kernel debugging (KGDB or JTAG)

Hi Marc,

Dne Tue, 02 Aug 2011 11:32:34 +0200 Marc Titinger [off-list ref]  
napsal(a):

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

quoted

Subject: kernel debugging (KGDB or JTAG)
To: linux-arm-kernel at lists.infradead.org
From: xhpohanka at gmail.com
Date: Tue, 2 Aug 2011 10:13:45 +0200

Dear all,

Hi Jan,

quoted

I'd like to ask if anyone has working setup for kernel debugging on arm
target. I have tried two boards (one with at91sam9g20, second with
freescale i.mx27) with Segger j-link and kgdb with similar and not very
useful results. I have Ubuntu 11.04 as development host and latest
codesourcery arm-none-(linux-gnu)eabi toolchain.

Using 2.6.39 I was able to compile the sources with KGDB enabled. I'm  
also
able to enter kdb terminal and connect with arm-none-eabi-gdb. Setting  
and
triggering breakpoints works well, but single stepping (which is  
essential
to me) does not. Here is the example

did you select "compile with debug info" in the kernel hacking menu ?

Of course :)

quoted

Breakpoint 1, 0xc00e40d4 in sys_sync () at
/home/honza/_dev/kernel/linux-2.6.39.y/fs/sync.c:190
190 }
(gdb) list
185 ret = err;
186 mutex_unlock(&mapping->host->i_mutex);
187
188 out:
189 return ret;
190 }
191 EXPORT_SYMBOL(vfs_fsync_range);
192
193 /**
194 * vfs_fsync - perform a fsync or fdatasync on a file
(gdb) s
Sending packet: $Hc148#48...Ack
Packet received: OK
Sending packet: $s#73...Ack
Packet received:
warning: Invalid remote reply:

... now gdb hangs forever

Using j-ling JTAG probe from segger I can't start debug session at all.
When JLinkGDBServer connects it resets the board and I'm not able to
resume the execution. I have found e.g. this howto

you must probably pass some option to tell the jtag interface not to  
issue the TRST signal and any init "pokes" it might do,  if you to  
attach to a running kernel instead of booting it through jtag.

I started a thread at segger support forum  
http://segger2.com/index.php?page=Thread&threadID=882, it was stated that  
there is no option to attach only, yet. On the other hand I don't  
understand why the board can't rerun from start (through u-boot etc.).  
Maybe openocd could help here, but I have not got a time to try it, yet.

regards
Jan

Cheers,
Marc.

quoted

http://www.timesys.com/embedded-linux/docs/Debug_Linux_kernel_with_a_JTAG_from_Segger
but as I said it is not working for me.

Here is the log from JLinkGDBServer

J-Link connected
Firmware: J-Link ARM V8 compiled Jul 5 2011 20:48:23
Hardware: V8.00
S/N: 58004787

J-Link found 2 JTAG devices, Total IRLen = 8
JTAG ID: 0x07926121 (ARM9)

Connected to 127.0.0.1
Reading all registers
WARNING: Failed to read cacheable memory @ address 0x00000000
Read 4 bytes @ address 0x00000000 (Data = 0x00000000)
Starting target CPU...


Any advice will be greatly appreciated...

with best regards
Jan

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