xref: /freebsd/sys/i386/linux/linux_sysvec.c (revision 77a0943ded95b9e6438f7db70c4a28e4d93946d4)

/*-
 * Copyright (c) 1994-1996 S�ren Schmidt
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer
 *    in this position and unchanged.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. The name of the author may not be used to endorse or promote products
 *    derived from this software withough specific prior written permission
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 *
 * $FreeBSD$
 */

/* XXX we use functions that might not exist. */
#include "opt_compat.h"

#ifndef COMPAT_43
#error "Unable to compile Linux-emulator due to missing COMPAT_43 option!"
#endif

#include <sys/param.h>
#include <sys/systm.h>
#include <sys/proc.h>
#include <sys/sysproto.h>
#include <sys/sysent.h>
#include <sys/imgact.h>
#include <sys/imgact_aout.h>
#include <sys/imgact_elf.h>
#include <sys/signalvar.h>
#include <sys/malloc.h>
#include <vm/vm.h>
#include <vm/vm_param.h>
#include <vm/vm_page.h>
#include <vm/vm_extern.h>
#include <sys/exec.h>
#include <sys/kernel.h>
#include <sys/module.h>
#include <machine/cpu.h>

#include <i386/linux/linux.h>
#include <i386/linux/linux_proto.h>
#include <compat/linux/linux_signal.h>
#include <compat/linux/linux_util.h>

MODULE_VERSION(linux, 1);

MALLOC_DEFINE(M_LINUX, "linux", "Linux mode structures");

#if BYTE_ORDER == LITTLE_ENDIAN
#define SHELLMAGIC      0x2123 /* #! */
#else
#define SHELLMAGIC      0x2321
#endif

extern char linux_sigcode[];
extern int linux_szsigcode;

extern struct sysent linux_sysent[LINUX_SYS_MAXSYSCALL];

extern struct linker_set linux_ioctl_handler_set;

static int	linux_fixup __P((register_t **stack_base,
				 struct image_params *iparams));
static int	elf_linux_fixup __P((register_t **stack_base,
				     struct image_params *iparams));
static void	linux_prepsyscall __P((struct trapframe *tf, int *args,
				       u_int *code, caddr_t *params));
static void     linux_sendsig __P((sig_t catcher, int sig, sigset_t *mask,
				   u_long code));

/*
 * Linux syscalls return negative errno's, we do positive and map them
 */
static int bsd_to_linux_errno[ELAST + 1] = {
  	-0,  -1,  -2,  -3,  -4,  -5,  -6,  -7,  -8,  -9,
 	-10, -35, -12, -13, -14, -15, -16, -17, -18, -19,
 	-20, -21, -22, -23, -24, -25, -26, -27, -28, -29,
 	-30, -31, -32, -33, -34, -11,-115,-114, -88, -89,
 	-90, -91, -92, -93, -94, -95, -96, -97, -98, -99,
	-100,-101,-102,-103,-104,-105,-106,-107,-108,-109,
	-110,-111, -40, -36,-112,-113, -39, -11, -87,-122,
	-116, -66,  -6,  -6,  -6,  -6,  -6, -37, -38,  -9,
  	-6, -6, -43, -42, -75, -6, -84
};

int bsd_to_linux_signal[LINUX_SIGTBLSZ] = {
	LINUX_SIGHUP, LINUX_SIGINT, LINUX_SIGQUIT, LINUX_SIGILL,
	LINUX_SIGTRAP, LINUX_SIGABRT, 0, LINUX_SIGFPE,
	LINUX_SIGKILL, LINUX_SIGBUS, LINUX_SIGSEGV, 0,
	LINUX_SIGPIPE, LINUX_SIGALRM, LINUX_SIGTERM, LINUX_SIGURG,
	LINUX_SIGSTOP, LINUX_SIGTSTP, LINUX_SIGCONT, LINUX_SIGCHLD,
	LINUX_SIGTTIN, LINUX_SIGTTOU, LINUX_SIGIO, LINUX_SIGXCPU,
	LINUX_SIGXFSZ, LINUX_SIGVTALRM, LINUX_SIGPROF, LINUX_SIGWINCH,
	0, LINUX_SIGUSR1, LINUX_SIGUSR2
};

