linux in msft search

I read about this somewhere else, but I had to try it out myself...

The first two links in Microsoft Search when looking for Linux is "how to remove Linux". Elegant.

you have to be kidding me with Vista

I am not one to rant, and certainly not one to not appreciate the complications with building an operating system.

But, you have got to be kidding me with the Vista crap. I have been using it on a work laptop (was provided with it) since about a week and I have had my laptop actually CRASH (blue screen) after plugging-in and unplugging a usb mouse, my usb cell phone and after trying to wake up after hibernating.

Oh, and unless I enable "sending of null packets to keep session active" and enable TCP keepalives in my putty sessions, I get "Network error: Software caused connection abort" every few minutes.

People pay to buy this crap?

Okay, rant over.

final sign on the "road to 64-bit"

I wrote about switching to 64-bit Ubuntu a few days ago.

Then I added an update a few days later with more information.

The major conclusion there was that if you have > 3GB RAM, unless you are using a customized kernel or the 64-bit Ubuntu, you are not going to be able to use more than 3GB RAM.

Anyways, not that I needed more convincing, but tuxradar has a damn good write-up with performance numbers comparing Ubuntu 9.04 with 32-bit and 64-bit version:

Ubuntu 9.04 32-bit v/s 64-bit performance numbers

I think this conclusion summarizes it nicely -
"Putting aside the issue of Flash for a moment, moving from 32-bit to 64-bit is pretty much painless. In fact, you can't tell the difference without running uname -a in a terminal - all the programs you're used to are likely to run identically, and ultimately it's only a matter of time before x86-64 becomes the standard."

There is no turning back, I am convinced 64-bit is the way to go.

update on "the road to 64-bit"

A couple of days ago, I wrote about moving to 64-bit ; seems like it's going to be a simple decision for me.

A 32-bit operating system is limited to 4 GB of memory ( you can only reference 2 ^ 32 = 4GB ). However, 32-bit Ubuntu is limited to 3 GB. If you are considering between 32-bit and 64-bit Ubuntu and you have more than 3 GB of memory that should be a simple decision.

There is a workaround however if you are still not convinced 64-bit is the way to go - install server kernel as it has support for upto 4 GB. But think about the future when your 4GB will not be enough and you add more memory?

There is a bug (=4GB memory">Bug 74179) that covers releasing a 32 bit option for high memory ( > 3 GB) system.

kerneltrap.org has a good page on kernel and high memory with a good explanation of physical memory versus virtual memory.

memory leak with inheritance and destructors

I use inheritance and virtual functions fairly frequently, but I am wondering how common this is:

A little bit of context -

When using inheritance, destructors are called in the reverse order of inheritance. If a base class pointer points to a derived class object, and later we use the delete operator to delete the object, then the derived class destructor is not called. Refer to the code that follows:

#include 
class base
{
public:
~base()
{

}
};

class derived : public base
{
public:
~derived()
{

}
};

void main()
{

base *ptr = new derived();
// some code
delete ptr;
}

The result is a memory leak.

Solution to avoid this -

Make the destructor virtual in the base class. A virtual destructor is one that is declared as virtual in the base class.

#include 
class base
{
public:
virtual ~base()
{

}
};

class derived : public base
{
public:
~derived()
{

}

};

void main()
{

base *ptr = new derived();
// some code
delete ptr;
}

Does this mean when using virtual functions, it is always a good idea have the destructor virtual as well?

what is ld-linux.so.2

Back in April, I wrote about a particular use of ld-linux.so.2. It's important to know however what the purpose of ld-linux.so.2 is in a little more detail.

ld-linux.so is the locater and loader of dynamic (shared libs) on your system. Most applications these days use shared libs (instead of statically built-in libs). When a program is loaded, Linux passes control to ld-linux.so.2 instead of normal entry point of the application. Now ld-linux.so.2 searches for and loads the unresolved libraries, and then it passes control to the application starting point.

To understand how a program loads, it's useful to understand ELF. The ELF (Executable and Linking Format) specification defines how an object file is composed and organized. With this information, the kernel and the binary loader (ld in our case) know how to load the file, where to look for the code, where to look the initializeddata, which shared library that needs to be loaded and so on.

ld-linux.so.2 is the runtime component for the linker (ld) which locates and loads into memory the dynamic libraries used by the applicaiton.

