int main(int argc, char* argv[]) {
  int a = 1;
  int b = 1;
  char x = 'A';
  char y = 'B';
  return 0;
}

-rws--x--x 1 windak user    6255 2009-10-25 02:50 test

#include <stdio.h>                                      
#include <stdlib.h>                                     
#include <signal.h>                                     
#include <syscall.h>                                    
#include <sys/ptrace.h>                                 
#include <sys/types.h>
#include <sys/wait.h>
#include <sys/user.h>
#include <unistd.h>
#include <errno.h>
int main(void) 
{                                                                                                                                                                                                          
        long long counter = 0;  /*  machine instruction counter */
        int wait_val;           /*  child's return value        */
        int pid;                /*  child's process id          */

        puts("Please wait");
        struct user_regs_struct regs;
        long ins;                    

        switch (pid = fork()) {
        case -1:               
                perror("fork");
                break;         
        case 0: /*  child process starts        */
                ptrace(PTRACE_TRACEME, 0, 0, 0);
                
                execl("/home/user/test", "test", NULL);
                
                break;
                /*  child process ends  */
        default:/*  parent process starts       */
                wait(&wait_val);
                /*
                 *   parent waits for child to stop at next
                 *   instruction (execl())
                 */
                while (wait_val == 1407 ) {
                        counter++;
                        if (ptrace(PTRACE_SINGLESTEP, pid, 0, 0) != 0)
                                perror("ptrace");
                        if (ptrace(PTRACE_GETREGS,pid,0,®s)!=0){
                         // perror("ptrace");
                        }
                        else {
                                ins = ptrace(PTRACE_PEEKTEXT, pid,
                                 regs.eip, NULL);

                                printf("Instruction executed: %lx\n", ins);
                        }
                        wait(&wait_val);
                        /*   wait for next instruction to complete  */
                }
                /*
                 * continue to stop, wait and release until
                 * the child is finished; wait_val != 1407
                 * Low=0177L and High=05 (SIGTRAP)
                 */
        }
        printf("Number of machine instructions : %lld\n", counter);
        return 0;
}

gdb test
(gdb) disass main
Dump of assembler code for function main:
0x0804831c <main+0>:    push   %ebp
0x0804831d <main+1>:    mov    %esp,%ebp
....
0x08048338 <main+28>:   movl   $0x1,-0x4(%ebp)
0x0804833f <main+35>:   movl   $0x1,-0x8(%ebp)
0x08048346 <main+42>:   movb   $0x41,-0x9(%ebp)
0x0804834a <main+46>:   movb   $0x42,-0xa(%ebp)
0x0804834e <main+50>:   mov    $0x0,%eax
0x08048353 <main+55>:   leave
0x08048354 <main+56>:   ret
(gdb) x/20 0x0804831c
0x804831c <main>:       0x83e58955      0xe48318ec      0x0000b8f0      0xc0830000
0x804832c <main+16>:    0x0fc0830f      0xc104e8c1      0xc42904e0      0x01fc45c7
0x804833c <main+32>:    0xc7000000      0x0001f845      0x45c60000      0x45c641f7
0x804834c <main+48>:    0x00b842f6      0xc9000000      0x909090c3      0x90909090
0x804835c:      0x90909090      0x5de58955      0x26748dc3      0x27bc8d00

Instruction executed: 83e58955
Instruction executed: ec83e589
Instruction executed: 8318ec83
Instruction executed: b8f0e483
Instruction executed: b8
Instruction executed: 830fc083
Instruction executed: c10fc083
Instruction executed: c104e8c1
Instruction executed: 2904e0c1
Instruction executed: 45c7c429
Instruction executed: 1fc45c7
Instruction executed: 1f845c7
Instruction executed: 41f745c6
Instruction executed: 42f645c6
Instruction executed: b8
Instruction executed: 9090c3c9
Instruction executed: 909090c3

$ uname -a
Linux windak-pc 2.6.28-11-generic #42-Ubuntu SMP Fri Apr 17 01:57:59 UTC 2009 i686 GNU/Linux
$ gcc -v
Reading specs from /usr/lib/gcc/i486-linux-gnu/3.4.6/specs
Configured with: ../src/configure -v --enable-languages=c,c++,f77,pascal --prefix=/usr --libexecdir=/usr/lib --with-gxx-include-dir=/usr/include/c++/3.4 --enable-shared --with-system-zlib --enable-nls --without-included-gettext --program-suffix=-3.4 --enable-__cxa_atexit --enable-clocale=gnu --enable-libstdcxx-debug --with-tune=pentium4 i486-linux-gnu
Thread model: posix
gcc version 3.4.6 (Ubuntu 3.4.6-1ubuntu2)

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/types.h>

int main(int argc, char **argv)
{
   int a = 1;
   int b = 1;
   char x = 'A';
   char y = 'B';
   int euid, uid;
   euid = geteuid();
   uid = getuid();
   printf("euid: %d\nuid: %d\n",euid,uid);
   sleep(100000);
   exit(EXIT_SUCCESS);
}

root@bsd# ls -l /tmp/test
-rws--x--x  1 puffy  monkey  6704 Oct 28 14:09 /tmp/test*
root@bsd# /tmp/test
euid: 0
uid: 0
^C
root@bsd# su -l monkey
-bash-3.2$ /tmp/test
euid: 1000
uid: 1000
^C
-bash-3.2$ logout
root@bsd# su -l puffy
-bash-3.2$ /tmp/test
euid: 1002
uid: 1002
^C
-bash-3.2$

cat test.c
int main(int argc, char* argv[]) {
  int a = 1;
  int b = 1;
  char x = 'A';
  char y = 'B';
  printf ("Euid : %d, ID: %d \n", geteuid(), getuid());
  return 0;
}
....
windak@windak-pc$./test
Euid : 1000, ID: 1000
....
user@windak-pc$./test
Euid : 1000, ID: 1001

int main(){
  execl("/home/user/test","test",0);
  return 0;
}

-rwx------ 1 windak windak    6582 2009-10-28 20:27 test
-rws--x--x 1 windak user    6368 2009-10-28 20:31 wrap

user@windak-pc$./wrap
Euid : 1000, ID: 1001
user@windak-pc$./ptrace
Please wait...
Number of machine instructions : 115862
...
windak@windak-pc$./ptrace
Please wait...
Euid : 1000, ID: 1000
Number of machine instructions : 237642