[mirror_ubuntu-jammy-kernel.git] / arch / s390 / kernel / process.c

/*
 *  arch/s390/kernel/process.c
 *
 *  S390 version
 *    Copyright (C) 1999 IBM Deutschland Entwicklung GmbH, IBM Corporation
 *    Author(s): Martin Schwidefsky (schwidefsky@de.ibm.com),
 *               Hartmut Penner (hp@de.ibm.com),
 *               Denis Joseph Barrow (djbarrow@de.ibm.com,barrow_dj@yahoo.com),
 *
 *  Derived from "arch/i386/kernel/process.c"
 *    Copyright (C) 1995, Linus Torvalds
 */

/*
 * This file handles the architecture-dependent parts of process handling..
 */

#include <linux/compiler.h>
#include <linux/cpu.h>
#include <linux/errno.h>
#include <linux/sched.h>
#include <linux/kernel.h>
#include <linux/mm.h>
#include <linux/smp.h>
#include <linux/smp_lock.h>
#include <linux/stddef.h>
#include <linux/unistd.h>
#include <linux/ptrace.h>
#include <linux/slab.h>
#include <linux/vmalloc.h>
#include <linux/user.h>
#include <linux/a.out.h>
#include <linux/interrupt.h>
#include <linux/delay.h>
#include <linux/reboot.h>
#include <linux/init.h>
#include <linux/module.h>
#include <linux/notifier.h>

#include <asm/uaccess.h>
#include <asm/pgtable.h>
#include <asm/system.h>
#include <asm/io.h>
#include <asm/processor.h>
#include <asm/irq.h>
#include <asm/timer.h>

asmlinkage void ret_from_fork(void) __asm__("ret_from_fork");

/*
 * Return saved PC of a blocked thread. used in kernel/sched.
 * resume in entry.S does not create a new stack frame, it
 * just stores the registers %r6-%r15 to the frame given by
 * schedule. We want to return the address of the caller of
 * schedule, so we have to walk the backchain one time to
 * find the frame schedule() store its return address.
 */
unsigned long thread_saved_pc(struct task_struct *tsk)
{
	struct stack_frame *sf, *low, *high;

	if (!tsk || !task_stack_page(tsk))
		return 0;
	low = task_stack_page(tsk);
	high = (struct stack_frame *) task_pt_regs(tsk);
	sf = (struct stack_frame *) (tsk->thread.ksp & PSW_ADDR_INSN);
	if (sf <= low || sf > high)
		return 0;
	sf = (struct stack_frame *) (sf->back_chain & PSW_ADDR_INSN);
	if (sf <= low || sf > high)
		return 0;
	return sf->gprs[8];
}

/*
 * Need to know about CPUs going idle?
 */
static ATOMIC_NOTIFIER_HEAD(idle_chain);

int register_idle_notifier(struct notifier_block *nb)
{
	return atomic_notifier_chain_register(&idle_chain, nb);
}
EXPORT_SYMBOL(register_idle_notifier);

int unregister_idle_notifier(struct notifier_block *nb)
{
	return atomic_notifier_chain_unregister(&idle_chain, nb);
}
EXPORT_SYMBOL(unregister_idle_notifier);

void do_monitor_call(struct pt_regs *regs, long interruption_code)
{
	/* disable monitor call class 0 */
	__ctl_clear_bit(8, 15);

	atomic_notifier_call_chain(&idle_chain, CPU_NOT_IDLE,
			    (void *)(long) smp_processor_id());
}

extern void s390_handle_mcck(void);
/*
 * The idle loop on a S390...
 */
static void default_idle(void)
{
	int cpu, rc;

	/* CPU is going idle. */
	cpu = smp_processor_id();

	local_irq_disable();
	if (need_resched()) {
		local_irq_enable();
		return;
	}

	rc = atomic_notifier_call_chain(&idle_chain,
			CPU_IDLE, (void *)(long) cpu);
	if (rc != NOTIFY_OK && rc != NOTIFY_DONE)
		BUG();
	if (rc != NOTIFY_OK) {
		local_irq_enable();
		return;
	}

	/* enable monitor call class 0 */
	__ctl_set_bit(8, 15);

