January 2012 - kernelnewbies@kernelnewbies.org

Using ipv6 stack functions in kernel module
by Łukasz Czyż Jan. 22, 2012

Jan. 22, 2012

Hello All I am wirting kernel module and I want to call some ipv6 stack function from it (like ip6_forward). I am including proper header files so compiler detects that functions, compiles module, but at the end it returns warning like that: WARNING: "ip6_forward" [/path/to/my/module.ko] undefined! Resulting module cannot be inserted as I get following output: insmod: error inserting 'module.ko': -1 Unknown symbol in module I guess that this issue takes place because corresponding macro EXPORT_SYMBOL(ip6_forward) is not defined in kernel source. But it seems strange to me that such a fundamental functions cannot be used by module writers. What is more, I found on net some exemplary module source and I found ip6_forward function called from it. I defined "GPL" as license of my module and I try to compile it under 3.0.4 kernel version. Lukasz

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Init global variables at run-time
by V l Jan. 22, 2012

Jan. 22, 2012

Can some one throw more light on this statement=> /* Init global variables at run-time, not as part of the declaration. * This is required to support init/de-init of the driver. Initialization * of globals as part of the declaration results in non-deterministic * behaviour since the value of the globals may be different on the * first time that the driver is initialized vs subsequent initializations. Thanks and Regards Sraddha

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Re: SIGKILL
by Mulyadi Santosa Jan. 22, 2012

Jan. 22, 2012

Hi Darshan :) On Thu, Jan 19, 2012 at 14:03, Darshan Ghumare <darshan.ghumare(a)gmail.com> wrote: > Hi Mulyadi, > > How SIGKILL is handle by Kernel? > Does SIGKILL & SIGTSTP handled separately than the rest of the signals? I hope you don't mind if I cc this answer to kernelnewbies as well. Hopefully you will get better answer. Well, SIGKILL is handled like other usual signal. The important point to notice is that sigkill is handled entirely in kernel space. What it means is that it cannot be overriden in user space (i.e installing your own signal handler). SIGKILL will tell the target process to terminate itself. So it pretty much will flow like normal process termination. However, the termination will be a bit rough. It will just kill....no time to wait for in flight I/O whatsoever. SIGSTOP...ehm, I think that is handled in kernel space too. The handler will basically move the process out of from run queue to the process stopped queue (or something like that, I forgot). Then it switch the process state from "running" to "stop". It's not the same like "sleep" btw. Hope it helps.... -- regards, Mulyadi Santosa Freelance Linux trainer and consultant blog: the-hydra.blogspot.com training: mulyaditraining.blogspot.com

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Calling a module method from inside the kernel - is it possible Inbox
by Kevin Wilson Jan. 21, 2012

Jan. 21, 2012

Hi, all, I want to calling a module method (I am developing the module) from inside the kernel. How can I achieve it ? (BTW, I know that vice versa is possible by EXPORT_SYMBOL.) rgs, Kevin

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from where to start..
by Sukrit Sangwan Jan. 21, 2012

Jan. 21, 2012

I want to become a kernel developer. I have never done anything related to kernel uptil now. I am unable to figure out how to start off. Please help me doing my first exercise on kernel development. -- Sukrit Sangwan B.Arch. III Yr. IIT Roorkee

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s3c24xx_console_init in s3c2440.c
by hz hanks Jan. 21, 2012

Jan. 21, 2012

Hi, all I'm studying s3c2440.c of uart driver. In it, there is a macro called s3c24xx_console_init which is just the function of s3c24xx_serial_initconsole in samsung.c. But I didnot find any place for the s3c2440 uart driver to call this function (s3c24xx_console_init only displayed once as a definition). Is there any one know the detail about this? I would appreciate any idea about it. Thank you.

