using openocd + gdb to debug linux kernel on arm926ejs

DISCUSSION f. achkar 6 participants 10 messages May 26, 2010 – Jul 23, 2010

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f. achkar

author

2010-05-26 19:12 UTC #0 lore raw

hi,
This is my second posting (I'm not sure the first one passed the filter) sorry for that ...

I'm newbie and have a s3c2450 based board (arm926ejs), I have a working compressed kernel image
zImage, this image boots properly via u-boot-1.1.6, however I simply
failed to debug remotely the vmlinux (root directory of linux source tree) via openocd-0.4.0 with a j-link segger. is there a good reference on how to properly debug the linux kernel via openocd/gdb for an arm target on a linux hot machine?

details:
1. let u-boot start the board;
2. I get the u-boot command prompt:

# bdinfo
      arch_number = 0x00000648
      env_t       = 0x00000000
      boot_params = 0x30000100
      DRAM bank   = 0x00000000
      -> start    = 0x30000000
      -> size     = 0x04000000
      DRAM bank   = 0x00000001
      -> start    = 0x38000000
      -> size     = 0x04000000
      ethaddr     = 00:40:5C:26:0A:5B
      ip_addr     = 192.168.3.5
      baudrate    = 115200 bps

3. halt the target via openocd/telnet;
4. cd to root directory of linux source code and issue:
gdb vmlinux
GNU gdb (GDB) 6.8.50.20090417
Copyright (C) 2009 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later
<http://gnu.org/licenses/gpl.html>
This is free software: you are free to change and redistribute it. There is NO WARRANTY, to the extent permitted by law. Type "show copying" and "show warranty" for details.
This GDB was configured as "--host=i686-pc-linux-gnu --target=arm-none-linux-gnueabi".
For bug reporting instructions, please see:
<http://www.gnu.org/software/gdb/bugs/>...
(gdb)

5.
(gdb) target remote localhost:3333
Remote debugging using localhost:3333
0xc3e01874 in ?? ()
0xc3e01874: ldr r3, [r0, #16]
(gdb)

6.
(gdb) set remote hardware-breakpoint-limit 2
(gdb) set remote hardware-watchpoint-limit 2

7.
(gdb) load
Loading section .init, size 0x7b000 lma 0xc0008000 Loading section .text, size 0x2bb618 lma 0xc0083000 Loading section __ksymtab, size 0x4a58 lma 0xc033f000 Loading section __ksymtab_gpl, size 0x1360 lma 0xc0343a58 Loading section __ksymtab_gpl_future, size 0x18 lma 0xc0344db8 Loading section __ksymtab_strings, size 0xcab7 lma 0xc0344dd0 Loading section __param, size 0x654 lma 0xc0351888 Loading section .data, size 0x21538 lma 0xc0352000 Start address 0xc0008000, load size 3582507
Transfer rate: 35 KB/sec, 15922 bytes/write.
(gdb)

8. if I do continue (gdb) c, then I don't see any output on the serial console (as normally do during zImage booting process!)

where I'm messing up?

thanks,
ferar

Steve Chen

2010-05-26 19:41 UTC #1 lore raw

Quoted 7 lines · f. achkar

hi,
This is my second posting (I'm not sure the first one passed the filter) sorry for that ...
I'm newbie and have a s3c2450 based board (arm926ejs), I have a working compressed kernel image
zImage, this image boots properly via u-boot-1.1.6, however I simply
failed to debug remotely the vmlinux (root directory of linux source tree) via openocd-0.4.0 with a j-link segger. is there a good reference on how to properly debug the linux kernel via openocd/gdb for an arm target on a linux hot machine?

Actually, Nicolas Pitre posted an response in your first try. In summary, use uImage for uboot. vmlinux won't work.

Regards,

Steve

Kees Jongenburger

2010-05-26 19:46 UTC #8 lore raw

In reply to f. achkar

Hello Ferar,

Quoted 4 lines · f. achkar

I'm newbie and have a s3c2450 based board (arm926ejs), I have a working compressed kernel image
zImage, this image boots properly via u-boot-1.1.6, however I simply
failed to debug remotely the vmlinux (root directory of linux source tree) via openocd-0.4.0 with a j-link segger. is there a good reference on how to properly debug the linux kernel via openocd/gdb for an arm target on a linux hot machine?

