Embedded symbolic information is always the best source, especially for
types.
But before going completely primitive and scanning through hexadecimal
dumps, you might want to consider using the C interpreter (sial) to
define you types and to access and print your data.
As long as you have a start address for your data (maybe from the
associated kernel module entry, or some print out at the console) and
are respecting the -D definitions that could impact the type definition
itself, you should be able to define (i.e. cut&paste) types and walk the
driver structures even in cases where symbolic information is completely
missing.
The interpreter has a couple of built-in primitives that can print types
and typed values (something like print(typed value|type)) if I remember
correctly. Somewhat akin to a pretty-print output.
-Luc
On Fri, 2008-08-08 at 09:32 -0400, Dave Anderson wrote:
> Durga Prasad wrote:
> > Hi,
> >
> > [1]:
> > I need to debug a kernel module (a device driver).
> > I added the desired module to crash using mod -S <path to module>. The
> > driver is compiled with -g option.
> > I could not see the structures defined within the module.
> >
> > Am I missing something?
>
> Accessing data in kernel modules can be spotty at best,
> but the embedded gdb module should typically be able
> to pick up structure definitions in modules.
>
> For example, these two structures are defined in ./fs/ext3/xattr.c
> like so:
>
> struct ext3_xattr_info {
> int name_index;
> const char *name;
> const void *value;
> size_t value_len;
> };
>
> struct ext3_xattr_search {
> struct ext3_xattr_entry *first;
> void *base;
> void *end;
> struct ext3_xattr_entry *here;
> int not_found;
> };
>
> Without the ext3 module debuginfo, crash (gdb) doesn't know what
> they are:
>
> # crash -s
> crash> struct ext3_xattr_search
> struct: invalid data structure reference: ext3_xattr_search
> crash> struct ext3_xattr_info
> struct: invalid data structure reference: ext3_xattr_info
> crash>
>
> Until after adding the module debuginfo data:
>
> crash> mod -s ext3
> MODULE NAME SIZE OBJECT FILE
> ffffffff8806be00 ext3 168017 /lib/modules/2.6.18-102.el5.perfmon2/kernel/fs/ext3/ext3.ko
> crash> struct ext3_xattr_search
> struct ext3_xattr_search {
> struct ext3_xattr_entry *first;
> void *base;
> void *end;
> struct ext3_xattr_entry *here;
> int not_found;
> }
> SIZE: 40
> crash> struct ext3_xattr_info
> struct ext3_xattr_info {
> int name_index;
> const char *name;
> const void *value;
> size_t value_len;
> }
> SIZE: 32
> crash>
>
> Then you may be able to "p" individual instances of the structures
> if there are symbolic/static declaration of them. Otherwise you
> can always cast the address of the structure to the structure type,
> as in:
>
> crash> struct ext3_xattr_info <address>
>
> If you cannot get the structure declaration after using "mod -[sS]",
> then you'll have to get primitive, and just dump the data at the
> relevant address with "rd".
>
> >
> > System info:
> > KERNEL: vmlinux.sles10sp2.smp.x86_64
> > DUMPFILE: 2008-08-08-18:57/vmcore
> > CPUS: 4
> >
> > RELEASE: 2.6.16.60-0.21-smp
> > VERSION: #1 SMP Tue May 6 12:41:02 UTC 2008
> > MACHINE: x86_64 (1995 Mhz)
> > MEMORY: 3.9 GB
> >
> >
> >
> > [2]:
> > I could get into live kernel debugging using crash on RHEL 5 after
> > installing relevant kernel-debug packages. How do I do the same on SLES 10?
> > As of now, I have been compiling the kernel with CONFIG_DEBUG_INFO set.
> > I can use the resulting vmlinux for post crash analysis, but not for
> > live analysis. Any light on how to accomplish this would be appreciated.
>
> For SLES I'm guessing that you could use the post-built (CONFIG_DEBUG_INFO) kernel,
> but also add the System.map file of the live kernel to the command line, as in:
>
> $ crash /boot/System.map vmlinux-post-built-with-debuginfo
>
> Crash will use the debuginfo data from the vmlinux file, but then go in
> and back-patch all the vmlinux file's minimal_symbols with the correct
> symbol values from the System.map file.
>
> But Bernhard Walle (bwalle@xxxxxxx) can answer that part of your question.
> He's active on this list, but I've added him to the cc: list to make
> sure he sees this.
>
> Dave Anderson
>
>
> >
> > Thanks
> > Durga Prasad
> >
>
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>
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