GNU Compiler Collection - August 2005

1. GCC(GNU Compiler Collection)
Tool Kit
Linux Users Group, JMI
An overview of GNU Compiler Collection and
its use for compiling C, C++
By: Saleem A. Ansari

2. The Free Software Compiler
An Introduction to GCC
 Virtually all other open software is based on it at
some level or another. Even other languages,
such as Perl and Python, are written in C, which
is compiled by the GNU compiler.
 This piece of software is more fundamental to
the entire free software movement than any
other. In fact, without it or something like it,
there would be no free software movement. Lin-
ux is possible because of GCC.

3. GCC is a product of the GNU
Project.
 The fundamental language of GCC is C. The en-
tire compiler system began as a C compiler and,
over time, the other languages were added to it.
 C++ Was the First Addition. Now can compile
C++, Objective-C, Java, Ada, Fortran ...
 The GCC set of compilers runs on many plat-
forms. We can do multi-platform compilation us-
ing the same machine. (Alpha, HPPA, Intel x86,
MIPS, PowerPC, Sparc)

4. GCC Components
 cc1: The actual C compiler.
 cc : A version of gcc that sets the default lan-
guage to C and automatically includes the
standard C libraries when linking.
 cc1plus : The actual C++ compiler.
 g++ / c++ : A version of gcc that sets the default
language to C++.
 jc1: The actual Java compiler.
 gcj The driver program used to compile Java.
 gcc: The driver program.

5. GCC Components contd.
 as : The GNU assembler. It is really a family of
assemblers because it can be compiled to work
with one of several different platforms. This pro-
gram is part of the binutils package.
 gdb : The GNU debugger, which can be used to
examine the values and actions inside a pro-
gram while it is running.
 Other tools : gprof (profiler), ld(linker),
ar(archive), make, nm, objcopy, objdump, ranlib,
strip ...

6. Developing Software using GCC
 You need a text editor: gedit, kedit, vi
emacs, joe, nedit etc.
 You need to learn atleast one of the lan-
guages supported by GCC: C, C++, Java,
Fortran etc.
 You need the GCC Toolkit Installed on the
system itself
 get-set-go...

7. The famous C program
/*hello.c*/
#include<stdio.h>
int main()
{
printf(“Hello GCCn”);
return 0;
}
Compilation:
cc ­c hello.c
cc ­o hello hello.o
./hello

8. The famous program in C++
/*hello.cpp*/
#include<iostream>
using namespace std;
int main(void)
{
cout << “Hello GCC” << endl;
return 0;
}
Compilation:
c++ ­c hello.cpp
c++ ­o hello hello.o
./hello

9. Command Line Options
 -c compile and produce object
code
 -o name of translated code file
 -l specify library
 -I specify include directory
 -Wall show all errors
 -std=__ assume the specified
standard
 -v give verbose output
 -s, -S result in assembly code
production
 -O1, O2, -O3 Optimization Levels

10. Yet another simple example. Illegal
memory access!!
#include<stdio.h>
int main()
{
char *str=”abc”;
str[0]=’d’;
str[1]=’e’;
str[2]=’f’;
puts(str);
return 0;
}

11. Here comes the debugger
 Use the GCC command line switch -g or
-ggdb to incorporate debugging information
into the object code
 Invoke the gdb and fire!!

12. Multiple Files: A simple example
/*mystring.c*/
#include<string.h> /*mystring.h*/
int palindrome(char s[]) int palindrome(char s[]);
{
int l=strlen(s)-1;
int i=0;
while(i<l)
if(s[i++]!=s[l--])
return 0;
return 1;
}

13. /*mystringtest.c*/
continued...
#include<stdio.h>
#include "mystring.h"
int main()
{
char str[50];
puts("Enter a string:");
gets(str);
if(palindrome(str))
printf("Its a palindrome");
else
printf("Its not a palindrome");
return 0;
}

14. MAKE indeed is a boon
MAKEFILE
--------------------------------------------------------------------------
CC=gcc
CFLAGS=-Wall -g
all: mystring.a test
test: mystring.a
$(CC) $(CFLAGS) -c mystringtest.c
$(CC) $(CFLAGS) -o test mystringtest.o mystring.a
clean:
rm -f test mystringtest.o mystring.o mystring.a
mystring.a: mystring.o
ar cvr mystring.a mystring.o
ranlib mystring.a
mystring.o:
$(CC) $(CFLAGS) -c mystring.c

15. Compiling a complete software
MPlayer as an example demonstration

16. For further information
 Manpages of gcc, make, gdb, nm, obj-
dump, objcopy...
 Info pages of binutils

17. Thats all for now!
Thanx