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linux_machdep.c revision 1.39.6.1
      1 /*	$NetBSD: linux_machdep.c,v 1.39.6.1 2017/02/14 16:59:31 snj Exp $ */
      2 
      3 /*-
      4  * Copyright (c) 2005 Emmanuel Dreyfus, all rights reserved.
      5  *
      6  * Redistribution and use in source and binary forms, with or without
      7  * modification, are permitted provided that the following conditions
      8  * are met:
      9  * 1. Redistributions of source code must retain the above copyright
     10  *    notice, this list of conditions and the following disclaimer.
     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. All advertising materials mentioning features or use of this software
     15  *    must display the following acknowledgement:
     16  *	This product includes software developed by Emmanuel Dreyfus
     17  * 4. The name of the author may not be used to endorse or promote
     18  *    products derived from this software without specific prior written
     19  *    permission.
     20  *
     21  * THIS SOFTWARE IS PROVIDED BY THE THE AUTHOR AND CONTRIBUTORS ``AS IS''
     22  * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
     23  * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
     24  * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS
     25  * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
     26  * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
     27  * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
     28  * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
     29  * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
     30  * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
     31  * POSSIBILITY OF SUCH DAMAGE.
     32  */
     33 
     34 #include <sys/cdefs.h>
     35 
     36 __KERNEL_RCSID(0, "$NetBSD: linux_machdep.c,v 1.39.6.1 2017/02/14 16:59:31 snj Exp $");
     37 
     38 #include <sys/param.h>
     39 #include <sys/types.h>
     40 #include <sys/systm.h>
     41 #include <sys/signal.h>
     42 #include <sys/exec.h>
     43 #include <sys/proc.h>
     44 #include <sys/ptrace.h> /* for process_read_fpregs() */
     45 #include <sys/ucontext.h>
     46 #include <sys/conf.h>
     47 
     48 #include <machine/reg.h>
     49 #include <machine/pcb.h>
     50 #include <machine/fpu.h>
     51 #include <machine/mcontext.h>
     52 #include <machine/specialreg.h>
     53 #include <machine/vmparam.h>
     54 #include <machine/cpufunc.h>
     55 
     56 /*
     57  * To see whether wscons is configured (for virtual console ioctl calls).
     58  */
     59 #if defined(_KERNEL_OPT)
     60 #include "wsdisplay.h"
     61 #endif
     62 #if (NWSDISPLAY > 0)
     63 #include <dev/wscons/wsconsio.h>
     64 #include <dev/wscons/wsdisplay_usl_io.h>
     65 #endif
     66 
     67 
     68 #include <compat/linux/common/linux_signal.h>
     69 #include <compat/linux/common/linux_errno.h>
     70 #include <compat/linux/common/linux_exec.h>
     71 #include <compat/linux/common/linux_ioctl.h>
     72 #include <compat/linux/common/linux_prctl.h>
     73 #include <compat/linux/common/linux_machdep.h>
     74 #include <compat/linux/common/linux_ipc.h>
     75 #include <compat/linux/common/linux_sem.h>