int linux_to_bsd_signal[LINUX_SIGTBLSZ] = {
	SIGHUP, SIGINT, SIGQUIT, SIGILL,
	SIGTRAP, SIGABRT, SIGBUS, SIGFPE,
	SIGKILL, SIGUSR1, SIGSEGV, SIGUSR2,
	SIGPIPE, SIGALRM, SIGTERM, SIGBUS,
	SIGCHLD, SIGCONT, SIGSTOP, SIGTSTP,
	SIGTTIN, SIGTTOU, SIGURG, SIGXCPU,
	SIGXFSZ, SIGVTALRM, SIGPROF, SIGWINCH,
	SIGIO, SIGURG, 0
};

/*
 * If FreeBSD & Linux have a difference of opinion about what a trap
 * means, deal with it here.
 */
static int
translate_traps(int signal, int trap_code)
{
	if (signal != SIGBUS)
		return signal;
	switch (trap_code) {
	case T_PROTFLT:
	case T_TSSFLT:
	case T_DOUBLEFLT:
	case T_PAGEFLT:
		return SIGSEGV;
	default:
		return signal;
	}
}

static int
linux_fixup(register_t **stack_base, struct image_params *imgp)
{
	register_t *argv, *envp;

	argv = *stack_base;
	envp = *stack_base + (imgp->argc + 1);
	(*stack_base)--;
	**stack_base = (intptr_t)(void *)envp;
	(*stack_base)--;
	**stack_base = (intptr_t)(void *)argv;
	(*stack_base)--;
	**stack_base = imgp->argc;
	return 0;
}

static int
elf_linux_fixup(register_t **stack_base, struct image_params *imgp)
{
	Elf32_Auxargs *args = (Elf32_Auxargs *)imgp->auxargs;
	register_t *pos;

	pos = *stack_base + (imgp->argc + imgp->envc + 2);

	if (args->trace) {
		AUXARGS_ENTRY(pos, AT_DEBUG, 1);
	}
	if (args->execfd != -1) {
		AUXARGS_ENTRY(pos, AT_EXECFD, args->execfd);
	}
	AUXARGS_ENTRY(pos, AT_PHDR, args->phdr);
	AUXARGS_ENTRY(pos, AT_PHENT, args->phent);
	AUXARGS_ENTRY(pos, AT_PHNUM, args->phnum);
	AUXARGS_ENTRY(pos, AT_PAGESZ, args->pagesz);
	AUXARGS_ENTRY(pos, AT_FLAGS, args->flags);
	AUXARGS_ENTRY(pos, AT_ENTRY, args->entry);
	AUXARGS_ENTRY(pos, AT_BASE, args->base);
	AUXARGS_ENTRY(pos, AT_UID, imgp->proc->p_cred->p_ruid);
	AUXARGS_ENTRY(pos, AT_EUID, imgp->proc->p_cred->p_svuid);
	AUXARGS_ENTRY(pos, AT_GID, imgp->proc->p_cred->p_rgid);
	AUXARGS_ENTRY(pos, AT_EGID, imgp->proc->p_cred->p_svgid);
	AUXARGS_ENTRY(pos, AT_NULL, 0);

	free(imgp->auxargs, M_TEMP);
	imgp->auxargs = NULL;

	(*stack_base)--;
	**stack_base = (long)imgp->argc;
	return 0;
}

extern int _ucodesel, _udatasel;
extern unsigned long _linux_sznonrtsigcode;

static void
linux_rt_sendsig(sig_t catcher, int sig, sigset_t *mask, u_long code)
{
	register struct proc *p = curproc;
	register struct trapframe *regs;
	struct linux_rt_sigframe *fp, frame;
	int oonstack;

	regs = p->p_md.md_regs;
	oonstack = p->p_sigstk.ss_flags & SS_ONSTACK;

