xref: /freebsd/sys/i386/linux/linux_machdep.c (revision 77a0943ded95b9e6438f7db70c4a28e4d93946d4)
1 /*-
2  * Copyright (c) 2000 Marcel Moolenaar
3  * All rights reserved.
4  *
5  * Redistribution and use in source and binary forms, with or without
6  * modification, are permitted provided that the following conditions
7  * are met:
8  * 1. Redistributions of source code must retain the above copyright
9  *    notice, this list of conditions and the following disclaimer
10  *    in this position and unchanged.
11  * 2. Redistributions in binary form must reproduce the above copyright
12  *    notice, this list of conditions and the following disclaimer in the
13  *    documentation and/or other materials provided with the distribution.
14  * 3. The name of the author may not be used to endorse or promote products
15  *    derived from this software without specific prior written permission.
16  *
17  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
18  * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
19  * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
20  * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
21  * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
22  * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
23  * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
24  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
25  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
26  * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
27  *
28  * $FreeBSD$
29  */
30 
31 #include <sys/param.h>
32 #include <sys/mman.h>
33 #include <sys/proc.h>
34 #include <sys/sysproto.h>
35 #include <sys/systm.h>
36 #include <sys/unistd.h>
37 #include <sys/resource.h>
38 #include <sys/resourcevar.h>
39 
40 #include <machine/frame.h>
41 #include <machine/psl.h>
42 #include <machine/segments.h>
43 #include <machine/sysarch.h>
44 
45 #include <vm/vm.h>
46 #include <sys/lock.h>
47 #include <vm/pmap.h>
48 #include <vm/vm_map.h>
49 
50 #include <i386/linux/linux.h>
51 #include <i386/linux/linux_proto.h>
52 #include <compat/linux/linux_ipc.h>
53 #include <compat/linux/linux_signal.h>
54 #include <compat/linux/linux_util.h>
55 
56 struct linux_descriptor {
57 	unsigned int  entry_number;
58 	unsigned long base_addr;
59 	unsigned int  limit;
60 	unsigned int  seg_32bit:1;
61 	unsigned int  contents:2;
62 	unsigned int  read_exec_only:1;
63 	unsigned int  limit_in_pages:1;
64 	unsigned int  seg_not_present:1;
65 	unsigned int  useable:1;
66 };
67 
68 struct linux_select_argv {
69 	int nfds;
70 	fd_set *readfds;
71 	fd_set *writefds;
72 	fd_set *exceptfds;
73 	struct timeval *timeout;
74 };
75 
76 int
77 linux_to_bsd_sigaltstack(int lsa)
78 {
79 	int bsa = 0;
80 
81 	if (lsa & LINUX_SS_DISABLE)
82 		bsa |= SS_DISABLE;
83 	if (lsa & LINUX_SS_ONSTACK)
84 		bsa |= SS_ONSTACK;
85 	if (lsa == LINUX_SS_ONSTACK_BC)
86 		bsa = SS_ONSTACK;
87 	return (bsa);
88 }
89 
90 int
91 bsd_to_linux_sigaltstack(int bsa)
92 {
93 	int lsa = 0;
94 
95 	if (bsa & SS_DISABLE)
96 		lsa |= LINUX_SS_DISABLE;
97 	if (bsa & SS_ONSTACK)
98 		lsa |= LINUX_SS_ONSTACK;
99 	return (lsa);
100 }
101 
102 int
103 linux_execve(struct proc *p, struct linux_execve_args *args)
104 {
105 	struct execve_args bsd;
106 	caddr_t sg;
107 
108 	sg = stackgap_init();
109 	CHECKALTEXIST(p, &sg, args->path);
110 
111 #ifdef DEBUG
112         printf("Linux-emul(%d): execve(%s)\n",
113 	    p->p_pid, args->path);
114 #endif
115 
116 	bsd.fname = args->path;
117 	bsd.argv = args->argp;
118 	bsd.envv = args->envp;
