[yocto] R: Kernel debugging over serial console?

[BITONTI Giuseppe (MM)]

Thanks Apelete for your help, but the command you suggested returns the following:

root at imx6qsabrelite:~# cat /sys/module/kgdboc/parameters/kgdboc
cat: can't open '/sys/module/kgdboc/parameters/kgdboc': No such file or directory

root at imx6qsabrelite:~# echo ttymxc1,115200 > /sys/module/kgdboc/parameters/kgdboc
-sh: can't create /sys/module/kgdboc/parameters/kgdboc: nonexistent directory

What I miss?

Giuseppe


-----Messaggio originale-----
Da: Apelete Seketeli [mailto:apelete at seketeli.net] 
Inviato: martedì 17 settembre 2013 15:15
A: BITONTI Giuseppe (MM)
Cc: yocto at yoctoproject.org
Oggetto: Re: [yocto] Kernel debugging over serial console?

Hello Giuseppe,

On 17-Sep-13, BITONTI Giuseppe (MM) wrote:
> I am trying to debug the kernel through kgdb for an imx6 sabre lite board with the following kernel built from poky 1.4:
> 
> root at imx6qsabrelite:~# uname -a
> Linux imx6qsabrelite 3.0.35-1.1.0+g2dc5560 #1 SMP PREEMPT Thu Aug 8 
> 15:15:39 CEST 2013 armv7l GNU/Linux
> 
> The system boot well but when I try to enter in debugging mode it returns:
> 
> root at imx6qsabrelite:~# echo g > /proc/sysrq-trigger SysRq : HELP : 
> loglevel(0-9) reBoot Crash terminate-all-tasks(E) 
> memory-full-oom-kill(F) kill-all-tasks(I) thaw-filesystems(J) saK 
> show-backtrace-all-active-cpus(L) show-memory-usage(M) 
> nice-all-RT-tasks(N) powerOff show-registers(P) show-all-timers(Q) 
> unRaw Sync show-task-states(T) Unmount ETM buffer dump 
> show-blocked-tasks(W) root at imx6qsabrelite:~#

I didn't dabble with OE or Yocto for a while, but from a pure Linux kernel point of view, it seems like something is amiss with your kgdb configuration.

> I have configured the kernel with the command:
> 
> bitbake -c menuconfig linux-imx
> 
> enabling:
> 
> -*- Magic SysRq key
> [*] Kernel debugging
> [*] Compile the kernel with debug info [*] KGDB: kernel debugger <*> 
> KGDB: use kgdb over the serial console
> 
> I have also edited defconfig file in fsl-community-bsp-dylan/sources/meta-fsl-arm/recipes-kernel/linux/linux-imx-3.0.35/mx6q/ adding:
> 
> CONFIG_FRAME_POINTER=y
> CONFIG_DEBUG_KERNEL=y
> CONFIG_KGDB=y
> CONFIG_DEBUG_INFO=y
> CONFIG_KGDB_SERIAL_CONSOLE=y
> CONFIG_MAGIC_SYSRQ=y
> 
> and added kernel parameter to bootargs with:
> 
> MX6QSABRELITE U-Boot > editenv mmcargs
> edit: setenv bootargs console=${console},${baudrate} root=${mmcroot} 
> kgdboc=ttymxc1,115200 MX6QSABRELITE U-Boot > saveenv Saving 
> Environment to MMC...
> Writing to MMC(0)... done
> MX6QSABRELITE U-Boot > boot

You kernel configuration looks ok, and the kgdboc parameter passed by u-boot to the kernel seems correct (at least syntactically speaking).
 
> but it still does not work.

Depending on the serial driver in use in the kernel, it sometimes happens that kgdboc is not configured despite the kgdboc parameter being passed to the kernel.
To check that kgdboc is configured like you intended, from user-sapce please try:

root at imx6qsabrelite:~# cat /sys/module/kgdboc/parameters/kgdboc

Guessing from what you wrote, it should return: ttymxc1,115200 If it doesn't, please try configuring kgdboc from user-space:

root at imx6qsabrelite:~# echo ttymxc1,115200 > /sys/module/kgdboc/parameters/kgdboc

And then:

root at imx6qsabrelite:~# echo g > /proc/sysrq-trigger

Should break the kernel and let you connect to kgdb using, for instance, a gdb client.

Hope it helps :-).

Cheers.
-- 
        Apelete