arch/parisc/kernel/signal.c

/*
 *  linux/arch/parisc/kernel/signal.c: Architecture-specific signal
 *  handling support.
 *
 *  Copyright (C) 2000 David Huggins-Daines <dhd@debian.org>
 *  Copyright (C) 2000 Linuxcare, Inc.
 *
 *  Based on the ia64, i386, and alpha versions.
 *
 *  Like the IA-64, we are a recent enough port (we are *starting*
 *  with glibc2.2) that we do not need to support the old non-realtime
 *  Linux signals.  Therefore we don't.  HP/UX signals will go in
 *  arch/parisc/hpux/signal.c when we figure out how to do them.
 */

#include <linux/sched.h>
#include <linux/mm.h>
#include <linux/smp.h>
#include <linux/smp_lock.h>
#include <linux/kernel.h>
#include <linux/signal.h>
#include <linux/errno.h>
#include <linux/wait.h>
#include <linux/ptrace.h>
#include <linux/unistd.h>
#include <linux/stddef.h>
#include <linux/compat.h>
#include <linux/elf.h>
#include <linux/personality.h>
#include <asm/ucontext.h>
#include <asm/rt_sigframe.h>
#include <asm/uaccess.h>
#include <asm/pgalloc.h>
#include <asm/cacheflush.h>
#include <asm/offsets.h>

#ifdef CONFIG_COMPAT
#include <linux/compat.h>
#include "signal32.h"
#endif

#define DEBUG_SIG 0 
#define DEBUG_SIG_LEVEL 2

#if DEBUG_SIG
#define DBG(LEVEL, ...) \
        ((DEBUG_SIG_LEVEL >= LEVEL) \
	? printk(__VA_ARGS__) : (void) 0)
#else
#define DBG(LEVEL, ...)
#endif
	

#define _BLOCKABLE (~(sigmask(SIGKILL) | sigmask(SIGSTOP)))

/* gcc will complain if a pointer is cast to an integer of different
 * size.  If you really need to do this (and we do for an ELF32 user
 * application in an ELF64 kernel) then you have to do a cast to an
 * integer of the same size first.  The A() macro accomplishes
 * this. */
#define A(__x)	((unsigned long)(__x))

int do_signal(sigset_t *oldset, struct pt_regs *regs, int in_syscall);

/*
 * Atomically swap in the new signal mask, and wait for a signal.
 */
#ifdef __LP64__
#include "sys32.h"
#endif

asmlinkage int
sys_rt_sigsuspend(sigset_t __user *unewset, size_t sigsetsize, struct pt_regs *regs)
{
	sigset_t saveset, newset;
#ifdef __LP64__
	compat_sigset_t newset32;

	if(personality(current->personality) == PER_LINUX32){
		/* XXX: Don't preclude handling different sized sigset_t's.  */
		if (sigsetsize != sizeof(compat_sigset_t))
			return -EINVAL;
		if (copy_from_user(&newset32, (compat_sigset_t __user *)unewset, sizeof(newset32)))
			return -EFAULT;
		sigset_32to64(&newset,&newset32);
		
	} else 
#endif
	{
		/* XXX: Don't preclude handling different sized sigset_t's.  */
		if (sigsetsize != sizeof(sigset_t))
			return -EINVAL;
	
		if (copy_from_user(&newset, unewset, sizeof(newset)))
			return -EFAULT;
	}

	sigdelsetmask(&newset, ~_BLOCKABLE);

	spin_lock_irq(&current->sighand->siglock);
	saveset = current->blocked;
	current->blocked = newset;
	recalc_sigpending();
	spin_unlock_irq(&current->sighand->siglock);

	regs->gr[28] = -EINTR;
	while (1) {
		current->state = TASK_INTERRUPTIBLE;
		schedule();
		if (do_signal(&saveset, regs, 1))
			return -EINTR;
	}
}

