Early boot debigging

Early boot debigging

[Alexander Kuleshov]

Hello all,

How can i debug early kernel booting, even before early_printk
(x86_64). I'm interesting in part which starts to execute right after
bootloader (https://github.com/torvalds/linux/blob/master/arch/x86/boot/header.S#L297).
How to do it better? Write grub and vmlinuz to disk with
losetup/grub-install and connect with gdb, or there is something
another way to do it?

Thank you.
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Re: Early boot debigging

[Guoqing Liu]

Hi  Alexander
  I think  you can try qemu, I think it's better.

good luck.

On Sat, Nov 29, 2014 at 2:41 PM, Alexander Kuleshov
<kuleshovmail@gmail.com> wrote:
> Hello all,
>
> How can i debug early kernel booting, even before early_printk
> (x86_64). I'm interesting in part which starts to execute right after
> bootloader (https://github.com/torvalds/linux/blob/master/arch/x86/boot/header.S#L297).
> How to do it better? Write grub and vmlinuz to disk with
> losetup/grub-install and connect with gdb, or there is something
> another way to do it?
>
> Thank you.
> --
> To unsubscribe from this list: send the line "unsubscribe linux-newbie" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html
> Please read the FAQ at http://www.linux-learn.org/faqs



-- 
good life
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Re: Early boot debigging

[Alexander Kuleshov]

Hello, thank you for reply,

yes, previously my plan was grub2 + vmlinuz/initrd + qemu.

I built disk with following instructions:

dd if=/dev/zero of=disk.img count=163840 bs=4096
fdisk fdisk (created one partition)
sudo losetup /dev/loop0 disk.img
sudo losetup /dev/loop1 disk.img -o 1048576
sudo mke2fs /dev/loop1
sudo mount /dev/loop1 /mnt
sudo grub-install --root-directory=/mnt --no-floppy --modules="normal
part_msdos ext2" /dev/loop0

Than i copied vmlinuz and initrd from my /boot directory to /mnt/boot
and created grub.cfg for grub:
and Added to the /mnt/boot/grub/grub.cfg following:

menuentry "My custom Linux" {
        set root=(hd0,1)
        linux /boot/vmlinuz-3.18.0-rc4+ root=/dev/sda1
        initrd /boot/initrd.img-3.18.0-rc4+
}

And reinstalled grub with previous command. Now i'm trying to run it
in qemu with:

qemu-system-x86_64 disk.img

I see grub menu, but after pressing on it only black screen without
any errors/logs and etc: http://tinypic.com/r/i2pugh/8

Can't understand what's wrong here

Thank you.

2014-11-29 14:35 GMT+06:00 Guoqing Liu <lgqgood@gmail.com>:
> Hi  Alexander
>   I think  you can try qemu, I think it's better.
>
> good luck.
>
> On Sat, Nov 29, 2014 at 2:41 PM, Alexander Kuleshov
> <kuleshovmail@gmail.com> wrote:
>> Hello all,
>>
>> How can i debug early kernel booting, even before early_printk
>> (x86_64). I'm interesting in part which starts to execute right after
>> bootloader (https://github.com/torvalds/linux/blob/master/arch/x86/boot/header.S#L297).
>> How to do it better? Write grub and vmlinuz to disk with
>> losetup/grub-install and connect with gdb, or there is something
>> another way to do it?
>>
>> Thank you.
>> --
>> To unsubscribe from this list: send the line "unsubscribe linux-newbie" in
>> the body of a message to majordomo@vger.kernel.org
>> More majordomo info at  http://vger.kernel.org/majordomo-info.html
>> Please read the FAQ at http://www.linux-learn.org/faqs
>
>
>
> --
> good life



-- 
_________________________
0xAX
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Re: Early boot debigging

[Guoqing Liu]

HI  Alexander
  I also meet some problem when using my system efi grub.
  I think if you just care about the kernel start process, you can
skip the grub.
  you can use follow cmd to emulate the kernel
  "qemu-system-x86_64 -kernel arch/x86_64/boot/bzImage -hda
linux-0.2.img -append root=/dev/sda"
  I do't know whether can solve your problem.

good luck.

