//-------------------------------------------------------------------
//	tryiopl3.cpp	 (A modification of our 'seeflags.cpp' demo)
//
//	This program allows us to verify two aspects of CPU behavior
//	pertaining to the software interrupt instruction 'int $9' in
//	the x86_64 Linux environment: (1) Attempting to execute this
//	software interrupt will normally cause a segmentation fault;
//	but (2) after we install our 'iokludge.c' kernel module, the
//	segmentation fault no longer occurs, but instead the RFLAGS-
//	register's IOPL-field is set to 3, thereby allowing a normal
//	program to access I/O ports via 'in' and 'out' instructions.
//
//		to compile:  $ g++ tryiopl3.cpp -o tryiopl3
//		to execute:  $ ./tryiopl3
//
//	programmer: ALLAN CRUSE
//	written on: 20 APR 2009
//-------------------------------------------------------------------

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

long long	rflags_image = ~0;

int main( int argc, char **argv )
{
	// see if we can execute this software interrupt without faulting
	asm(" int $9 ");

	// transfer the image of the RFLAGS register to a global variable
	asm(" pushfq \n popq rflags_image ");

	// display the values of the variable and its 2-bit IOPL-subfield
	printf( "\n    RFLAGS = 0x%016llX ", rflags_image ); 
	printf( " IOPL = %X \n\n", (rflags_image >> 12)&3 );
}