Re: Virtualbox + kgdb: Can't see vmlinux symbols

[valdis . kletnieks]

On Fri, 16 Jun 2017 13:24:58 -0700, Kamran Khan said:
> This is happening only with kernel 4.8+.
>
> When I compile kernel 4.4 with a stock Ubuntu Xenial .config, symbols
> appear just fine.
>
> When I compile kernel 4.8/4.10 with Yakkety/Zesty stock configs the
> symbols disappear.

What happens when you try to compile 4.8/r.10 with a Xenial .config?

I'm willing to bet the problem is that the Xenial config turns on symbols
and Yakkety/Zesty disable them by default.

See these for further info:

CONFIG_DEBUG_INFO=y
CONFIG_DEBUG_INFO_REDUCED=y
CONFIG_DEBUG_INFO_SPLIT=y

It appears that you'll need DEBUG_INFO_REDUCED=n for kgdb to work properly.


pgp4jwrnxYEv6.pgp
Description: PGP signature
___
Kernelnewbies mailing list
Kernelnewbies@kernelnewbies.org
https://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies

Re: Virtualbox + kgdb: Can't see vmlinux symbols

[Kamran Khan]

This is happening only with kernel 4.8+.

When I compile kernel 4.4 with a stock Ubuntu Xenial .config, symbols
appear just fine.

When I compile kernel 4.8/4.10 with Yakkety/Zesty stock configs the
symbols disappear.

On Wed, Jun 14, 2017 at 4:58 PM, Kamran Khan  wrote:
> I have an Ubuntu 16.04 VM running in Virtualbox.
>
> I'm building kernel from git using make deb-pkg.
>
> After I install all the deb packages (including debug symbols) on the
> VM and restart it, I can see in uname -r output that the appropriate
> kernel was booted from.
>
> I'm passing the following parameters to the kernel:
>
>> kgdboc=ttyS0,115200 kgdbwait
>
> Once the kernel boots, I am able to connect to it via socat + gdb from host.
>
> I'm using the full uncompressed vmlinux file to start the gdb which
> contains all the debugging symbols.
>
> However, I can't see any of the symbols in backtrace etc.
>
>> $ du -sh vmlinux
>> 425M vmlinux
>> $ gdb vmlinux
>> GNU gdb (Ubuntu 7.11.1-0ubuntu1~16.04) 7.11.1
>> Copyright (C) 2016 Free Software Foundation, Inc.
>> License GPLv3+: GNU GPL version 3 or later [gnu.org]
>> [...]
>> For help, type "help".
>> Type "apropos word" to search for commands related to "word"...
>> Reading symbols from vmlinux...done.
>> (gdb) target remote /dev/pts/2
>> Remote debugging using /dev/pts/2
>> 0xb113c5b4 in ?? ()
>> (gdb) bt
>> #0  0xb113c5b4 in ?? ()
>> #1  0xb035421c7dd0 in ?? ()
>> #2  0xb113c60c in ?? ()
>> #3  0xb035421c7e00 in ?? ()
>> #4  0xb153035a in ?? ()
>> #5  0x0002 in irq_stack_union ()
>> #6  0x013a7408 in ?? ()
>> #7  0x8fb8bd0d3b00 in ?? ()
>> #8  0xb035421c7e18 in ?? ()
>> #9  0xb15307df in ?? ()
>> #10 0x8fb8b8779900 in ?? ()
>> #11 0xb035421c7e38 in ?? ()
>> #12 0xb12ab412 in ?? ()
>> #13 0x8fb8bd0d3b00 in ?? ()
>
>
> Any ideas what am I doing wrong?
>
> Thanks,
> Kamran.