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git clone of linux kernel provides only compressed pack files
by Manavendra Nath Manav Jan. 20, 2012

Jan. 20, 2012

Hi All, I cloned 3.2 kernel from git repository, but I am not seeing any source files. The .git directory contains .git/objects/pack/*.pack file which is huge and it seems all source code with commit revision is stored there. When I do "git unpack-objects -r < xyz.pack", it completes 100% but still no source files show up. The only thing it generates is some more entries in .git/objects/ directory. The same problem also occurs when I try to clone android repository. Pls help, I am sure I am missing some obvious step here. [root@pe1800xs src]# git clone --recursive -v http://git.kernel.org/pub/scm/linux/kernel/git/stable/linux-stable.git Cloning into linux-stable... remote: Counting objects: 2446667, done. remote: Compressing objects: 100% (391011/391011), done. Receiving objects: 18% (447106/2446667), 259.18 MiB | 43 KiB/s [root@pe1800xs .git]# du -h 4.0K ./objects/info 284M ./objects/pack 285M ./objects 8.0K ./info 4.0K ./refs/tags 4.0K ./refs/heads 12K ./refs 48K ./hooks 4.0K ./branches 285M . [e518816@pe1800xs common]$ git unpack-objects -r < .git/objects/pack/pack-d2d041c2bd4a39fdfdf37c896f64a3c1b53d3d2b.pack Unpacking objects: 100% (2074089/2074089), done. >From the man page of git-unpack-objects: "Objects that already exist in the repository will not be unpacked from the pack-file. Therefore, nothing will be unpacked if you use this command on a pack-file that exists within the target repository." I guess this is the problem I am facing. How do I extract the linux souce files (HEAD branch) from pack file? -- Thanks & Regards, Manavendra Nath Manav

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[OOT] About the symbols in binary file.
by nilesh Jan. 20, 2012

Jan. 20, 2012

Hi, The question is not completely related to kernel. But I came across similar question when debugging in kernel. I tried dissecting the SSL library using 'nm' command. It is showing the list of symbols along with some generic addresses (to be used when relocating). Also there are some characters 't', 'T', 'U'. I guess these correspond to properties of symbols - like static, extern etc. Could someone please point out what exactly each character corresponds to? I mean looking at the character, we should be able to denote if it's a static symbol or inline etc. Do we have any such mapping? 00000499 t tls1_PRF 00000019 t tls1_P_hash 00000000 T tls1_alert_code 00000937 T tls1_cert_verify_mac 00000ffa T tls1_change_cipher_state 00000a22 T tls1_enc 000006fc T tls1_final_finish_mac 0000063d T tls1_generate_master_secret 00001734 T tls1_mac 00000d2a T tls1_setup_key_block -- Thanks, Nilesh

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Does Linux process exist information leakage?
by 夏业添 Jan. 20, 2012

Jan. 20, 2012

Hi, My tutor asked me to test whether one process leaves information in memory after it is dead. I tried to search some article about such thing on the Internet but there seems to be no one discuss about it. And after that, I tried to write some program in the User Mode to test it, using fork() to create lots of processes and filling char 'a' into a 102400 bytes char array in each process. Then I used malloc() to get some memory to seek char 'a' in a new one process or many new processes, but failed. All memory I malloced was full of zero. As the man page of malloc said:"The memory is not initialized", I believe that the memory which was got by malloc() could be used by other process, and therefor information leakage exists. But how can I test it? Or where can I get related information? Thanks!

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Best way to debug an Intel Core i5 hang - likely graphics (possibly power) related
by Graeme Russ Jan. 20, 2012

Jan. 20, 2012

This may not be the best place to post this question, so please excuse... I have a brand new Intel i5 / z68 EUFI motherboard (ASRock Z68 Pro3 Gen3) with 8GB RAM running Fedora 16 (64 bit) which is experiencing lockups which send the video crazy (flashing screen) but there is nothing appearing in /var/log/messages to indicate what is going wrong (no oops). I'm sure it is graphics related. I thought of Cc'ing the i915 maintainer (Keith Packard) but figured I should wait until I am sure I _think_ it might be power related as the hang never seems to occur while I'm actively using the computer - Only after I have stopped for a few minutes does it happen but not always. I have had it run overnight without a problem, I've had times when it has slept several times before hanging, and times when it has hung the very first sleep after reboot I have pulled the latest mainline vanilla kernel (from about two days ago) and have it configured, build and installed it so I am in a position to do whatever hacking is required to isolate the issue So where should I begin? I have already posted a bug report in Bugzilla (https://bugzilla.kernel.org/show_bug.cgi?id=42597) but I want to isolate the problem to improve the report. I'm somewhat familiar with kernel hacking, git, diffs etc, so I'm not at all afraid of some pretty intensive hacking. I have a second PC and Null-Modem cable (plus Ethernet of course) if that helps, although I am not familiar with using tools like GDB so anything requiring on-line debugging will need a bit of explaining Regards, Graeme

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