119 	return (execve(p, &bsd));
120 }
121 
122 int
123 linux_ipc(struct proc *p, struct linux_ipc_args *args)
124 {
125 	switch (args->what) {
126 	case LINUX_SEMOP:
127 		return (linux_semop(p, args));
128 	case LINUX_SEMGET:
129 		return (linux_semget(p, args));
130 	case LINUX_SEMCTL:
131 		return (linux_semctl(p, args));
132 	case LINUX_MSGSND:
133 		return (linux_msgsnd(p, args));
134 	case LINUX_MSGRCV:
135 		return (linux_msgrcv(p, args));
136 	case LINUX_MSGGET:
137 		return (linux_msgget(p, args));
138 	case LINUX_MSGCTL:
139 		return (linux_msgctl(p, args));
140 	case LINUX_SHMAT:
141 		return (linux_shmat(p, args));
142 	case LINUX_SHMDT:
143 		return (linux_shmdt(p, args));
144 	case LINUX_SHMGET:
145 		return (linux_shmget(p, args));
146 	case LINUX_SHMCTL:
147 		return (linux_shmctl(p, args));
148 	}
149 
150 	uprintf("LINUX: 'ipc' typ=%d not implemented\n", args->what);
151 	return (ENOSYS);
152 }
153 
154 int
155 linux_select(struct proc *p, struct linux_select_args *args)
156 {
157 	struct linux_select_argv linux_args;
158 	struct linux_newselect_args newsel;
159 	int error;
160 
161 #ifdef SELECT_DEBUG
162 	printf("Linux-emul(%ld): select(%x)\n", (long)p->p_pid, args->ptr);
163 #endif
164 
165 	error = copyin(args->ptr, &linux_args, sizeof(linux_args));
166 	if (error)
167 		return (error);
168 
169 	newsel.nfds = linux_args.nfds;
170 	newsel.readfds = linux_args.readfds;
171 	newsel.writefds = linux_args.writefds;
172 	newsel.exceptfds = linux_args.exceptfds;
173 	newsel.timeout = linux_args.timeout;
174 	return (linux_newselect(p, &newsel));
175 }
176 
177 int
178 linux_fork(struct proc *p, struct linux_fork_args *args)
179 {
180 	int error;
181 
182 #ifdef DEBUG
183 	printf("Linux-emul(%ld): fork()\n", (long)p->p_pid);
184 #endif
185 
186 	if ((error = fork(p, (struct fork_args *)args)) != 0)
187 		return (error);
188 
189 	if (p->p_retval[1] == 1)
190 		p->p_retval[0] = 0;
191 	return (0);
192 }
193 
194 int
195 linux_vfork(struct proc *p, struct linux_vfork_args *args)
196 {
197 	int error;
198 
199 #ifdef DEBUG
200 	printf("Linux-emul(%ld): vfork()\n", (long)p->p_pid);
201 #endif
202 
203 	if ((error = vfork(p, (struct vfork_args *)args)) != 0)
204 		return (error);
205 	/* Are we the child? */
206 	if (p->p_retval[1] == 1)
207 		p->p_retval[0] = 0;
208 	return (0);
209 }
210 
211 #define CLONE_VM	0x100
212 #define CLONE_FS	0x200
213 #define CLONE_FILES	0x400
214 #define CLONE_SIGHAND	0x800
215 #define CLONE_PID	0x1000
216 
217 int
218 linux_clone(struct proc *p, struct linux_clone_args *args)
219 {
220 	int error, ff = RFPROC;
221 	struct proc *p2;
222 	int exit_signal;
223 	vm_offset_t start;
224 	struct rfork_args rf_args;
225 
226 #ifdef DEBUG
227 	if (args->flags & CLONE_PID)
228 		printf("linux_clone(%ld): CLONE_PID not yet supported\n",
229 		    (long)p->p_pid);
230 	printf("linux_clone(%ld): invoked with flags %x and stack %x\n",
231 	    (long)p->p_pid, (unsigned int)args->flags,
232 	    (unsigned int)args->stack);
233 #endif
234 
235 	if (!args->stack)
236 		return (EINVAL);
237 
238 	exit_signal = args->flags & 0x000000ff;
239 	if (exit_signal >= LINUX_NSIG)
240 		return (EINVAL);
241 
242 	if (exit_signal <= LINUX_SIGTBLSZ)
243 		exit_signal = linux_to_bsd_signal[_SIG_IDX(exit_signal)];
244 
245 	/* RFTHREAD probably not necessary here, but it shouldn't hurt */
246 	ff |= RFTHREAD;
247 
248 	if (args->flags & CLONE_VM)
249 		ff |= RFMEM;
250 	if (args->flags & CLONE_SIGHAND)
251 		ff |= RFSIGSHARE;