#ifdef DEBUG
	printf("Linux-emul(%ld): linux_rt_sendsig(%p, %d, %p, %lu)\n",
	    (long)p->p_pid, catcher, sig, (void*)mask, code);
#endif
	/*
	 * Allocate space for the signal handler context.
	 */
	if ((p->p_flag & P_ALTSTACK) && !oonstack &&
	    SIGISMEMBER(p->p_sigacts->ps_sigonstack, sig)) {
		fp = (struct linux_rt_sigframe *)(p->p_sigstk.ss_sp +
		    p->p_sigstk.ss_size - sizeof(struct linux_rt_sigframe));
		p->p_sigstk.ss_flags |= SS_ONSTACK;
	} else {
		fp = (struct linux_rt_sigframe *)regs->tf_esp - 1;
	}

	/*
	 * grow() will return FALSE if the fp will not fit inside the stack
	 *	and the stack can not be grown. useracc will return FALSE
	 *	if access is denied.
	 */
	if ((grow_stack (p, (int)fp) == FALSE) ||
	    !useracc((caddr_t)fp, sizeof (struct linux_rt_sigframe),
	    VM_PROT_WRITE)) {
		/*
		 * Process has trashed its stack; give it an illegal
		 * instruction to halt it in its tracks.
		 */
		SIGACTION(p, SIGILL) = SIG_DFL;
		SIGDELSET(p->p_sigignore, SIGILL);
		SIGDELSET(p->p_sigcatch, SIGILL);
		SIGDELSET(p->p_sigmask, SIGILL);
#ifdef DEBUG
		printf("Linux-emul(%ld): linux_rt_sendsig -- bad stack %p, SS_ONSTACK: 0x%x ",
	    (long)p->p_pid, fp, p->p_sigstk.ss_flags & SS_ONSTACK);
#endif
		psignal(p, SIGILL);
		return;
	}

	/*
	 * Build the argument list for the signal handler.
	 */
	if (p->p_sysent->sv_sigtbl)
		if (sig <= p->p_sysent->sv_sigsize)
			sig = p->p_sysent->sv_sigtbl[_SIG_IDX(sig)];

	frame.sf_handler = catcher;
	frame.sf_sig = sig;
	frame.sf_siginfo = &fp->sf_si;
	frame.sf_ucontext = &fp->sf_sc;

	/* Fill siginfo structure. */
	frame.sf_si.lsi_signo = sig;
	frame.sf_si.lsi_code = code;
	frame.sf_si.lsi_addr = (void *)regs->tf_err;

	/*
	 * Build the signal context to be used by sigreturn.
	 */
	frame.sf_sc.uc_flags = 0;		/* XXX ??? */
	frame.sf_sc.uc_link = NULL;		/* XXX ??? */

	frame.sf_sc.uc_stack.ss_sp = p->p_sigstk.ss_sp;
	frame.sf_sc.uc_stack.ss_flags =
	    bsd_to_linux_sigaltstack(p->p_sigstk.ss_flags);
	frame.sf_sc.uc_stack.ss_size = p->p_sigstk.ss_size;

	bsd_to_linux_sigset(mask, &frame.sf_sc.uc_sigmask);

	frame.sf_sc.uc_mcontext.sc_mask   = frame.sf_sc.uc_sigmask.__bits[0];
	frame.sf_sc.uc_mcontext.sc_gs     = rgs();
	frame.sf_sc.uc_mcontext.sc_fs     = regs->tf_fs;
	frame.sf_sc.uc_mcontext.sc_es     = regs->tf_es;
	frame.sf_sc.uc_mcontext.sc_ds     = regs->tf_ds;
	frame.sf_sc.uc_mcontext.sc_edi    = regs->tf_edi;
	frame.sf_sc.uc_mcontext.sc_esi    = regs->tf_esi;
	frame.sf_sc.uc_mcontext.sc_ebp    = regs->tf_ebp;
	frame.sf_sc.uc_mcontext.sc_ebx    = regs->tf_ebx;
	frame.sf_sc.uc_mcontext.sc_edx    = regs->tf_edx;
	frame.sf_sc.uc_mcontext.sc_ecx    = regs->tf_ecx;
	frame.sf_sc.uc_mcontext.sc_eax    = regs->tf_eax;
	frame.sf_sc.uc_mcontext.sc_eip    = regs->tf_eip;
	frame.sf_sc.uc_mcontext.sc_cs     = regs->tf_cs;
	frame.sf_sc.uc_mcontext.sc_eflags = regs->tf_eflags;
	frame.sf_sc.uc_mcontext.sc_esp_at_signal = regs->tf_esp;
	frame.sf_sc.uc_mcontext.sc_ss     = regs->tf_ss;
	frame.sf_sc.uc_mcontext.sc_err    = regs->tf_err;
	frame.sf_sc.uc_mcontext.sc_trapno = code;	/* XXX ???? */

