March 2015 - kernelnewbies@kernelnewbies.org - Kernelnewbies Mailing Lists

Re: Raw binary Image of linux
by victorascroft＠gmail.com March 16, 2015

March 16, 2015

Hello, On 15-03-16 09:33:21, chirag garg wrote: > Hello , > > I perform the following steps to run linux kernel on imx6: > > Download 3.18 kernel from www.kernel.org > Make steps: > make CROSSarm-linux-gnueabi- ARCH=arm imx_v6_v7_defconfig > make CROSS_COMPILE=arm-linux-gnueabi- ARCH=arm uImage LOADADDR=10001000 > > cp linux-3.18.4/arch/arm/boot/uImage Sd_card So you copied the kernel image to SD card. > Run uImage on the imx6 board... Can you provide some more information on this point? When you copied the uImage to SD card, did you do something else to perhaps update the uImage on the module, or is the module setup to boot from SD card? And what about the device tree blob? Did you have a look at the uboot environment variables? What was the earlier kernel version the board was booting with? > > Output : > > ## Booting kernel from Legacy Image at 10800000 ... > Image Name: Linux-3.18.4 > Image Type: ARM Linux Kernel Image (uncompressed) > Data Size: 5445640 Bytes = 5.2 MB > Load Address: 10001000 > Entry Point: 10001000 > Verifying Checksum ... OK > Loading Kernel Image ... OK > OK > > Starting kernel ... > > > what could be the problem in this ? why Is this kernel not able start on > imx6 platform ? That output is on the serial debug console? Is the console parameter in uboot set appropriately to what the kernel expects? - Sanchayan. > > Thanks in advance, > Regards, > > Chirag Garg > IIT Madras , Rise Lab > > On Mon, Mar 9, 2015 at 11:01 PM, <victorascroft(a)gmail.com> wrote: > > > Hello, > > > > On 15-03-09 21:53:34, chirag garg wrote: > > > Hello, > > > > > > On Mon, Mar 9, 2015 at 9:01 PM, <victorascroft(a)gmail.com> wrote: > > > > > > > Hello, > > > > > > > > On 15-03-09 11:20:55, chirag garg wrote: > > > > > Hi all, > > > > > > > > > > I am new to the linux kernel source code. I want to compile linux > > source > > > > > code for imx6 ARM based platform. > > > > > I want to generate raw binary image (.bin file) and .dtb file. Can > > any > > > > one > > > > > help me in this.? > > > > > > > > Which iMX6 platform is this? Depending on the platform, it would be as > > > > simple as doing make imx_v6_v7_defconfig and then using the correct dtb > > > > for the platform. Boards like Nitrogen, Sabre or Wandaboard should boot > > > > easily with the recent kernels. > > > > > > > > I am using freescale imx6 quad core saberlite board. Available on the > > > freescale site > > > http://www.freescale.com/webapp/sps/site/prod_summary.jsp?code=i.MX6Q > > > > > > Where should be this dtb available according to the board. I am trying to > > > boot 3.14 linux kernel. > > > > The DTS files for all ARM boards are available in the following > > directory > > > > http://lxr.free-electrons.com/source/arch/arm/boot/dts/?v=3.14 > > > > > > http://lxr.free-electrons.com/source/arch/arm/configs/imx_v6_v7_defconfig?v… > > > > imx_v6_v7_defconfig is the config file for imx platform. > > > > -Regards, > > Sanchayan. > > > > > > > > > > > > Do you have a custom board or one of those easily available development > > > > platforms? > > > > > > > > Board is easily available in the market. > > > > > > > > > > - Regards, > > > > Sanchayan.. > > > > > > > > > > > > > > Thanks in advance > > > > > Regards > > > > > > > > > > Chirag Garg > > > > > IIT Madras , Rise Lab > > > > > > > > > > > Regards > > > Chirag Garg > > > IIT Madras , Rise Lab > > > > > > > > > > > _______________________________________________ > > > > > Kernelnewbies mailing list > > > > > Kernelnewbies(a)kernelnewbies.org > > > > > http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies > > > > > > > > > >

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Re: Raw binary Image of linux
by victorascroft＠gmail.com March 16, 2015