252 	if (!(args->flags & CLONE_FILES))
253 		ff |= RFFDG;
254 
255 	error = 0;
256 	start = 0;
257 
258 	rf_args.flags = ff;
259 	if ((error = rfork(p, &rf_args)) != 0)
260 		return (error);
261 
262 	p2 = pfind(p->p_retval[0]);
263 	if (p2 == 0)
264 		return (ESRCH);
265 
266 	p2->p_sigparent = exit_signal;
267 	p2->p_md.md_regs->tf_esp = (unsigned int)args->stack;
268 
269 #ifdef DEBUG
270 	printf ("linux_clone(%ld): successful rfork to %ld\n", (long)p->p_pid,
271 	    (long)p2->p_pid);
272 #endif
273 
274 	return (0);
275 }
276 
277 /* XXX move */
278 struct linux_mmap_argv {
279 	linux_caddr_t addr;
280 	int len;
281 	int prot;
282 	int flags;
283 	int fd;
284 	int pos;
285 };
286 
287 #define STACK_SIZE  (2 * 1024 * 1024)
288 #define GUARD_SIZE  (4 * PAGE_SIZE)
289 
290 int
291 linux_mmap(struct proc *p, struct linux_mmap_args *args)
292 {
293 	struct mmap_args /* {
294 		caddr_t addr;
295 		size_t len;
296 		int prot;
297 		int flags;
298 		int fd;
299 		long pad;
300 		off_t pos;
301 	} */ bsd_args;
302 	int error;
303 	struct linux_mmap_argv linux_args;
304 
305 	error = copyin(args->ptr, &linux_args, sizeof(linux_args));
306 	if (error)
307 		return (error);
308 
309 #ifdef DEBUG
310 	printf("Linux-emul(%ld): mmap(%p, %d, %d, 0x%08x, %d, %d)",
311 	    (long)p->p_pid, (void *)linux_args.addr, linux_args.len,
312 	    linux_args.prot, linux_args.flags, linux_args.fd, linux_args.pos);
313 #endif
314 
315 	bsd_args.flags = 0;
316 	if (linux_args.flags & LINUX_MAP_SHARED)
317 		bsd_args.flags |= MAP_SHARED;
318 	if (linux_args.flags & LINUX_MAP_PRIVATE)
319 		bsd_args.flags |= MAP_PRIVATE;
320 	if (linux_args.flags & LINUX_MAP_FIXED)
321 		bsd_args.flags |= MAP_FIXED;
322 	if (linux_args.flags & LINUX_MAP_ANON)
323 		bsd_args.flags |= MAP_ANON;
324 	if (linux_args.flags & LINUX_MAP_GROWSDOWN) {
325 		bsd_args.flags |= MAP_STACK;
326 
327 		/* The linux MAP_GROWSDOWN option does not limit auto
328 		 * growth of the region.  Linux mmap with this option
329 		 * takes as addr the inital BOS, and as len, the initial
330 		 * region size.  It can then grow down from addr without
331 		 * limit.  However, linux threads has an implicit internal
332 		 * limit to stack size of STACK_SIZE.  Its just not
333 		 * enforced explicitly in linux.  But, here we impose
334 		 * a limit of (STACK_SIZE - GUARD_SIZE) on the stack
335 		 * region, since we can do this with our mmap.
336 		 *
337 		 * Our mmap with MAP_STACK takes addr as the maximum
338 		 * downsize limit on BOS, and as len the max size of
339 		 * the region.  It them maps the top SGROWSIZ bytes,
340 		 * and autgrows the region down, up to the limit
341 		 * in addr.
342 		 *
343 		 * If we don't use the MAP_STACK option, the effect
344 		 * of this code is to allocate a stack region of a
345 		 * fixed size of (STACK_SIZE - GUARD_SIZE).
346 		 */
347 
348 		/* This gives us TOS */
349 		bsd_args.addr = linux_args.addr + linux_args.len;
350 
351 		if (bsd_args.addr > p->p_vmspace->vm_maxsaddr) {
352 			/* Some linux apps will attempt to mmap
353 			 * thread stacks near the top of their
354 			 * address space.  If their TOS is greater
355 			 * than vm_maxsaddr, vm_map_growstack()
356 			 * will confuse the thread stack with the
357 			 * process stack and deliver a SEGV if they
358 			 * attempt to grow the thread stack past their
359 			 * current stacksize rlimit.  To avoid this,
360 			 * adjust vm_maxsaddr upwards to reflect
361 			 * the current stacksize rlimit rather
362 			 * than the maximum possible stacksize.