___
Kernelnewbies mailing list
Kernelnewbies@kernelnewbies.org
https://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies

Re: ./include/linux/err.h:35:16: warning: dereference of noderef expression

[Luc Van Oostenryck]

On Tue, Jun 13, 2017 at 11:55:26AM +0200, Charlemagne Lasse wrote:
> Hi,
> 
> I have following code which generates a warning when compiling with "make 
> C=1".
> 
> ~~~
> struct task_struct *kthread;
> kthread = kthread_create(x, y, "z");
> if (IS_ERR(kthread)) {
> ~~~
> 
> The warning is
> 
> ./include/linux/err.h:35:16: warning: dereference of noderef expression
> 
> And disappears when I remove the IS_ERR. How do I correctly work
> around this incorrect warning?
> 
> Btw. I am using Debian stretch amd64. It seems like this is related to
> the __force used in the parameter list of IS_ERR. Removing it also
> removes the warning.

The warning is indeed related to '__force' but it should be
the other way around.
Anyway, by just reading your three lines of code, you shouldn't
receive this warning, with or without the __force.
 
> If it is fixed in sparse's git then when will there be a new release of it?

I can't reproduce your problem even on a three years old version
of sparse (more exactly git version d917662d5 of sparse, anything
older has build problems with half-recent kernels).

The pre-processed version of your file could be interesting
as well as the output of the make command but with the 'V=1'
option added.
 

Regards,
-- Luc Van Oostenryck

___
Kernelnewbies mailing list
Kernelnewbies@kernelnewbies.org
https://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies

./include/linux/err.h:35:16: warning: dereference of noderef expression

[Charlemagne Lasse]

Hi,

I have following code which generates a warning when compiling with "make C=1".

~~~
struct task_struct *kthread;
kthread = kthread_create(x, y, "z");
if (IS_ERR(kthread)) {
~~~

The warning is

./include/linux/err.h:35:16: warning: dereference of noderef expression

And disappears when I remove the IS_ERR. How do I correctly work
around this incorrect warning?

Btw. I am using Debian stretch amd64. It seems like this is related to
the __force used in the parameter list of IS_ERR. Removing it also
removes the warning.

If it is fixed in sparse's git then when will there be a new release of it?

Greetings,
Charlemagne Lasse

___
Kernelnewbies mailing list
Kernelnewbies@kernelnewbies.org
https://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies

Re: Virtualbox + kgdb: Can't see vmlinux symbols

[Kamran Khan]

Disabling CONFIG_RANDOMIZE_MEMORY did not help. Disabled
CONFIG_RANDOMIZE_BASE as well and the symbols came up.

The weird thing is that CONFIG_RANDOMIZE_BASE is enabled on Xenial
(4.4) kernel as well, but somehow having it enabled on Zesty (4.10)
kernel throws off kgdb.

Thanks,
Kamran.

On Fri, Jun 16, 2017 at 3:02 PM, Kamran Khan  wrote:
> The debug symbols are on for all of them, and gdb *does* load the
> symbols. I have a suspicion that KASLR that was introduced around 4.7
> might be the culprit here. CONFIG_RANDOMIZE_MEMORY is an option that's
> not present in the Xenial config.
>
> Anyone here has attached kgdb to 4.8/4.10?
>
> Thanks,
> Kamran.
>
> On Fri, Jun 16, 2017 at 1:41 PM,   wrote:
>> On Fri, 16 Jun 2017 13:24:58 -0700, Kamran Khan said:
>>> This is happening only with kernel 4.8+.
>>>
>>> When I compile kernel 4.4 with a stock Ubuntu Xenial .config, symbols
>>> appear just fine.
>>>
>>> When I compile kernel 4.8/4.10 with Yakkety/Zesty stock configs the
>>> symbols disappear.
>>
>> What happens when you try to compile 4.8/r.10 with a Xenial .config?
>>
>> I'm willing to bet the problem is that the Xenial config turns on symbols
>> and Yakkety/Zesty disable them by default.
>>
>> See these for further info:
>>
>> CONFIG_DEBUG_INFO=y
>> CONFIG_DEBUG_INFO_REDUCED=y
>> CONFIG_DEBUG_INFO_SPLIT=y
>>
>> It appears that you'll need DEBUG_INFO_REDUCED=n for kgdb to work properly.