#ifdef CONFIG_HOTPLUG_CPU
	if (cpu_is_offline(cpu)) {
		preempt_enable_no_resched();
		cpu_die();
	}
#endif

	local_mcck_disable();
	if (test_thread_flag(TIF_MCCK_PENDING)) {
		local_mcck_enable();
		local_irq_enable();
		s390_handle_mcck();
		return;
	}

	/* Wait for external, I/O or machine check interrupt. */
	__load_psw_mask(PSW_KERNEL_BITS | PSW_MASK_WAIT |
			PSW_MASK_IO | PSW_MASK_EXT);
}

void cpu_idle(void)
{
	for (;;) {
		while (!need_resched())
			default_idle();

		preempt_enable_no_resched();
		schedule();
		preempt_disable();
	}
}

void show_regs(struct pt_regs *regs)
{
	struct task_struct *tsk = current;

        printk("CPU:    %d    %s\n", task_thread_info(tsk)->cpu, print_tainted());
        printk("Process %s (pid: %d, task: %p, ksp: %p)\n",
	       current->comm, current->pid, (void *) tsk,
	       (void *) tsk->thread.ksp);

	show_registers(regs);
	/* Show stack backtrace if pt_regs is from kernel mode */
	if (!(regs->psw.mask & PSW_MASK_PSTATE))
		show_trace(0,(unsigned long *) regs->gprs[15]);
}

extern void kernel_thread_starter(void);

__asm__(".align 4\n"
	"kernel_thread_starter:\n"
	"    la    2,0(10)\n"
	"    basr  14,9\n"
	"    la    2,0\n"
	"    br    11\n");

int kernel_thread(int (*fn)(void *), void * arg, unsigned long flags)
{
	struct pt_regs regs;

	memset(&regs, 0, sizeof(regs));
	regs.psw.mask = PSW_KERNEL_BITS | PSW_MASK_IO | PSW_MASK_EXT;
	regs.psw.addr = (unsigned long) kernel_thread_starter | PSW_ADDR_AMODE;
	regs.gprs[9] = (unsigned long) fn;
	regs.gprs[10] = (unsigned long) arg;
	regs.gprs[11] = (unsigned long) do_exit;
	regs.orig_gpr2 = -1;

	/* Ok, create the new process.. */
	return do_fork(flags | CLONE_VM | CLONE_UNTRACED,
		       0, &regs, 0, NULL, NULL);
}

/*
 * Free current thread data structures etc..
 */
void exit_thread(void)
{
}

void flush_thread(void)
{
	clear_used_math();
	clear_tsk_thread_flag(current, TIF_USEDFPU);
}

void release_thread(struct task_struct *dead_task)
{
}

int copy_thread(int nr, unsigned long clone_flags, unsigned long new_stackp,
	unsigned long unused,
        struct task_struct * p, struct pt_regs * regs)
{
        struct fake_frame
          {
	    struct stack_frame sf;
            struct pt_regs childregs;
          } *frame;

        frame = container_of(task_pt_regs(p), struct fake_frame, childregs);
        p->thread.ksp = (unsigned long) frame;
	/* Store access registers to kernel stack of new process. */
        frame->childregs = *regs;
	frame->childregs.gprs[2] = 0;	/* child returns 0 on fork. */
        frame->childregs.gprs[15] = new_stackp;
        frame->sf.back_chain = 0;

        /* new return point is ret_from_fork */
        frame->sf.gprs[8] = (unsigned long) ret_from_fork;

        /* fake return stack for resume(), don't go back to schedule */
        frame->sf.gprs[9] = (unsigned long) frame;

	/* Save access registers to new thread structure. */
	save_access_regs(&p->thread.acrs[0]);