/*
 * Do a signal return - restore sigcontext.
 */

/* Trampoline for calling rt_sigreturn() */
#define INSN_LDI_R25_0	 0x34190000 /* ldi  0,%r25 (in_syscall=0) */
#define INSN_LDI_R25_1	 0x34190002 /* ldi  1,%r25 (in_syscall=1) */
#define INSN_LDI_R20	 0x3414015a /* ldi  __NR_rt_sigreturn,%r20 */
#define INSN_BLE_SR2_R0  0xe4008200 /* be,l 0x100(%sr2,%r0),%sr0,%r31 */
#define INSN_NOP	 0x08000240 /* nop */
/* For debugging */
#define INSN_DIE_HORRIBLY 0x68000ccc /* stw %r0,0x666(%sr0,%r0) */

static long
restore_sigcontext(struct sigcontext __user *sc, struct pt_regs *regs)
{
	long err = 0;

	err |= __copy_from_user(regs->gr, sc->sc_gr, sizeof(regs->gr));
	err |= __copy_from_user(regs->fr, sc->sc_fr, sizeof(regs->fr));
	err |= __copy_from_user(regs->iaoq, sc->sc_iaoq, sizeof(regs->iaoq));
	err |= __copy_from_user(regs->iasq, sc->sc_iasq, sizeof(regs->iasq));
	err |= __get_user(regs->sar, &sc->sc_sar);
	DBG(2,"restore_sigcontext: iaoq is 0x%#lx / 0x%#lx\n", 
			regs->iaoq[0],regs->iaoq[1]);
	DBG(2,"restore_sigcontext: r28 is %ld\n", regs->gr[28]);
	return err;
}

void
sys_rt_sigreturn(struct pt_regs *regs, int in_syscall)
{
	struct rt_sigframe __user *frame;
	struct siginfo si;
	sigset_t set;
	unsigned long usp = (regs->gr[30] & ~(0x01UL));
	unsigned long sigframe_size = PARISC_RT_SIGFRAME_SIZE;
#ifdef __LP64__
	compat_sigset_t compat_set;
	struct compat_rt_sigframe __user * compat_frame;
	
	if(personality(current->personality) == PER_LINUX32)
		sigframe_size = PARISC_RT_SIGFRAME_SIZE32;
#endif


	/* Unwind the user stack to get the rt_sigframe structure. */
	frame = (struct rt_sigframe __user *)
		(usp - sigframe_size);
	DBG(2,"sys_rt_sigreturn: frame is %p\n", frame);

#ifdef __LP64__
	compat_frame = (struct compat_rt_sigframe __user *)frame;
	
	if(personality(current->personality) == PER_LINUX32){
		DBG(2,"sys_rt_sigreturn: ELF32 process.\n");
		if (__copy_from_user(&compat_set, &compat_frame->uc.uc_sigmask, sizeof(compat_set)))
			goto give_sigsegv;
		sigset_32to64(&set,&compat_set);
	} else
#endif
	{
		if (__copy_from_user(&set, &frame->uc.uc_sigmask, sizeof(set)))
			goto give_sigsegv;
	}
		
	sigdelsetmask(&set, ~_BLOCKABLE);
	spin_lock_irq(&current->sighand->siglock);
	current->blocked = set;
	recalc_sigpending();
	spin_unlock_irq(&current->sighand->siglock);

	/* Good thing we saved the old gr[30], eh? */
#ifdef __LP64__
	if(personality(current->personality) == PER_LINUX32){
		DBG(1,"sys_rt_sigreturn: compat_frame->uc.uc_mcontext 0x%p\n",
				&compat_frame->uc.uc_mcontext);
// FIXME: Load upper half from register file
		if (restore_sigcontext32(&compat_frame->uc.uc_mcontext, 
					&compat_frame->regs, regs))
			goto give_sigsegv;
		DBG(1,"sys_rt_sigreturn: usp %#08lx stack 0x%p\n", 
				usp, &compat_frame->uc.uc_stack);
		if (do_sigaltstack32(&compat_frame->uc.uc_stack, NULL, usp) == -EFAULT)
			goto give_sigsegv;
	} else
#endif
	{
		DBG(1,"sys_rt_sigreturn: frame->uc.uc_mcontext 0x%p\n",
				&frame->uc.uc_mcontext);
		if (restore_sigcontext(&frame->uc.uc_mcontext, regs))
			goto give_sigsegv;
		DBG(1,"sys_rt_sigreturn: usp %#08lx stack 0x%p\n", 
				usp, &frame->uc.uc_stack);
		if (do_sigaltstack(&frame->uc.uc_stack, NULL, usp) == -EFAULT)
			goto give_sigsegv;
	}
		


