segnonp.c

/* $Id: segnonp.c,v 1.4 2014/12/16 18:22:19 kostik Exp kostik $ */

#include <sys/param.h>
#include <sys/types.h>
#include <machine/segments.h>
#include <machine/sysarch.h>
#include <err.h>
#include <errno.h>
#include <signal.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <ucontext.h>
#include <unistd.h>

static int
s2ds(int sel)
{

	return (LSEL(sel, SEL_UPL));
}

static int
alloc_sel(char *base, size_t len, int type, int p)
{
	int sel;
	union descriptor descs[1], descsk[1];
	uintptr_t pb;

	memset(descs, 0, sizeof(descs));
	if (len > PAGE_SIZE) {
		len = roundup(len, PAGE_SIZE);
		len /= PAGE_SIZE;
		descs[0].sd.sd_lolimit = len & 0xffff;
		descs[0].sd.sd_hilimit = (len >> 16) & 0xf;
		descs[0].sd.sd_gran = 1;
	} else {
		descs[0].sd.sd_lolimit = len;
		descs[0].sd.sd_hilimit = 0;
		descs[0].sd.sd_gran = 0;
	}
	pb = (uintptr_t)base;
	descs[0].sd.sd_lobase = pb & 0xffffff;
	descs[0].sd.sd_hibase = (pb >> 24) & 0xff;
	descs[0].sd.sd_type = type;
	descs[0].sd.sd_dpl = SEL_UPL;
	descs[0].sd.sd_p = p;
	descs[0].sd.sd_def32 = 1;

	if ((sel = i386_set_ldt(LDT_AUTO_ALLOC, descs, 1)) == -1)
		fprintf(stderr, "i386_set_ldt: %s\n", strerror(errno));
	else if (i386_get_ldt(sel, descsk, 1) == -1) {
		fprintf(stderr, "i386_get_ldt: %s\n", strerror(errno));
		sel = -1;
	} else if (memcmp(descs, descsk, sizeof(descs)) != 0) {
		fprintf(stderr, "descs != descsk\n");
		sel = -1;
	} else
		fprintf(stderr, "selector %d\n", sel);

	return (sel);
}

static int sel;

static void
sighandler(int signo __unused, siginfo_t *si __unused, void *u)
{
	ucontext_t *up;

	up = u;
	up->uc_mcontext.mc_ss = s2ds(sel);
}

static void load_gs(int seg) __used;
static void
load_gs(int seg)
{

	__asm __volatile("movw\t%0,%%gs"
	    : : "r" ((short)s2ds(seg)) : "memory");
}

int
main(void)
{
	struct sigaction sa;
	int error;

	sel = alloc_sel(0, 0xffffffff, SDT_MEMERA, 0);
	if (sel == -1)
		exit(1);
	memset(&sa, 0, sizeof(sa));
	sa.sa_sigaction = sighandler;
	sa.sa_flags = SA_SIGINFO;
	error = sigaction(SIGUSR1, &sa, NULL);
	if (error != 0)
		err(1, "sigaction");
#if 0
	load_gs(sel);
#else
	raise(SIGUSR1);
#endif

	return (0);
}