#ifndef CONFIG_64BIT
        /*
	 * save fprs to current->thread.fp_regs to merge them with
	 * the emulated registers and then copy the result to the child.
	 */
	save_fp_regs(&current->thread.fp_regs);
	memcpy(&p->thread.fp_regs, &current->thread.fp_regs,
	       sizeof(s390_fp_regs));
        p->thread.user_seg = __pa((unsigned long) p->mm->pgd) | _SEGMENT_TABLE;
	/* Set a new TLS ?  */
	if (clone_flags & CLONE_SETTLS)
		p->thread.acrs[0] = regs->gprs[6];
#else /* CONFIG_64BIT */
	/* Save the fpu registers to new thread structure. */
	save_fp_regs(&p->thread.fp_regs);
        p->thread.user_seg = __pa((unsigned long) p->mm->pgd) | _REGION_TABLE;
	/* Set a new TLS ?  */
	if (clone_flags & CLONE_SETTLS) {
		if (test_thread_flag(TIF_31BIT)) {
			p->thread.acrs[0] = (unsigned int) regs->gprs[6];
		} else {
			p->thread.acrs[0] = (unsigned int)(regs->gprs[6] >> 32);
			p->thread.acrs[1] = (unsigned int) regs->gprs[6];
		}
	}
#endif /* CONFIG_64BIT */
	/* start new process with ar4 pointing to the correct address space */
	p->thread.mm_segment = get_fs();
        /* Don't copy debug registers */
        memset(&p->thread.per_info,0,sizeof(p->thread.per_info));

        return 0;
}

asmlinkage long sys_fork(struct pt_regs regs)
{
	return do_fork(SIGCHLD, regs.gprs[15], &regs, 0, NULL, NULL);
}

asmlinkage long sys_clone(struct pt_regs regs)
{
        unsigned long clone_flags;
        unsigned long newsp;
	int __user *parent_tidptr, *child_tidptr;

        clone_flags = regs.gprs[3];
        newsp = regs.orig_gpr2;
	parent_tidptr = (int __user *) regs.gprs[4];
	child_tidptr = (int __user *) regs.gprs[5];
        if (!newsp)
                newsp = regs.gprs[15];
        return do_fork(clone_flags, newsp, &regs, 0,
		       parent_tidptr, child_tidptr);
}

/*
 * This is trivial, and on the face of it looks like it
 * could equally well be done in user mode.
 *
 * Not so, for quite unobvious reasons - register pressure.
 * In user mode vfork() cannot have a stack frame, and if
 * done by calling the "clone()" system call directly, you
 * do not have enough call-clobbered registers to hold all
 * the information you need.
 */
asmlinkage long sys_vfork(struct pt_regs regs)
{
	return do_fork(CLONE_VFORK | CLONE_VM | SIGCHLD,
		       regs.gprs[15], &regs, 0, NULL, NULL);
}

/*
 * sys_execve() executes a new program.
 */
asmlinkage long sys_execve(struct pt_regs regs)
{
        int error;
        char * filename;

        filename = getname((char __user *) regs.orig_gpr2);
        error = PTR_ERR(filename);
        if (IS_ERR(filename))
                goto out;
        error = do_execve(filename, (char __user * __user *) regs.gprs[3],
			  (char __user * __user *) regs.gprs[4], &regs);
	if (error == 0) {
		task_lock(current);
		current->ptrace &= ~PT_DTRACE;
		task_unlock(current);
		current->thread.fp_regs.fpc = 0;
		if (MACHINE_HAS_IEEE)
			asm volatile("sfpc %0,%0" : : "d" (0));
	}
        putname(filename);
out:
        return error;
}


/*
 * fill in the FPU structure for a core dump.
 */
int dump_fpu (struct pt_regs * regs, s390_fp_regs *fpregs)
{
#ifndef CONFIG_64BIT
        /*
	 * save fprs to current->thread.fp_regs to merge them with
	 * the emulated registers and then copy the result to the dump.
	 */
	save_fp_regs(&current->thread.fp_regs);
	memcpy(fpregs, &current->thread.fp_regs, sizeof(s390_fp_regs));
#else /* CONFIG_64BIT */
	save_fp_regs(fpregs);
#endif /* CONFIG_64BIT */
	return 1;
}

unsigned long get_wchan(struct task_struct *p)
{
	struct stack_frame *sf, *low, *high;
	unsigned long return_address;
	int count;