	/* If we are on the syscall path IAOQ will not be restored, and
	 * if we are on the interrupt path we must not corrupt gr31.
	 */
	if (in_syscall)
		regs->gr[31] = regs->iaoq[0];
#if DEBUG_SIG
	DBG(1,"sys_rt_sigreturn: returning to %#lx, DUMPING REGS:\n", regs->iaoq[0]);
	show_regs(regs);
#endif
	return;

give_sigsegv:
	DBG(1,"sys_rt_sigreturn: Sending SIGSEGV\n");
	si.si_signo = SIGSEGV;
	si.si_errno = 0;
	si.si_code = SI_KERNEL;
	si.si_pid = current->pid;
	si.si_uid = current->uid;
	si.si_addr = &frame->uc;
	force_sig_info(SIGSEGV, &si, current);
	return;
}

/*
 * Set up a signal frame.
 */

static inline void __user *
get_sigframe(struct k_sigaction *ka, unsigned long sp, size_t frame_size)
{
	/*FIXME: ELF32 vs. ELF64 has different frame_size, but since we
	  don't use the parameter it doesn't matter */

	DBG(1,"get_sigframe: ka = %#lx, sp = %#lx, frame_size = %#lx\n",
			(unsigned long)ka, sp, frame_size);
	
	if ((ka->sa.sa_flags & SA_ONSTACK) != 0 && ! on_sig_stack(sp))
		sp = current->sas_ss_sp; /* Stacks grow up! */

	DBG(1,"get_sigframe: Returning sp = %#lx\n", (unsigned long)sp);
	return (void __user *) sp; /* Stacks grow up.  Fun. */
}

static long
setup_sigcontext(struct sigcontext __user *sc, struct pt_regs *regs, int in_syscall)
		 
{
	unsigned long flags = 0;
	long err = 0;

	if (on_sig_stack((unsigned long) sc))
		flags |= PARISC_SC_FLAG_ONSTACK;
	if (in_syscall) {
		flags |= PARISC_SC_FLAG_IN_SYSCALL;
		/* regs->iaoq is undefined in the syscall return path */
		err |= __put_user(regs->gr[31], &sc->sc_iaoq[0]);
		err |= __put_user(regs->gr[31]+4, &sc->sc_iaoq[1]);
		err |= __put_user(regs->sr[3], &sc->sc_iasq[0]);
		err |= __put_user(regs->sr[3], &sc->sc_iasq[1]);
		DBG(1,"setup_sigcontext: iaoq %#lx / %#lx (in syscall)\n",
			regs->gr[31], regs->gr[31]+4);
	} else {
		err |= __copy_to_user(sc->sc_iaoq, regs->iaoq, sizeof(regs->iaoq));
		err |= __copy_to_user(sc->sc_iasq, regs->iasq, sizeof(regs->iasq));
		DBG(1,"setup_sigcontext: iaoq %#lx / %#lx (not in syscall)\n", 
			regs->iaoq[0], regs->iaoq[1]);
	}

	err |= __put_user(flags, &sc->sc_flags);
	err |= __copy_to_user(sc->sc_gr, regs->gr, sizeof(regs->gr));
	err |= __copy_to_user(sc->sc_fr, regs->fr, sizeof(regs->fr));
	err |= __put_user(regs->sar, &sc->sc_sar);
	DBG(1,"setup_sigcontext: r28 is %ld\n", regs->gr[28]);