March 16, 2015

Hello, On 15-03-09 21:53:34, chirag garg wrote: > Hello, > > On Mon, Mar 9, 2015 at 9:01 PM, <victorascroft(a)gmail.com> wrote: > > > Hello, > > > > On 15-03-09 11:20:55, chirag garg wrote: > > > Hi all, > > > > > > I am new to the linux kernel source code. I want to compile linux source > > > code for imx6 ARM based platform. > > > I want to generate raw binary image (.bin file) and .dtb file. Can any > > one > > > help me in this.? > > > > Which iMX6 platform is this? Depending on the platform, it would be as > > simple as doing make imx_v6_v7_defconfig and then using the correct dtb > > for the platform. Boards like Nitrogen, Sabre or Wandaboard should boot > > easily with the recent kernels. > > > > I am using freescale imx6 quad core saberlite board. Available on the > freescale site > http://www.freescale.com/webapp/sps/site/prod_summary.jsp?code=i.MX6Q > > Where should be this dtb available according to the board. I am trying to > boot 3.14 linux kernel. The DTS files for all ARM boards are available in the following directory http://lxr.free-electrons.com/source/arch/arm/boot/dts/?v=3.14 http://lxr.free-electrons.com/source/arch/arm/configs/imx_v6_v7_defconfig?v… imx_v6_v7_defconfig is the config file for imx platform. -Regards, Sanchayan. > > > > Do you have a custom board or one of those easily available development > > platforms? > > > > Board is easily available in the market. > > > > - Regards, > > Sanchayan.. > > > > > > > > Thanks in advance > > > Regards > > > > > > Chirag Garg > > > IIT Madras , Rise Lab > > > > > Regards > Chirag Garg > IIT Madras , Rise Lab > > > > > _______________________________________________ > > > Kernelnewbies mailing list > > > Kernelnewbies(a)kernelnewbies.org > > > http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies > > > >

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Re: Question on mutex code
by Matthias Bonne March 16, 2015

March 16, 2015

On 03/16/15 00:10, Rabin Vincent wrote: > On Sun, Mar 15, 2015 at 11:49:07PM +0200, Matthias Bonne wrote: >> So the counter is set to 1 before taking the spinlock, which I think >> might cause the race. Did I miss something? > > Yes, you miss the fact that __mutex_slowpath_needs_to_unlock() is 0 for > the CONFIG_DEBUG_MUTEXES case: > > #ifdef CONFIG_DEBUG_MUTEXES > # include "mutex-debug.h" > # include <asm-generic/mutex-null.h> > /* > * Must be 0 for the debug case so we do not do the unlock outside of the > * wait_lock region. debug_mutex_unlock() will do the actual unlock in this > * case. > */ > # undef __mutex_slowpath_needs_to_unlock > # define __mutex_slowpath_needs_to_unlock() 0 > Right, I overlooked this part. Thanks to both of you for the clarifications.

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Re: Question on mutex code
by Matthias Bonne March 15, 2015

March 15, 2015

On 03/15/15 03:09, Davidlohr Bueso wrote: > On Sat, 2015-03-14 at 18:03 -0700, Davidlohr Bueso wrote: >> Good analysis, but not quite accurate for one simple fact: mutex >> trylocks _only_ use fastpaths (obviously just depend on the counter >> cmpxchg to 0), so you never fallback to the slowpath you are mentioning, >> thus the race is non existent. Please see the arch code. > > For debug we use the trylock slowpath, but so does everything else, so > again you cannot hit this scenario. > > You are correct of course - this is why I said that CONFIG_DEBUG_MUTEXES must be enabled for this to happen. Can you explain why this scenario is still not possible in the debug case? The debug case uses mutex-null.h, which contains these macros: #define __mutex_fastpath_lock(count, fail_fn) fail_fn(count) #define __mutex_fastpath_lock_retval(count) (-1) #define __mutex_fastpath_unlock(count, fail_fn) fail_fn(count) #define __mutex_fastpath_trylock(count, fail_fn) fail_fn(count) #define __mutex_slowpath_needs_to_unlock() 1 So both mutex_trylock() and mutex_unlock() always use the slow paths. The slowpath for mutex_unlock() is __mutex_unlock_slowpath(), which simply calls __mutex_unlock_common_slowpath(), and the latter starts like this: /* * As a performance measurement, release the lock before doing other * wakeup related duties to follow. This allows other tasks to acquire * the lock sooner, while still handling cleanups in past unlock calls. * This can be done as we do not enforce strict equivalence between the * mutex counter and wait_list. * * * Some architectures leave the lock unlocked in the fastpath failure * case, others need to leave it locked. In the later case we have to * unlock it here - as the lock counter is currently 0 or negative. */ if (__mutex_slowpath_needs_to_unlock()) atomic_set(&lock->count, 1); spin_lock_mutex(&lock->wait_lock, flags); [...] So the counter is set to 1 before taking the spinlock, which I think might cause the race. Did I miss something?