#ifdef DEBUG
	printf("Linux-emul(%ld): rt_sendsig flags: 0x%x, sp: %p, ss: 0x%x, mask: 0x%x\n",
	    (long)p->p_pid, frame.sf_sc.uc_stack.ss_flags,  p->p_sigstk.ss_sp,
	    p->p_sigstk.ss_size, frame.sf_sc.uc_mcontext.sc_mask);
#endif

	if (copyout(&frame, fp, sizeof(frame)) != 0) {
		/*
		 * Process has trashed its stack; give it an illegal
		 * instruction to halt it in its tracks.
		 */
		sigexit(p, SIGILL);
		/* NOTREACHED */
	}

	/*
	 * Build context to run handler in.
	 */
	regs->tf_esp = (int)fp;
	regs->tf_eip = PS_STRINGS - *(p->p_sysent->sv_szsigcode) +
	    _linux_sznonrtsigcode;
	regs->tf_eflags &= ~PSL_VM;
	regs->tf_cs = _ucodesel;
	regs->tf_ds = _udatasel;
	regs->tf_es = _udatasel;
	regs->tf_fs = _udatasel;
	load_gs(_udatasel);
	regs->tf_ss = _udatasel;
}


/*
 * Send an interrupt to process.
 *
 * Stack is set up to allow sigcode stored
 * in u. to call routine, followed by kcall
 * to sigreturn routine below.  After sigreturn
 * resets the signal mask, the stack, and the
 * frame pointer, it returns to the user
 * specified pc, psl.
 */

static void
linux_sendsig(sig_t catcher, int sig, sigset_t *mask, u_long code)
{
	register struct proc *p = curproc;
	register struct trapframe *regs;
	struct linux_sigframe *fp, frame;
	linux_sigset_t lmask;
	int oonstack, i;

	if (SIGISMEMBER(p->p_sigacts->ps_siginfo, sig)) {
		/* Signal handler installed with SA_SIGINFO. */
		linux_rt_sendsig(catcher, sig, mask, code);
		return;
	}

	regs = p->p_md.md_regs;
	oonstack = p->p_sigstk.ss_flags & SS_ONSTACK;

#ifdef DEBUG
	printf("Linux-emul(%ld): linux_sendsig(%p, %d, %p, %lu)\n",
	    (long)p->p_pid, catcher, sig, (void*)mask, code);
#endif

	/*
	 * Allocate space for the signal handler context.
	 */
	if ((p->p_flag & P_ALTSTACK) && !oonstack &&
	    SIGISMEMBER(p->p_sigacts->ps_sigonstack, sig)) {
		fp = (struct linux_sigframe *)(p->p_sigstk.ss_sp +
		    p->p_sigstk.ss_size - sizeof(struct linux_sigframe));
		p->p_sigstk.ss_flags |= SS_ONSTACK;
	} else {
		fp = (struct linux_sigframe *)regs->tf_esp - 1;
	}

	/*
	 * grow() will return FALSE if the fp will not fit inside the stack
	 *	and the stack can not be grown. useracc will return FALSE
	 *	if access is denied.
	 */
	if ((grow_stack (p, (int)fp) == FALSE) ||
	    !useracc((caddr_t)fp, sizeof (struct linux_sigframe),
	    VM_PROT_WRITE)) {
		/*
		 * Process has trashed its stack; give it an illegal
		 * instruction to halt it in its tracks.
		 */
		SIGACTION(p, SIGILL) = SIG_DFL;
		SIGDELSET(p->p_sigignore, SIGILL);
		SIGDELSET(p->p_sigcatch, SIGILL);
		SIGDELSET(p->p_sigmask, SIGILL);
		psignal(p, SIGILL);
		return;
	}