	return err;
}

static long
setup_rt_frame(int sig, struct k_sigaction *ka, siginfo_t *info,
	       sigset_t *set, struct pt_regs *regs, int in_syscall)
{
	struct rt_sigframe __user *frame;
	unsigned long rp, usp;
	unsigned long haddr, sigframe_size;
	struct siginfo si;
	int err = 0;
#ifdef __LP64__
	compat_int_t compat_val;
	struct compat_rt_sigframe __user * compat_frame;
	compat_sigset_t compat_set;
#endif
	
	usp = (regs->gr[30] & ~(0x01UL));
	/*FIXME: frame_size parameter is unused, remove it. */
	frame = get_sigframe(ka, usp, sizeof(*frame));

	DBG(1,"SETUP_RT_FRAME: START\n");
	DBG(1,"setup_rt_frame: frame %p info %p\n", frame, info);

	
#ifdef __LP64__

	compat_frame = (struct compat_rt_sigframe __user *)frame;
	
	if(personality(current->personality) == PER_LINUX32) {
		DBG(1,"setup_rt_frame: frame->info = 0x%p\n", &compat_frame->info);
		err |= compat_copy_siginfo_to_user(&compat_frame->info, info);
		DBG(1,"SETUP_RT_FRAME: 1\n");
		compat_val = (compat_int_t)current->sas_ss_sp;
		err |= __put_user(compat_val, &compat_frame->uc.uc_stack.ss_sp);
		DBG(1,"SETUP_RT_FRAME: 2\n");
		compat_val = (compat_int_t)current->sas_ss_size;
		err |= __put_user(compat_val, &compat_frame->uc.uc_stack.ss_size);
		DBG(1,"SETUP_RT_FRAME: 3\n");
		compat_val = sas_ss_flags(regs->gr[30]);		
		err |= __put_user(compat_val, &compat_frame->uc.uc_stack.ss_flags);		
		DBG(1,"setup_rt_frame: frame->uc = 0x%p\n", &compat_frame->uc);
		DBG(1,"setup_rt_frame: frame->uc.uc_mcontext = 0x%p\n", &compat_frame->uc.uc_mcontext);
		err |= setup_sigcontext32(&compat_frame->uc.uc_mcontext, 
					&compat_frame->regs, regs, in_syscall);
		sigset_64to32(&compat_set,set);
		err |= __copy_to_user(&compat_frame->uc.uc_sigmask, &compat_set, sizeof(compat_set));
	} else
#endif
	{	
		DBG(1,"setup_rt_frame: frame->info = 0x%p\n", &frame->info);
		err |= copy_siginfo_to_user(&frame->info, info);
		err |= __put_user(current->sas_ss_sp, &frame->uc.uc_stack.ss_sp);
		err |= __put_user(current->sas_ss_size, &frame->uc.uc_stack.ss_size);
		err |= __put_user(sas_ss_flags(regs->gr[30]),
				  &frame->uc.uc_stack.ss_flags);
		DBG(1,"setup_rt_frame: frame->uc = 0x%p\n", &frame->uc);
		DBG(1,"setup_rt_frame: frame->uc.uc_mcontext = 0x%p\n", &frame->uc.uc_mcontext);
		err |= setup_sigcontext(&frame->uc.uc_mcontext, regs, in_syscall);
		/* FIXME: Should probably be converted aswell for the compat case */
		err |= __copy_to_user(&frame->uc.uc_sigmask, set, sizeof(*set));
	}
	
	if (err)
		goto give_sigsegv;

