- kernelnewbies@kernelnewbies.org - Kernelnewbies Mailing Lists

Reserve physical page
by Prateek Sharma Aug. 7, 2011

Aug. 7, 2011

Hello everyone, I am wondering whether it is possible to reserve a particular physical page in the kernel. The GFP pages can start from _any_ location, and i cannot find a way to specify a starting pfn. I need a few dozen pages to store a bitmap starting at a particular physical page frame number. Perhaps i am trying to do this wrong? I am trying to establish a (one-way) communication between KVM and a guest VM, by assuming that if KVM knows the physical address in the VM , it can access that bitmap. Thanks !

3 5

One more question on alignment
by subin gangadharan Aug. 6, 2011

Aug. 6, 2011

Hi, This is a text excerpt from the article [1]. Below paragraph I didn't understand quite well.Mainly in bold letters.Could anybody please explain how this will lead to an infinite loop. Atomicity All modern processors offer atomic instructions. These special instructions are crucial for synchronizing two or more concurrent tasks. As the name implies, atomic instructions must be *indivisible* -- that's why they're so handy for synchronization: they can't be preempted. It turns out that in order for atomic instructions to perform correctly, the addresses you pass them must be at least four-byte aligned. This is because of a subtle interaction between atomic instructions and virtual memory. If an address is unaligned, it requires at least two memory accesses. But what happens if the desired data spans two pages of virtual memory? This could lead to a situation where the first page is resident while the last page is not. Upon access, in the middle of the instruction, a page fault would be generated, executing the virtual memory management swap-in code, destroying the atomicity of the instruction. To keep things simple and correct, both the 68K and PowerPC require that atomically manipulated addresses always be at least four-byte aligned. *Unfortunately, the PowerPC does not throw an exception when atomically storing to an unaligned address. Instead, the store simply always fails. This is bad because most atomic functions are written to retry upon a failed store, under the assumption they were preempted. These two circumstances combine to where your program will go into an infinite loop if you attempt to atomically store to an unaligned address. Oops.* [1] http://www.ibm.com/developerworks/library/pa-dalign/. -- With Regards Subin Gangadharan Everything should be made as simple as possible,but not simpler.

2 2

Compiling kernel module ...
by Abu Rasheda Aug. 6, 2011

Aug. 6, 2011

I am compiling my driver and have run into following scenario. Socket create function got a new parameter in Vanila kenrel 2.6.33. while Scientific Linux has it back ported to 2.6.32. How do I handle this kind of situation ? so that my driver compiles for both kernel versions.

3 5

Debugging the linux kernel core dump
by Akash Aug. 6, 2011

Aug. 6, 2011

Hello, I have a core dump from following machine : <http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies> # uname -a Linux sing-vto2-dst 2.6.34.8-0.2-desktop #1 SMP PREEMPT 2011-04-06 18:11:26 +0200 x86_64 x86_64 x86_64 GNU/Linux I have opened this core in gdb # gdb vmlinux-2.6.34.8-0.2-desktop kernel.core0 GNU gdb 6.6 (build 2009-10-05) Copyright (C) 2006 Free Software Foundation, Inc. GDB is free software, covered by the GNU General Public License, and you are welcome to change it and/or distribute copies of it under certain conditions. Type "show copying" to see the conditions. There is absolutely no warranty for GDB. Type "show warranty" for details. (no debugging symbols found) Program terminated with signal 11, Segmentation fault. #0 0xffffffff8100ba60 in default_idle () How can I add symbols to gdb ? When I try to add symbols from System.map I get following error : (gdb) add-symbol-file System.map-2.6.34.8-0.2-desktop The address where System.map-2.6.34.8-0.2-desktop has been loaded is missing At what address should the System.map be added ? How can I find out that address ? Thanks for any help. Akash

3 6

How to get current core id in kernel source
by J.Hwan Kim Aug. 6, 2011

Aug. 6, 2011

Hi, everyone I wish to get the current core id in which the code is being processed, in device driver code. What function or global variable can I use ? Thanks in advance. Best Regards, J.Hwan Kim

2 1

how to freeze the 2.6 kernel on SMP m/c
by san deep Aug. 6, 2011

Aug. 6, 2011

Hi, Could you please suggest how to freeze the 2.6 kernel(SMP m/c) with my own dlkm with less number of code. I tried the below mentioned code snippet, it hangs only the terminal on which i executed the insmod command. Please correct the below code to freeze whole kernel. #include <linux/module.h> #include <linux/kernel.h> #include <linux/spinlock.h> #include <linux/delay.h> int init_module(void) { spinlock_t lock = SPIN_LOCK_UNLOCKED; while (1) { spin_lock(&lock); msleep(100); } //spin_unlock(lock); printk(KERN_INFO "Hello world :).\n"); return 0; } void cleanup_module(void) { printk(KERN_INFO "Goodbye world :(.\n"); } Thanks and Regards, Sandeep

2 1

can i simply "re-version" the kernel down to 2.x?
by Robert P. J. Day Aug. 6, 2011

Aug. 6, 2011

for reasons that don't need explaining, i need to rebuild my current 3.0.0... kernel so that it returns a "uname" version number of "2.whatever". i simply have an app i want to run that checks the output of "uname" and if it doesn't see a major number of "2", it goes a bit squirrelly. there's no *technical* reason i can see for the app to be that restrictive, so i was just going to hack the top level Makefile of my git clone and label this as a 2.99.99 kernel. is there anything that would break because of that kind of hackery? rday -- ======================================================================== Robert P. J. Day Ottawa, Ontario, CANADA http://crashcourse.ca Twitter: http://twitter.com/rpjday LinkedIn: http://ca.linkedin.com/in/rpjday ========================================================================