A little more about ELF (from wikipedia).

Each ELF file is made up of one ELF header, followed by file data. The file data can include:

• Program header table, describing zero or more segments
• Section header table, describing zero or more sections
• Data referred to by entries in the program header table, or the section header table

The segments contain information that is necessary for runtime execution of the file, while sections contain important data for linking and relocation.

There are a few useful tools to read ELF files:

• ldd prints the shared library dependencies.
  
• readelf is a Unix binary utility that displays information about one or more ELF files.
• objdump provides a wide range of information about ELF files and other object formats.

example:

rutul@ubuntu:~/test_progs$ gcc hello_world.c
rutul@ubuntu:~/test_progs$ ldd a.out
       linux-gate.so.1 =>  (0xb7ef2000)
       libc.so.6 => /lib/tls/i686/cmov/libc.so.6 (0xb7d80000)
       /lib/ld-linux.so.2 (0xb7ef3000)
rutul@ubuntu:~/test_progs$
rutul@ubuntu:~/test_progs$ readelf -l a.out

Elf file type is EXEC (Executable file)
Entry point 0x8048310
There are 8 program headers, starting at offset 52

Program Headers:
 Type           Offset   VirtAddr   PhysAddr   FileSiz MemSiz  Flg Align
 PHDR           0x000034 0x08048034 0x08048034 0x00100 0x00100 R E 0x4
 INTERP         0x000134 0x08048134 0x08048134 0x00013 0x00013 R   0x1
     [Requesting program interpreter: /lib/ld-linux.so.2]
 LOAD           0x000000 0x08048000 0x08048000 0x004c4 0x004c4 R E 0x1000
 LOAD           0x000f0c 0x08049f0c 0x08049f0c 0x00108 0x00110 RW  0x1000
 DYNAMIC        0x000f20 0x08049f20 0x08049f20 0x000d0 0x000d0 RW  0x4
 NOTE           0x000148 0x08048148 0x08048148 0x00020 0x00020 R   0x4
 GNU_STACK      0x000000 0x00000000 0x00000000 0x00000 0x00000 RW  0x4
 GNU_RELRO      0x000f0c 0x08049f0c 0x08049f0c 0x000f4 0x000f4 R   0x1

Section to Segment mapping:
 Segment Sections...
  00   
  01     .interp
  02     .interp .note.ABI-tag .hash .gnu.hash .dynsym .dynstr .gnu.version .gn
u.version_r .rel.dyn .rel.plt .init .plt .text .fini .rodata .eh_frame
  03     .ctors .dtors .jcr .dynamic .got .got.plt .data .bss
  04     .dynamic
  05     .note.ABI-tag
  06   
  07     .ctors .dtors .jcr .dynamic .got
rutul@ubuntu:~/test_progs$

the road to 64-bit?

I am trying out a spanking new laptop with Intel T4300 (Dual Core) CPU which came pre-installed with a 64-bit Windows.

Since it's time to get Ubuntu setup on here, the question I am researching is if I should make the leap to 64-bit Ubuntu.

From what I have read so far on the discussion boards, there is not much in terms of what is missing on the 64-bit. The two questions:
a) Is there any benefit of running 64-bit?
b) Is "everything" supported on 64-bit?

a) Maybe I will not notice a performance improvement on applications like Firefox or Eclipse. If I am doing any image or video processing, maybe that shows improvement. I suppose I might even see improvement in mp3 decoding/encoding.
Though, the major benefit it seems is in using 64-bit is to expand the user-base. The key being, the more people use it, the more issues get reported and resolved.

b) If there are any missing packages on 64-bit, I should have an idea of those before I get set up. That is an exercise in itself.
One of the issues I read with versions before 8.04 was that the kernel did not have tickless support, which meant a drain on the battery. That's not going to be an issue since I am planning to install 9.04.
There were a few complains about flash and java plug-ins in Firefox.

I suppose the best option is to try it out and when you run into issues turn to the trusty Ubuntu forums for help.

Ok, ready drive...