	/* Set up to return from userspace.  If provided, use a stub
	   already in userspace. The first words of tramp are used to
	   save the previous sigrestartblock trampoline that might be
	   on the stack. We start the sigreturn trampoline at 
	   SIGRESTARTBLOCK_TRAMP+X. */
	err |= __put_user(in_syscall ? INSN_LDI_R25_1 : INSN_LDI_R25_0,
			&frame->tramp[SIGRESTARTBLOCK_TRAMP+0]);
	err |= __put_user(INSN_LDI_R20, 
			&frame->tramp[SIGRESTARTBLOCK_TRAMP+1]);
	err |= __put_user(INSN_BLE_SR2_R0, 
			&frame->tramp[SIGRESTARTBLOCK_TRAMP+2]);
	err |= __put_user(INSN_NOP, &frame->tramp[SIGRESTARTBLOCK_TRAMP+3]);

#if DEBUG_SIG
	/* Assert that we're flushing in the correct space... */
	{
		int sid;
		asm ("mfsp %%sr3,%0" : "=r" (sid));
		DBG(1,"setup_rt_frame: Flushing 64 bytes at space %#x offset %p\n",
		       sid, frame->tramp);
	}
#endif

	flush_user_dcache_range((unsigned long) &frame->tramp[0],
			   (unsigned long) &frame->tramp[TRAMP_SIZE]);
	flush_user_icache_range((unsigned long) &frame->tramp[0],
			   (unsigned long) &frame->tramp[TRAMP_SIZE]);

	/* TRAMP Words 0-4, Lenght 5 = SIGRESTARTBLOCK_TRAMP
	 * TRAMP Words 5-9, Length 4 = SIGRETURN_TRAMP
	 * So the SIGRETURN_TRAMP is at the end of SIGRESTARTBLOCK_TRAMP
	 */
	rp = (unsigned long) &frame->tramp[SIGRESTARTBLOCK_TRAMP];

	if (err)
		goto give_sigsegv;

	haddr = A(ka->sa.sa_handler);
	/* The sa_handler may be a pointer to a function descriptor */
#ifdef __LP64__
	if(personality(current->personality) == PER_LINUX32) {
#endif
		if (haddr & PA_PLABEL_FDESC) {
			Elf32_Fdesc fdesc;
			Elf32_Fdesc __user *ufdesc = (Elf32_Fdesc __user *)A(haddr & ~3);

			err = __copy_from_user(&fdesc, ufdesc, sizeof(fdesc));

			if (err)
				goto give_sigsegv;

			haddr = fdesc.addr;
			regs->gr[19] = fdesc.gp;
		}
#ifdef __LP64__
	} else {
		Elf64_Fdesc fdesc;
		Elf64_Fdesc __user *ufdesc = (Elf64_Fdesc __user *)A(haddr & ~3);
		
		err = __copy_from_user(&fdesc, ufdesc, sizeof(fdesc));
		
		if (err)
			goto give_sigsegv;
		
		haddr = fdesc.addr;
		regs->gr[19] = fdesc.gp;
		DBG(1,"setup_rt_frame: 64 bit signal, exe=%#lx, r19=%#lx, in_syscall=%d\n",
		     haddr, regs->gr[19], in_syscall);
	}
#endif

	/* The syscall return path will create IAOQ values from r31.
	 */
	sigframe_size = PARISC_RT_SIGFRAME_SIZE;
#ifdef __LP64__
	if(personality(current->personality) == PER_LINUX32)
		sigframe_size = PARISC_RT_SIGFRAME_SIZE32;
#endif
	if (in_syscall) {
		regs->gr[31] = haddr;
#ifdef __LP64__
		if(personality(current->personality) == PER_LINUX)
			sigframe_size |= 1;
#endif
	} else {
		unsigned long psw = USER_PSW;
#ifdef __LP64__
		if(personality(current->personality) == PER_LINUX)
			psw |= PSW_W;
#endif

		/* If we are singlestepping, arrange a trap to be delivered
		   when we return to userspace. Note the semantics -- we
		   should trap before the first insn in the handler is
		   executed. Ref:
			http://sources.redhat.com/ml/gdb/2004-11/msg00245.html
		 */
		if (pa_psw(current)->r) {
			pa_psw(current)->r = 0;
			psw |= PSW_R;
			mtctl(-1, 0);
		}

		regs->gr[0] = psw;
		regs->iaoq[0] = haddr | 3;
		regs->iaoq[1] = regs->iaoq[0] + 4;
	}

	regs->gr[2]  = rp;                /* userland return pointer */
	regs->gr[26] = sig;               /* signal number */
	