	if (!p || p == current || p->state == TASK_RUNNING || !task_stack_page(p))
		return 0;
	low = task_stack_page(p);
	high = (struct stack_frame *) task_pt_regs(p);
	sf = (struct stack_frame *) (p->thread.ksp & PSW_ADDR_INSN);
	if (sf <= low || sf > high)
		return 0;
	for (count = 0; count < 16; count++) {
		sf = (struct stack_frame *) (sf->back_chain & PSW_ADDR_INSN);
		if (sf <= low || sf > high)
			return 0;
		return_address = sf->gprs[8] & PSW_ADDR_INSN;
		if (!in_sched_functions(return_address))
			return return_address;
	}
	return 0;
}
Commit	Line	Data
1da177e4 LT	1	/*
	2	* arch/s390/kernel/process.c
	3	*
	4	* S390 version
	5	* Copyright (C) 1999 IBM Deutschland Entwicklung GmbH, IBM Corporation
	6	* Author(s): Martin Schwidefsky (schwidefsky@de.ibm.com),
	7	* Hartmut Penner (hp@de.ibm.com),
	8	* Denis Joseph Barrow (djbarrow@de.ibm.com,barrow_dj@yahoo.com),
	9	*
	10	* Derived from "arch/i386/kernel/process.c"
	11	* Copyright (C) 1995, Linus Torvalds
	12	*/
	13
	14	/*
	15	* This file handles the architecture-dependent parts of process handling..
	16	*/
	17
1da177e4 LT	18	#include <linux/compiler.h>
	19	#include <linux/cpu.h>
	20	#include <linux/errno.h>
	21	#include <linux/sched.h>
	22	#include <linux/kernel.h>
	23	#include <linux/mm.h>
	24	#include <linux/smp.h>
	25	#include <linux/smp_lock.h>
	26	#include <linux/stddef.h>
	27	#include <linux/unistd.h>
	28	#include <linux/ptrace.h>
	29	#include <linux/slab.h>
	30	#include <linux/vmalloc.h>
	31	#include <linux/user.h>
	32	#include <linux/a.out.h>
	33	#include <linux/interrupt.h>
	34	#include <linux/delay.h>
	35	#include <linux/reboot.h>
	36	#include <linux/init.h>
	37	#include <linux/module.h>
	38	#include <linux/notifier.h>
	39
	40	#include <asm/uaccess.h>
	41	#include <asm/pgtable.h>
	42	#include <asm/system.h>
	43	#include <asm/io.h>
	44	#include <asm/processor.h>
	45	#include <asm/irq.h>
	46	#include <asm/timer.h>
	47
	48	asmlinkage void ret_from_fork(void) __asm__("ret_from_fork");
	49
	50	/*
	51	* Return saved PC of a blocked thread. used in kernel/sched.
	52	* resume in entry.S does not create a new stack frame, it
	53	* just stores the registers %r6-%r15 to the frame given by
	54	* schedule. We want to return the address of the caller of
	55	* schedule, so we have to walk the backchain one time to
	56	* find the frame schedule() store its return address.
	57	*/
	58	unsigned long thread_saved_pc(struct task_struct *tsk)
	59	{
eb33c190	60	struct stack_frame sf, low, *high;
1da177e4	61
eb33c190 HC	62	if (!tsk \|\| !task_stack_page(tsk))
	63	return 0;
	64	low = task_stack_page(tsk);
	65	high = (struct stack_frame *) task_pt_regs(tsk);
	66	sf = (struct stack_frame *) (tsk->thread.ksp & PSW_ADDR_INSN);
	67	if (sf <= low \|\| sf > high)
	68	return 0;
	69	sf = (struct stack_frame *) (sf->back_chain & PSW_ADDR_INSN);
	70	if (sf <= low \|\| sf > high)
	71	return 0;
1da177e4 LT	72	return sf->gprs[8];
	73	}
	74
	75	/*
	76	* Need to know about CPUs going idle?
	77	*/
e041c683	78	static ATOMIC_NOTIFIER_HEAD(idle_chain);
1da177e4 LT	79
	80	int register_idle_notifier(struct notifier_block *nb)
	81	{