Guoqing

On Sat, Nov 29, 2014 at 7:26 PM, Alexander Kuleshov
<kuleshovmail@gmail.com> wrote:
> Hello, thank you for reply,
>
> yes, previously my plan was grub2 + vmlinuz/initrd + qemu.
>
> I built disk with following instructions:
>
> dd if=/dev/zero of=disk.img count=163840 bs=4096
> fdisk fdisk (created one partition)
> sudo losetup /dev/loop0 disk.img
> sudo losetup /dev/loop1 disk.img -o 1048576
> sudo mke2fs /dev/loop1
> sudo mount /dev/loop1 /mnt
> sudo grub-install --root-directory=/mnt --no-floppy --modules="normal
> part_msdos ext2" /dev/loop0
>
> Than i copied vmlinuz and initrd from my /boot directory to /mnt/boot
> and created grub.cfg for grub:
> and Added to the /mnt/boot/grub/grub.cfg following:
>
> menuentry "My custom Linux" {
>         set root=(hd0,1)
>         linux /boot/vmlinuz-3.18.0-rc4+ root=/dev/sda1
>         initrd /boot/initrd.img-3.18.0-rc4+
> }
>
> And reinstalled grub with previous command. Now i'm trying to run it
> in qemu with:
>
> qemu-system-x86_64 disk.img
>
> I see grub menu, but after pressing on it only black screen without
> any errors/logs and etc: http://tinypic.com/r/i2pugh/8
>
> Can't understand what's wrong here
>
> Thank you.
>
> 2014-11-29 14:35 GMT+06:00 Guoqing Liu <lgqgood@gmail.com>:
>> Hi  Alexander
>>   I think  you can try qemu, I think it's better.
>>
>> good luck.
>>
>> On Sat, Nov 29, 2014 at 2:41 PM, Alexander Kuleshov
>> <kuleshovmail@gmail.com> wrote:
>>> Hello all,
>>>
>>> How can i debug early kernel booting, even before early_printk
>>> (x86_64). I'm interesting in part which starts to execute right after
>>> bootloader (https://github.com/torvalds/linux/blob/master/arch/x86/boot/header.S#L297).
>>> How to do it better? Write grub and vmlinuz to disk with
>>> losetup/grub-install and connect with gdb, or there is something
>>> another way to do it?
>>>
>>> Thank you.
>>> --
>>> To unsubscribe from this list: send the line "unsubscribe linux-newbie" in
>>> the body of a message to majordomo@vger.kernel.org
>>> More majordomo info at  http://vger.kernel.org/majordomo-info.html
>>> Please read the FAQ at http://www.linux-learn.org/faqs
>>
>>
>>
>> --
>> good life
>
>
>
> --
> _________________________
> 0xAX



-- 
good life
--
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Re: Early boot debigging

[Guoqing Liu]

On Sun, Nov 30, 2014 at 1:07 AM, Guoqing Liu <lgqgood@gmail.com> wrote:
> HI  Alexander
>   I also meet some problem when using my system efi grub.
>   I think if you just care about the kernel start process, you can
> skip the grub.
>   you can use follow cmd to emulate the kernel
>   "qemu-system-x86_64 -kernel arch/x86_64/boot/bzImage -hda
> linux-0.2.img -append root=/dev/sda"
>   I do't know whether can solve your problem.
>
> good luck.
>
> Guoqing
>
> On Sat, Nov 29, 2014 at 7:26 PM, Alexander Kuleshov
> <kuleshovmail@gmail.com> wrote:
>> Hello, thank you for reply,
>>
>> yes, previously my plan was grub2 + vmlinuz/initrd + qemu.
>>
>> I built disk with following instructions:
>>
>> dd if=/dev/zero of=disk.img count=163840 bs=4096
>> fdisk fdisk (created one partition)
>> sudo losetup /dev/loop0 disk.img
>> sudo losetup /dev/loop1 disk.img -o 1048576
>> sudo mke2fs /dev/loop1
>> sudo mount /dev/loop1 /mnt
>> sudo grub-install --root-directory=/mnt --no-floppy --modules="normal
>> part_msdos ext2" /dev/loop0
>>
>> Than i copied vmlinuz and initrd from my /boot directory to /mnt/boot
>> and created grub.cfg for grub:
>> and Added to the /mnt/boot/grub/grub.cfg following:
>>
>> menuentry "My custom Linux" {
>>         set root=(hd0,1)
>>         linux /boot/vmlinuz-3.18.0-rc4+ root=/dev/sda1
>>         initrd /boot/initrd.img-3.18.0-rc4+
>> }
>>
>> And reinstalled grub with previous command. Now i'm trying to run it
>> in qemu with:
>>
>> qemu-system-x86_64 disk.img
>>
>> I see grub menu, but after pressing on it only black screen without
>> any errors/logs and etc: http://tinypic.com/r/i2pugh/8
>>
>> Can't understand what's wrong here
>>
>> Thank you.
>>
>> 2014-11-29 14:35 GMT+06:00 Guoqing Liu <lgqgood@gmail.com>:
>>> Hi  Alexander
>>>   I think  you can try qemu, I think it's better.
>>>
>>> good luck.
>>>
>>> On Sat, Nov 29, 2014 at 2:41 PM, Alexander Kuleshov
>>> <kuleshovmail@gmail.com> wrote:
>>>> Hello all,
>>>>
>>>> How can i debug early kernel booting, even before early_printk
>>>> (x86_64). I'm interesting in part which starts to execute right after
>>>> bootloader (https://github.com/torvalds/linux/blob/master/arch/x86/boot/header.S#L297).
>>>> How to do it better? Write grub and vmlinuz to disk with
>>>> losetup/grub-install and connect with gdb, or there is something
>>>> another way to do it?
>>>>
>>>> Thank you.
>>>> --
>>>> To unsubscribe from this list: send the line "unsubscribe linux-newbie" in
>>>> the body of a message to majordomo@vger.kernel.org
>>>> More majordomo info at  http://vger.kernel.org/majordomo-info.html
>>>> Please read the FAQ at http://www.linux-learn.org/faqs
>>>
>>>
>>>
>>> --
>>> good life
>>
>>
>>
>> --
>> _________________________
>> 0xAX
>
>
>
> --
> good life


