//-------------------------------------------------------------------
//	invoke17.cpp
//
//	This Linux application repeatedly invokes kernel system-call
//	number 17 (documented as an 'obsolete' system-call for Linux
//	kernel versions 2.4 and later).  Normally this program shows
//	no change in the value of the integer whose address is given
//	as an argument to the system-call.  But, if our 'myexport.o' 
//	and 'newcall.o' modules are installed in the running kernel, 
//	to provide a different behavior, then this program will show 
//	the new effect of that system call, incrementing the integer 
//	each time that system-call is invoked. 
//
//		compile using:  ./gcc invoke17.cpp -o invoke17
//		execute using:  ./invoke17
//	
//	Reference: Moshe Bar, "Linux Internals," McGraw-Hill (2000).
//
//	programmer: ALLAN CRUSE
//	written on: 24 JUN 2004
//	revised on: 28 SEP 2004
//-------------------------------------------------------------------

#include <stdio.h>	// needed for printf() 


int exec_syscall_17( int *num )
{
	int	retval = -1;
	
	asm(" 	movl	$17, %eax	");
	asm("	movl	%0, %%ebx " : : "m" (num) );
	asm("	int	$0x80		");
	asm("	movl	%%eax, %0 " : "=m" (retval) );
	
	return	retval;
}	
	

int main( int argc, char **argv )
{
	int	number = 15;

	printf( "\nDemonstrating system-call 17 ... \n" );

	for (int i = 0; i <= 5; i++)
		{	
		printf( "\n#%d:  number=%d ", i, number );
		exec_syscall_17( &number );
		}
	printf( "\n\n" );
}