e041c683	82	return atomic_notifier_chain_register(&idle_chain, nb);
1da177e4 LT	83	}
	84	EXPORT_SYMBOL(register_idle_notifier);
	85
	86	int unregister_idle_notifier(struct notifier_block *nb)
	87	{
e041c683	88	return atomic_notifier_chain_unregister(&idle_chain, nb);
1da177e4 LT	89	}
	90	EXPORT_SYMBOL(unregister_idle_notifier);
	91
	92	void do_monitor_call(struct pt_regs *regs, long interruption_code)
	93	{
	94	/* disable monitor call class 0 */
	95	__ctl_clear_bit(8, 15);
	96
e041c683	97	atomic_notifier_call_chain(&idle_chain, CPU_NOT_IDLE,
1da177e4 LT	98	(void *)(long) smp_processor_id());
	99	}
	100
77fa2245	101	extern void s390_handle_mcck(void);
1da177e4 LT	102	/*
	103	* The idle loop on a S390...
	104	*/
cdb04527	105	static void default_idle(void)
1da177e4	106	{
1da177e4 LT	107	int cpu, rc;
1da177e4 LT	108
64c7c8f8 NP	109	/* CPU is going idle. */
	110	cpu = smp_processor_id();
	111
1da177e4	112	local_irq_disable();
64c7c8f8	113	if (need_resched()) {
1da177e4	114	local_irq_enable();
64c7c8f8 NP	115	return;
64c7c8f8 NP	116	}
1da177e4	117
e041c683 AS	118	rc = atomic_notifier_call_chain(&idle_chain,
e041c683 AS	119	CPU_IDLE, (void *)(long) cpu);
1da177e4 LT	120	if (rc != NOTIFY_OK && rc != NOTIFY_DONE)
	121	BUG();
	122	if (rc != NOTIFY_OK) {
	123	local_irq_enable();
	124	return;
	125	}
	126
	127	/* enable monitor call class 0 */
	128	__ctl_set_bit(8, 15);
	129
	130	#ifdef CONFIG_HOTPLUG_CPU
1fca251f HC	131	if (cpu_is_offline(cpu)) {
1fca251f HC	132	preempt_enable_no_resched();
1da177e4	133	cpu_die();
1fca251f	134	}
1da177e4 LT	135	#endif
1da177e4 LT	136
77fa2245 HC	137	local_mcck_disable();
	138	if (test_thread_flag(TIF_MCCK_PENDING)) {
	139	local_mcck_enable();
	140	local_irq_enable();
	141	s390_handle_mcck();
	142	return;
	143	}
	144
	145	/* Wait for external, I/O or machine check interrupt. */
	146	__load_psw_mask(PSW_KERNEL_BITS \| PSW_MASK_WAIT \|
	147	PSW_MASK_IO \| PSW_MASK_EXT);
1da177e4 LT	148	}
	149
	150	void cpu_idle(void)
	151	{
5bfb5d69 NP	152	for (;;) {
	153	while (!need_resched())
	154	default_idle();
	155
	156	preempt_enable_no_resched();
	157	schedule();
	158	preempt_disable();
	159	}
1da177e4 LT	160	}
	161
	162	void show_regs(struct pt_regs *regs)
	163	{
	164	struct task_struct *tsk = current;
	165
30af7120	166	printk("CPU: %d %s\n", task_thread_info(tsk)->cpu, print_tainted());
1da177e4 LT	167	printk("Process %s (pid: %d, task: %p, ksp: %p)\n",
	168	current->comm, current->pid, (void *) tsk,
	169	(void *) tsk->thread.ksp);
	170
	171	show_registers(regs);
	172	/* Show stack backtrace if pt_regs is from kernel mode */
	173	if (!(regs->psw.mask & PSW_MASK_PSTATE))
	174	show_trace(0,(unsigned long *) regs->gprs[15]);
	175	}
	176
	177	extern void kernel_thread_starter(void);
	178
	179	__asm__(".align 4\n"
	180	"kernel_thread_starter:\n"
	181	" la 2,0(10)\n"
	182	" basr 14,9\n"
	183	" la 2,0\n"
	184	" br 11\n");
	185
	186	int kernel_thread(int (fn)(void ), void * arg, unsigned long flags)
	187	{
	188	struct pt_regs regs;
	189
	190	memset(&regs, 0, sizeof(regs));
	191	regs.psw.mask = PSW_KERNEL_BITS \| PSW_MASK_IO \| PSW_MASK_EXT;
	192	regs.psw.addr = (unsigned long) kernel_thread_starter \| PSW_ADDR_AMODE;