363 			 * It would be better to adjust the
364 			 * mmap'ed region, but some apps do not check
365 			 * mmap's return value.
366 			 */
367 			p->p_vmspace->vm_maxsaddr = (char *)USRSTACK -
368 			    p->p_rlimit[RLIMIT_STACK].rlim_cur;
369 		}
370 
371 		/* This gives us our maximum stack size */
372 		if (linux_args.len > STACK_SIZE - GUARD_SIZE)
373 			bsd_args.len = linux_args.len;
374 		else
375 			bsd_args.len  = STACK_SIZE - GUARD_SIZE;
376 
377 		/* This gives us a new BOS.  If we're using VM_STACK, then
378 		 * mmap will just map the top SGROWSIZ bytes, and let
379 		 * the stack grow down to the limit at BOS.  If we're
380 		 * not using VM_STACK we map the full stack, since we
381 		 * don't have a way to autogrow it.
382 		 */
383 		bsd_args.addr -= bsd_args.len;
384 	} else {
385 		bsd_args.addr = linux_args.addr;
386 		bsd_args.len  = linux_args.len;
387 	}
388 
389 	bsd_args.prot = linux_args.prot | PROT_READ;	/* always required */
390 	if (linux_args.flags & LINUX_MAP_ANON)
391 		bsd_args.fd = -1;
392 	else
393 		bsd_args.fd = linux_args.fd;
394 	bsd_args.pos = linux_args.pos;
395 	bsd_args.pad = 0;
396 
397 #ifdef DEBUG
398 	printf("-> (%p, %d, %d, 0x%08x, %d, %d)\n", (void *)bsd_args.addr,
399 	    bsd_args.len, bsd_args.prot, bsd_args.flags, bsd_args.fd,
400 	    (int)bsd_args.pos);
401 #endif
402 
403 	return (mmap(p, &bsd_args));
404 }
405 
406 int
407 linux_pipe(struct proc *p, struct linux_pipe_args *args)
408 {
409 	int error;
410 	int reg_edx;
411 
412 #ifdef DEBUG
413 	printf("Linux-emul(%ld): pipe(*)\n", (long)p->p_pid);
414 #endif
415 
416 	reg_edx = p->p_retval[1];
417 	error = pipe(p, 0);
418 	if (error) {
419 		p->p_retval[1] = reg_edx;
420 		return (error);
421 	}
422 
423 	error = copyout(p->p_retval, args->pipefds, 2*sizeof(int));
424 	if (error) {
425 		p->p_retval[1] = reg_edx;
426 		return (error);
427 	}
428 
429 	p->p_retval[1] = reg_edx;
430 	p->p_retval[0] = 0;
431 	return (0);
432 }
433 
434 int
435 linux_ioperm(struct proc *p, struct linux_ioperm_args *args)
436 {
437 	struct sysarch_args sa;
438 	struct i386_ioperm_args *iia;
439 	caddr_t sg;
440 
441 	sg = stackgap_init();
442 	iia = stackgap_alloc(&sg, sizeof(struct i386_ioperm_args));
443 	iia->start = args->start;
444 	iia->length = args->length;
445 	iia->enable = args->enable;
446 	sa.op = I386_SET_IOPERM;
447 	sa.parms = (char *)iia;
448 	return (sysarch(p, &sa));
449 }
450 
451 int
452 linux_iopl(struct proc *p, struct linux_iopl_args *args)
453 {
454 	int error;
455 
456 	if (args->level < 0 || args->level > 3)
457 		return (EINVAL);
458 	if ((error = suser(p)) != 0)
459 		return (error);
460 	if (securelevel > 0)
461 		return (EPERM);
462 	p->p_md.md_regs->tf_eflags = (p->p_md.md_regs->tf_eflags & ~PSL_IOPL) |
463 	    (args->level * (PSL_IOPL / 3));
464 	return (0);
465 }
466 
467 int
468 linux_modify_ldt(p, uap)
469 	struct proc *p;
470 	struct linux_modify_ldt_args *uap;
471 {
472 	int error;
473 	caddr_t sg;
474 	struct sysarch_args args;
475 	struct i386_ldt_args *ldt;
476 	struct linux_descriptor ld;