     76 #include <compat/linux/linux_syscall.h>
     77 #include <compat/linux/linux_syscallargs.h>
     78 
     79 static void linux_buildcontext(struct lwp *, void *, void *);
     80 
     81 void
     82 linux_setregs(struct lwp *l, struct exec_package *epp, vaddr_t stack)
     83 {
     84 	struct pcb *pcb = lwp_getpcb(l);
     85 	struct trapframe *tf;
     86 
     87 	/* If we were using the FPU, forget about it. */
     88 	if (pcb->pcb_fpcpu != NULL)
     89 		fpusave_lwp(l, 0);
     90 
     91 	l->l_md.md_flags &= ~MDP_USEDFPU;
     92 	pcb->pcb_flags = 0;
     93 	pcb->pcb_savefpu.fp_fxsave.fx_fcw = __NetBSD_NPXCW__;
     94 	pcb->pcb_savefpu.fp_fxsave.fx_mxcsr = __INITIAL_MXCSR__;
     95 	pcb->pcb_savefpu.fp_fxsave.fx_mxcsr_mask = __INITIAL_MXCSR_MASK__;
     96 
     97 	l->l_proc->p_flag &= ~PK_32;
     98 
     99 	tf = l->l_md.md_regs;
    100 	tf->tf_rax = 0;
    101 	tf->tf_rbx = 0;
    102 	tf->tf_rcx = epp->ep_entry;
    103 	tf->tf_rdx = 0;
    104 	tf->tf_rsi = 0;
    105 	tf->tf_rdi = 0;
    106 	tf->tf_rbp = 0;
    107 	tf->tf_rsp = stack;
    108 	tf->tf_r8 = 0;
    109 	tf->tf_r9 = 0;
    110 	tf->tf_r10 = 0;
    111 	tf->tf_r11 = 0;
    112 	tf->tf_r12 = 0;
    113 	tf->tf_r13 = 0;
    114 	tf->tf_r14 = 0;
    115 	tf->tf_r15 = 0;
    116 	tf->tf_rip = epp->ep_entry;
    117 	tf->tf_rflags = PSL_USERSET;
    118 	tf->tf_cs = GSEL(GUCODE_SEL, SEL_UPL);
    119 	tf->tf_ss = GSEL(GUDATA_SEL, SEL_UPL);
    120 	tf->tf_ds = 0;
    121 	tf->tf_es = 0;
    122 	cpu_fsgs_zero(l);
    123 
    124 	return;
    125 }
    126 
    127 void
    128 linux_sendsig(const ksiginfo_t *ksi, const sigset_t *mask)
    129 {
    130 	struct lwp *l = curlwp;
    131 	struct proc *p = l->l_proc;
    132 	struct pcb *pcb = lwp_getpcb(l);
    133 	struct sigacts *ps = p->p_sigacts;
    134 	int onstack, error;
    135 	int sig = ksi->ksi_signo;
    136 	struct linux_rt_sigframe *sfp, sigframe;
    137 	struct linux__fpstate *fpsp, fpstate;
    138 	struct fpreg fpregs;
    139 	struct trapframe *tf = l->l_md.md_regs;
    140 	sig_t catcher = SIGACTION(p, sig).sa_handler;
    141 	linux_sigset_t lmask;
    142 	char *sp;
    143 
    144 	/* Do we need to jump onto the signal stack? */
    145 	onstack =
    146 	    (l->l_sigstk.ss_flags & (SS_DISABLE | SS_ONSTACK)) == 0 &&
    147 	    (SIGACTION(p, sig).sa_flags & SA_ONSTACK) != 0;
    148 
    149 	/* Allocate space for the signal handler context. */
    150 	if (onstack)
    151 		sp = ((char *)l->l_sigstk.ss_sp +
    152 		    l->l_sigstk.ss_size);
    153 	else
    154 		sp = (char *)tf->tf_rsp - 128;
    155 
    156 	/*
    157 	 * Save FPU state, if any
    158 	 */
    159 	if (l->l_md.md_flags & MDP_USEDFPU) {
    160 		sp = (char *)
    161 		    (((long)sp - sizeof(struct linux__fpstate)) & ~0xfUL);
    162 		fpsp = (struct linux__fpstate *)sp;
    163 	} else
    164 		fpsp = NULL;
    165 
    166 	/*
    167 	 * Populate the rt_sigframe
    168 	 */
    169 	sp = (char *)
    170 	    ((((long)sp - sizeof(struct linux_rt_sigframe)) & ~0xfUL) - 8);
    171 	sfp = (struct linux_rt_sigframe *)sp;
    172 
    173 	memset(&sigframe, 0, sizeof(sigframe));
    174 	if (ps->sa_sigdesc[sig].sd_vers != 0)
    175 		sigframe.pretcode =
