Debugging Loadable Modules Using GDB

[John Baldwin]

On Monday, August 30, 2010 12:12:50 pm Alexander Fiveg wrote:
> On Mon, Aug 30, 2010 at 08:16:11AM -0400, John Baldwin wrote:
>  > On Friday, August 27, 2010 4:11:41 pm Alexander Fiveg wrote:
> > > Hi,
> > > from "FreeBSD Developers' Handbook, 10.7 Debugging Loadable Modules Using
> > > GDB":
> > > "...
> > > (kgdb) add-symbol-file /sys/modules/linux/linux.ko 0xc0ae22d0
> > > ...
> > > "
> > > Actually I couldn't debug my modules using .ko-file. Moreover, I've find out 
> > that .ko files do not contain sections with debugging info. With .kld-file 
> > debugging works out. Do I something incorrectly or the info in the Developers 
> > Book is outdated?
> > 
> > With newer versions of kgdb you shouldn't need to manually invoke 'add-symbol-
> > file'.  Kernel modules are treated as shared libraries and should 
> > automatically be loaded.  Try using 'info sharedlibrary' to see the list of 
> > kernel modules and if symbols for them are loaded already.
> Yes, the .ko files are loaded automatically. The problem is that they do
> not contain debugging info. I have always to load the .kld file in order to 
> debug a module:
> 
> (kgdb) f 9
> #9  0xc4dc558b in rm_8254_delayed_interrupt_per_packet () from
> /boot/kernel/if_ringmap.ko
> (kgdb) info locals
> No symbol table info available.
> 
> (kgdb) add-symbol-file /home/alexandre/p4/ringmap/current/sys/modules/ringmap/if_ringmap.kld 0xc4dafc70
> add symbol table from file "/home/alexandre/p4/ringmap/current/sys/modules/ringmap/if_ringmap.kld"
> at
> 	.text_addr = 0xc4dafc70
> (y or n) y
> Reading symbols from /home/alexandre/p4/ringmap/current/sys/modules/ringmap/if_ringmap.kld...done.
> 
> (kgdb) f 9 
> #9  0xc4dc558b in rm_8254_delayed_interrupt_per_packet ()
>     at /home/alexandre/p4/ringmap/current/sys/modules/ringmap/../../dev/e1000/ringmap_8254.c:142
> 142	co->ring->slot[slot_num].ts = co->ring->last_ts;
> 
> (kgdb) info locals
> co = (struct capt_object *) 0xc4d68380
> adapter = (struct adapter *) 0xc4e77000
> __func__ = "E\000\000�\034@\000\000\211\203�E\000\000\017\206B\022\000\000\2039\000\213A\004\017\205�\f\000\000\001��1�"
> 
> 
> Is there any way to get the all symbols and needed debug info without
> loading the .kld file ?

How are you compiling the kld?  If you are building it by hand, use
'make DEBUG_FLAGS=-g' when you build and install the kld.  That should build
with debug symbols enabled and install the ko.symbols file which kgdb will
find and use.

-- 
John Baldwin