Did you read
http://elinux.org/DebuggingTheLinuxKernelUsingGdb ?

Quoted 6 lines

details:
1. let u-boot start the board;
2. I get the u-boot command prompt:
3. halt the target via openocd/telnet;

If you plan on replacing the kernel using gdb you need really to stop at a known location
The moment you halt the target needs to be after memory initialization and prior to the kernel being loaded

Quoted 15 lines

4. cd to root directory of linux source code and issue:
gdb vmlinux
GNU gdb (GDB) 6.8.50.20090417
Copyright (C) 2009 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later
<http://gnu.org/licenses/gpl.html>
This is free software: you are free to change and redistribute it. There is NO WARRANTY, to the extent permitted by law. ?Type "show copying" and "show warranty" for details.
This GDB was configured as "--host=i686-pc-linux-gnu --target=arm-none-linux-gnueabi".
For bug reporting instructions, please see:
<http://www.gnu.org/software/gdb/bugs/>...
(gdb)

Quoted 6 lines

5.
(gdb) target remote localhost:3333
Remote debugging using localhost:3333
0xc3e01874 in ?? ()
0xc3e01874: ? ?ldr ? ?r3, [r0, #16]
(gdb)

Is this kernel code?

Quoted 4 lines

8. if I do continue (gdb) c, then I don't see any output on the serial console (as normally do during zImage booting process!)
where I'm messing up?

First try just booting and connecting to the target afterwards. All you really need is a vmlinuz so don't load the kernel over JTAG

Hope this helps

Greetings

f. achkar

author

2010-05-26 19:51 UTC #2 lore raw

In reply to Steve Chen

Quoted 10 lines · Steve Chen

Quoted 8 lines · f. achkar
hi,
This is my second posting (I'm not sure the first one passed the filter) sorry for that ...
I'm newbie and have a s3c2450 based board (arm926ejs), I have a working compressed kernel image
zImage, this image boots properly via u-boot-1.1.6, however I simply
failed to debug remotely the vmlinux (root directory of linux source tree) via openocd-0.4.0 with a j-link segger. is there a good reference on how to properly debug the linux kernel via openocd/gdb for an arm target on a linux hot machine?

Quoted 7 lines

Actually, Nicolas Pitre posted an response in your first try. In summary, use uImage for uboot. vmlinux won't work.
Regards,
Steve

Steve,
thanks, I'm not sure I got what you mean! if I do the following:
gdb arch/arm/boot/uImage
GNU gdb (GDB) 6.8.50.20090417
...
"/home/ferar/DW-SB02-linux-final/arch/arm/boot/uImage": not in executable format: File format not recognized
(gdb) target remote localhost:3333
Remote debugging using localhost:3333
0xc0008164 in ?? ()
0xc0008164: b 0xc0008160
(gdb) set remote hardware-breakpoint-limit 2
(gdb) set remote hardware-watchpoint-limit 2
(gdb) load
No executable file specified.
Use the "file" or "exec-file" command.

Note it is not executable format, I need to load and debug the kernel not just boot (I don't have booting issues) I'm having trouble trying to debug the kernel via jtag (openocd) gdb as outlined in the detail part of my previous post! I wonder if you people got that portion of the post? thanks,
ferar

