kernel debugging (KGDB or JTAG)

[Marc Titinger]

----------------------------------------
> 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, 

>
> 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 ? 

>
> 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. 


Cheers,
Marc. 


> 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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