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

On Tue, May 5, 2009 at 5:28 PM, Jason Wessel [off-list ref]wrote:

srikanth krishnakar wrote:

quoted

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@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@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
**********