June 2016 - kernelnewbies@kernelnewbies.org - Kernelnewbies Mailing Lists

Kernel panic after insmod
by Manavendra Nath Manav June 27, 2016

June 27, 2016

Can someone explain the following kernel module code. I'm not familiar with x86 assembly so have problem understanding this part. Also it seems this code is able to modify the kernel stack. /******************start****************/ #include <linux/module.h> MODULE_LICENSE("GPL"); int __init init(void) __attribute__((noreturn)) { unsigned long long cr0 = read_cr0(); write_cr0(cr0 & ~(1 << 4)); /* Clear Extension Type (ET) bit */ *(unsigned char *)sys_kill = 0xc3; /* opcode for "ret" */ write_cr0(cr0); /* Optional code ahead to hide traces of this module. */ __this_module.refcnt = 1; __this_module.state = MODULE_STATE_LIVE; asm ( "mov %0, %%rsp\n\t" "mov %1, %%rdi\n\t" /* name = __this_module.name */ "xor %%rsi, %%rsi\n\t" /* flags = 0 */ "jmp sys_delete_module\n\t" /* call delete_module(name, flags) */ :: "r"(current->stack + THREAD_SIZE - sizeof(struct pt_regs) - 8), "r"(__ this_module.name) : ); } void __exit exit(void) { return; } /*******************end*****************/

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Mount jffs2 as rootfs error
by Chen, NoamX June 26, 2016

June 26, 2016

Hi all, I've encountered a problem. I'm trying to mount jffs2 rootfs. When the fs is mounted the following warning is displayed: Jffs2: Node totlen on flash (0xffffffff) != totlen from node ref (0x00000044) While the node ref varies, the node totlen on flash does not. This warning did not occur when used ramfs as rootfs, and jffs2 rootfs was mounted manually. This warning occurs when jffs2 fs tries to mark a node as obsolete. In any other sense, the fs appears operable, and I'm able to create files and delete files. Regardless, every so often the warning is displayed and aside from being annoyed by it, I fear it will eventually lead to the corruption of the fs. I use buildroot to build the rootfs image. Buildroot configuration: BR2_TARGET_ROOTFS_JFFS2=y BR2_TARGET_ROOTFS_JFFS2_FLASH_64=y BR2_TARGET_ROOTFS_JFFS2_EBSIZE=0x10000 BR2_TARGET_ROOTFS_JFFS2_PAD=y BR2_TARGET_ROOTFS_JFFS2_PADSIZE=0x00B00000 BR2_TARGET_ROOTFS_JFFS2_LE=y Linux configuration: CONFIG_JFFS2_FS=y CONFIG_JFFS2_FS_DEBUG=0 CONFIG_JFFS2_FS_WRITEBUFFER=y CONFIG_JFFS2_ZLIB=y CONFIG_JFFS2_RTIME=y The rootfs.jffs2 image is loaded to flash at offset 0x00500000, corresponding to /dev/mtdblock3 partition: > cat /proc/mtd dev: size erasesize name mtd0: 00100000 00010000 "u-boot" mtd1: 003f0000 00010000 "kernel" mtd2: 00010000 00010000 "dtb" mtd3: 00b00000 00010000 "rootfs" I pass bootargs = "root=/dev/mtdblock3 rw rootfstype=jffs2, earlycon=uart8250,mmio32,0xf4200000,115200n8 console=tty0 console=ttyS0,115200n8 consoleblank=0"; > cat /etc/fstab # <file system> <mount pt> <type> <options> <dump> <pass> /dev/root / jffs2 rw,noauto 0 1 I found that when I decreased the partition size to 0x450000 this warning was abolished, however, there was not enough space for /etc/dropbear, and I wasn't able to find a "sweet-spot" where there is enough space and no warning. I tried various padding sizes, and removing padding altogether, but to no avail. I tried padding the flash partition itself with 0xff during the construction of the flash binary (the content of the simulation). I've built some rootfs.jffs2 images with varying configurations, but none solved the issue. I looked at hexdumps of the rootfs.jffs2 image, an empty jffs2 partition and the created /dev/mtdblock3 inside the simulation-but have found nothing out of the ordinary. Any help or a lead will be greatly appreciated, Noam --------------------------------------------------------------------- Intel Israel (74) Limited This e-mail and any attachments may contain confidential material for the sole use of the intended recipient(s). Any review or distribution by others is strictly prohibited. If you are not the intended recipient, please contact the sender and delete all copies.