	193	regs.gprs[9] = (unsigned long) fn;
	194	regs.gprs[10] = (unsigned long) arg;
	195	regs.gprs[11] = (unsigned long) do_exit;
	196	regs.orig_gpr2 = -1;
	197
	198	/* Ok, create the new process.. */
	199	return do_fork(flags \| CLONE_VM \| CLONE_UNTRACED,
	200	0, &regs, 0, NULL, NULL);
	201	}
	202
	203	/*
	204	* Free current thread data structures etc..
	205	*/
	206	void exit_thread(void)
	207	{
	208	}
	209
	210	void flush_thread(void)
	211	{
	212	clear_used_math();
	213	clear_tsk_thread_flag(current, TIF_USEDFPU);
	214	}
	215
	216	void release_thread(struct task_struct *dead_task)
	217	{
	218	}
	219
	220	int copy_thread(int nr, unsigned long clone_flags, unsigned long new_stackp,
	221	unsigned long unused,
	222	struct task_struct * p, struct pt_regs * regs)
	223	{
	224	struct fake_frame
	225	{
	226	struct stack_frame sf;
	227	struct pt_regs childregs;
	228	} *frame;
	229
c7584fb6	230	frame = container_of(task_pt_regs(p), struct fake_frame, childregs);
1da177e4 LT	231	p->thread.ksp = (unsigned long) frame;
	232	/* Store access registers to kernel stack of new process. */
	233	frame->childregs = *regs;
	234	frame->childregs.gprs[2] = 0; /* child returns 0 on fork. */
	235	frame->childregs.gprs[15] = new_stackp;
	236	frame->sf.back_chain = 0;
	237
	238	/* new return point is ret_from_fork */
	239	frame->sf.gprs[8] = (unsigned long) ret_from_fork;
	240
	241	/* fake return stack for resume(), don't go back to schedule */
	242	frame->sf.gprs[9] = (unsigned long) frame;
	243
	244	/* Save access registers to new thread structure. */
	245	save_access_regs(&p->thread.acrs[0]);
	246
347a8dc3	247	#ifndef CONFIG_64BIT
1da177e4 LT	248	/*
	249	* save fprs to current->thread.fp_regs to merge them with
	250	* the emulated registers and then copy the result to the child.
	251	*/
	252	save_fp_regs(&current->thread.fp_regs);
	253	memcpy(&p->thread.fp_regs, &current->thread.fp_regs,
	254	sizeof(s390_fp_regs));
	255	p->thread.user_seg = __pa((unsigned long) p->mm->pgd) \| _SEGMENT_TABLE;
	256	/* Set a new TLS ? */
	257	if (clone_flags & CLONE_SETTLS)
	258	p->thread.acrs[0] = regs->gprs[6];
347a8dc3	259	#else /* CONFIG_64BIT */
1da177e4 LT	260	/* Save the fpu registers to new thread structure. */
	261	save_fp_regs(&p->thread.fp_regs);
	262	p->thread.user_seg = __pa((unsigned long) p->mm->pgd) \| _REGION_TABLE;
	263	/* Set a new TLS ? */
	264	if (clone_flags & CLONE_SETTLS) {
	265	if (test_thread_flag(TIF_31BIT)) {
	266	p->thread.acrs[0] = (unsigned int) regs->gprs[6];
	267	} else {
	268	p->thread.acrs[0] = (unsigned int)(regs->gprs[6] >> 32);
	269	p->thread.acrs[1] = (unsigned int) regs->gprs[6];
	270	}
	271	}
347a8dc3	272	#endif /* CONFIG_64BIT */
1da177e4 LT	273	/* start new process with ar4 pointing to the correct address space */
	274	p->thread.mm_segment = get_fs();
	275	/* Don't copy debug registers */
	276	memset(&p->thread.per_info,0,sizeof(p->thread.per_info));
	277
	278	return 0;
	279	}
	280
	281	asmlinkage long sys_fork(struct pt_regs regs)
	282	{
	283	return do_fork(SIGCHLD, regs.gprs[15], &regs, 0, NULL, NULL);
	284	}
	285
	286	asmlinkage long sys_clone(struct pt_regs regs)