#ifdef __LP64__
	if(personality(current->personality) == PER_LINUX32){
		regs->gr[25] = A(&compat_frame->info); /* siginfo pointer */
		regs->gr[24] = A(&compat_frame->uc);   /* ucontext pointer */
	} else
#endif
	{		
		regs->gr[25] = A(&frame->info); /* siginfo pointer */
		regs->gr[24] = A(&frame->uc);   /* ucontext pointer */
	}
	
	DBG(1,"setup_rt_frame: making sigreturn frame: %#lx + %#lx = %#lx\n",
	       regs->gr[30], sigframe_size,
	       regs->gr[30] + sigframe_size);
	/* Raise the user stack pointer to make a proper call frame. */
	regs->gr[30] = (A(frame) + sigframe_size);


	DBG(1,"setup_rt_frame: sig deliver (%s,%d) frame=0x%p sp=%#lx iaoq=%#lx/%#lx rp=%#lx\n",
	       current->comm, current->pid, frame, regs->gr[30],
	       regs->iaoq[0], regs->iaoq[1], rp);

	return 1;

give_sigsegv:
	DBG(1,"setup_rt_frame: sending SIGSEGV\n");
	if (sig == SIGSEGV)
		ka->sa.sa_handler = SIG_DFL;
	si.si_signo = SIGSEGV;
	si.si_errno = 0;
	si.si_code = SI_KERNEL;
	si.si_pid = current->pid;
	si.si_uid = current->uid;
	si.si_addr = frame;
	force_sig_info(SIGSEGV, &si, current);
	return 0;
}

/*
 * OK, we're invoking a handler.
 */	

static long
handle_signal(unsigned long sig, siginfo_t *info, struct k_sigaction *ka,
		sigset_t *oldset, struct pt_regs *regs, int in_syscall)
{
	DBG(1,"handle_signal: sig=%ld, ka=%p, info=%p, oldset=%p, regs=%p\n",
	       sig, ka, info, oldset, regs);
	
	/* Set up the stack frame */
	if (!setup_rt_frame(sig, ka, info, oldset, regs, in_syscall))
		return 0;

	spin_lock_irq(&current->sighand->siglock);
	sigorsets(&current->blocked,&current->blocked,&ka->sa.sa_mask);
	if (!(ka->sa.sa_flags & SA_NODEFER))
		sigaddset(&current->blocked,sig);
	recalc_sigpending();
	spin_unlock_irq(&current->sighand->siglock);
	return 1;
}

/*
 * Note that 'init' is a special process: it doesn't get signals it doesn't
 * want to handle. Thus you cannot kill init even with a SIGKILL even by
 * mistake.
 *
 * We need to be able to restore the syscall arguments (r21-r26) to
 * restart syscalls.  Thus, the syscall path should save them in the
 * pt_regs structure (it's okay to do so since they are caller-save
 * registers).  As noted below, the syscall number gets restored for
 * us due to the magic of delayed branching.
 */

asmlinkage int
do_signal(sigset_t *oldset, struct pt_regs *regs, int in_syscall)
{
	siginfo_t info;
	struct k_sigaction ka;
	int signr;

	DBG(1,"\ndo_signal: oldset=0x%p, regs=0x%p, sr7 %#lx, in_syscall=%d\n",
	       oldset, regs, regs->sr[7], in_syscall);

	/* Everyone else checks to see if they are in kernel mode at
	   this point and exits if that's the case.  I'm not sure why
	   we would be called in that case, but for some reason we
	   are. */

	if (!oldset)
		oldset = &current->blocked;

	DBG(1,"do_signal: oldset %08lx / %08lx\n", 
		oldset->sig[0], oldset->sig[1]);


