How to find address of stack top : C

In technical interviews, sometimes candidates are asked how they would find the address of the top of the stack in their system by programming in C. One simple program that should work mostly is:

int main()
{
int i;
printf("Top of the stack is %p", &i);
return 0;
}

As local variables are stored on stack, this would give an approximate top of stack. There can be variations of this program that are also few-liners like above and give more accurate results. Any more example piece of code to find stack top?

LaMacchia Loophole

Year 1993. A 21 year-old student at MIT named David LaMacchia set up a bulletin board system called "Cynosure." It generated a lot of traffic worldwide. People used this service to download software they wanted or upload what they had. It was online for about six weeks before being taken down by the authorities. Software companies claimed that they lost one million dollars from Cynosure. Federal grand jury charged LaMacchia with 'one count of conspiring with unknown persons to violate the wire-fraud statute'. What LaMacchia did wasn't criminal conduct under the Copyright Act. The infringement was not for the purpose of commercial advantage. So, the charge was dismissed . The lawmakers had not thought that someone might engage in these types of activities with a non-financial motive. In 1997, Congress closed this loophole with NET (No Electronic Theft) Act.

No archives (*.a ) in Solaris anymore

While discussing static libraries in one of my previous posts, I commented that libm is provided as both dynamic library ( libm.so ) as well as static archive ( libm.a ).

Well, that is not true for Solaris anymore. Solaris 10 doesn't ship with a single static library.
Doing
ls -la |grep *.a
in /usr/lib where libraries are usually present returned no results. Tried in some more directories with same result.
I don't know when static libraries were dropped from Solaris. My guess is that it was Solaris 10, but any pointers to information would be welcome.

FLV to MPEG converter

Many times we come across videos on net we want to download but can't as they are in FLV format/flash video. There is an online opensource tool to download such online videos from sites such as YouTube. The tool converts the FLV files into MPEG format online, which can then be saved to a computer. The online FLV converter is a very useful tool. I downloaded this hilarious video clip from YouTube using this online tool.



The quality of download was very good and it was fast. Try it out!

Static linking : library options in command line

In my last post I asked why it's advised that library options be the last in the command line in case of static linking.

Here is the explanation:
The symbols on the command line are resolved from left to right.
Stating linking looks through the static library for "undefined" symbols when it is processed.
Now in case of

cc -lfoo hello.c

there are no undefined symbols when libfoo.a gets processed and so nothing gets extracted from it. When the object file is processed, it doesn't find any symbol and it gives an error "Undefined symbol"
If hello.c is put before -lfoo as in

cc hello.c -lfoo

there are undefined symbols when libfoo gets processed and so they get extracted. This works fine.

Dynamic linking doesn't have this issue as all symbols are available through the virtual address space of the output file.
Static libraries have other issues like bigger executable size, and lack of ABI ( application needs to be relinked with each new version of the library).
One advantage of having static libraries is that the executables linked to them are somewhat faster at runtime because all the linking occurs before loadtime. This helps in benchmarking. Math library libm is provided as a shared object (libm.so) as well as static library (archive libm.a) since benchmarking makes a heavy use of this library.

quirk of static linking

A question related to linking today.

Why is it advised to put the library options at the end of command line for compilation?

Hint: If we have a static library, say libfoo.a which we want to link to our program hello.c

cc hello.c -lfoo
rather than

cc -lfoo hello.c

-l option tells the compiler to link to library [lib]foo. Note that "lib" from libfoo is dropped and only "foo" part is given with -l.

How Nerdy are you?

Took this Nerd test and was worried I was going to score a "less nerdy" type. But the result were pleasantly surprising. It said " All hail the monstrous nerd. You are by far the SUPREME NERD GOD!!!"
Perhaps, my score was helped by a few dirty clothes in my room, and Solaris.
For now, I am in heaven!

RAID Primer

Found a brief and good online paper on different types of RAID ( Redundant Array of Independent Discs ). It explains RAID concepts with a brief explanation of each type along with their pros and cons.
The paper can be read here.

Top 10 funniest gadgets

While surfing the net today, I stumbled upon this list of top 10 funniest gadgets.
My favorite are DVD rewinder and USB powered butt cooler. What are yours?

Microsoft threatens Linux with patents

According to a news article, Microsoft has alleged that Linux and other Open Source software violate its patents. This includes 42 by Linux kernel alone and many by OpenOffice, totalling 235 patents in all.

Looks like an open source arm-twisting effort by MS directly related to their deal with Novell last year.

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