and follow is my debug log:
################################################################
ingocn@apple:/opt/source/kernel/out$ gdb vmlinux
GNU gdb (Ubuntu 7.7-0ubuntu3.1) 7.7
Copyright (C) 2014 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 "x86_64-linux-gnu".
Type "show configuration" for configuration details.
For bug reporting instructions, please see:
<http://www.gnu.org/software/gdb/bugs/>.
Find the GDB manual and other documentation resources online at:
<http://www.gnu.org/software/gdb/documentation/>.
For help, type "help".
Type "apropos word" to search for commands related to "word"...
Reading symbols from vmlinux...done.
(gdb) target remote localhost:1234
Remote debugging using localhost:1234
0x0000000000000000 in irq_stack_union ()
(gdb) l
1 /*
2 *  linux/arch/x86_64/kernel/head.S -- start in 32bit and switch to 64bit
3 *
4 *  Copyright (C) 2000 Andrea Arcangeli <andrea@suse.de> SuSE
5 *  Copyright (C) 2000 Pavel Machek <pavel@suse.cz>
6 *  Copyright (C) 2000 Karsten Keil <kkeil@suse.de>
7 *  Copyright (C) 2001,2002 Andi Kleen <ak@suse.de>
8 *  Copyright (C) 2005 Eric Biederman <ebiederm@xmission.com>
9 */
10
(gdb) l
11
12 #include <linux/linkage.h>
13 #include <linux/threads.h>
14 #include <linux/init.h>
15 #include <asm/segment.h>
16 #include <asm/pgtable.h>
17 #include <asm/page.h>
18 #include <asm/msr.h>
19 #include <asm/cache.h>
20 #include <asm/processor-flags.h>
(gdb) l
21 #include <asm/percpu.h>
22 #include <asm/nops.h>
23
24 #ifdef CONFIG_PARAVIRT
25 #include <asm/asm-offsets.h>
26 #include <asm/paravirt.h>
27 #define GET_CR2_INTO(reg) GET_CR2_INTO_RAX ; movq %rax, reg
28 #else
29 #define GET_CR2_INTO(reg) movq %cr2, reg
30 #define INTERRUPT_RETURN iretq
(gdb) l
31 #endif
32
33 /* we are not able to switch in one step to the final KERNEL ADDRESS SPACE
34 * because we need identity-mapped pages.
35 *
36 */
37
38 #define pud_index(x) (((x) >> PUD_SHIFT) & (PTRS_PER_PUD-1))
39
40 L4_PAGE_OFFSET = pgd_index(__PAGE_OFFSET)
(gdb) l
41 L3_PAGE_OFFSET = pud_index(__PAGE_OFFSET)
42 L4_START_KERNEL = pgd_index(__START_KERNEL_map)
43 L3_START_KERNEL = pud_index(__START_KERNEL_map)
44
45 .text
46 __HEAD
47 .code64
48 .globl startup_64
49 startup_64:
50 /*
(gdb) bt
#0  0x0000000000000000 in irq_stack_union ()
#1  0x0000000000000000 in ?? ()
(gdb) help
List of classes of commands:

aliases -- Aliases of other commands
breakpoints -- Making program stop at certain points
data -- Examining data
files -- Specifying and examining files
internals -- Maintenance commands
obscure -- Obscure features
running -- Running the program
stack -- Examining the stack
status -- Status inquiries
support -- Support facilities
tracepoints -- Tracing of program execution without stopping the program
user-defined -- User-defined commands

Type "help" followed by a class name for a list of commands in that class.
Type "help all" for the list of all commands.
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(gdb) c
Continuing.
################################################################
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