user_visible_state.c

#include <stdio.h>
#include <stdint.h>
#include <xmmintrin.h>

/* returns GDT limit */
static uint16_t show_gdt_and_idt(void)
{
	struct {
		unsigned short limit;
		unsigned long base;
	} __attribute__((packed)) val;

	uint16_t ret;

	__asm__ ("sgdt %0" : "=m" (val));
	printf("GDT:    base = 0x%016lX limit = 0x%04hX\n", val.base, val.limit);

	ret = val.limit;

	__asm__ ("sidt %0" : "=m" (val));
	printf("IDT:    base = 0x%016lX limit = 0x%04hX\n", val.base, val.limit);

	return ret;
}

static void show_ldt(void)
{
	unsigned short ldt;
	asm ("sldt %0" : "=rm" (ldt));
	printf("LDT:    0x%04hX\n", ldt);
}

static void show_tr(void)
{
	unsigned short tr;
	asm ("str %0" : "=rm" (tr));
	printf("TR:     0x%04X\n", tr);
}

static void show_msw(void)
{
	unsigned short msw;
	asm ("smsww %0" : "=rm" (msw));
	printf("MSW:    0x%04X\n", msw);
}

static void show_flags(void)
{
	unsigned long flags;
	asm ("sub $128, %%sp\n\t"
	     "pushf\n\t"
	     "pop %0\n\t"
	     "add $128, %%sp" : "=r" (flags));
	printf("FLAGS:  0x%016lX\n", flags);
}

static void show_rdtscp(void)
{
	unsigned int cpu;
	__builtin_ia32_rdtscp(&cpu);
	printf("RDTSCP: cpu %d\n", cpu);
}

static void show_segment(uint16_t index)
{
	uint32_t has_limit = 0, has_ar = 0, limit, ar;
	asm ("lsl %[index], %[limit]\n\t"
	     "jnz 1f\n\t"
	     "mov $1, %[has_limit]\n\t"
	     "1:"
	     : [limit] "=r" (limit), [has_limit] "+rm" (has_limit)
	     : [index] "r" ((index << 3) + 3));
	asm ("larl %[index], %[ar]\n\t"
	     "jnz 1f\n\t"
	     "mov $1, %[has_ar]\n\t"
	     "1:"
	     : [ar] "=r" (ar), [has_ar] "+rm" (has_ar)
	     : [index] "r" ((index << 3) + 3));

	if (!has_limit && !has_ar)
		return;

	printf("GDT entry %02hu", index);

	if (has_limit)
		printf(" limit: 0x%08X", limit);

	if (has_ar) {
#define ARBITS(low, high) ((ar >> low) & ((1 << (high - low + 1)) - 1))
#define ARSTR(bit, str) (ARBITS(bit,bit) ? " " str : "")
		printf(" access rights: 0x%08X (type=%d DPL=%d%s%s%s%s%s%s)",
		       ar, ARBITS(8,11), ARBITS(13,14),
		       ARSTR(12, "S"), ARSTR(15, "P"),
		       ARSTR(20, "software-available"),
		       ARSTR(21, "L"), ARSTR(22, "D/B"), ARSTR(23, "G"));
#undef ARSTR
#undef ARBITS
	}

	printf("\n");
}

int main()
{
	uint16_t gdtlimit = show_gdt_and_idt();
	show_ldt();
	show_tr();
	show_msw();
	show_flags();
	show_rdtscp();
	for (int i = 0; i <= gdtlimit; i++)
		show_segment(i);
}