	287	{
	288	unsigned long clone_flags;
	289	unsigned long newsp;
	290	int __user parent_tidptr, child_tidptr;
	291
	292	clone_flags = regs.gprs[3];
	293	newsp = regs.orig_gpr2;
	294	parent_tidptr = (int __user *) regs.gprs[4];
	295	child_tidptr = (int __user *) regs.gprs[5];
	296	if (!newsp)
	297	newsp = regs.gprs[15];
	298	return do_fork(clone_flags, newsp, &regs, 0,
	299	parent_tidptr, child_tidptr);
	300	}
	301
	302	/*
	303	* This is trivial, and on the face of it looks like it
	304	* could equally well be done in user mode.
	305	*
	306	* Not so, for quite unobvious reasons - register pressure.
	307	* In user mode vfork() cannot have a stack frame, and if
	308	* done by calling the "clone()" system call directly, you
	309	* do not have enough call-clobbered registers to hold all
	310	* the information you need.
	311	*/
	312	asmlinkage long sys_vfork(struct pt_regs regs)
	313	{
	314	return do_fork(CLONE_VFORK \| CLONE_VM \| SIGCHLD,
	315	regs.gprs[15], &regs, 0, NULL, NULL);
	316	}
	317
	318	/*
	319	* sys_execve() executes a new program.
	320	*/
	321	asmlinkage long sys_execve(struct pt_regs regs)
	322	{
	323	int error;
	324	char * filename;
	325
	326	filename = getname((char __user *) regs.orig_gpr2);
	327	error = PTR_ERR(filename);
	328	if (IS_ERR(filename))
	329	goto out;
	330	error = do_execve(filename, (char __user * __user *) regs.gprs[3],
	331	(char __user * __user *) regs.gprs[4], &regs);
	332	if (error == 0) {
	333	task_lock(current);
	334	current->ptrace &= ~PT_DTRACE;
	335	task_unlock(current);
	336	current->thread.fp_regs.fpc = 0;
337	if (MACHINE_HAS_IEEE)
338	asm volatile("sfpc %0,%0" : : "d" (0));
339	}
340	putname(filename);
341	out:
342	return error;
343	}
344
345
346	/*
347	* fill in the FPU structure for a core dump.
348	*/
349	int dump_fpu (struct pt_regs * regs, s390_fp_regs *fpregs)
350	{
347a8dc3	351	#ifndef CONFIG_64BIT
1da177e4 LT	352	/*
	353	* save fprs to current->thread.fp_regs to merge them with
	354	* the emulated registers and then copy the result to the dump.
	355	*/
	356	save_fp_regs(&current->thread.fp_regs);
	357	memcpy(fpregs, &current->thread.fp_regs, sizeof(s390_fp_regs));
347a8dc3	358	#else /* CONFIG_64BIT */
1da177e4	359	save_fp_regs(fpregs);
347a8dc3	360	#endif /* CONFIG_64BIT */
1da177e4 LT	361	return 1;
	362	}
	363
1da177e4 LT	364	unsigned long get_wchan(struct task_struct *p)
	365	{
	366	struct stack_frame sf, low, *high;
	367	unsigned long return_address;
	368	int count;
	369
30af7120	370	if (!p \|\| p == current \|\| p->state == TASK_RUNNING \|\| !task_stack_page(p))
1da177e4	371	return 0;
30af7120 AV	372	low = task_stack_page(p);
30af7120 AV	373	high = (struct stack_frame *) task_pt_regs(p);
1da177e4 LT	374	sf = (struct stack_frame *) (p->thread.ksp & PSW_ADDR_INSN);
	375	if (sf <= low \|\| sf > high)
	376	return 0;
	377	for (count = 0; count < 16; count++) {
	378	sf = (struct stack_frame *) (sf->back_chain & PSW_ADDR_INSN);
	379	if (sf <= low \|\| sf > high)
	380	return 0;
	381	return_address = sf->gprs[8] & PSW_ADDR_INSN;
	382	if (!in_sched_functions(return_address))
	383	return return_address;
	384	}
	385	return 0;
	386	}
	387