    176 		    (char *)(u_long)ps->sa_sigdesc[sig].sd_tramp;
    177 	else
    178 		sigframe.pretcode = NULL;
    179 
    180 	/*
    181 	 * The user context
    182 	 */
    183 	sigframe.uc.luc_flags = 0;
    184 	sigframe.uc.luc_link = NULL;
    185 
    186 	/* This is used regardless of SA_ONSTACK in Linux */
    187 	sigframe.uc.luc_stack.ss_sp = l->l_sigstk.ss_sp;
    188 	sigframe.uc.luc_stack.ss_size = l->l_sigstk.ss_size;
    189 	sigframe.uc.luc_stack.ss_flags = 0;
    190 	if (l->l_sigstk.ss_flags & SS_ONSTACK)
    191 		sigframe.uc.luc_stack.ss_flags |= LINUX_SS_ONSTACK;
    192 	if (l->l_sigstk.ss_flags & SS_DISABLE)
    193 		sigframe.uc.luc_stack.ss_flags |= LINUX_SS_DISABLE;
    194 
    195 	sigframe.uc.luc_mcontext.r8 = tf->tf_r8;
    196 	sigframe.uc.luc_mcontext.r9 = tf->tf_r9;
    197 	sigframe.uc.luc_mcontext.r10 = tf->tf_r10;
    198 	sigframe.uc.luc_mcontext.r11 = tf->tf_r11;
    199 	sigframe.uc.luc_mcontext.r12 = tf->tf_r12;
    200 	sigframe.uc.luc_mcontext.r13 = tf->tf_r13;
    201 	sigframe.uc.luc_mcontext.r14 = tf->tf_r14;
    202 	sigframe.uc.luc_mcontext.r15 = tf->tf_r15;
    203 	sigframe.uc.luc_mcontext.rdi = tf->tf_rdi;
    204 	sigframe.uc.luc_mcontext.rsi = tf->tf_rsi;
    205 	sigframe.uc.luc_mcontext.rbp = tf->tf_rbp;
    206 	sigframe.uc.luc_mcontext.rbx = tf->tf_rbx;
    207 	sigframe.uc.luc_mcontext.rdx = tf->tf_rdx;
    208 	sigframe.uc.luc_mcontext.rax = tf->tf_rax;
    209 	sigframe.uc.luc_mcontext.rcx = tf->tf_rcx;
    210 	sigframe.uc.luc_mcontext.rsp = tf->tf_rsp;
    211 	sigframe.uc.luc_mcontext.rip = tf->tf_rip;
    212 	sigframe.uc.luc_mcontext.eflags = tf->tf_rflags;
    213 	sigframe.uc.luc_mcontext.cs = tf->tf_cs;
    214 	sigframe.uc.luc_mcontext.gs = tf->tf_gs;
    215 	sigframe.uc.luc_mcontext.fs = tf->tf_fs;
    216 	sigframe.uc.luc_mcontext.err = tf->tf_err;
    217 	sigframe.uc.luc_mcontext.trapno = tf->tf_trapno;
    218 	native_to_linux_sigset(&lmask, mask);
    219 	sigframe.uc.luc_mcontext.oldmask = lmask.sig[0];
    220 	sigframe.uc.luc_mcontext.cr2 = (long)pcb->pcb_onfault;
    221 	sigframe.uc.luc_mcontext.fpstate = fpsp;
    222 	native_to_linux_sigset(&sigframe.uc.luc_sigmask, mask);
    223 	native_to_linux_siginfo(&sigframe.info, &ksi->ksi_info);
    224 	sendsig_reset(l, sig);
    225 	mutex_exit(p->p_lock);
    226 	error = 0;
    227 
    228 	/*
    229 	 * Save FPU state, if any
    230 	 */
    231 	if (fpsp != NULL) {
    232 		(void)process_read_fpregs(l, &fpregs);
    233 		memset(&fpstate, 0, sizeof(fpstate));
    234 		fpstate.cwd = fpregs.fp_fcw;
    235 		fpstate.swd = fpregs.fp_fsw;
    236 		fpstate.twd = fpregs.fp_ftw;
    237 		fpstate.fop = fpregs.fp_fop;
    238 		fpstate.rip = fpregs.fp_rip;
    239 		fpstate.rdp = fpregs.fp_rdp;
    240 		fpstate.mxcsr = fpregs.fp_mxcsr;
    241 		fpstate.mxcsr_mask = fpregs.fp_mxcsr_mask;
    242 		memcpy(&fpstate.st_space, &fpregs.fp_st,
    243 		    sizeof(fpstate.st_space));
    244 		memcpy(&fpstate.xmm_space, &fpregs.fp_xmm,
    245 		    sizeof(fpstate.xmm_space));
    246 		error = copyout(&fpstate, fpsp, sizeof(fpstate));
    247 	}
    248 
    249 	if (error == 0)
    250 		error = copyout(&sigframe, sp, sizeof(sigframe));
    251 
    252 	mutex_enter(p->p_lock);
