OK

Does that mean that I cannot debug the source until after the MMU is turned on?

-----Original Message-----
From: Wolfgang Denk [mailto:wd@denx.de]
Sent: Friday, October 10, 2003 2:01 PM
To: Joao Vicente
Cc: linuxppc-embedded@lists.linuxppc.org
Subject: Re: Problem debugging ppc kernel with DDD/GDB/BDI2000 on a
custom MPC8260 board


Dear Joao,

in message [off-list ref] you wrote:

Once inside gdb, I am typing 'target remote 10.121.10.22:2001' after
which I am obtaing the following output:
0x00000000 in ?? ()

OK.

One thing I cant get my head around is that if the  system.map file
shows _start address at 0xc000000, how can the gdb relate the symbols on
vmlinux, assuming they are are expected to be at 0xc0000000?

0xC....... is a kernel virtual address which will be valid as soon as
Linux  turns  on  the  MMU  (which   it   does   very   early   durin
initialization).

I have also tried to load the symbol file at 0x00000000 with the
'add-symbol-file vmlinux 0x00000000' followed by 'target remote
10.121.10.22:2001'. Does this make any sense if the code is not
relocatable ?

No, this makes no sense.

My intention here is not to have this build to work with my board, but
to just be able to display the symbols and trace the flow of the kernel,
so that I can then start customising it for the custom hardware.

Ummm... In my experience a better approach would be to figure out the
necessary changes _before_ even attempting to boot the kernel. Inter-
preting the effects of a misconfigured kernel it not exactly easy  as
funny things might happen.

In order to customise the build for my board, what would be your
sugestion. Should I modify config.in in order to launch an independent

Yes. Create a new configuration option for your board.

config on the build, or use one of the given ones and hard code a
XXX_CONFIG specific for my board onto include/linux/autoconf.h or some

Modifying include/linux/autoconf.h makes no  sense.  This  file  gets
automagically created dureing the kernel config & build steps.

For instance, I have noticed that there is specific CONFIG_ADS8260
#ifdefs throughout the ppc arch source, but no standard configuration is
available from 'make menuconfig'. Is this because this board's port is
not complete, or should a default config be selected on menuconfig, and
the CONFIG_ADS8260 added into a top header file ?

My guess is that this port was only completed in more recent versions
of the (linuxppc_2_4_devel) kernel tree.

The u-boot README file is an excellent source of documentation for
porting the u-boot for custom boards, which has been extremelly helpful
on my exercise on porting u-boot (along with your kind guiding help).
Do you know of any similar documentation as far as customising the
kernel for a custom board ?

Except for the source code, no.

Best regards,

Wolfgang Denk

--
Software Engineering:  Embedded and Realtime Systems,  Embedded Linux
Phone: (+49)-8142-4596-87  Fax: (+49)-8142-4596-88  Email: wd@denx.de
Philosophy is a game with objectives and no rules.
Mathematics is a game with rules and no objectives.

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