	/*
	 * Build the argument list for the signal handler.
	 */
	if (p->p_sysent->sv_sigtbl)
		if (sig <= p->p_sysent->sv_sigsize)
			sig = p->p_sysent->sv_sigtbl[_SIG_IDX(sig)];

	frame.sf_handler = catcher;
	frame.sf_sig = sig;

	bsd_to_linux_sigset(mask, &lmask);

	/*
	 * Build the signal context to be used by sigreturn.
	 */
	frame.sf_sc.sc_mask   = lmask.__bits[0];
	frame.sf_sc.sc_gs     = rgs();
	frame.sf_sc.sc_fs     = regs->tf_fs;
	frame.sf_sc.sc_es     = regs->tf_es;
	frame.sf_sc.sc_ds     = regs->tf_ds;
	frame.sf_sc.sc_edi    = regs->tf_edi;
	frame.sf_sc.sc_esi    = regs->tf_esi;
	frame.sf_sc.sc_ebp    = regs->tf_ebp;
	frame.sf_sc.sc_ebx    = regs->tf_ebx;
	frame.sf_sc.sc_edx    = regs->tf_edx;
	frame.sf_sc.sc_ecx    = regs->tf_ecx;
	frame.sf_sc.sc_eax    = regs->tf_eax;
	frame.sf_sc.sc_eip    = regs->tf_eip;
	frame.sf_sc.sc_cs     = regs->tf_cs;
	frame.sf_sc.sc_eflags = regs->tf_eflags;
	frame.sf_sc.sc_esp_at_signal = regs->tf_esp;
	frame.sf_sc.sc_ss     = regs->tf_ss;
	frame.sf_sc.sc_err    = regs->tf_err;
	frame.sf_sc.sc_trapno = code;	/* XXX ???? */

	bzero(&frame.sf_fpstate, sizeof(struct linux_fpstate));

	for (i = 0; i < (LINUX_NSIG_WORDS-1); i++)
		frame.sf_extramask[i] = lmask.__bits[i+1];

	if (copyout(&frame, fp, sizeof(frame)) != 0) {
		/*
		 * Process has trashed its stack; give it an illegal
		 * instruction to halt it in its tracks.
		 */
		sigexit(p, SIGILL);
		/* NOTREACHED */
	}

	/*
	 * Build context to run handler in.
	 */
	regs->tf_esp = (int)fp;
	regs->tf_eip = PS_STRINGS - *(p->p_sysent->sv_szsigcode);
	regs->tf_eflags &= ~PSL_VM;
	regs->tf_cs = _ucodesel;
	regs->tf_ds = _udatasel;
	regs->tf_es = _udatasel;
	regs->tf_fs = _udatasel;
	load_gs(_udatasel);
	regs->tf_ss = _udatasel;
}

/*
 * System call to cleanup state after a signal
 * has been taken.  Reset signal mask and
 * stack state from context left by sendsig (above).
 * Return to previous pc and psl as specified by
 * context left by sendsig. Check carefully to
 * make sure that the user has not modified the
 * psl to gain improper privileges or to cause
 * a machine fault.
 */
int
linux_sigreturn(p, args)
	struct proc *p;
	struct linux_sigreturn_args *args;
{
	struct linux_sigframe frame;
	register struct trapframe *regs;
	linux_sigset_t lmask;
	int eflags, i;

	regs = p->p_md.md_regs;

#ifdef DEBUG
	printf("Linux-emul(%ld): linux_sigreturn(%p)\n",
	    (long)p->p_pid, (void *)args->sfp);
#endif
	/*
	 * The trampoline code hands us the sigframe.
	 * It is unsafe to keep track of it ourselves, in the event that a
	 * program jumps out of a signal handler.
	 */
	if (copyin((caddr_t)args->sfp, &frame, sizeof(frame)) != 0)
		return (EFAULT);