477 	union descriptor *desc;
478 
479 	sg = stackgap_init();
480 
481 	if (uap->ptr == NULL)
482 		return (EINVAL);
483 
484 	switch (uap->func) {
485 	case 0x00: /* read_ldt */
486 		ldt = stackgap_alloc(&sg, sizeof(*ldt));
487 		ldt->start = 0;
488 		ldt->descs = uap->ptr;
489 		ldt->num = uap->bytecount / sizeof(union descriptor);
490 		args.op = I386_GET_LDT;
491 		args.parms = (char*)ldt;
492 		error = sysarch(p, &args);
493 		p->p_retval[0] *= sizeof(union descriptor);
494 		break;
495 	case 0x01: /* write_ldt */
496 	case 0x11: /* write_ldt */
497 		if (uap->bytecount != sizeof(ld))
498 			return (EINVAL);
499 
500 		error = copyin(uap->ptr, &ld, sizeof(ld));
501 		if (error)
502 			return (error);
503 
504 		ldt = stackgap_alloc(&sg, sizeof(*ldt));
505 		desc = stackgap_alloc(&sg, sizeof(*desc));
506 		ldt->start = ld.entry_number;
507 		ldt->descs = desc;
508 		ldt->num = 1;
509 		desc->sd.sd_lolimit = (ld.limit & 0x0000ffff);
510 		desc->sd.sd_hilimit = (ld.limit & 0x000f0000) >> 16;
511 		desc->sd.sd_lobase = (ld.base_addr & 0x00ffffff);
512 		desc->sd.sd_hibase = (ld.base_addr & 0xff000000) >> 24;
513 		desc->sd.sd_type = SDT_MEMRO | ((ld.read_exec_only ^ 1) << 1) |
514 			(ld.contents << 2);
515 		desc->sd.sd_dpl = 3;
516 		desc->sd.sd_p = (ld.seg_not_present ^ 1);
517 		desc->sd.sd_xx = 0;
518 		desc->sd.sd_def32 = ld.seg_32bit;
519 		desc->sd.sd_gran = ld.limit_in_pages;
520 		args.op = I386_SET_LDT;
521 		args.parms = (char*)ldt;
522 		error = sysarch(p, &args);
523 		break;
524 	default:
525 		error = EINVAL;
526 		break;
527 	}
528 
529 	if (error == EOPNOTSUPP) {
530 		printf("linux: modify_ldt needs kernel option USER_LDT\n");
531 		error = ENOSYS;
532 	}
533 
534 	return (error);
535 }
536 
537 int
538 linux_sigaction(struct proc *p, struct linux_sigaction_args *args)
539 {
540 	linux_osigaction_t osa;
541 	linux_sigaction_t act, oact;
542 	int error;
543 
544 #ifdef DEBUG
545 	printf("Linux-emul(%ld): sigaction(%d, %p, %p)\n", (long)p->p_pid,
546 	       args->sig, (void *)args->nsa, (void *)args->osa);
547 #endif
548 
549 	if (args->nsa != NULL) {
550 		error = copyin(args->nsa, &osa, sizeof(linux_osigaction_t));
551 		if (error)
552 			return (error);
553 		act.lsa_handler = osa.lsa_handler;
554 		act.lsa_flags = osa.lsa_flags;
555 		act.lsa_restorer = osa.lsa_restorer;
556 		LINUX_SIGEMPTYSET(act.lsa_mask);
557 		act.lsa_mask.__bits[0] = osa.lsa_mask;
558 	}
559 
560 	error = linux_do_sigaction(p, args->sig, args->nsa ? &act : NULL,
561 	    args->osa ? &oact : NULL);
562 
563 	if (args->osa != NULL && !error) {
564 		osa.lsa_handler = oact.lsa_handler;
565 		osa.lsa_flags = oact.lsa_flags;
566 		osa.lsa_restorer = oact.lsa_restorer;
567 		osa.lsa_mask = oact.lsa_mask.__bits[0];
568 		error = copyout(&osa, args->osa, sizeof(linux_osigaction_t));
569 	}
570 
571 	return (error);
572 }
573 
574 /*
575  * Linux has two extra args, restart and oldmask.  We dont use these,
576  * but it seems that "restart" is actually a context pointer that
577  * enables the signal to happen with a different register set.
