[Kgdb-bugreport] KGDBOC testing on linux-2.6.30-rc4

[srikanth krishnakar]

On Tue, May 5, 2009 at 5:28 PM, Jason Wessel <jason.wessel at windriver.com>wrote:

> srikanth krishnakar wrote:
> > Hi all,
> >
> > Target : PowerPC, Virtex-440 Generic
> > Serial port : Xilinx 16550 Uart ( depends on OF_PLATFORM)
> >
> > Further investigation of KGDBOC on PowerPC shows that kgdboc hangs at :
> >
> > In file : arch/powerpc/include/asm/kgdb.h
> >
> > *static inline void* arch_kgdb_breakpoint(*void*)
> > {
> >         *asm*(*".long 0x7d821008"*); /* *twge r2, r2 **/     * << ----
> > KGDBOC Hangs here* * << ---*
> >
> >
> > -----------------------------------------
> > Debug Log:
> >
> > root at 10.1.2.55:~# echo g >
> > /proc/sysrq-trigger
> > SysRq :
> > GDB
> >
> > 1------------------------>sysrq_handle_gdb
> >
> > Entering KGDB
> > 1-1----------------------->kgdb_breakpoint
> > 1-2----------------------->kgdb_breakpoint
> > 1-3----------------------->kgdb_breakpoint
> > 1-1----------------------->arch_kgdb_breakpoint
> >
> > ---------------------------------------------
> >
> >
> > Any comments or suggestions ????
> >
>
> I had used the 2.6.30-rc3 kernel with the PowerPC 604 system I have and
> it was working fine, but the 4xx archs are a bit different.
>
> What happens next after you execute the inline assembly is that an
> exception occurs, and that is the point that the kgdb entry will
> actually execute.  IE:
>
> arch/powerpc/kernel/traps.c
>
> program_check_exception()
>
> From there kgdb should be entered and the I/O driver gets activated.
> You could put another printk in kgdb_handle_exception() in kernel/kgdb.c
> to make sure it actually gets there.
>
> Generally when the system hangs hard on an initial entry to kgdb it
> means there is a problem with the I/O polling driver or there is
> something else eating the kgdb exception and the kgdb exception handler
> was never fired in the first place.
>
> Jason.
>

Hi Jason,

Re attempted with inserting a printk in kernel/kgdb.c
kgdb_handle_exception() function but seems the kgdb exception has never
occurred !!

------------------
Debug Log:

root at 10.1.2.55:~# echo g > /proc/sysrq-trigger
SysRq : GDB
1------------------------>sysrq_handle_gdb
Entering KGDB
1-1----------------------->kgdb_breakpoint
1-2----------------------->kgdb_breakpoint
1-3----------------------->kgdb_breakpoint
1-1----------------------->arch_kgdb_breakpoint


(gdb) target remote /dev/ttyS0
Remote debugging using /dev/ttyS0
Ignoring packet error, continuing...
warning: unrecognized item "timeout" in "qSupported" response
Ignoring packet error, continuing...
Ignoring packet error, continuing...

-------------------

Inserted printk's in kernel kgdb.c  :
int
kgdb_handle_exception(int evector, int signo, int ecode, struct pt_regs
*regs)
{

printk("1------------------------>%s\n",__FUNCTION__);
        if (kgdb_reenter_check(ks)) {
-----------------------------

*Does the PowerPC uses PowerPC64 hooks ??*

as seen below from arch/powerpc/kernel/kgdb.c

/* KGDB functions to use existing PowerPC64 hooks. */
static int kgdb_debugger(struct pt_regs *regs)
{
        printk("1------------------------>%s\n",__FUNCTION__);
        return *kgdb_handle_exception*(0, computeSignal(TRAP(regs)), 0,
regs);

-------------------------------


Thanks For your co-operation, patience and help.


Regards
Srikanth
**********
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