	/* May need to force signal if handle_signal failed to deliver */
	while (1) {
	  
		signr = get_signal_to_deliver(&info, &ka, regs, NULL);
		DBG(3,"do_signal: signr = %d, regs->gr[28] = %ld\n", signr, regs->gr[28]); 
	
		if (signr <= 0)
		  break;
		
		/* Restart a system call if necessary. */
		if (in_syscall) {
			/* Check the return code */
			switch (regs->gr[28]) {
		        case -ERESTART_RESTARTBLOCK:
				current_thread_info()->restart_block.fn = do_no_restart_syscall;
			case -ERESTARTNOHAND:
				DBG(1,"ERESTARTNOHAND: returning -EINTR\n");
				regs->gr[28] = -EINTR;
				break;

			case -ERESTARTSYS:
				if (!(ka.sa.sa_flags & SA_RESTART)) {
					DBG(1,"ERESTARTSYS: putting -EINTR\n");
					regs->gr[28] = -EINTR;
					break;
				}
			/* fallthrough */
			case -ERESTARTNOINTR:
				/* A syscall is just a branch, so all
				   we have to do is fiddle the return pointer. */
				regs->gr[31] -= 8; /* delayed branching */
				/* Preserve original r28. */
				regs->gr[28] = regs->orig_r28;
				break;
			}
		}
		/* Whee!  Actually deliver the signal.  If the
		   delivery failed, we need to continue to iterate in
		   this loop so we can deliver the SIGSEGV... */
		if (handle_signal(signr, &info, &ka, oldset, regs, in_syscall)) {
			DBG(1,KERN_DEBUG "do_signal: Exit (success), regs->gr[28] = %ld\n",
				regs->gr[28]);
			return 1;
		}
	}
	/* end of while(1) looping forever if we can't force a signal */

	/* Did we come from a system call? */
	if (in_syscall) {
		/* Restart the system call - no handlers present */
		if (regs->gr[28] == -ERESTART_RESTARTBLOCK) {
			unsigned int *usp = (unsigned int *)regs->gr[30];

			/* Setup a trampoline to restart the syscall
			 * with __NR_restart_syscall
			 *
			 *  0: <return address (orig r31)>
			 *  4: <2nd half for 64-bit>
			 *  8: ldw 0(%sp), %r31
			 * 12: be 0x100(%sr2, %r0)
			 * 16: ldi __NR_restart_syscall, %r20
			 */
#ifndef __LP64__
			put_user(regs->gr[31], &usp[0]);
			put_user(0x0fc0109f, &usp[2]);
#else
			put_user(regs->gr[31] >> 32, &usp[0]);
			put_user(regs->gr[31] & 0xffffffff, &usp[1]);
			put_user(0x0fc010df, &usp[2]);
#endif
			put_user(0xe0008200, &usp[3]);
			put_user(0x34140000, &usp[4]);

			/* Stack is 64-byte aligned, and we only 
			 * need to flush 1 cache line */
			asm("fdc 0(%%sr3, %0)\n"
			    "fic 0(%%sr3, %0)\n"
			    "sync\n"
			    : : "r"(regs->gr[30]));

			regs->gr[31] = regs->gr[30] + 8;
			/* Preserve original r28. */
			regs->gr[28] = regs->orig_r28;
		} else if (regs->gr[28] == -ERESTARTNOHAND ||
		           regs->gr[28] == -ERESTARTSYS ||
		           regs->gr[28] == -ERESTARTNOINTR) {
			/* Hooray for delayed branching.  We don't
                           have to restore %r20 (the system call
                           number) because it gets loaded in the delay
                           slot of the branch external instruction. */
			regs->gr[31] -= 8;
			/* Preserve original r28. */
			regs->gr[28] = regs->orig_r28;
		}
	}
	
	DBG(1,"do_signal: Exit (not delivered), regs->gr[28] = %ld\n", 
		regs->gr[28]);

	return 0;
}