SPO600 - Lab 4 - Code Building Lab

In lab number 4, we will be building a software package.
In the first step, we will choose a software package from the Free Software Foundation's GNU Project.
A full list of software packages can be found here: Link.

I have decided to build the software package of Barcode. Barcode is a "a tool to convert text strings to printed bars. It supports a variety of standard codes to represent the textual strings and creates postscript output."

Now after picking the package we would like to work with, we will log into our Linux system and download the package using "wget" command:

 wget ftp://ftp.gnu.org/gnu/barcode/barcode-0.99.tar.gz

This is what we should be getting from the console:

barcode-0.99.tar.gz 100%[===================>] 869.85K  2.87MB/s    in 0.3s

2017-10-01 19:47:58 (2.87 MB/s) - ‘barcode-0.99.tar.gz’ saved [890730]

 Next, we will unzip the file we have downloaded using the "tar" command:

 tar -zxvf barcode-0.99.tar.gz

 After we unzipping the file, we can see there should be an instruction file (often named as INSTALL). In this case, the INSTALL file tells us to look at INSTALL.generic for basic instructions. By reading the file INSTALL.generic we can see the following instructions:

From the document, we understand that the next step would be to run the "configure" command.
After the configuration is done, we will run the command "make" to compile the package.
The fourth step "make install" would install the programs and relevant data, which is something we do not want, so we won't do this part.
 After running the command "make" which should be finished in a few minutes, we will get a new file called "barcode".
By running it we can test the software package:

It works!


Part 2: Build and test glibc

In this part we will find and build the source code for the latest released version of the GNU Standard C Library (glibc), which can be found at the glibc website.
Now we will download it to our system using the "wget" command:

wget http://ftp.gnu.org/gnu/glibc/glibc-2.26.tar.gz

 This is what we are supposed to be getting:

glibc-2.26.tar.gz   100%[===================>]  28.00M  19.6MB/s    in 1.4s

2017-10-01 20:00:41 (19.6 MB/s) - ‘glibc-2.26.tar.gz’ saved [29355499/29355499] 

Next, we will unpack the file using "tar -zxvf".
Same as with more other software packages, the installing instructions are within the INSTALL file, which we will now open and skim through it.
The INSTALL file states that:

The GNU C Library cannot be compiled in the source directory.  You must
build it in a separate build directory.  For example, if you have
unpacked the GNU C Library sources in '/src/gnu/glibc-VERSION', create a
directory '/src/gnu/glibc-build' to put the object files in.  This
allows removing the whole build directory in case an error occurs, which
is the safest way to get a fresh start and should always be done.

As a safety measure so we will create a new folder called "glibc-build" and compile the file there, using a prefix to our command:

../glibc-2.26/configure --prefix=/home/ragarunov/glibc-build

Then we will run the command "make".
After a long compiling process, we can finally begin to test our library!

Testing:
The library provides us the file "testrun.sh" that can be used to test our own version. Using that, we can test our version of glibc by creating a simple Hello World program in C:

It works!
Now, we will try to put a bug and run the program. We will do so with a simple array and a loop:
[ragarunov@xerxes glibc-build]$ cat test.c

#include <stdio.h>

int main () {
        int num[4] = {1, 2, 3, 4};
        int i;

        for (i = 0; i<5; i++) {
                printf("%d", num[i]);
                printf("\n");
        }

        return 0;
}

After compiling and running the command:

./testrun.sh /home/ragarunov/lab4/glibc-build/test

Prints:

1
2
3
4
1219370488

 In both tests, the library worked well and compiled the files as necessary!

Override:
The override mechanism is commonly used in object oriented programming languages as a feature to provide subclasses implementations that will replace (or override) that implementation that has already been given by its parent class.

Multiarch:
Multiarch is a term that refers the capability of a system to install and run applications of multiple different binary targets on the same system. It is used to simplify cross-building of libraries and headers that are required for a system during building.