	/*
	 * Check for security violations.
	 */
#define	EFLAGS_SECURE(ef, oef)	((((ef) ^ (oef)) & ~PSL_USERCHANGE) == 0)
	eflags = frame.sf_sc.sc_eflags;
	/*
	 * XXX do allow users to change the privileged flag PSL_RF.  The
	 * cpu sets PSL_RF in tf_eflags for faults.  Debuggers should
	 * sometimes set it there too.  tf_eflags is kept in the signal
	 * context during signal handling and there is no other place
	 * to remember it, so the PSL_RF bit may be corrupted by the
	 * signal handler without us knowing.  Corruption of the PSL_RF
	 * bit at worst causes one more or one less debugger trap, so
	 * allowing it is fairly harmless.
	 */
	if (!EFLAGS_SECURE(eflags & ~PSL_RF, regs->tf_eflags & ~PSL_RF)) {
    		return(EINVAL);
	}

	/*
	 * Don't allow users to load a valid privileged %cs.  Let the
	 * hardware check for invalid selectors, excess privilege in
	 * other selectors, invalid %eip's and invalid %esp's.
	 */
#define	CS_SECURE(cs)	(ISPL(cs) == SEL_UPL)
	if (!CS_SECURE(frame.sf_sc.sc_cs)) {
		trapsignal(p, SIGBUS, T_PROTFLT);
		return(EINVAL);
	}

	p->p_sigstk.ss_flags &= ~SS_ONSTACK;
	lmask.__bits[0] = frame.sf_sc.sc_mask;
	for (i = 0; i < (LINUX_NSIG_WORDS-1); i++)
		lmask.__bits[i+1] = frame.sf_extramask[i];
	linux_to_bsd_sigset(&lmask, &p->p_sigmask);
	SIG_CANTMASK(p->p_sigmask);

	/*
	 * Restore signal context.
	 */
	/* %gs was restored by the trampoline. */
	regs->tf_fs     = frame.sf_sc.sc_fs;
	regs->tf_es     = frame.sf_sc.sc_es;
	regs->tf_ds     = frame.sf_sc.sc_ds;
	regs->tf_edi    = frame.sf_sc.sc_edi;
	regs->tf_esi    = frame.sf_sc.sc_esi;
	regs->tf_ebp    = frame.sf_sc.sc_ebp;
	regs->tf_ebx    = frame.sf_sc.sc_ebx;
	regs->tf_edx    = frame.sf_sc.sc_edx;
	regs->tf_ecx    = frame.sf_sc.sc_ecx;
	regs->tf_eax    = frame.sf_sc.sc_eax;
	regs->tf_eip    = frame.sf_sc.sc_eip;
	regs->tf_cs     = frame.sf_sc.sc_cs;
	regs->tf_eflags = eflags;
	regs->tf_esp    = frame.sf_sc.sc_esp_at_signal;
	regs->tf_ss     = frame.sf_sc.sc_ss;

	return (EJUSTRETURN);
}

/*
 * System call to cleanup state after a signal
 * has been taken.  Reset signal mask and
 * stack state from context left by rt_sendsig (above).
 * Return to previous pc and psl as specified by
 * context left by sendsig. Check carefully to
 * make sure that the user has not modified the
 * psl to gain improper privileges or to cause
 * a machine fault.
 */
int
linux_rt_sigreturn(p, args)
	struct proc *p;
	struct linux_rt_sigreturn_args *args;
{
	struct sigaltstack_args sasargs;
	struct linux_ucontext 	 uc;
	struct linux_sigcontext *context;
	linux_stack_t *lss;
	stack_t *ss;
	register struct trapframe *regs;
	int eflags;
	caddr_t sg = stackgap_init();

	regs = p->p_md.md_regs;

#ifdef DEBUG
	printf("Linux-emul(%ld): linux_rt_sigreturn(%p)\n",
	    (long)p->p_pid, (void *)args->ucp);
#endif
	/*
	 * The trampoline code hands us the ucontext.
	 * It is unsafe to keep track of it ourselves, in the event that a
	 * program jumps out of a signal handler.
	 */
	if (copyin((caddr_t)args->ucp, &uc, sizeof(uc)) != 0)
		return (EFAULT);

	context = &uc.uc_mcontext;

