86/kernel/setup_32.c
index 9c0ef4945a58..62adc5f20be5 100644
--- a/arch/x86/kernel/setup_32.c
+++ b/arch/x86/kernel/setup_32.c
@@ -45,6 +45,7 @@
#include <linux/dmi.h>
#include <linux/pfn.h>
#include <linux/pci.h>
+#include <linux/init_ohci1394_dma.h>
#include <video/edid.h>
@@ -787,6 +788,16 @@ void __init setup_arch(char **cmdline_p)
smp_alloc_memory(); /* AP processor realmode stacks in low memory*/
#endif
paging_init();
+
+ /*
+ * NOTE: On x86-32, only from this point on, fixmaps are ready for use.
+ */
+
+#ifdef CONFIG_PROVIDE_OHCI1394_DMA_INIT
+ if (init_ohci1394_dma_early)
+ init_ohci1394_dma_on_all_controllers();
+#endif
+
remapped_pgdat_init();
sparse_init();
zone_sizes_init();
diff --git a/arch/x86/kernel/setup_64.c b/arch/x86/kernel/setup_64.c
index 697533e86822..77fb87bf6e5a 100644
--- a/arch/x86/kernel/setup_64.c
+++ b/arch/x86/kernel/setup_64.c
@@ -41,6 +41,7 @@
#include <linux/dma-mapping.h>
#include <linux/ctype.h>
#include <linux/uaccess.h>
+#include <linux/init_ohci1394_dma.h>
#include <asm/mtrr.h>
#include <asm/uaccess.h>
@@ -253,6 +254,11 @@ void __attribute__((weak)) __init memory_setup(void)
machine_specific_memory_setup();
}
+/*
+ * setup_arch - architecture-specific boot-time initializations
+ *
+ * Note: On x86_64, fixmaps are ready for use even before this is called.
+ */
void __init setup_arch(char **cmdline_p)
{
unsigned i;
@@ -302,6 +308,11 @@ void __init setup_arch(char **cmdline_p)
parse_early_param();
+#ifdef CONFIG_PROVIDE_OHCI1394_DMA_INIT
+ if (init_ohci1394_dma_early)
+ init_ohci1394_dma_on_all_controllers();
+#endif
+
finish_e820_parsing();
early_gart_iommu_check();