[mirror_ubuntu-artful-kernel.git] / arch / arm64 / kernel / process.c

/*
 * Based on arch/arm/kernel/process.c
 *
 * Original Copyright (C) 1995  Linus Torvalds
 * Copyright (C) 1996-2000 Russell King - Converted to ARM.
 * Copyright (C) 2012 ARM Ltd.
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 2 as
 * published by the Free Software Foundation.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */

#include <stdarg.h>

#include <linux/compat.h>
#include <linux/efi.h>
#include <linux/export.h>
#include <linux/sched.h>
#include <linux/kernel.h>
#include <linux/mm.h>
#include <linux/stddef.h>
#include <linux/unistd.h>
#include <linux/user.h>
#include <linux/delay.h>
#include <linux/reboot.h>
#include <linux/interrupt.h>
#include <linux/kallsyms.h>
#include <linux/init.h>
#include <linux/cpu.h>
#include <linux/elfcore.h>
#include <linux/pm.h>
#include <linux/tick.h>
#include <linux/utsname.h>
#include <linux/uaccess.h>
#include <linux/random.h>
#include <linux/hw_breakpoint.h>
#include <linux/personality.h>
#include <linux/notifier.h>
#include <trace/events/power.h>

#include <asm/alternative.h>
#include <asm/compat.h>
#include <asm/cacheflush.h>
#include <asm/fpsimd.h>
#include <asm/mmu_context.h>
#include <asm/processor.h>
#include <asm/stacktrace.h>

#ifdef CONFIG_CC_STACKPROTECTOR
#include <linux/stackprotector.h>
unsigned long __stack_chk_guard __read_mostly;
EXPORT_SYMBOL(__stack_chk_guard);
#endif

/*
 * Function pointers to optional machine specific functions
 */
void (*pm_power_off)(void);
EXPORT_SYMBOL_GPL(pm_power_off);

void (*arm_pm_restart)(enum reboot_mode reboot_mode, const char *cmd);

/*
 * This is our default idle handler.
 */
void arch_cpu_idle(void)
{
	/*
	 * This should do all the clock switching and wait for interrupt
	 * tricks
	 */
	trace_cpu_idle_rcuidle(1, smp_processor_id());
	cpu_do_idle();
	local_irq_enable();
	trace_cpu_idle_rcuidle(PWR_EVENT_EXIT, smp_processor_id());
}

#ifdef CONFIG_HOTPLUG_CPU
void arch_cpu_idle_dead(void)
{
       cpu_die();
}
#endif

/*
 * Called by kexec, immediately prior to machine_kexec().
 *
 * This must completely disable all secondary CPUs; simply causing those CPUs
 * to execute e.g. a RAM-based pin loop is not sufficient. This allows the
 * kexec'd kernel to use any and all RAM as it sees fit, without having to
 * avoid any code or data used by any SW CPU pin loop. The CPU hotplug
 * functionality embodied in disable_nonboot_cpus() to achieve this.
 */
void machine_shutdown(void)
{
	disable_nonboot_cpus();
}

/*
 * Halting simply requires that the secondary CPUs stop performing any
 * activity (executing tasks, handling interrupts). smp_send_stop()
 * achieves this.
 */
void machine_halt(void)
{
	local_irq_disable();
	smp_send_stop();
	while (1);
}

/*
 * Power-off simply requires that the secondary CPUs stop performing any
 * activity (executing tasks, handling interrupts). smp_send_stop()
 * achieves this. When the system power is turned off, it will take all CPUs
 * with it.
 */
void machine_power_off(void)
{
	local_irq_disable();
	smp_send_stop();
	if (pm_power_off)
		pm_power_off();
}

/*
 * Restart requires that the secondary CPUs stop performing any activity
 * while the primary CPU resets the system. Systems with multiple CPUs must
 * provide a HW restart implementation, to ensure that all CPUs reset at once.
 * This is required so that any code running after reset on the primary CPU
 * doesn't have to co-ordinate with other CPUs to ensure they aren't still
 * executing pre-reset code, and using RAM that the primary CPU's code wishes
 * to use. Implementing such co-ordination would be essentially impossible.
 */
void machine_restart(char *cmd)
{
	/* Disable interrupts first */
	local_irq_disable();
	smp_send_stop();

	/*
	 * UpdateCapsule() depends on the system being reset via
	 * ResetSystem().
	 */
	if (efi_enabled(EFI_RUNTIME_SERVICES))
		efi_reboot(reboot_mode, NULL);

	/* Now call the architecture specific reboot code. */
	if (arm_pm_restart)
		arm_pm_restart(reboot_mode, cmd);
	else
		do_kernel_restart(cmd);

	/*
	 * Whoops - the architecture was unable to reboot.
	 */
	printk("Reboot failed -- System halted\n");
	while (1);
}

void __show_regs(struct pt_regs *regs)
{
	int i, top_reg;
	u64 lr, sp;

	if (compat_user_mode(regs)) {
		lr = regs->compat_lr;
		sp = regs->compat_sp;
		top_reg = 12;
	} else {
		lr = regs->regs[30];
		sp = regs->sp;
		top_reg = 29;
	}

	show_regs_print_info(KERN_DEFAULT);
	print_symbol("PC is at %s\n", instruction_pointer(regs));
	print_symbol("LR is at %s\n", lr);
	printk("pc : [<%016llx>] lr : [<%016llx>] pstate: %08llx\n",
	       regs->pc, lr, regs->pstate);
	printk("sp : %016llx\n", sp);
	for (i = top_reg; i >= 0; i--) {
		printk("x%-2d: %016llx ", i, regs->regs[i]);
		if (i % 2 == 0)
			printk("\n");
	}
	printk("\n");
}

void show_regs(struct pt_regs * regs)
{
	printk("\n");
	__show_regs(regs);
}

static void tls_thread_flush(void)
{
	asm ("msr tpidr_el0, xzr");

	if (is_compat_task()) {
		current->thread.tp_value = 0;

		/*
		 * We need to ensure ordering between the shadow state and the
		 * hardware state, so that we don't corrupt the hardware state
		 * with a stale shadow state during context switch.
		 */
		barrier();
		asm ("msr tpidrro_el0, xzr");
	}
}

void flush_thread(void)
{
	fpsimd_flush_thread();
	tls_thread_flush();
	flush_ptrace_hw_breakpoint(current);
}

void release_thread(struct task_struct *dead_task)
{
}

int arch_dup_task_struct(struct task_struct *dst, struct task_struct *src)
{
	if (current->mm)
		fpsimd_preserve_current_state();
	*dst = *src;
	return 0;
}

asmlinkage void ret_from_fork(void) asm("ret_from_fork");

int copy_thread(unsigned long clone_flags, unsigned long stack_start,
		unsigned long stk_sz, struct task_struct *p)
{
	struct pt_regs *childregs = task_pt_regs(p);

	memset(&p->thread.cpu_context, 0, sizeof(struct cpu_context));

	if (likely(!(p->flags & PF_KTHREAD))) {
		*childregs = *current_pt_regs();
		childregs->regs[0] = 0;

		/*
		 * Read the current TLS pointer from tpidr_el0 as it may be
		 * out-of-sync with the saved value.
		 */
		asm("mrs %0, tpidr_el0" : "=r" (*task_user_tls(p)));

		if (stack_start) {
			if (is_compat_thread(task_thread_info(p)))
				childregs->compat_sp = stack_start;
			else
				childregs->sp = stack_start;
		}

		/*
		 * If a TLS pointer was passed to clone (4th argument), use it
		 * for the new thread.
		 */
		if (clone_flags & CLONE_SETTLS)
			p->thread.tp_value = childregs->regs[3];
	} else {
		memset(childregs, 0, sizeof(struct pt_regs));
		childregs->pstate = PSR_MODE_EL1h;
		if (IS_ENABLED(CONFIG_ARM64_UAO) &&
		    cpus_have_cap(ARM64_HAS_UAO))
			childregs->pstate |= PSR_UAO_BIT;
		p->thread.cpu_context.x19 = stack_start;
		p->thread.cpu_context.x20 = stk_sz;
	}
	p->thread.cpu_context.pc = (unsigned long)ret_from_fork;
	p->thread.cpu_context.sp = (unsigned long)childregs;

	ptrace_hw_copy_thread(p);

	return 0;
}

static void tls_thread_switch(struct task_struct *next)
{
	unsigned long tpidr, tpidrro;

	asm("mrs %0, tpidr_el0" : "=r" (tpidr));
	*task_user_tls(current) = tpidr;

	tpidr = *task_user_tls(next);
	tpidrro = is_compat_thread(task_thread_info(next)) ?
		  next->thread.tp_value : 0;

	asm(
	"	msr	tpidr_el0, %0\n"
	"	msr	tpidrro_el0, %1"
	: : "r" (tpidr), "r" (tpidrro));
}

/* Restore the UAO state depending on next's addr_limit */
static void uao_thread_switch(struct task_struct *next)
{
	if (IS_ENABLED(CONFIG_ARM64_UAO)) {
		if (task_thread_info(next)->addr_limit == KERNEL_DS)
			asm(ALTERNATIVE("nop", SET_PSTATE_UAO(1), ARM64_HAS_UAO));
		else
			asm(ALTERNATIVE("nop", SET_PSTATE_UAO(0), ARM64_HAS_UAO));
	}
}

/*
 * Thread switching.
 */
struct task_struct *__switch_to(struct task_struct *prev,
				struct task_struct *next)
{
	struct task_struct *last;

	fpsimd_thread_switch(next);
	tls_thread_switch(next);
	hw_breakpoint_thread_switch(next);
	contextidr_thread_switch(next);
	uao_thread_switch(next);

	/*
	 * Complete any pending TLB or cache maintenance on this CPU in case
	 * the thread migrates to a different CPU.
	 */
	dsb(ish);

	/* the actual thread switch */
	last = cpu_switch_to(prev, next);

	return last;
}

unsigned long get_wchan(struct task_struct *p)
{
	struct stackframe frame;
	unsigned long stack_page;
	int count = 0;
	if (!p || p == current || p->state == TASK_RUNNING)
		return 0;

	frame.fp = thread_saved_fp(p);
	frame.sp = thread_saved_sp(p);
	frame.pc = thread_saved_pc(p);
#ifdef CONFIG_FUNCTION_GRAPH_TRACER
	frame.graph = p->curr_ret_stack;
#endif
	stack_page = (unsigned long)task_stack_page(p);
	do {
		if (frame.sp < stack_page ||
		    frame.sp >= stack_page + THREAD_SIZE ||
		    unwind_frame(p, &frame))
			return 0;
		if (!in_sched_functions(frame.pc))
			return frame.pc;
	} while (count ++ < 16);
	return 0;
}

unsigned long arch_align_stack(unsigned long sp)
{
	if (!(current->personality & ADDR_NO_RANDOMIZE) && randomize_va_space)
		sp -= get_random_int() & ~PAGE_MASK;
	return sp & ~0xf;
}

unsigned long arch_randomize_brk(struct mm_struct *mm)
{
	unsigned long range_end = mm->brk;

	if (is_compat_task())
		range_end += 0x02000000;
	else
		range_end += 0x40000000;

	return randomize_range(mm->brk, range_end, 0) ? : mm->brk;
}
Commit	Line	Data
	1	/*
	2	* Based on arch/arm/kernel/process.c
	3	*
	4	* Original Copyright (C) 1995 Linus Torvalds
	5	* Copyright (C) 1996-2000 Russell King - Converted to ARM.
	6	* Copyright (C) 2012 ARM Ltd.
	7	*
	8	* This program is free software; you can redistribute it and/or modify
	9	* it under the terms of the GNU General Public License version 2 as
	10	* published by the Free Software Foundation.
	11	*
	12	* This program is distributed in the hope that it will be useful,
	13	* but WITHOUT ANY WARRANTY; without even the implied warranty of
	14	* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
	15	* GNU General Public License for more details.
	16	*
	17	* You should have received a copy of the GNU General Public License
	18	* along with this program. If not, see <http://www.gnu.org/licenses/>.
	19	*/
	20
	21	#include <stdarg.h>
	22
	23	#include <linux/compat.h>
	24	#include <linux/efi.h>
	25	#include <linux/export.h>
	26	#include <linux/sched.h>
	27	#include <linux/kernel.h>
	28	#include <linux/mm.h>
	29	#include <linux/stddef.h>
	30	#include <linux/unistd.h>
	31	#include <linux/user.h>
	32	#include <linux/delay.h>
	33	#include <linux/reboot.h>
	34	#include <linux/interrupt.h>
	35	#include <linux/kallsyms.h>
	36	#include <linux/init.h>
	37	#include <linux/cpu.h>
	38	#include <linux/elfcore.h>
	39	#include <linux/pm.h>
	40	#include <linux/tick.h>
	41	#include <linux/utsname.h>
	42	#include <linux/uaccess.h>
	43	#include <linux/random.h>
	44	#include <linux/hw_breakpoint.h>
	45	#include <linux/personality.h>
	46	#include <linux/notifier.h>
	47	#include <trace/events/power.h>
	48
	49	#include <asm/alternative.h>
	50	#include <asm/compat.h>
	51	#include <asm/cacheflush.h>
	52	#include <asm/fpsimd.h>
	53	#include <asm/mmu_context.h>
	54	#include <asm/processor.h>
	55	#include <asm/stacktrace.h>
	56
	57	#ifdef CONFIG_CC_STACKPROTECTOR
	58	#include <linux/stackprotector.h>
	59	unsigned long __stack_chk_guard __read_mostly;
	60	EXPORT_SYMBOL(__stack_chk_guard);
	61	#endif
	62
	63	/*
	64	* Function pointers to optional machine specific functions
	65	*/
	66	void (*pm_power_off)(void);
	67	EXPORT_SYMBOL_GPL(pm_power_off);
	68
	69	void (arm_pm_restart)(enum reboot_mode reboot_mode, const char cmd);
	70
	71	/*
	72	* This is our default idle handler.
	73	*/
	74	void arch_cpu_idle(void)
	75	{
	76	/*
	77	* This should do all the clock switching and wait for interrupt
	78	* tricks
	79	*/
	80	trace_cpu_idle_rcuidle(1, smp_processor_id());
	81	cpu_do_idle();
	82	local_irq_enable();
	83	trace_cpu_idle_rcuidle(PWR_EVENT_EXIT, smp_processor_id());
	84	}
	85
	86	#ifdef CONFIG_HOTPLUG_CPU
	87	void arch_cpu_idle_dead(void)
	88	{
	89	cpu_die();
	90	}
	91	#endif
	92
	93	/*
	94	* Called by kexec, immediately prior to machine_kexec().
	95	*
	96	* This must completely disable all secondary CPUs; simply causing those CPUs
	97	* to execute e.g. a RAM-based pin loop is not sufficient. This allows the
	98	* kexec'd kernel to use any and all RAM as it sees fit, without having to
	99	* avoid any code or data used by any SW CPU pin loop. The CPU hotplug
	100	* functionality embodied in disable_nonboot_cpus() to achieve this.
	101	*/
	102	void machine_shutdown(void)
	103	{
	104	disable_nonboot_cpus();
	105	}
	106
	107	/*
	108	* Halting simply requires that the secondary CPUs stop performing any
	109	* activity (executing tasks, handling interrupts). smp_send_stop()
	110	* achieves this.
	111	*/
	112	void machine_halt(void)
	113	{
	114	local_irq_disable();
	115	smp_send_stop();
	116	while (1);
	117	}
	118
	119	/*
	120	* Power-off simply requires that the secondary CPUs stop performing any
	121	* activity (executing tasks, handling interrupts). smp_send_stop()
	122	* achieves this. When the system power is turned off, it will take all CPUs
	123	* with it.
	124	*/
	125	void machine_power_off(void)
	126	{
	127	local_irq_disable();
	128	smp_send_stop();
	129	if (pm_power_off)
	130	pm_power_off();
	131	}
	132
	133	/*
	134	* Restart requires that the secondary CPUs stop performing any activity
	135	* while the primary CPU resets the system. Systems with multiple CPUs must
	136	* provide a HW restart implementation, to ensure that all CPUs reset at once.
	137	* This is required so that any code running after reset on the primary CPU
	138	* doesn't have to co-ordinate with other CPUs to ensure they aren't still
	139	* executing pre-reset code, and using RAM that the primary CPU's code wishes
	140	* to use. Implementing such co-ordination would be essentially impossible.
	141	*/
	142	void machine_restart(char *cmd)
	143	{
	144	/* Disable interrupts first */
	145	local_irq_disable();
	146	smp_send_stop();
	147
	148	/*
	149	* UpdateCapsule() depends on the system being reset via
	150	* ResetSystem().
	151	*/
	152	if (efi_enabled(EFI_RUNTIME_SERVICES))
	153	efi_reboot(reboot_mode, NULL);
	154
	155	/* Now call the architecture specific reboot code. */
	156	if (arm_pm_restart)
	157	arm_pm_restart(reboot_mode, cmd);
	158	else
	159	do_kernel_restart(cmd);
	160
	161	/*
	162	* Whoops - the architecture was unable to reboot.
	163	*/
	164	printk("Reboot failed -- System halted\n");
	165	while (1);
	166	}
	167
	168	void __show_regs(struct pt_regs *regs)
	169	{
	170	int i, top_reg;
	171	u64 lr, sp;
	172
	173	if (compat_user_mode(regs)) {
	174	lr = regs->compat_lr;
	175	sp = regs->compat_sp;
	176	top_reg = 12;
	177	} else {
	178	lr = regs->regs[30];
	179	sp = regs->sp;
	180	top_reg = 29;
	181	}
	182
	183	show_regs_print_info(KERN_DEFAULT);
	184	print_symbol("PC is at %s\n", instruction_pointer(regs));
	185	print_symbol("LR is at %s\n", lr);
	186	printk("pc : [<%016llx>] lr : [<%016llx>] pstate: %08llx\n",
	187	regs->pc, lr, regs->pstate);
	188	printk("sp : %016llx\n", sp);
	189	for (i = top_reg; i >= 0; i--) {
	190	printk("x%-2d: %016llx ", i, regs->regs[i]);
	191	if (i % 2 == 0)
	192	printk("\n");
	193	}
	194	printk("\n");
	195	}
	196
	197	void show_regs(struct pt_regs * regs)
	198	{
	199	printk("\n");
	200	__show_regs(regs);
	201	}
	202
	203	static void tls_thread_flush(void)
	204	{
	205	asm ("msr tpidr_el0, xzr");
	206
	207	if (is_compat_task()) {
	208	current->thread.tp_value = 0;
	209
	210	/*
	211	* We need to ensure ordering between the shadow state and the
	212	* hardware state, so that we don't corrupt the hardware state
	213	* with a stale shadow state during context switch.
	214	*/
	215	barrier();
	216	asm ("msr tpidrro_el0, xzr");
	217	}
	218	}
	219
	220	void flush_thread(void)
	221	{
	222	fpsimd_flush_thread();
	223	tls_thread_flush();
	224	flush_ptrace_hw_breakpoint(current);
	225	}
	226
	227	void release_thread(struct task_struct *dead_task)
	228	{
	229	}
	230
	231	int arch_dup_task_struct(struct task_struct dst, struct task_struct src)
	232	{
	233	if (current->mm)
	234	fpsimd_preserve_current_state();
	235	dst = src;
	236	return 0;
	237	}
	238
	239	asmlinkage void ret_from_fork(void) asm("ret_from_fork");
	240
	241	int copy_thread(unsigned long clone_flags, unsigned long stack_start,
	242	unsigned long stk_sz, struct task_struct *p)
	243	{
	244	struct pt_regs *childregs = task_pt_regs(p);
	245
	246	memset(&p->thread.cpu_context, 0, sizeof(struct cpu_context));
	247
	248	if (likely(!(p->flags & PF_KTHREAD))) {
	249	childregs = current_pt_regs();
	250	childregs->regs[0] = 0;
	251
	252	/*
	253	* Read the current TLS pointer from tpidr_el0 as it may be
	254	* out-of-sync with the saved value.
	255	*/
	256	asm("mrs %0, tpidr_el0" : "=r" (*task_user_tls(p)));
	257
	258	if (stack_start) {
	259	if (is_compat_thread(task_thread_info(p)))
	260	childregs->compat_sp = stack_start;
	261	else
	262	childregs->sp = stack_start;
	263	}
	264
	265	/*
	266	* If a TLS pointer was passed to clone (4th argument), use it
	267	* for the new thread.
	268	*/
	269	if (clone_flags & CLONE_SETTLS)
	270	p->thread.tp_value = childregs->regs[3];
	271	} else {
	272	memset(childregs, 0, sizeof(struct pt_regs));
	273	childregs->pstate = PSR_MODE_EL1h;
	274	if (IS_ENABLED(CONFIG_ARM64_UAO) &&
	275	cpus_have_cap(ARM64_HAS_UAO))
	276	childregs->pstate \|= PSR_UAO_BIT;
	277	p->thread.cpu_context.x19 = stack_start;
	278	p->thread.cpu_context.x20 = stk_sz;
	279	}
	280	p->thread.cpu_context.pc = (unsigned long)ret_from_fork;
	281	p->thread.cpu_context.sp = (unsigned long)childregs;
	282
	283	ptrace_hw_copy_thread(p);
	284
	285	return 0;
	286	}
	287
	288	static void tls_thread_switch(struct task_struct *next)
	289	{
	290	unsigned long tpidr, tpidrro;
	291
	292	asm("mrs %0, tpidr_el0" : "=r" (tpidr));
	293	*task_user_tls(current) = tpidr;
	294
	295	tpidr = *task_user_tls(next);
	296	tpidrro = is_compat_thread(task_thread_info(next)) ?
	297	next->thread.tp_value : 0;
	298
	299	asm(
	300	" msr tpidr_el0, %0\n"
	301	" msr tpidrro_el0, %1"
	302	: : "r" (tpidr), "r" (tpidrro));
	303	}
	304
	305	/* Restore the UAO state depending on next's addr_limit */
	306	static void uao_thread_switch(struct task_struct *next)
	307	{
	308	if (IS_ENABLED(CONFIG_ARM64_UAO)) {
	309	if (task_thread_info(next)->addr_limit == KERNEL_DS)
	310	asm(ALTERNATIVE("nop", SET_PSTATE_UAO(1), ARM64_HAS_UAO));
	311	else
	312	asm(ALTERNATIVE("nop", SET_PSTATE_UAO(0), ARM64_HAS_UAO));
	313	}
	314	}
	315
	316	/*
	317	* Thread switching.
	318	*/
	319	struct task_struct __switch_to(struct task_struct prev,
	320	struct task_struct *next)
	321	{
	322	struct task_struct *last;
	323
	324	fpsimd_thread_switch(next);
	325	tls_thread_switch(next);
	326	hw_breakpoint_thread_switch(next);
	327	contextidr_thread_switch(next);
	328	uao_thread_switch(next);
	329
	330	/*
	331	* Complete any pending TLB or cache maintenance on this CPU in case
	332	* the thread migrates to a different CPU.
	333	*/
	334	dsb(ish);
	335
	336	/* the actual thread switch */
	337	last = cpu_switch_to(prev, next);
	338
	339	return last;
	340	}
	341
	342	unsigned long get_wchan(struct task_struct *p)
	343	{
	344	struct stackframe frame;
	345	unsigned long stack_page;
	346	int count = 0;
	347	if (!p \|\| p == current \|\| p->state == TASK_RUNNING)
	348	return 0;
	349
	350	frame.fp = thread_saved_fp(p);
	351	frame.sp = thread_saved_sp(p);
	352	frame.pc = thread_saved_pc(p);
	353	#ifdef CONFIG_FUNCTION_GRAPH_TRACER
	354	frame.graph = p->curr_ret_stack;
	355	#endif
	356	stack_page = (unsigned long)task_stack_page(p);
	357	do {
	358	if (frame.sp < stack_page \|\|
	359	frame.sp >= stack_page + THREAD_SIZE \|\|
	360	unwind_frame(p, &frame))
	361	return 0;
	362	if (!in_sched_functions(frame.pc))
	363	return frame.pc;
	364	} while (count ++ < 16);
	365	return 0;
	366	}
	367
	368	unsigned long arch_align_stack(unsigned long sp)
	369	{
	370	if (!(current->personality & ADDR_NO_RANDOMIZE) && randomize_va_space)
	371	sp -= get_random_int() & ~PAGE_MASK;
	372	return sp & ~0xf;
	373	}
	374
	375	unsigned long arch_randomize_brk(struct mm_struct *mm)
	376	{
	377	unsigned long range_end = mm->brk;
	378
	379	if (is_compat_task())
	380	range_end += 0x02000000;
	381	else
	382	range_end += 0x40000000;
	383
	384	return randomize_range(mm->brk, range_end, 0) ? : mm->brk;
	385	}