	/*
	 * Check for security violations.
	 */
#define	EFLAGS_SECURE(ef, oef)	((((ef) ^ (oef)) & ~PSL_USERCHANGE) == 0)
	eflags = context->sc_eflags;
	/*
	 * XXX do allow users to change the privileged flag PSL_RF.  The
	 * cpu sets PSL_RF in tf_eflags for faults.  Debuggers should
	 * sometimes set it there too.  tf_eflags is kept in the signal
	 * context during signal handling and there is no other place
	 * to remember it, so the PSL_RF bit may be corrupted by the
	 * signal handler without us knowing.  Corruption of the PSL_RF
	 * bit at worst causes one more or one less debugger trap, so
	 * allowing it is fairly harmless.
	 */
	if (!EFLAGS_SECURE(eflags & ~PSL_RF, regs->tf_eflags & ~PSL_RF)) {
    		return(EINVAL);
	}

	/*
	 * Don't allow users to load a valid privileged %cs.  Let the
	 * hardware check for invalid selectors, excess privilege in
	 * other selectors, invalid %eip's and invalid %esp's.
	 */
#define	CS_SECURE(cs)	(ISPL(cs) == SEL_UPL)
	if (!CS_SECURE(context->sc_cs)) {
		trapsignal(p, SIGBUS, T_PROTFLT);
		return(EINVAL);
	}

	p->p_sigstk.ss_flags &= ~SS_ONSTACK;
	linux_to_bsd_sigset(&uc.uc_sigmask, &p->p_sigmask);
	SIG_CANTMASK(p->p_sigmask);

	/*
	 * Restore signal context
	 */
	/* %gs was restored by the trampoline. */
	regs->tf_fs     = context->sc_fs;
	regs->tf_es     = context->sc_es;
	regs->tf_ds     = context->sc_ds;
	regs->tf_edi    = context->sc_edi;
	regs->tf_esi    = context->sc_esi;
	regs->tf_ebp    = context->sc_ebp;
	regs->tf_ebx    = context->sc_ebx;
	regs->tf_edx    = context->sc_edx;
	regs->tf_ecx    = context->sc_ecx;
	regs->tf_eax    = context->sc_eax;
	regs->tf_eip    = context->sc_eip;
	regs->tf_cs     = context->sc_cs;
	regs->tf_eflags = eflags;
	regs->tf_esp    = context->sc_esp_at_signal;
	regs->tf_ss     = context->sc_ss;

	/*
	 * call sigaltstack & ignore results..
	 */
	ss = stackgap_alloc(&sg, sizeof(stack_t));
	lss = &uc.uc_stack;
	ss->ss_sp = lss->ss_sp;
	ss->ss_size = lss->ss_size;
	ss->ss_flags = linux_to_bsd_sigaltstack(lss->ss_flags);

#ifdef DEBUG
	printf("Linux-emul(%ld): rt_sigret  flags: 0x%x, sp: %p, ss: 0x%x, mask: 0x%x\n",
	    (long)p->p_pid, ss->ss_flags, ss->ss_sp, ss->ss_size, context->sc_mask);
#endif
	sasargs.ss = ss;
	sasargs.oss = NULL;
	(void) sigaltstack(p, &sasargs);

	return (EJUSTRETURN);
}

static void
linux_prepsyscall(struct trapframe *tf, int *args, u_int *code, caddr_t *params)
{
	args[0] = tf->tf_ebx;
	args[1] = tf->tf_ecx;
	args[2] = tf->tf_edx;
	args[3] = tf->tf_esi;
	args[4] = tf->tf_edi;
	*params = NULL;		/* no copyin */
}

/*
 * If a linux binary is exec'ing something, try this image activator
 * first.  We override standard shell script execution in order to
 * be able to modify the interpreter path.  We only do this if a linux
 * binary is doing the exec, so we do not create an EXEC module for it.
 */
static int	exec_linux_imgact_try __P((struct image_params *iparams));

static int
exec_linux_imgact_try(imgp)
    struct image_params *imgp;
{
    const char *head = (const char *)imgp->image_header;
    int error = -1;