3 3

Reboot not calling module_exit of LKM
by Ramesh.P Aug. 5, 2011

Aug. 5, 2011

Hi, Good day! When a system is rebooted, the loadable kernel modules 'module_exit' functions are not called. I see this behavior in a custom kernel. My questions are a. Is this applicable in mainline/normal kernel too? b. If yes, what are the reasons? (One reason may be, not to get into new problems while cleaning up the module) c. Is there anyway for the kernel module to know the system is getting rebooted? (Apart from letting userspace to indicate the kernel module). Appreciate your help and apologize if this is already answered in this forum. Thanks, Ramesh

2 2

trouble with __aquires(lock) __releases(lock)
by Jim Cromie Aug. 5, 2011

Aug. 5, 2011

Im trying to use macros from include/linux/compiler.h and theyre giving me warnings that dont look right. after thrashing on my own hacks, I looked to well established uses for guidance. But make C=1 fs/file.o also gives errors, similar to mine. What am I missing ? or has some bitrot set in ? 202static int expand_fdtable(struct files_struct *files, int nr) 203 __releases(files->file_lock) 204 __acquires(files->file_lock) 205{ 206 struct fdtable *new_fdt, *cur_fdt; 207 208 spin_unlock(&files->file_lock); 209 new_fdt = alloc_fdtable(nr); 210 spin_lock(&files->file_lock); ... 247int expand_files(struct files_struct *files, int nr) 248{ ... 268 /* All good, so we try */ 269 return expand_fdtable(files, nr); 270} CHECK /home/jimc/projects/lx/linux-2.6/fs/file.c /home/jimc/projects/lx/linux-2.6/fs/file.c:32:5: warning: symbol 'sysctl_nr_open_min' was not declared. Should it be static? /home/jimc/projects/lx/linux-2.6/fs/file.c:33:5: warning: symbol 'sysctl_nr_open_max' was not declared. Should it be static? /home/jimc/projects/lx/linux-2.6/fs/file.c:416:21: warning: symbol 'init_files' was not declared. Should it be static? /home/jimc/projects/lx/linux-2.6/include/linux/spinlock.h:325:2: warning: context problem in 'expand_fdtable': '_raw_spin_unlock' expected different context /home/jimc/projects/lx/linux-2.6/include/linux/spinlock.h:325:2: context 'lock': wanted >= 1, got 0 /home/jimc/projects/lx/linux-2.6/fs/file.c:269:23: warning: context problem in 'expand_files': 'expand_fdtable' expected different context /home/jimc/projects/lx/linux-2.6/fs/file.c:269:23: context 'file_lock': wanted >= 1, got 0

1 0

Need help: GCC cross compiler and OS/platform dependency
by amit mehta Aug. 5, 2011

Aug. 5, 2011

This is not a Linux kernel query, rather a generic OS related information that i seek. I was going through the manpages of gcc and if you go further down, you'll find infomation on "-b" flag. Quoting from gcc man page: " -b machine The argument machine specifies the target machine for compilation. The value to use for machine is the same as was specified as the machine type when configuring GCC as a cross-compiler. For example, if a cross-compiler was configured with configure arm-elf, meaning to compile for an arm processor with elf binaries, then you would specify -b arm-elf to run that cross compiler. Because there are other options beginning with -b, the configuration must contain a hyphen. " So what i understood is that on my x86_64 bit machine, gcc -b arm-elf <foo.c> will not work, instead, you should have something like this: i586-elf-gcc <foo.c>, which will produce an object code which can run on i586 platform. (Please correct if i'm wrong). I dig little further by trying to build gcc cross compiler for x86(32 bit) target for educational purpose by following the instructions provided here: http://wiki.osdev.org/GCC_Cross-Compiler Though I was able to build the gcc(i586-elf-gcc), I haven't been able to build C library and the C runtime magic yet, partly due to the build failure and mostly due to incognizance on the details of these pieces working together. hence please throw in some light on how these different pieces work together. <<<snip>>> goon:/usr/local/cross/bin # ./i586-elf-gcc -v Using built-in specs. COLLECT_GCC=./i586-elf-gcc COLLECT_LTO_WRAPPER=/usr/local/cross/libexec/gcc/i586-elf/4.6.0/lto-wrapper Target: i586-elf Configured with: ../gcc-4.6.0/configure --target=i586-elf --prefix=/usr/local/cross --disable-n\ ls --enable-languages=c --without-headers Thread model: single gcc version 4.6.0 (GCC) <<<snip>>> <<<error>>> goon:/usr/src/build-gcc # make all-target-libgcc checking for i586-elf-gcc... /usr/src/build-gcc/./gcc/xgcc -B/usr/src/build-gcc/./gcc/ -B/usr/local/cross/i586-elf/bin/ -B/usr/local/cross/i586-elf/lib/ -isystem /usr/local/cross/i586-elf/include -isystem /usr/local/cross/i586-elf/sys-include checking for suffix of object files... configure: error: in `/usr/src/build-gcc/i586-elf/libgcc': configure: error: cannot compute suffix of object files: cannot compile See `config.log' for more details. make: *** [configure-target-libgcc] Error 1 goon:/usr/src/build-gcc # grep -i error config.log | /* Override any GCC internal prototype to avoid an error. conftest.c:10:19: error: ppl_c.h: No such file or directory conftest.c:16: error: 'choke' undeclared (first use in this function) conftest.c:16: error: (Each undeclared identifier is reported only once conftest.c:16: error: for each function it appears in.) conftest.c:16: error: expected ';' before 'me' stage2_werror_flag='' <<<error>>> -Amit

1 0