I was a little curious to find out how my program gets executed. In order to find that out, I decided to write a simple c program which is here:
#include <stdio.h>
int main()
{
sleep(30);
printf("Just testing an application!");
}
I have kept the sleep(30) in the beginning of the program so as to give me time to execute the DTrace script, about which I will be talking a little later.
Now i complied it with Sun Compiler and GCC
kumar@myosbox:~/Desktop/Demos$ suncc -o sunCCOutput simplec.c
kumar@myosbox:~/Desktop/Demos$ gcc -o gccOutput simplec.c
Now I wrote a simple DTrace script using the pid provider in order to figure out how printf is implemented (execution detail - functions which get invoked when printf function is called) in these compilers. The dtrace script is below:
pid$1::$2:entry
{
self->trace = 1;
}
pid$1::$2:return
/self->trace/
{
self->trace = 0;
}
pid$1:::entry,
pid$1:::return
/self->trace/
{
}
Now it was the time to execute this script and compare the outputs. I am going to redirect the output of this script into two text files (sunCCOutput.txt and gccOutput.txt).
kumar@myosbox:~/Desktop/Demos$ ./sunCCOutput
kumar@myosbox:~/Desktop/Demos$ pfexec dtrace -F -s pid.d `pgrep sunCCOutput` printf > SunCCOutput.txt
dtrace: script 'pid.d' matched 6712 probes
kumar@myosbox:~/Desktop/Demos$ ./gccOutput
kumar@myosbox:~/Desktop/Demos$ pfexec dtrace -F -s pid.d `pgrep gccOutput` printf > gccOutput.txt
dtrace: script 'pid.d' matched 6714 probes
Now, the content of the file SunCCOutput.txt is as follows:
CPU FUNCTION
1 -> printf
1 -> _setorientation
1 <- _setorientation
1 -> _ndoprnt
1 -> _findbuf
1 -> isatty
1 -> ___errno
1 <- ___errno
1 -> ioctl
1 <- ioctl
1 <- isatty
1 -> _setbufend
1 -> getxfdat
1 <- getxfdat
1 -> isseekable
1 -> ___errno
1 <- ___errno
1 -> fstat64
1 <- fstat64
1 -> ___errno
1 <- ___errno
1 <- isseekable
1 <- _setbufend
1 <- _findbuf
1 -> _realbufend
1 -> getxfdat
1 <- getxfdat
1 <- _realbufend
1 -> memcpy
1 <- memmove
1 <- memcpy
1 -> memchr
1 <- memchr
1 -> ferror
1 <- ferror
1 <- _ndoprnt
1 -> ferror
1 <- ferror
Contents of the file gccOutput.txt is as follows:
So you can see that there is no difference between gcc and suncc when if comes to implement the printf function. But its is so interesting to see that there are 19 function calls made everytime I use a printf in my c program! WOW! ;) I wonder if I could know it this easily if there was no Dtrace!
CPU FUNCTION
1 -> printf
1 -> _setorientation
1 <- _setorientation
1 -> _ndoprnt
1 -> _findbuf
1 -> isatty
1 -> ___errno
1 <- ___errno
1 -> ioctl
1 <- ioctl
1 <- isatty
1 -> _setbufend
1 -> getxfdat
1 <- getxfdat
1 -> isseekable
1 -> ___errno
1 <- ___errno
1 -> fstat64
1 <- fstat64
1 -> ___errno
1 <- ___errno
1 <- isseekable
1 <- _setbufend
1 <- _findbuf
1 -> _realbufend
1 -> getxfdat
1 <- getxfdat
1 <- _realbufend
1 -> memcpy
1 <- memmove
1 <- memcpy
1 -> memchr
1 <- memchr
1 -> ferror
1 <- ferror
1 <- _ndoprnt
1 -> ferror
1 <- ferror
So the chat was moved to Text mode... And you know how we students are.. 