Steve Chen

2010-05-26 20:11 UTC #3 lore raw

Quoted 35 lines · f. achkar

Quoted 10 lines · Steve Chen
Quoted 8 lines · f. achkar
hi,
This is my second posting (I'm not sure the first one passed the filter) sorry for that ...
I'm newbie and have a s3c2450 based board (arm926ejs), I have a working compressed kernel image
zImage, this image boots properly via u-boot-1.1.6, however I simply
failed to debug remotely the vmlinux (root directory of linux source tree) via openocd-0.4.0 with a j-link segger. is there a good reference on how to properly debug the linux kernel via openocd/gdb for an arm target on a linux hot machine?
Quoted 7 lines
Actually, Nicolas Pitre posted an response in your first try. ?In summary, use uImage for uboot. ?vmlinux won't work.
Regards,
Steve
Steve,
thanks, ?I'm not sure I got what you mean! ?if I do the following:
gdb arch/arm/boot/uImage
GNU gdb (GDB) 6.8.50.20090417
...
"/home/ferar/DW-SB02-linux-final/arch/arm/boot/uImage": not in executable format: File format not recognized
(gdb) target remote localhost:3333
Remote debugging using localhost:3333
0xc0008164 in ?? ()
0xc0008164: ? ?b ? ?0xc0008160
(gdb) set remote hardware-breakpoint-limit 2
(gdb) set remote hardware-watchpoint-limit 2
(gdb) load
No executable file specified.
Use the "file" or "exec-file" command.

Quoted 7 lines

Note it is not executable format, I need to load and debug the kernel not just boot (I don't have booting issues) I'm having trouble trying to debug the kernel via jtag (openocd) ?gdb as outlined in the detail part of my previous post! I wonder if you people got that portion of the post? thanks,
ferar

I have never used gdb to debug the kernel, so I'm not qualify to answer your questions. In general, if you need to use gdb (actually more accurately kgdb), you need to something like

1.  Enable kgdb in the kernel config.
2.  Boot your kernel as usual.
3.  run cross-gdb on your host machine.
4.  Do remote debugging in gdb from your host via either serial or

Ethernet depends on how you have it configured.

Regards,

Steve

f. achkar

author

2010-05-26 20:25 UTC #9 lore raw

In reply to Kees Jongenburger

Quoted 4 lines · Kees Jongenburger

Hello Ferar,
On Wed, May 26, 2010 at 9:12 PM, f. achkar <[email protected]> wrote:

Quoted 8 lines

Quoted 5 lines
I'm newbie and have a s3c2450 based board (arm926ejs), I have a working compressed kernel image
zImage, this image boots properly via u-boot-1.1.6, however I simply
failed to debug remotely the vmlinux (root directory of linux source tree) via openocd-0.4.0 with a j-link segger. is there a good reference on how to properly debug the linux kernel via openocd/gdb for an arm target on a linux hot machine?
Did you read
http://elinux.org/DebuggingTheLinuxKernelUsingGdb ?

Yes and many other similar documents! and the steps below are based on those readings :(

Quoted 5 lines

Quoted 5 lines
details:
1. let u-boot start the board;
2. I get the u-boot command prompt:

Quoted 7 lines

Quoted 2 lines
3. halt the target via openocd/telnet;
If you plan on replacing the kernel using gdb you need really to stop at a known location
The moment you halt the target needs to be after memory initialization and prior to the kernel being loaded

yes I halt the target after memory initialization as done by uboot which also prepares the tagged list required by the kernel @

boot_params = 0x30000100

Quoted 16 lines

Quoted 16 lines
4. cd to root directory of linux source code and issue:
gdb vmlinux
GNU gdb (GDB) 6.8.50.20090417
Copyright (C) 2009 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later
<http://gnu.org/licenses/gpl.html>
This is free software: you are free to change and redistribute it. There is NO WARRANTY, to the extent permitted by law. Type "show copying" and "show warranty" for details.
This GDB was configured as "--host=i686-pc-linux-gnu --target=arm-none-linux-gnueabi".
For bug reporting instructions, please see:
<http://www.gnu.org/software/gdb/bugs/>...
(gdb)

Quoted 9 lines

Quoted 7 lines
5.
(gdb) target remote localhost:3333
Remote debugging using localhost:3333
0xc3e01874 in ?? ()
0xc3e01874: ldr r3, [r0, #16]
(gdb)
Is this kernel code?

I'm not sure, also not sure why gdb showed that particular memory location!

Quoted 9 lines

Quoted 6 lines
8. if I do continue (gdb) c, then I don't see any output on the serial console (as normally do during zImage booting process!)
where I'm messing up?
First try just booting and connecting to the target afterwards. All you really need is a vmlinuz so don't load the kernel over JTAG

do you mean the following steps:
1. arm-linux-gdb vmlinux
2.
target remote localhost:3333
set remote hardware-breakpoint-limit 2
set remote hardware-watchpoint-limit 2

3. reset the target and let u-boot/zImage finish running until I get the bash# of busy box then try to insert break points as needed?

many thanks ...