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Setting cred->security field of a newly created process
by noyb noybee March 15, 2015

March 15, 2015

How do I go about setting the cred->security field of the task_struct of a newly created process? There is no specific condition, all it has to do is assign the security field of the parent to the child, as soon as it is created. I looked into the security_task_struct hook, but apparently that doesn't contain the task_struct of the child(obviously, since it is called before the creation to check for permission), but also the clone_flags variable can't be used because that doesn't contain an option for copying the cred->security field too. Also, when are the hooks cred_alloc_blank, cred_free, cred_prepare, cred_commit & cred_transfer hooks called?

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Start it again .. Returning the Kernel Writing
by Ruben Safir March 15, 2015

March 15, 2015

Hello I'm taking a class on operating systems and it includes, happily, many Linux examples, outlining OS internal structures and algorithms. I wanted to delve into the Scheduler, particularly the CFS that has been implemented and to try running and testing things such as what is outlined here http://www.embedded.com/design/operating-systems/4371651/Comparing-the-real… In order to do this, I need to compile and code the Kernel and Kernel modules. I've done this many many time in years gone by, but the current kernel has seemed to have grown even more than I anticipated. For those who work on the kernel and drivers everyday, what would you recommend as a best approach to tinker with the scheduler or even tinker with struct.h entries. I set up a VM with oracles virtualbox, and even that was new to me. I used to keep a usb drive to development and rebooting when I last attempted this. Ruben

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Understanding the mapping of physical memory to kernel address space
by Sunny Shah March 15, 2015

March 15, 2015

Hello, This is my first mail on this list, so please let me know if I'm erring. I'm reading Bovet and Cesati's "Understanding the Linux Kernel", specifically the chapter "Memory Addressing", sub-section "Kernel Page Tables". Here they describe how Linux initializes its page tables for various RAM sizes and how much of the physical address space is mapped onto the kernel virtual address space. I have several questions from my reading: - My understanding is that the 32 bit virtual address space of a process is split into 2 parts - the first 3 GiB for the user space and the remaining 1GiB for the kernel (with the same kernel mapping being used for all processes. However, although the kernel is mapped into the higher portion of the address space, it resides in the lower 1 GiB of RAM. Is this correct? - There is a frequent mention of "mapping RAM to the kernel address space". Is the whole RAM mapped to the kernel space? What would happen in the case of a machine having only 1 GiB of RAM? - Related to the above, what exactly is max_low_pfn? It is mentioned it is the "Page frame number of the last page frame directly mapped by the kernel (low memory)". What would it's value be for a machine with 1 GiB RAM? For a machine with 4 GiB RAM, would it be the number of the frame covering the last portion of kernel space (896 MiB)? Sorry if my questions are a bit vague. I'm still new to this and having difficulty relating everything. Thanks, Sunny

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the study of programming languages
by Meyer Lansky March 15, 2015

March 15, 2015

Hello. Prompt true kernel developer assembler must know or not? Today, as far as it is relevant ? Thank you for your attention !

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kernel development returning to after 10 years
by Ruben Safir March 15, 2015

March 15, 2015

Hello I'm taking a class on operating systems and it includes, happily, many Linux examples, outlining OS internal structures and algorithms. I wanted to delve into the Scheduler, particularly the CFS that has been implemented and to try running and testing things such as what is outlined here http://www.embedded.com/design/operating-systems/4371651/Comparing-the-real… In order to do this, I need to compile and code the Kernel and Kernel modules. I've done this many many time in years gone by, but the current kernel has seemed to have grown even more than I anticipated. For those who work on the kernel and drivers everyday, what would you recommend as a best approach to tinker with the scheduler or even tinker with struct.h entries. I set up a VM with oracles virtualbox, and even that was new to me. I used to keep a usb drive to development and rebooting when I last attempted this. Ruben

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mntinfo of process
by Nilesh Chate March 15, 2015

March 15, 2015

Hi, Considering the the output of #cat /proc/pid/mountinfo I have this line for one of my process 39 38 0:10 /1 /dev/console rw,relatime shared:7 - devpts devpts rw,mode=600,ptmxmode=000 Here, /1 is root: root of the mount within the filesystem.(man 5 proc) What is this /1? Thanks.

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