Debugging Loadable Modules Using GDB

[Alexander Fiveg]

On Mon, Aug 30, 2010 at 05:34:01PM -0400, John Baldwin wrote:
> On Monday, August 30, 2010 4:34:04 pm Alexander Fiveg wrote:
> > On Mon, Aug 30, 2010 at 01:10:37PM -0400, John Baldwin wrote:
> >  > 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 Book is outdated?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.
> > Thanks a lot!. That is what I want to know. But I think this option is not 
> > mentioned anywhere. I could not find it in "man make make.conf" and also 
> > no mention about it in FreeBSD Developers' Handbook. 
> 
> It's a bit of a "feature" of the bsd.*.mk files that if you define
> 'DEBUG_FLAGS' it is added to CFLAGS (and CXXFLAGS) and that any resulting
> binaries are not stripped, etc.  The same trick can be used to build debug
> versions of binaries and libraries.  It probably is underdocumented.  Not
> sure make.conf(5) is the right place as the typical usage is on the command
> line, not in /etc/make.conf or /etc/src.conf.  However, I can't think of a
> better place.  Maybe src.conf(5)?

Anyway, "FreeBSD Developers' Handbook" wouldn't be wrong place for it :)

> 
> -- 
 > John Baldwin

-- 
Alexander Fiveg <pebu3op at googlemail.com>
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