/* check whether cpuid instruction reports nx bit
 * 2007 lnussel@suse.d, GPL
 */
#include <stdio.h>

// test for cpuid instruction, from AMD processor manual
static int have_cpuid()
{
	unsigned a = 0;
	__asm__ __volatile__(
	"pushfl\n"                  // save EFLAGS
	"pop    %%eax\n"            // store EFLAGS in EAX
	"mov    %%eax, %%ebx\n"     // save in EBX for later testing
	"xor    $0x200000, %%eax\n" // toggle bit 21
	"push   %%eax\n"            // push to stack
	"popfl\n"                   // save changed EAX to EFLAGS
	"pushfl\n"                  // push EFLAGS to TOS
	"pop    %%eax\n"            // store EFLAGS in EAX
	"xor    %%ebx, %%eax\n"     // see if bit 21 has changed
	: "=a" (a)
	:
	: "ebx"
	);

	return a!=0;
}

static int have_pae()
{
	unsigned d = 0;
	__asm__ __volatile__(
	"movl $0x1, %%eax\n"        // load cpuid function 1
	"cpuid\n"
	: "=d" (d)
	:
	: "eax", "ebx", "ecx"
	);
	return (d&0x40);
}

static int have_nx()
{
	unsigned d = 0;
	__asm__ __volatile__(
	"movl $0x80000000, %%eax\n"        // check extended functions
	"cpuid\n"
	"cmpl $0x80000000, %%eax\n"
	"jbe nonx\n"
	"movl $0x80000001, %%eax\n"
	"cpuid\n"
	"jmp out\n"
	"nonx:\n"
	"xorl %%edx, %%edx\n"
	"out:\n"
	: "=d" (d)
	:
	: "eax", "ebx", "ecx"
	);
	return (d&(1<<20));
}

int main(void)
{
	if(!have_cpuid())
	{
		puts("- system does not support the cpuid instruction");
		return 1;
	}

	if(!have_pae())
	{
		puts("- system does not support pae");
		return 1;
	}

	if(!have_nx())
	{
		puts("- system does not support NX");
		return 1;
	}

	puts("+ NX supported");
	
	return 0;
}