    253 
    254 	if (error != 0) {
    255 		sigexit(l, SIGILL);
    256 		return;
    257 	}
    258 
    259 	if ((vaddr_t)catcher >= VM_MAXUSER_ADDRESS) {
    260 		sigexit(l, SIGILL);
    261 		return;
    262 	}
    263 
    264 	linux_buildcontext(l, catcher, sp);
    265 	tf->tf_rdi = sigframe.info.lsi_signo;
    266 	tf->tf_rax = 0;
    267 	tf->tf_rsi = (long)&sfp->info;
    268 	tf->tf_rdx = (long)&sfp->uc;
    269 
    270 	/*
    271 	 * Remember we use signal stack
    272 	 */
    273 	if (onstack)
    274 		l->l_sigstk.ss_flags |= SS_ONSTACK;
    275 	return;
    276 }
    277 
    278 int
    279 linux_sys_modify_ldt(struct lwp *l, const struct linux_sys_modify_ldt_args *v, register_t *retval)
    280 {
    281 	printf("linux_sys_modify_ldt\n");
    282 	return 0;
    283 }
    284 
    285 int
    286 linux_sys_iopl(struct lwp *l, const struct linux_sys_iopl_args *v, register_t *retval)
    287 {
    288 	return 0;
    289 }
    290 
    291 int
    292 linux_sys_ioperm(struct lwp *l, const struct linux_sys_ioperm_args *v, register_t *retval)
    293 {
    294 	return 0;
    295 }
    296 
    297 dev_t
    298 linux_fakedev(dev_t dev, int raw)
    299 {
    300 
    301        extern const struct cdevsw ptc_cdevsw, pts_cdevsw;
    302        const struct cdevsw *cd = cdevsw_lookup(dev);
    303 
    304        if (raw) {
    305 #if (NWSDISPLAY > 0)
    306 	       extern const struct cdevsw wsdisplay_cdevsw;
    307 	       if (cd == &wsdisplay_cdevsw)
    308 		       return makedev(LINUX_CONS_MAJOR, (minor(dev) + 1));
    309 #endif
    310        }
    311 
    312        if (cd == &ptc_cdevsw)
    313 	       return makedev(LINUX_PTC_MAJOR, minor(dev));
    314        if (cd == &pts_cdevsw)
    315 	       return makedev(LINUX_PTS_MAJOR, minor(dev));
    316 
    317 	return ((minor(dev) & 0xff) | ((major(dev) & 0xfff) << 8)
    318 	    | (((unsigned long long int) (minor(dev) & ~0xff)) << 12)
    319 	    | (((unsigned long long int) (major(dev) & ~0xfff)) << 32));
    320 }
    321 
    322 int
    323 linux_machdepioctl(struct lwp *l, const struct linux_sys_ioctl_args *v, register_t *retval)
    324 {
    325 	return 0;
    326 }
    327 
    328 int
    329 linux_sys_rt_sigreturn(struct lwp *l, const void *v, register_t *retval)
    330 {
    331 	struct linux_ucontext *luctx;
    332 	struct trapframe *tf = l->l_md.md_regs;
    333 	struct linux_sigcontext *lsigctx;
    334 	struct linux__fpstate fpstate;
    335 	struct linux_rt_sigframe frame, *fp;
    336 	ucontext_t uctx;
    337 	mcontext_t *mctx;
    338 	struct fxsave64 *fxarea;
    339 	int error;
    340 
    341 	fp = (struct linux_rt_sigframe *)(tf->tf_rsp - 8);
    342 	if ((error = copyin(fp, &frame, sizeof(frame))) != 0) {
    343 		mutex_enter(l->l_proc->p_lock);
    344 		sigexit(l, SIGILL);
    345 		return error;
    346 	}
    347 	luctx = &frame.uc;
    348 	lsigctx = &luctx->luc_mcontext;
    349 
    350 	memset(&uctx, 0, sizeof(uctx));
    351 	mctx = (mcontext_t *)&uctx.uc_mcontext;
    352 	fxarea = (struct fxsave64 *)&mctx->__fpregs;
    353 
    354 	/*
    355 	 * Set the flags. Linux always have CPU, stack and signal state,
    356 	 * FPU is optional. uc_flags is not used to tell what we have.