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spidev on davinci
by Denis Obrezkov June 26, 2016

June 26, 2016

Hello, I am trying to use spidev to send messages via spi on OMAP-L137 EVM board. I have an spidev entry in /dev, but when I try to send data, I have the following message: spidev spi1.0: SPI transfer failed: -22 spi_master spi1: failed to transfer one message from queue Debugging using printk, I found out that a probe function is called, and after this transfer_one_message is called. In transfer_one_message master->transfer_one() function is called and returned with the error. But I can't find the implementation of transfer_one function for davinci_spi. So, I have two questions: What implementation is used by default when transfer_one implementation isn't provided? Should I write my own implementation of transfer_one function& -- Regards, Denis Obrezkov

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Identifying whether a pci device is x1, x4, x8 or x16
by Kevin Wilson June 24, 2016

June 24, 2016

Hi all, Is there a way to find out whether a PCI device in a given Linux machine is x1, x4, x8 or x16, in terms of physical dimensions (without opening the box...) Regards, Kevin

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Linux Regulator userspace-consumer driver binding
by Daniel Steger June 24, 2016

June 24, 2016

I'm working on developing a driver for the max15301/15303 linear supply. I eventually want to push this upstream. The regulator driver for the supply has been created and loads properly. What I would like to do now is regression test the driver from userspace. I noticed that there are two different userspace drivers already present in the regulator framework. The first is the userpsace-consumer driver. The second is the virtual regulator driver. Both seem to create sysfs hooks for regulators. I have enabled the userspace-consumer and virtual driver in the kernel config. I can see that the modules are listed in the modules.builtin file. What seems to confuse me is how to bind the consumer driver to the regulator. Typically I would think this can be done in the device tree but the userspace-consumer driver doesn't support device tree. My question is, what is a good method to bind the userspace-consumer driver to the regulator under test? Would it be more appropriate to use the userspace-consumer driver or virtual driver? Thank you, Daniel

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Regarding getrandom syscall
by Avantika Rawat June 24, 2016

June 24, 2016

Hi ALL, I am trying to use getrandom syscall in kernel 3.10.20 by following this link https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=… i have compiled the kernel and now want to call the getrandom syscall from userspace to generate random numbers. But i am getting following error while calling the getrandom () from userspace. (.text.startup+0x18): undefined reference to `getrandom' (.text.startup+0x1c): undefined reference to `getrandom' -- Regards, Avantika Rawat

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What is the point of this function?
by Andrea Benelli June 23, 2016

June 23, 2016

Hello, i was looking at the *linux/sched.h* (kernel version 4.6.2) source code and i found this function at line *1174*: static inline bool cpus_share_cache(int this_cpu, int that_cpu) { return true; } I'm not able to understand the utility of a function that just return a true value. i've noticed that there are a lot of functions like this (function that just return a constant). so...why? thanks.

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Linux Kernel | Process Open Files
by Shahab Khalid June 23, 2016

June 23, 2016

Hi all, I am trying to get process open files of active processes. I am reading linux dump. I am able to get actives process. I am trying to reach d_name in dentry structure but unfortunately the I am receiving the denrty ZERO (0). I am reaching the dentry as task_structure->files_struct->fdtable->file->path->dentry till struct path I am receiving some address but dentry is zero.

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confused about use of "INITRD_COMPRESS" lines in top-level Makefile
by Robert P. J. Day June 22, 2016

June 22, 2016

currently poring over the initramfs code, and i'm a bit curious about the following. in usr/Kconfig, all the possible compression protocols can be selected, and by default are: config RD_GZIP bool "Support initial ramdisks compressed using gzip" default y select DECOMPRESS_GZIP help Support loading of a gzip-encoded initial ramdisk or cpio buffer. If unsure, say Y. config RD_BZIP2 bool "Support initial ramdisks compressed using bzip2" default y select DECOMPRESS_BZIP2 help Support loading of a bzip2-encoded initial ramdisk or cpio buffer. If unsure, say N. ... etc etc ... but in the top-level Makefile, here are the lines that ostensibly select which compression to actually use: # Select initial ramdisk compression format, default is gzip(1). # This shall be used by the dracut(8) tool while creating an initramfs image. # INITRD_COMPRESS-y := gzip INITRD_COMPRESS-$(CONFIG_RD_BZIP2) := bzip2 INITRD_COMPRESS-$(CONFIG_RD_LZMA) := lzma INITRD_COMPRESS-$(CONFIG_RD_XZ) := xz INITRD_COMPRESS-$(CONFIG_RD_LZO) := lzo INITRD_COMPRESS-$(CONFIG_RD_LZ4) := lz4 # do not export INITRD_COMPRESS, since we didn't actually # choose a sane default compression above. # export INITRD_COMPRESS := $(INITRD_COMPRESS-y) so as i read this, the single compression protocol selected will be the last one configured in that list, but where is that variable eventually used? where is the build code or utility that examines the value eventually set and invokes dracut, as the comment suggests? rday -- ======================================================================== Robert P. J. Day Ottawa, Ontario, CANADA http://crashcourse.ca Twitter: http://twitter.com/rpjday LinkedIn: http://ca.linkedin.com/in/rpjday ========================================================================

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oh yeah
by ty armour June 21, 2016

June 21, 2016

if you all want to you can build computers microchip by microchip, just post tutorials on it if you do! these are fun things to think about. IM like a few years out but im sure ill get it done

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