___
Kernelnewbies mailing list
Kernelnewbies@kernelnewbies.org
https://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies

Re: Virtualbox + kgdb: Can't see vmlinux symbols

[Kamran Khan]

The debug symbols are on for all of them, and gdb *does* load the
symbols. I have a suspicion that KASLR that was introduced around 4.7
might be the culprit here. CONFIG_RANDOMIZE_MEMORY is an option that's
not present in the Xenial config.

Anyone here has attached kgdb to 4.8/4.10?

Thanks,
Kamran.

On Fri, Jun 16, 2017 at 1:41 PM,   wrote:
> On Fri, 16 Jun 2017 13:24:58 -0700, Kamran Khan said:
>> This is happening only with kernel 4.8+.
>>
>> When I compile kernel 4.4 with a stock Ubuntu Xenial .config, symbols
>> appear just fine.
>>
>> When I compile kernel 4.8/4.10 with Yakkety/Zesty stock configs the
>> symbols disappear.
>
> What happens when you try to compile 4.8/r.10 with a Xenial .config?
>
> I'm willing to bet the problem is that the Xenial config turns on symbols
> and Yakkety/Zesty disable them by default.
>
> See these for further info:
>
> CONFIG_DEBUG_INFO=y
> CONFIG_DEBUG_INFO_REDUCED=y
> CONFIG_DEBUG_INFO_SPLIT=y
>
> It appears that you'll need DEBUG_INFO_REDUCED=n for kgdb to work properly.

___
Kernelnewbies mailing list
Kernelnewbies@kernelnewbies.org
https://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies

Re: VFS: mount_bdev and fill_super

[Rohan Puri]

On 16-Jun-2017 11:44 AM, "Shrikant Giridhar" 
wrote:

> I just had a quick look at mount_bdev() code for Linux v3.15, mount_bdev()
> can return only root dentry or error.

I'm sorry I should have been clearer. I was referring to the documentation
mount() where it says that the call can return something other than the root
dentry.

I have not looked at the doc.


More specifically, I don't understand how the what's the purpose of the if
condition checking for s_root in mount_bdev(). Apologies if this is a
trivial
question.

If s_root is set it means the superblock is already filled up so call
fill_super() only if s_root is NULL meaning superblock is not filled yet.

Tracking the calls all the way down didn't seem to make it clearer
and I couldn't find specific documentation about the interface.

> Also please include the kernel version to which you are referring.

I have the 4.12-rc5 kernel.

---
Shrikant


- Rohan
___
Kernelnewbies mailing list
Kernelnewbies@kernelnewbies.org
https://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies

Re: VFS: mount_bdev and fill_super

[Shrikant Giridhar]

> I just had a quick look at mount_bdev() code for Linux v3.15, mount_bdev()
> can return only root dentry or error.

I'm sorry I should have been clearer. I was referring to the documentation
mount() where it says that the call can return something other than the root
dentry.

More specifically, I don't understand how the what's the purpose of the if
condition checking for s_root in mount_bdev(). Apologies if this is a trivial
question. Tracking the calls all the way down didn't seem to make it clearer
and I couldn't find specific documentation about the interface.

> Also please include the kernel version to which you are referring.

I have the 4.12-rc5 kernel.

---
Shrikant

___
Kernelnewbies mailing list
Kernelnewbies@kernelnewbies.org
https://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies

Re: Struct sk_buff_head

[Kamil Konieczny]

Hi,

On 06/07/2017 09:36 PM, wiktoria.lewicka wrote:
> I read code from file include/linux/skbuff.h and I have question about 
> sk_buff_head structure. 
> [...]
> Is this union replace sk_buff_head structure? 
> I didn`t found any field in sk_buff, which may use sk_buff_head, [...]

As I can see it, sk_buff can be on double-linked list,
and then it is linked by next and prev,
or it is referenced by red-black tree, rb_node,
depending of some network logic (packet type ?)

Both are used by functions operating on structures.

-- 
Best regards,
Kamil Konieczny
Samsung R Institute Poland


___
Kernelnewbies mailing list
Kernelnewbies@kernelnewbies.org
https://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies