xref: /linux/arch/sparc/kernel/process_64.c (revision 2da68a77) 
1 // SPDX-License-Identifier: GPL-2.0
2 /*  arch/sparc64/kernel/process.c
3  *
4  *  Copyright (C) 1995, 1996, 2008 David S. Miller (davem@davemloft.net)
5  *  Copyright (C) 1996       Eddie C. Dost   (ecd@skynet.be)
6  *  Copyright (C) 1997, 1998 Jakub Jelinek   (jj@sunsite.mff.cuni.cz)
7  */
8 
9 /*
10  * This file handles the architecture-dependent parts of process handling..
11  */
12 #include <linux/errno.h>
13 #include <linux/export.h>
14 #include <linux/sched.h>
15 #include <linux/sched/debug.h>
16 #include <linux/sched/task.h>
17 #include <linux/sched/task_stack.h>
18 #include <linux/kernel.h>
19 #include <linux/mm.h>
20 #include <linux/fs.h>
21 #include <linux/smp.h>
22 #include <linux/stddef.h>
23 #include <linux/ptrace.h>
24 #include <linux/slab.h>
25 #include <linux/user.h>
26 #include <linux/delay.h>
27 #include <linux/compat.h>
28 #include <linux/tick.h>
29 #include <linux/init.h>
30 #include <linux/cpu.h>
31 #include <linux/perf_event.h>
32 #include <linux/elfcore.h>
33 #include <linux/sysrq.h>
34 #include <linux/nmi.h>
35 #include <linux/context_tracking.h>
36 #include <linux/signal.h>
37 
38 #include <linux/uaccess.h>
39 #include <asm/page.h>
40 #include <asm/pgalloc.h>
41 #include <asm/processor.h>
42 #include <asm/pstate.h>
43 #include <asm/elf.h>
44 #include <asm/fpumacro.h>
45 #include <asm/head.h>
46 #include <asm/cpudata.h>
47 #include <asm/mmu_context.h>
48 #include <asm/unistd.h>
49 #include <asm/hypervisor.h>
50 #include <asm/syscalls.h>
51 #include <asm/irq_regs.h>
52 #include <asm/smp.h>
53 #include <asm/pcr.h>
54 
55 #include "kstack.h"
56 
57 /* Idle loop support on sparc64. */
58 void arch_cpu_idle(void)
59 {
60 	if (tlb_type != hypervisor) {
61 		touch_nmi_watchdog();
62 		raw_local_irq_enable();
63 	} else {
64 		unsigned long pstate;
65 
66 		raw_local_irq_enable();
67 
68                 /* The sun4v sleeping code requires that we have PSTATE.IE cleared over
69                  * the cpu sleep hypervisor call.
70                  */
71 		__asm__ __volatile__(
72 			"rdpr %%pstate, %0\n\t"
73 			"andn %0, %1, %0\n\t"
74 			"wrpr %0, %%g0, %%pstate"
75 			: "=&r" (pstate)
76 			: "i" (PSTATE_IE));
77 
78 		if (!need_resched() && !cpu_is_offline(smp_processor_id())) {
79 			sun4v_cpu_yield();
80 			/* If resumed by cpu_poke then we need to explicitly
81 			 * call scheduler_ipi().
82 			 */
83 			scheduler_poke();
84 		}
85 
86 		/* Re-enable interrupts. */
87 		__asm__ __volatile__(
88 			"rdpr %%pstate, %0\n\t"
89 			"or %0, %1, %0\n\t"
90 			"wrpr %0, %%g0, %%pstate"
91 			: "=&r" (pstate)
92 			: "i" (PSTATE_IE));
93 	}
94 }
95 
96 #ifdef CONFIG_HOTPLUG_CPU
97 void arch_cpu_idle_dead(void)
98 {
99 	sched_preempt_enable_no_resched();
100 	cpu_play_dead();
101 }
102 #endif
103 
104 #ifdef CONFIG_COMPAT
105 static void show_regwindow32(struct pt_regs *regs)
106 {
107 	struct reg_window32 __user *rw;
108 	struct reg_window32 r_w;
109 
110 	__asm__ __volatile__ ("flushw");
111 	rw = compat_ptr((unsigned int)regs->u_regs[14]);
112 	if (copy_from_user (&r_w, rw, sizeof(r_w))) {
113 		return;
114 	}
115 
116 	printk("l0: %08x l1: %08x l2: %08x l3: %08x "
117 	       "l4: %08x l5: %08x l6: %08x l7: %08x\n",
118 	       r_w.locals[0], r_w.locals[1], r_w.locals[2], r_w.locals[3],
119 	       r_w.locals[4], r_w.locals[5], r_w.locals[6], r_w.locals[7]);
120 	printk("i0: %08x i1: %08x i2: %08x i3: %08x "
121 	       "i4: %08x i5: %08x i6: %08x i7: %08x\n",
122 	       r_w.ins[0], r_w.ins[1], r_w.ins[2], r_w.ins[3],
123 	       r_w.ins[4], r_w.ins[5], r_w.ins[6], r_w.ins[7]);
124 }
125 #else
126 #define show_regwindow32(regs)	do { } while (0)
127 #endif
128 
129 static void show_regwindow(struct pt_regs *regs)
130 {
131 	struct reg_window __user *rw;
132 	struct reg_window *rwk;
133 	struct reg_window r_w;
134 
135 	if ((regs->tstate & TSTATE_PRIV) || !(test_thread_flag(TIF_32BIT))) {
136 		__asm__ __volatile__ ("flushw");
137 		rw = (struct reg_window __user *)
138 			(regs->u_regs[14] + STACK_BIAS);
139 		rwk = (struct reg_window *)
140 			(regs->u_regs[14] + STACK_BIAS);
141 		if (!(regs->tstate & TSTATE_PRIV)) {
142 			if (copy_from_user (&r_w, rw, sizeof(r_w))) {
143 				return;
144 			}
145 			rwk = &r_w;
146 		}
147 	} else {
148 		show_regwindow32(regs);
149 		return;
150 	}
151 	printk("l0: %016lx l1: %016lx l2: %016lx l3: %016lx\n",
152 	       rwk->locals[0], rwk->locals[1], rwk->locals[2], rwk->locals[3]);
153 	printk("l4: %016lx l5: %016lx l6: %016lx l7: %016lx\n",
154 	       rwk->locals[4], rwk->locals[5], rwk->locals[6], rwk->locals[7]);
155 	printk("i0: %016lx i1: %016lx i2: %016lx i3: %016lx\n",
156 	       rwk->ins[0], rwk->ins[1], rwk->ins[2], rwk->ins[3]);
157 	printk("i4: %016lx i5: %016lx i6: %016lx i7: %016lx\n",
158 	       rwk->ins[4], rwk->ins[5], rwk->ins[6], rwk->ins[7]);
159 	if (regs->tstate & TSTATE_PRIV)
160 		printk("I7: <%pS>\n", (void *) rwk->ins[7]);
161 }
162 
163 void show_regs(struct pt_regs *regs)
164 {
165 	show_regs_print_info(KERN_DEFAULT);
166 
167 	printk("TSTATE: %016lx TPC: %016lx TNPC: %016lx Y: %08x    %s\n", regs->tstate,
168 	       regs->tpc, regs->tnpc, regs->y, print_tainted());
169 	printk("TPC: <%pS>\n", (void *) regs->tpc);
170 	printk("g0: %016lx g1: %016lx g2: %016lx g3: %016lx\n",
171 	       regs->u_regs[0], regs->u_regs[1], regs->u_regs[2],
172 	       regs->u_regs[3]);
173 	printk("g4: %016lx g5: %016lx g6: %016lx g7: %016lx\n",
174 	       regs->u_regs[4], regs->u_regs[5], regs->u_regs[6],
175 	       regs->u_regs[7]);
176 	printk("o0: %016lx o1: %016lx o2: %016lx o3: %016lx\n",
177 	       regs->u_regs[8], regs->u_regs[9], regs->u_regs[10],
178 	       regs->u_regs[11]);
179 	printk("o4: %016lx o5: %016lx sp: %016lx ret_pc: %016lx\n",
180 	       regs->u_regs[12], regs->u_regs[13], regs->u_regs[14],
181 	       regs->u_regs[15]);
182 	printk("RPC: <%pS>\n", (void *) regs->u_regs[15]);
183 	show_regwindow(regs);
184 	show_stack(current, (unsigned long *)regs->u_regs[UREG_FP], KERN_DEFAULT);
185 }
186 
187 union global_cpu_snapshot global_cpu_snapshot[NR_CPUS];
188 static DEFINE_SPINLOCK(global_cpu_snapshot_lock);
189 
190 static void __global_reg_self(struct thread_info *tp, struct pt_regs *regs,
191 			      int this_cpu)
192 {
193 	struct global_reg_snapshot *rp;
194 
195 	flushw_all();
196 
197 	rp = &global_cpu_snapshot[this_cpu].reg;
198 
199 	rp->tstate = regs->tstate;
200 	rp->tpc = regs->tpc;
201 	rp->tnpc = regs->tnpc;
202 	rp->o7 = regs->u_regs[UREG_I7];
203 
204 	if (regs->tstate & TSTATE_PRIV) {
205 		struct reg_window *rw;
206 
207 		rw = (struct reg_window *)
208 			(regs->u_regs[UREG_FP] + STACK_BIAS);
209 		if (kstack_valid(tp, (unsigned long) rw)) {
210 			rp->i7 = rw->ins[7];
211 			rw = (struct reg_window *)
212 				(rw->ins[6] + STACK_BIAS);
213 			if (kstack_valid(tp, (unsigned long) rw))
214 				rp->rpc = rw->ins[7];
215 		}
216 	} else {
217 		rp->i7 = 0;
218 		rp->rpc = 0;
219 	}
220 	rp->thread = tp;
221 }
222 
223 /* In order to avoid hangs we do not try to synchronize with the
224  * global register dump client cpus.  The last store they make is to
225  * the thread pointer, so do a short poll waiting for that to become
226  * non-NULL.
227  */
228 static void __global_reg_poll(struct global_reg_snapshot *gp)
229 {
230 	int limit = 0;
231 
232 	while (!gp->thread && ++limit < 100) {
233 		barrier();
234 		udelay(1);
235 	}
236 }
237 
238 void arch_trigger_cpumask_backtrace(const cpumask_t *mask, bool exclude_self)
239 {
240 	struct thread_info *tp = current_thread_info();
241 	struct pt_regs *regs = get_irq_regs();
242 	unsigned long flags;
243 	int this_cpu, cpu;
244 
245 	if (!regs)
246 		regs = tp->kregs;
247 
248 	spin_lock_irqsave(&global_cpu_snapshot_lock, flags);
249 
250 	this_cpu = raw_smp_processor_id();
251 
252 	memset(global_cpu_snapshot, 0, sizeof(global_cpu_snapshot));
253 
254 	if (cpumask_test_cpu(this_cpu, mask) && !exclude_self)
255 		__global_reg_self(tp, regs, this_cpu);
256 
257 	smp_fetch_global_regs();
258 
259 	for_each_cpu(cpu, mask) {
260 		struct global_reg_snapshot *gp;
261 
262 		if (exclude_self && cpu == this_cpu)
263 			continue;
264 
265 		gp = &global_cpu_snapshot[cpu].reg;
266 
267 		__global_reg_poll(gp);
268 
269 		tp = gp->thread;
270 		printk("%c CPU[%3d]: TSTATE[%016lx] TPC[%016lx] TNPC[%016lx] TASK[%s:%d]\n",
271 		       (cpu == this_cpu ? '*' : ' '), cpu,
272 		       gp->tstate, gp->tpc, gp->tnpc,
273 		       ((tp && tp->task) ? tp->task->comm : "NULL"),
274 		       ((tp && tp->task) ? tp->task->pid : -1));
275 
276 		if (gp->tstate & TSTATE_PRIV) {
277 			printk("             TPC[%pS] O7[%pS] I7[%pS] RPC[%pS]\n",
278 			       (void *) gp->tpc,
279 			       (void *) gp->o7,
280 			       (void *) gp->i7,
281 			       (void *) gp->rpc);
282 		} else {
283 			printk("             TPC[%lx] O7[%lx] I7[%lx] RPC[%lx]\n",
284 			       gp->tpc, gp->o7, gp->i7, gp->rpc);
285 		}
286 
287 		touch_nmi_watchdog();
288 	}
289 
290 	memset(global_cpu_snapshot, 0, sizeof(global_cpu_snapshot));
291 
292 	spin_unlock_irqrestore(&global_cpu_snapshot_lock, flags);
293 }
294 
295 #ifdef CONFIG_MAGIC_SYSRQ
296 
297 static void sysrq_handle_globreg(int key)
298 {
299 	trigger_all_cpu_backtrace();
300 }
301 
302 static const struct sysrq_key_op sparc_globalreg_op = {
303 	.handler	= sysrq_handle_globreg,
304 	.help_msg	= "global-regs(y)",
305 	.action_msg	= "Show Global CPU Regs",
306 };
307 
308 static void __global_pmu_self(int this_cpu)
309 {
310 	struct global_pmu_snapshot *pp;
311 	int i, num;
312 
313 	if (!pcr_ops)
314 		return;
315 
316 	pp = &global_cpu_snapshot[this_cpu].pmu;
317 
318 	num = 1;
319 	if (tlb_type == hypervisor &&
320 	    sun4v_chip_type >= SUN4V_CHIP_NIAGARA4)
321 		num = 4;
322 
323 	for (i = 0; i < num; i++) {
324 		pp->pcr[i] = pcr_ops->read_pcr(i);
325 		pp->pic[i] = pcr_ops->read_pic(i);
326 	}
327 }
328 
329 static void __global_pmu_poll(struct global_pmu_snapshot *pp)
330 {
331 	int limit = 0;
332 
333 	while (!pp->pcr[0] && ++limit < 100) {
334 		barrier();
335 		udelay(1);
336 	}
337 }
338 
339 static void pmu_snapshot_all_cpus(void)
340 {
341 	unsigned long flags;
342 	int this_cpu, cpu;
343 
344 	spin_lock_irqsave(&global_cpu_snapshot_lock, flags);
345 
346 	memset(global_cpu_snapshot, 0, sizeof(global_cpu_snapshot));
347 
348 	this_cpu = raw_smp_processor_id();
349 
350 	__global_pmu_self(this_cpu);
351 
352 	smp_fetch_global_pmu();
353 
354 	for_each_online_cpu(cpu) {
355 		struct global_pmu_snapshot *pp = &global_cpu_snapshot[cpu].pmu;
356 
357 		__global_pmu_poll(pp);
358 
359 		printk("%c CPU[%3d]: PCR[%08lx:%08lx:%08lx:%08lx] PIC[%08lx:%08lx:%08lx:%08lx]\n",
360 		       (cpu == this_cpu ? '*' : ' '), cpu,
361 		       pp->pcr[0], pp->pcr[1], pp->pcr[2], pp->pcr[3],
362 		       pp->pic[0], pp->pic[1], pp->pic[2], pp->pic[3]);
363 
364 		touch_nmi_watchdog();
365 	}
366 
367 	memset(global_cpu_snapshot, 0, sizeof(global_cpu_snapshot));
368 
369 	spin_unlock_irqrestore(&global_cpu_snapshot_lock, flags);
370 }
371 
372 static void sysrq_handle_globpmu(int key)
373 {
374 	pmu_snapshot_all_cpus();
375 }
376 
377 static const struct sysrq_key_op sparc_globalpmu_op = {
378 	.handler	= sysrq_handle_globpmu,
379 	.help_msg	= "global-pmu(x)",
380 	.action_msg	= "Show Global PMU Regs",
381 };
382 
383 static int __init sparc_sysrq_init(void)
384 {
385 	int ret = register_sysrq_key('y', &sparc_globalreg_op);
386 
387 	if (!ret)
388 		ret = register_sysrq_key('x', &sparc_globalpmu_op);
389 	return ret;
390 }
391 
392 core_initcall(sparc_sysrq_init);
393 
394 #endif
395 
396 /* Free current thread data structures etc.. */
397 void exit_thread(struct task_struct *tsk)
398 {
399 	struct thread_info *t = task_thread_info(tsk);
400 
401 	if (t->utraps) {
402 		if (t->utraps[0] < 2)
403 			kfree (t->utraps);
404 		else
405 			t->utraps[0]--;
406 	}
407 }
408 
409 void flush_thread(void)
410 {
411 	struct thread_info *t = current_thread_info();
412 	struct mm_struct *mm;
413 
414 	mm = t->task->mm;
415 	if (mm)
416 		tsb_context_switch(mm);
417 
418 	set_thread_wsaved(0);
419 
420 	/* Clear FPU register state. */
421 	t->fpsaved[0] = 0;
422 }
423 
424 /* It's a bit more tricky when 64-bit tasks are involved... */
425 static unsigned long clone_stackframe(unsigned long csp, unsigned long psp)
426 {
427 	bool stack_64bit = test_thread_64bit_stack(psp);
428 	unsigned long fp, distance, rval;
429 
430 	if (stack_64bit) {
431 		csp += STACK_BIAS;
432 		psp += STACK_BIAS;
433 		__get_user(fp, &(((struct reg_window __user *)psp)->ins[6]));
434 		fp += STACK_BIAS;
435 		if (test_thread_flag(TIF_32BIT))
436 			fp &= 0xffffffff;
437 	} else
438 		__get_user(fp, &(((struct reg_window32 __user *)psp)->ins[6]));
439 
440 	/* Now align the stack as this is mandatory in the Sparc ABI
441 	 * due to how register windows work.  This hides the
442 	 * restriction from thread libraries etc.
443 	 */
444 	csp &= ~15UL;
445 
446 	distance = fp - psp;
447 	rval = (csp - distance);
448 	if (raw_copy_in_user((void __user *)rval, (void __user *)psp, distance))
449 		rval = 0;
450 	else if (!stack_64bit) {
451 		if (put_user(((u32)csp),
452 			     &(((struct reg_window32 __user *)rval)->ins[6])))
453 			rval = 0;
454 	} else {
455 		if (put_user(((u64)csp - STACK_BIAS),
456 			     &(((struct reg_window __user *)rval)->ins[6])))
457 			rval = 0;
458 		else
459 			rval = rval - STACK_BIAS;
460 	}
461 
462 	return rval;
463 }
464 
465 /* Standard stuff. */
466 static inline void shift_window_buffer(int first_win, int last_win,
467 				       struct thread_info *t)
468 {
469 	int i;
470 
471 	for (i = first_win; i < last_win; i++) {
472 		t->rwbuf_stkptrs[i] = t->rwbuf_stkptrs[i+1];
473 		memcpy(&t->reg_window[i], &t->reg_window[i+1],
474 		       sizeof(struct reg_window));
475 	}
476 }
477 
478 void synchronize_user_stack(void)
479 {
480 	struct thread_info *t = current_thread_info();
481 	unsigned long window;
482 
483 	flush_user_windows();
484 	if ((window = get_thread_wsaved()) != 0) {
485 		window -= 1;
486 		do {
487 			struct reg_window *rwin = &t->reg_window[window];
488 			int winsize = sizeof(struct reg_window);
489 			unsigned long sp;
490 
491 			sp = t->rwbuf_stkptrs[window];
492 
493 			if (test_thread_64bit_stack(sp))
494 				sp += STACK_BIAS;
495 			else
496 				winsize = sizeof(struct reg_window32);
497 
498 			if (!copy_to_user((char __user *)sp, rwin, winsize)) {
499 				shift_window_buffer(window, get_thread_wsaved() - 1, t);
500 				set_thread_wsaved(get_thread_wsaved() - 1);
501 			}
502 		} while (window--);
503 	}
504 }
505 
506 static void stack_unaligned(unsigned long sp)
507 {
508 	force_sig_fault(SIGBUS, BUS_ADRALN, (void __user *) sp);
509 }
510 
511 static const char uwfault32[] = KERN_INFO \
512 	"%s[%d]: bad register window fault: SP %08lx (orig_sp %08lx) TPC %08lx O7 %08lx\n";
513 static const char uwfault64[] = KERN_INFO \
514 	"%s[%d]: bad register window fault: SP %016lx (orig_sp %016lx) TPC %08lx O7 %016lx\n";
515 
516 void fault_in_user_windows(struct pt_regs *regs)
517 {
518 	struct thread_info *t = current_thread_info();
519 	unsigned long window;
520 
521 	flush_user_windows();
522 	window = get_thread_wsaved();
523 
524 	if (likely(window != 0)) {
525 		window -= 1;
526 		do {
527 			struct reg_window *rwin = &t->reg_window[window];
528 			int winsize = sizeof(struct reg_window);
529 			unsigned long sp, orig_sp;
530 
531 			orig_sp = sp = t->rwbuf_stkptrs[window];
532 
533 			if (test_thread_64bit_stack(sp))
534 				sp += STACK_BIAS;
535 			else
536 				winsize = sizeof(struct reg_window32);
537 
538 			if (unlikely(sp & 0x7UL))
539 				stack_unaligned(sp);
540 
541 			if (unlikely(copy_to_user((char __user *)sp,
542 						  rwin, winsize))) {
543 				if (show_unhandled_signals)
544 					printk_ratelimited(is_compat_task() ?
545 							   uwfault32 : uwfault64,
546 							   current->comm, current->pid,
547 							   sp, orig_sp,
548 							   regs->tpc,
549 							   regs->u_regs[UREG_I7]);
550 				goto barf;
551 			}
552 		} while (window--);
553 	}
554 	set_thread_wsaved(0);
555 	return;
556 
557 barf:
558 	set_thread_wsaved(window + 1);
559 	force_sig(SIGSEGV);
560 }
561 
562 /* Copy a Sparc thread.  The fork() return value conventions
563  * under SunOS are nothing short of bletcherous:
564  * Parent -->  %o0 == childs  pid, %o1 == 0
565  * Child  -->  %o0 == parents pid, %o1 == 1
566  */
567 int copy_thread(struct task_struct *p, const struct kernel_clone_args *args)
568 {
569 	unsigned long clone_flags = args->flags;
570 	unsigned long sp = args->stack;
571 	unsigned long tls = args->tls;
572 	struct thread_info *t = task_thread_info(p);
573 	struct pt_regs *regs = current_pt_regs();
574 	struct sparc_stackf *parent_sf;
575 	unsigned long child_stack_sz;
576 	char *child_trap_frame;
577 
578 	/* Calculate offset to stack_frame & pt_regs */
579 	child_stack_sz = (STACKFRAME_SZ + TRACEREG_SZ);
580 	child_trap_frame = (task_stack_page(p) +
581 			    (THREAD_SIZE - child_stack_sz));
582 
583 	t->new_child = 1;
584 	t->ksp = ((unsigned long) child_trap_frame) - STACK_BIAS;
585 	t->kregs = (struct pt_regs *) (child_trap_frame +
586 				       sizeof(struct sparc_stackf));
587 	t->fpsaved[0] = 0;
588 
589 	if (unlikely(args->fn)) {
590 		memset(child_trap_frame, 0, child_stack_sz);
591 		__thread_flag_byte_ptr(t)[TI_FLAG_BYTE_CWP] =
592 			(current_pt_regs()->tstate + 1) & TSTATE_CWP;
593 		t->kregs->u_regs[UREG_G1] = (unsigned long) args->fn;
594 		t->kregs->u_regs[UREG_G2] = (unsigned long) args->fn_arg;
595 		return 0;
596 	}
597 
598 	parent_sf = ((struct sparc_stackf *) regs) - 1;
599 	memcpy(child_trap_frame, parent_sf, child_stack_sz);
600 	if (t->flags & _TIF_32BIT) {
601 		sp &= 0x00000000ffffffffUL;
602 		regs->u_regs[UREG_FP] &= 0x00000000ffffffffUL;
603 	}
604 	t->kregs->u_regs[UREG_FP] = sp;
605 	__thread_flag_byte_ptr(t)[TI_FLAG_BYTE_CWP] =
606 		(regs->tstate + 1) & TSTATE_CWP;
607 	if (sp != regs->u_regs[UREG_FP]) {
608 		unsigned long csp;
609 
610 		csp = clone_stackframe(sp, regs->u_regs[UREG_FP]);
611 		if (!csp)
612 			return -EFAULT;
613 		t->kregs->u_regs[UREG_FP] = csp;
614 	}
615 	if (t->utraps)
616 		t->utraps[0]++;
617 
618 	/* Set the return value for the child. */
619 	t->kregs->u_regs[UREG_I0] = current->pid;
620 	t->kregs->u_regs[UREG_I1] = 1;
621 
622 	/* Set the second return value for the parent. */
623 	regs->u_regs[UREG_I1] = 0;
624 
625 	if (clone_flags & CLONE_SETTLS)
626 		t->kregs->u_regs[UREG_G7] = tls;
627 
628 	return 0;
629 }
630 
631 /* TIF_MCDPER in thread info flags for current task is updated lazily upon
632  * a context switch. Update this flag in current task's thread flags
633  * before dup so the dup'd task will inherit the current TIF_MCDPER flag.
634  */
635 int arch_dup_task_struct(struct task_struct *dst, struct task_struct *src)
636 {
637 	if (adi_capable()) {
638 		register unsigned long tmp_mcdper;
639 
640 		__asm__ __volatile__(
641 			".word 0x83438000\n\t"	/* rd  %mcdper, %g1 */
642 			"mov %%g1, %0\n\t"
643 			: "=r" (tmp_mcdper)
644 			:
645 			: "g1");
646 		if (tmp_mcdper)
647 			set_thread_flag(TIF_MCDPER);
648 		else
649 			clear_thread_flag(TIF_MCDPER);
650 	}
651 
652 	*dst = *src;
653 	return 0;
654 }
655 
656 unsigned long __get_wchan(struct task_struct *task)
657 {
658 	unsigned long pc, fp, bias = 0;
659 	struct thread_info *tp;
660 	struct reg_window *rw;
661         unsigned long ret = 0;
662 	int count = 0;
663 
664 	tp = task_thread_info(task);
665 	bias = STACK_BIAS;
666 	fp = task_thread_info(task)->ksp + bias;
667 
668 	do {
669 		if (!kstack_valid(tp, fp))
670 			break;
671 		rw = (struct reg_window *) fp;
672 		pc = rw->ins[7];
673 		if (!in_sched_functions(pc)) {
674 			ret = pc;
675 			goto out;
676 		}
677 		fp = rw->ins[6] + bias;
678 	} while (++count < 16);
679 
680 out:
681 	return ret;
682 }
683