578  */
579 int
580 linux_sigsuspend(struct proc *p, struct linux_sigsuspend_args *args)
581 {
582 	struct sigsuspend_args bsd;
583 	sigset_t *sigmask;
584 	linux_sigset_t mask;
585 	caddr_t sg = stackgap_init();
586 
587 #ifdef DEBUG
588 	printf("Linux-emul(%ld): sigsuspend(%08lx)\n",
589 	       (long)p->p_pid, (unsigned long)args->mask);
590 #endif
591 
592 	sigmask = stackgap_alloc(&sg, sizeof(sigset_t));
593 	LINUX_SIGEMPTYSET(mask);
594 	mask.__bits[0] = args->mask;
595 	linux_to_bsd_sigset(&mask, sigmask);
596 	bsd.sigmask = sigmask;
597 	return (sigsuspend(p, &bsd));
598 }
599 
600 int
601 linux_rt_sigsuspend(p, uap)
602 	struct proc *p;
603 	struct linux_rt_sigsuspend_args *uap;
604 {
605 	linux_sigset_t lmask;
606 	sigset_t *bmask;
607 	struct sigsuspend_args bsd;
608 	caddr_t sg = stackgap_init();
609 	int error;
610 
611 #ifdef DEBUG
612 	printf("Linux-emul(%ld): rt_sigsuspend(%p, %d)\n", (long)p->p_pid,
613 	       (void *)uap->newset, uap->sigsetsize);
614 #endif
615 
616 	if (uap->sigsetsize != sizeof(linux_sigset_t))
617 		return (EINVAL);
618 
619 	error = copyin(uap->newset, &lmask, sizeof(linux_sigset_t));
620 	if (error)
621 		return (error);
622 
623 	bmask = stackgap_alloc(&sg, sizeof(sigset_t));
624 	linux_to_bsd_sigset(&lmask, bmask);
625 	bsd.sigmask = bmask;
626 	return (sigsuspend(p, &bsd));
627 }
628 
629 int
630 linux_pause(struct proc *p, struct linux_pause_args *args)
631 {
632 	struct sigsuspend_args bsd;
633 	sigset_t *sigmask;
634 	caddr_t sg = stackgap_init();
635 
636 #ifdef DEBUG
637 	printf("Linux-emul(%d): pause()\n", p->p_pid);
638 #endif
639 
640 	sigmask = stackgap_alloc(&sg, sizeof(sigset_t));
641 	*sigmask = p->p_sigmask;
642 	bsd.sigmask = sigmask;
643 	return (sigsuspend(p, &bsd));
644 }
645 
646 int
647 linux_sigaltstack(p, uap)
648 	struct proc *p;
649 	struct linux_sigaltstack_args *uap;
650 {
651 	struct sigaltstack_args bsd;
652 	stack_t *ss, *oss;
653 	linux_stack_t lss;
654 	int error;
655 	caddr_t sg = stackgap_init();
656 
657 #ifdef DEBUG
658 	printf("Linux-emul(%ld): sigaltstack(%p, %p)\n",
659 	    (long)p->p_pid, uap->uss, uap->uoss);
660 #endif
661 
662 	if (uap->uss == NULL) {
663 		ss = NULL;
664 	} else {
665 		error = copyin(uap->uss, &lss, sizeof(linux_stack_t));
666 		if (error)
667 			return (error);
668 
669 		ss = stackgap_alloc(&sg, sizeof(stack_t));
670 		ss->ss_sp = lss.ss_sp;
671 		ss->ss_size = lss.ss_size;
672 		ss->ss_flags = linux_to_bsd_sigaltstack(lss.ss_flags);
673 	}
674 	oss = (uap->uoss != NULL)
675 	    ? stackgap_alloc(&sg, sizeof(stack_t))
676 	    : NULL;
677 
678 	bsd.ss = ss;
679 	bsd.oss = oss;
680 	error = sigaltstack(p, &bsd);
681 
682 	if (!error && oss != NULL) {
683 		lss.ss_sp = oss->ss_sp;
684 		lss.ss_size = oss->ss_size;
685 		lss.ss_flags = bsd_to_linux_sigaltstack(oss->ss_flags);
686 		error = copyout(&lss, uap->uoss, sizeof(linux_stack_t));
687 	}
688 
689 	return (error);
690 }
691