Quoted 4 lines

Hope this helps
Greetings

f. achkar

author

2010-05-26 20:34 UTC #4 lore raw

In reply to Steve Chen

Quoted 49 lines · Steve Chen

Quoted 39 lines · f. achkar
Quoted 12 lines · Steve Chen
Quoted 9 lines · f. achkar
hi,
This is my second posting (I'm not sure the first one passed the filter) sorry for that ...
I'm newbie and have a s3c2450 based board (arm926ejs), I have a working compressed kernel image
zImage, this image boots properly via u-boot-1.1.6, however I simply
failed to debug remotely the vmlinux (root directory of linux source tree) via openocd-0.4.0 with a j-link segger. is there a good reference on how to properly debug the linux kernel via openocd/gdb for an arm target on a linux hot machine?
Quoted 8 lines
Actually, Nicolas Pitre posted an response in your first try. In summary, use uImage for uboot. vmlinux won't work.
Regards,
Steve
Steve,
thanks, I'm not sure I got what you mean! if I do the following:
gdb arch/arm/boot/uImage
GNU gdb (GDB) 6.8.50.20090417
...
"/home/ferar/DW-SB02-linux-final/arch/arm/boot/uImage": not in executable format: File format not recognized
(gdb) target remote localhost:3333
Remote debugging using localhost:3333
0xc0008164 in ?? ()
0xc0008164: b 0xc0008160
(gdb) set remote hardware-breakpoint-limit 2
(gdb) set remote hardware-watchpoint-limit 2
(gdb) load
No executable file specified.
Use the "file" or "exec-file" command.
Quoted 8 lines
Note it is not executable format, I need to load and debug the kernel not just boot (I don't have booting issues) I'm having trouble trying to debug the kernel via jtag (openocd) gdb as outlined in the detail part of my previous post! I wonder if you people got that portion of the post? thanks,
ferar

Quoted 4 lines

I have never used gdb to debug the kernel, so I'm not qualify to answer your questions. In general, if you need to use gdb (actually more accurately kgdb), you need to something like

thanks Steve,
let say I'm 95% sure that if you have jtag you don't need kgdb you simply use gdb through the IEEE 1149.1 standard (1990!). Also for you information you can use the jtag for boundary scan which also quite useful (I think ;-/ ).

I'm sure few intelligent humans on this form have the know-how, and hope they share that with the rest of us.
best regards,
ferar

Quoted 10 lines

1.  Enable kgdb in the kernel config.
2.  Boot your kernel as usual.
3.  run cross-gdb on your host machine.
4.  Do remote debugging in gdb from your host via either serial or

Ethernet depends on how you have it configured.

Regards,

Steve

Jeff Hane

2010-07-21 22:44 UTC #5 lore raw

debugging kernel with gdb

In reply to Steve Chen

Hello,

I'm bringing up a new chip with an ARM1136 and trying to step thru the
code with gdb but because it's been optimized it's not working so well. The code was being compiled with -O2 and -g. I thought the obvious thing to do is just change this to -O0 in the top level Makefile; however this results in the following message.

Error: selected processor does not support `ldrexb

I'm trying to figure out if optimization can't be turned off or if I
have some issue with my toolchain.

thanks,
jeff

Baurzhan Ismagulov

2010-07-22 17:15 UTC #6 lore raw

debugging kernel with gdb

Quoted 3 lines · Jeff Hane

The code was being compiled with -O2 and -g. I thought the obvious thing to do is just change this to -O0 in the top level Makefile; however this results in the following message.

This doesn't work (I've never looked why) and is not supported.

With kind regards,
Baurzhan.

ikjn

2010-07-23 06:53 UTC #7 lore raw

debugging kernel with gdb

try -O1.
it's better

Quoted 15 lines · Baurzhan Ismagulov

Quoted 3 lines · Jeff Hane
The code was being compiled with -O2 and -g. ?I thought the obvious thing to do is just change this to -O0 in the top level Makefile; however this results in the following message.
This doesn't work (I've never looked why) and is not supported.
With kind regards,
Baurzhan.
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