    357 	 */
    358 	uctx.uc_flags = (_UC_SIGMASK|_UC_CPU|_UC_STACK|_UC_CLRSTACK);
    359 	if (lsigctx->fpstate != NULL)
    360 		uctx.uc_flags |= _UC_FPU;
    361 	uctx.uc_link = NULL;
    362 
    363 	/*
    364 	 * Signal set
    365 	 */
    366 	linux_to_native_sigset(&uctx.uc_sigmask, &luctx->luc_sigmask);
    367 
    368 	/*
    369 	 * CPU state
    370 	 */
    371 	mctx->__gregs[_REG_R8] = lsigctx->r8;
    372 	mctx->__gregs[_REG_R9] = lsigctx->r9;
    373 	mctx->__gregs[_REG_R10] = lsigctx->r10;
    374 	mctx->__gregs[_REG_R11] = lsigctx->r11;
    375 	mctx->__gregs[_REG_R12] = lsigctx->r12;
    376 	mctx->__gregs[_REG_R13] = lsigctx->r13;
    377 	mctx->__gregs[_REG_R14] = lsigctx->r14;
    378 	mctx->__gregs[_REG_R15] = lsigctx->r15;
    379 	mctx->__gregs[_REG_RDI] = lsigctx->rdi;
    380 	mctx->__gregs[_REG_RSI] = lsigctx->rsi;
    381 	mctx->__gregs[_REG_RBP] = lsigctx->rbp;
    382 	mctx->__gregs[_REG_RBX] = lsigctx->rbx;
    383 	mctx->__gregs[_REG_RAX] = lsigctx->rax;
    384 	mctx->__gregs[_REG_RDX] = lsigctx->rdx;
    385 	mctx->__gregs[_REG_RCX] = lsigctx->rcx;
    386 	mctx->__gregs[_REG_RIP] = lsigctx->rip;
    387 	mctx->__gregs[_REG_RFLAGS] = lsigctx->eflags;
    388 	mctx->__gregs[_REG_CS] = lsigctx->cs;
    389 	mctx->__gregs[_REG_GS] = lsigctx->gs;
    390 	mctx->__gregs[_REG_FS] = lsigctx->fs;
    391 	mctx->__gregs[_REG_ERR] = lsigctx->err;
    392 	mctx->__gregs[_REG_TRAPNO] = lsigctx->trapno;
    393 	mctx->__gregs[_REG_ES] = tf->tf_es;
    394 	mctx->__gregs[_REG_DS] = tf->tf_ds;
    395 	mctx->__gregs[_REG_RSP] = lsigctx->rsp; /* XXX */
    396 	mctx->__gregs[_REG_SS] = tf->tf_ss;
    397 
    398 	/*
    399 	 * FPU state
    400 	 */
    401 	if (lsigctx->fpstate != NULL) {
    402 		error = copyin(lsigctx->fpstate, &fpstate, sizeof(fpstate));
    403 		if (error != 0) {
    404 			mutex_enter(l->l_proc->p_lock);
    405 			sigexit(l, SIGILL);
    406 			return error;
    407 		}
    408 
    409 		fxarea->fx_fcw = fpstate.cwd;
    410 		fxarea->fx_fsw = fpstate.swd;
    411 		fxarea->fx_ftw = fpstate.twd;
    412 		fxarea->fx_fop = fpstate.fop;
    413 		fxarea->fx_rip = fpstate.rip;
    414 		fxarea->fx_rdp = fpstate.rdp;
    415 		fxarea->fx_mxcsr = fpstate.mxcsr;
    416 		fxarea->fx_mxcsr_mask = fpstate.mxcsr_mask;
    417 		memcpy(&fxarea->fx_st, &fpstate.st_space,
    418 		    sizeof(fxarea->fx_st));
    419 		memcpy(&fxarea->fx_xmm, &fpstate.xmm_space,
    420 		    sizeof(fxarea->fx_xmm));
    421 	}
    422 
    423 	/*
    424 	 * And the stack
    425 	 */
    426 	uctx.uc_stack.ss_flags = 0;
    427 	if (luctx->luc_stack.ss_flags & LINUX_SS_ONSTACK)
    428 		uctx.uc_stack.ss_flags |= SS_ONSTACK;
    429 
    430 	if (luctx->luc_stack.ss_flags & LINUX_SS_DISABLE)
    431 		uctx.uc_stack.ss_flags |= SS_DISABLE;
    432 
    433 	uctx.uc_stack.ss_sp = luctx->luc_stack.ss_sp;
    434 	uctx.uc_stack.ss_size = luctx->luc_stack.ss_size;
    435 
    436 	/*
    437 	 * And let setucontext deal with that.
