Kernel 2.4.20: kgdb problem

Hello,

I experienced many problems trying to use ans set kgdb/gdb with a ppc
kernel 2.4.20. (Note: No problem with kgdb & kernel version 2.4.17)

I used gcc 3.2.1 to compile the kernel and gdb 5.2.1 as remote debugger.

I enabled kgdb feature and added "-g -ggdb -O" compile options running
make nenuconfig

 Problem: I first tried to compile kernel with "-fno-omit-frame-pointer"
but the compiled kernel was hanging somewhere in network init. I did not
have this problem with 2.4.17 version.

 Question-1: Is the frames pointer in a ppc kernel really mandatory to
allow debugging (as for i386 platform) ?

Problem: I did not succeed to disable optimization (-O0). In this case
the linker complains about unreferrenced inline functions.

Question-2: Does it exist a way to compile a ppc kernel without
optimization ?

Once the kernel is compiled with kgdb, I am able to establish a
connection with gdb, but the behavior of debugging operations (step one
instruction, continue up to <addr> ...) is really erratic.

I set to 1 the kdebug static var in pcc-stuc.c to enable tracing of data
exchanged between kgdb and gdb. I saw that after a step instruction the
kernel could completely loose its debug capabilities (no more signal are
driven to ppc_stub.c/handle_exception()).

It seems that the Debug infrastructure has been modified in 2.4.20
kernel. The dbcr0 debug register is now maintenained in "thread_struct"
structure instead of in "pt_regs" struct. Question-3: Is this change
sufficient to explain the problems I experienced (context switching
problem ?). If yes does it exist a patch to fix it ?

Thanks by advance

MACCOTTA Frédéric
Dept 0899    -    Location  :  B3-1E-214
IBM FRANCE    -    06610 LA GAUDE
Phone  :  04.92.11.47.22
E-Mail  :  frederic.maccotta@fr.ibm.com

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On Thu, Aug 14, 2003 at 09:34:30AM +0200, Frederic Maccotta wrote:

I experienced many problems trying to use ans set kgdb/gdb with a ppc
kernel 2.4.20. (Note: No problem with kgdb & kernel version 2.4.17)

I used gcc 3.2.1 to compile the kernel and gdb 5.2.1 as remote debugger.

I enabled kgdb feature and added "-g -ggdb -O" compile options running
make nenuconfig

You don't need to add -O.

 Problem: I first tried to compile kernel with "-fno-omit-frame-pointer"
but the compiled kernel was hanging somewhere in network init. I did not
have this problem with 2.4.17 version.

 Question-1: Is the frames pointer in a ppc kernel really mandatory to
allow debugging (as for i386 platform) ?

You do not need to change this setting to get KGDB to work on PPC.

Problem: I did not succeed to disable optimization (-O0). In this case
the linker complains about unreferrenced inline functions.

Question-2: Does it exist a way to compile a ppc kernel without
optimization ?

No.  This is probably FAQ'ed somewhere, and google can explain all of
the reasons why the linux kernel MUST be compiled with some level of
optimization.

Once the kernel is compiled with kgdb, I am able to establish a
connection with gdb, but the behavior of debugging operations (step one
instruction, continue up to <addr> ...) is really erratic.

What board are you trying to use KGDB with?

--
Tom Rini
http://gate.crashing.org/~trini/

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