    /*
     * The interpreter for shell scripts run from a linux binary needs
     * to be located in /compat/linux if possible in order to recursively
     * maintain linux path emulation.
     */
    if (((const short *)head)[0] == SHELLMAGIC) {
	    /*
	     * Run our normal shell image activator.  If it succeeds attempt
	     * to use the alternate path for the interpreter.  If an alternate
	     * path is found, use our stringspace to store it.
	     */
	    if ((error = exec_shell_imgact(imgp)) == 0) {
		    char *rpath = NULL;

		    linux_emul_find(imgp->proc, NULL, linux_emul_path,
			imgp->interpreter_name, &rpath, 0);
		    if (rpath != imgp->interpreter_name) {
			    int len = strlen(rpath) + 1;

			    if (len <= MAXSHELLCMDLEN) {
				memcpy(imgp->interpreter_name, rpath, len);
			    }
			    free(rpath, M_TEMP);
		    }
	    }
    }
    return(error);
}

struct sysentvec linux_sysvec = {
	LINUX_SYS_MAXSYSCALL,
	linux_sysent,
	0xff,
	LINUX_SIGTBLSZ,
	bsd_to_linux_signal,
	ELAST + 1,
	bsd_to_linux_errno,
	translate_traps,
	linux_fixup,
	linux_sendsig,
	linux_sigcode,
	&linux_szsigcode,
	linux_prepsyscall,
	"Linux a.out",
	aout_coredump,
	exec_linux_imgact_try,
	LINUX_MINSIGSTKSZ
};

struct sysentvec elf_linux_sysvec = {
	LINUX_SYS_MAXSYSCALL,
	linux_sysent,
	0xff,
	LINUX_SIGTBLSZ,
	bsd_to_linux_signal,
	ELAST + 1,
	bsd_to_linux_errno,
	translate_traps,
	elf_linux_fixup,
	linux_sendsig,
	linux_sigcode,
	&linux_szsigcode,
	linux_prepsyscall,
	"Linux ELF",
	elf_coredump,
	exec_linux_imgact_try,
	LINUX_MINSIGSTKSZ
};

static Elf32_Brandinfo linux_brand = {
					ELFOSABI_LINUX,
					"/compat/linux",
					"/lib/ld-linux.so.1",
					&elf_linux_sysvec
				 };

static Elf32_Brandinfo linux_glibc2brand = {
					ELFOSABI_LINUX,
					"/compat/linux",
					"/lib/ld-linux.so.2",
					&elf_linux_sysvec
				 };

Elf32_Brandinfo *linux_brandlist[] = {
					&linux_brand,
					&linux_glibc2brand,
					NULL
				};

static int
linux_elf_modevent(module_t mod, int type, void *data)
{
	Elf32_Brandinfo **brandinfo;
	int error;

	error = 0;

	switch(type) {
	case MOD_LOAD:
		for (brandinfo = &linux_brandlist[0]; *brandinfo != NULL;
		     ++brandinfo)
			if (elf_insert_brand_entry(*brandinfo) < 0)
				error = EINVAL;
		if (error == 0) {
			linux_ioctl_register_handlers(
				&linux_ioctl_handler_set);
			if (bootverbose)
				printf("Linux ELF exec handler installed\n");
		} else
			printf("cannot insert Linux ELF brand handler\n");
		break;
	case MOD_UNLOAD:
		for (brandinfo = &linux_brandlist[0]; *brandinfo != NULL;
		     ++brandinfo)
			if (elf_brand_inuse(*brandinfo))
				error = EBUSY;
		if (error == 0) {
			for (brandinfo = &linux_brandlist[0];
			     *brandinfo != NULL; ++brandinfo)
				if (elf_remove_brand_entry(*brandinfo) < 0)
					error = EINVAL;
		}
		if (error == 0) {
			linux_ioctl_unregister_handlers(
				&linux_ioctl_handler_set);
			if (bootverbose)
				printf("Linux ELF exec handler removed\n");
		} else
			printf("Could not deinstall ELF interpreter entry\n");
		break;
	default:
		break;
	}
	return error;
}

static moduledata_t linux_elf_mod = {
	"linuxelf",
	linux_elf_modevent,
	0
};

DECLARE_MODULE(linuxelf, linux_elf_mod, SI_SUB_EXEC, SI_ORDER_ANY);