    438 	 */
    439 	mutex_enter(l->l_proc->p_lock);
    440 	error = setucontext(l, &uctx);
    441 	mutex_exit(l->l_proc->p_lock);
    442 	if (error)
    443 		return error;
    444 
    445 	return EJUSTRETURN;
    446 }
    447 
    448 int
    449 linux_sys_arch_prctl(struct lwp *l,
    450     const struct linux_sys_arch_prctl_args *uap, register_t *retval)
    451 {
    452 	/* {
    453 		syscallarg(int) code;
    454 		syscallarg(unsigned long) addr;
    455 	} */
    456 	void *addr = (void *)SCARG(uap, addr);
    457 
    458 	switch(SCARG(uap, code)) {
    459 	case LINUX_ARCH_SET_GS:
    460 		return x86_set_sdbase(addr, 'g', l, true);
    461 
    462 	case LINUX_ARCH_GET_GS:
    463 		return x86_get_sdbase(addr, 'g');
    464 
    465 	case LINUX_ARCH_SET_FS:
    466 		return x86_set_sdbase(addr, 'f', l, true);
    467 
    468 	case LINUX_ARCH_GET_FS:
    469 		return x86_get_sdbase(addr, 'f');
    470 
    471 	default:
    472 #ifdef DEBUG_LINUX
    473 		printf("linux_sys_arch_prctl: unexpected code %d\n",
    474 		    SCARG(uap, code));
    475 #endif
    476 		return EINVAL;
    477 	}
    478 	/* NOTREACHED */
    479 }
    480 
    481 const int linux_vsyscall_to_syscall[] = {
    482 	LINUX_SYS_gettimeofday,
    483 	LINUX_SYS_time,
    484 	LINUX_SYS_nosys,	/* nosys */
    485 	LINUX_SYS_nosys,	/* nosys */
    486 };
    487 
    488 int
    489 linux_usertrap(struct lwp *l, vaddr_t trapaddr, void *arg)
    490 {
    491 	struct trapframe *tf = arg;
    492 	uint64_t retaddr;
    493 	size_t vsyscallnr;
    494 
    495 	/*
    496 	 * Check for a vsyscall. %rip must be the fault address,
    497 	 * and the address must be in the Linux vsyscall area.
    498 	 * Also, vsyscalls are only done at 1024-byte boundaries.
    499 	 */
    500 
    501 	if (__predict_true(trapaddr < LINUX_VSYSCALL_START))
    502 		return 0;
    503 
    504 	if (trapaddr != tf->tf_rip)
    505 		return 0;
    506 
    507 	if ((tf->tf_rip & (LINUX_VSYSCALL_SIZE - 1)) != 0)
    508 		return 0;
    509 
    510 	vsyscallnr = (tf->tf_rip - LINUX_VSYSCALL_START) / LINUX_VSYSCALL_SIZE;
    511 
    512 	if (vsyscallnr > LINUX_VSYSCALL_MAXNR)
    513 		return 0;
    514 
    515 	/*
    516 	 * Get the return address from the top of the stack,
    517 	 * and fix up the return address.
    518 	 * This assumes the faulting instruction was callq *reg,
    519 	 * which is the only way that vsyscalls are ever entered.
    520 	 */
    521 	if (copyin((void *)tf->tf_rsp, &retaddr, sizeof retaddr) != 0)
    522 		return 0;
    523 	if ((vaddr_t)retaddr >= VM_MAXUSER_ADDRESS)
    524 		return 0;
    525 	tf->tf_rip = retaddr;
    526 	tf->tf_rax = linux_vsyscall_to_syscall[vsyscallnr];
    527 	tf->tf_rsp += 8;	/* "pop" the return address */
    528 
    529 #if 0
    530 	printf("usertrap: rip %p rsp %p retaddr %p vsys %d sys %d\n",
    531 	    (void *)tf->tf_rip, (void *)tf->tf_rsp, (void *)retaddr,
    532 	    vsyscallnr, (int)tf->tf_rax);
    533 #endif
    534 
    535 	(*l->l_proc->p_md.md_syscall)(tf);
    536 
    537 	return 1;
    538 }
    539 
    540 static void
    541 linux_buildcontext(struct lwp *l, void *catcher, void *f)
    542 {
    543 	struct trapframe *tf = l->l_md.md_regs;
    544 
    545 	tf->tf_ds = GSEL(GUDATA_SEL, SEL_UPL);
    546 	tf->tf_rip = (u_int64_t)catcher;
    547 	tf->tf_cs = GSEL(GUCODE_SEL, SEL_UPL);
    548 	tf->tf_rflags &= ~PSL_CLEARSIG;
    549 	tf->tf_rsp = (u_int64_t)f;
    550 	tf->tf_ss = GSEL(GUDATA_SEL, SEL_UPL);
    551 }
    552