howoto get load address of a kernel module or libraries

In case of kernel modules, cat /proc/modules will give you a rough guide to where things are loaded. I f you are debugging some kernel crash in a module, you might get more of a clue about exactly where the  crash is by looking at /proc/kallsyms.

The shared library loader ld.so may change the virtual addresses at which a shared library is loaded depending on the needs of a binary. Its reason is the size of code, data and other sections may vary from one binary to the next. The process of rearranging the address space is called relocation. Relocation is also the reason why you have to compile shared libraries as position-independent code with gcc -fPIC.Additionally, each shared library can contain different segments (for static zeroed data, static initialized data, program text, TLS, etc.). Each of those segments will occupy different regions of the address space and will likely have different permissions.

So if you want to know the load address of a shared library used by your process, u should check it for your process itself. cat /proc/<pid>/maps will give you the mapping information of the process with process id <pid>. One line of information will look something like this:

003fb000-00410000 r-xp 00000000 08:01 504990 /lib/ld-2.3.2.so
  
003fb000-00410000: Virtual memory range.

 r-x:
Permissions for the mapping. The chars denote read, write, and
execute. What is shown in maps is the permissions requested by
the application. The actual permissions may differ because of
hardware limitations.

p: Is the mapping shared or private.

00000000: Offset in backing file.

08:01: Device number for the backing file.

504990: Inode number for the backing file.

/lib/ld-2.3.2.so:
Name of the backing file. This name does not have proper
escaping of special chars, so with a carefully crafted file
name, this entire maps file may be fubar.

The ldd utility prints the shared library dependencies of an executable. If the ldd is native, it will provide the load addresses for all shared libraries. For example, following output is the shared library dependecies of ls command in my system.
ldd /bin/ls
    librt.so.1 => /lib64/librt.so.1 (0x0000003af7c00000)
    libacl.so.1 => /lib64/libacl.so.1 (0x0000003b00600000)
    libselinux.so.1 => /lib64/libselinux.so.1 (0x0000003965200000)
    libc.so.6 => /lib64/libc.so.6 (0x0000003af4000000)
    libpthread.so.0 => /lib64/libpthread.so.0 (0x0000003af4c00000)
    /lib64/ld-linux-x86-64.so.2 (0x0000003af3000000)
    libattr.so.1 => /lib64/libattr.so.1 (0x0000003b00a00000)
    libdl.so.2 => /lib64/libdl.so.2 (0x0000003af4800000)
    libsepol.so.1 => /lib64/libsepol.so.1 (0x0000003964e00000)

 

Exclude certain string pattern from grep

If we want to exclude a file while grep, we can --exclude=<filename>.
For excluding a directory we can use --exclude-dir=<directory name>.
But if we want to exclude a string pattern from grep how we will do it? For example, in my source code I want to see where all the define ART_BUILD is used. When I grepped it, I got ART_BUILD_NUM also in the grep result. I want exclude it from the result. How I will do it?

Well, I coudn't find direct solution for it. But, I got th result using the following command.
grep -nr <pattern to grep>  . | grep -v <pattern to be excluded>

I don't know whether a better solution is present or not. But served the purpose

How to fix Skype crash 26-May-2011

Skype was crashing in my system yesterday(26-May-2011) onwards. I just fixed it by removing
In Ubuntu:
/home/<username>/.Skype/shared.xml.
In windows xp:
c:\Documents and Settings/<username>/Application Data/Skype/shared.xml
In win 7:
Win 7: C:\Users\%username%\AppData\Roaming\Skype


Next time when you start skype it may ask whether you agree to the Skype End User Licence Agreement. Just say "I agree" and it should work fine

host key and Virtual Box (how to Alt-Tab out of virtual box)

From the host OS, if you Alt-tab into the virtual box it will work as usual. But if you do Alt-tab inside virtual box, switching will happen between the windows opened inside that. This is because the keyboard is controlled by the virtual machine now. Just pressing the host key without hold returns control back to the host OS. All the key presses after that will go to the host itself. So, if you want switch out of virtual press host key once and then Alt-Tab. Check this link. for more information.