arch/xtensa/kernel/signal.c

   1 // TODO coprocessor stuff
   2 /*
   3  *  linux/arch/xtensa/kernel/signal.c
   4  *
   5  *  Copyright (C) 1991, 1992  Linus Torvalds
   6  *  1997-11-28  Modified for POSIX.1b signals by Richard Henderson
   7  *
   8  *  Joe Taylor <joe@tensilica.com>
   9  *  Chris Zankel <chris@zankel.net>
  10  *
  11  *
  12  *
  13  */
  14
  15 #include <xtensa/config/core.h>
  16 #include <xtensa/hal.h>
  17 #include <linux/sched.h>
  18 #include <linux/mm.h>
  19 #include <linux/smp.h>
  20 #include <linux/smp_lock.h>
  21 #include <linux/kernel.h>
  22 #include <linux/signal.h>
  23 #include <linux/errno.h>
  24 #include <linux/wait.h>
  25 #include <linux/ptrace.h>
  26 #include <linux/unistd.h>
  27 #include <linux/stddef.h>
  28 #include <linux/personality.h>
  29 #include <asm/ucontext.h>
  30 #include <asm/uaccess.h>
  31 #include <asm/pgtable.h>
  32 #include <asm/cacheflush.h>
  33
  34 #define DEBUG_SIG  0
  35
  36 #define _BLOCKABLE (~(sigmask(SIGKILL) | sigmask(SIGSTOP)))
  37
  38 asmlinkage long sys_wait4(pid_t pid,unsigned int * stat_addr, int options,
  39                           struct rusage * ru);
  40 asmlinkage int do_signal(struct pt_regs *regs, sigset_t *oldset);
  41
  42 extern struct task_struct *coproc_owners[];
  43
  44
  45 /*
  46  * Atomically swap in the new signal mask, and wait for a signal.
  47  */
  48
  49 int sys_sigsuspend(struct pt_regs *regs)
  50 {
  51         old_sigset_t mask = (old_sigset_t) regs->areg[3];
  52         sigset_t saveset;
  53
  54         mask &= _BLOCKABLE;
  55         spin_lock_irq(&current->sighand->siglock);
  56         saveset = current->blocked;
  57         siginitset(&current->blocked, mask);
  58         recalc_sigpending();
  59         spin_unlock_irq(&current->sighand->siglock);
  60
  61         regs->areg[2] = -EINTR;
  62         while (1) {
  63                 current->state = TASK_INTERRUPTIBLE;
  64                 schedule();
  65                 if (do_signal(regs, &saveset))
  66                         return -EINTR;
  67         }
  68 }
  69
  70 asmlinkage int
  71 sys_rt_sigsuspend(struct pt_regs *regs)
  72 {
  73         sigset_t *unewset = (sigset_t *) regs->areg[4];
  74         size_t sigsetsize = (size_t) regs->areg[3];
  75         sigset_t saveset, newset;
  76         /* XXX: Don't preclude handling different sized sigset_t's.  */
  77         if (sigsetsize != sizeof(sigset_t))
  78                 return -EINVAL;
  79
  80         if (copy_from_user(&newset, unewset, sizeof(newset)))
  81                 return -EFAULT;
  82         sigdelsetmask(&newset, ~_BLOCKABLE);
  83         spin_lock_irq(&current->sighand->siglock);
  84         saveset = current->blocked;
  85         current->blocked = newset;
  86         recalc_sigpending();
  87         spin_unlock_irq(&current->sighand->siglock);
  88
  89         regs->areg[2] = -EINTR;
  90         while (1) {
  91                 current->state = TASK_INTERRUPTIBLE;
  92                 schedule();
  93                 if (do_signal(regs, &saveset))
  94                         return -EINTR;
  95         }
  96 }
  97
  98 asmlinkage int
  99 sys_sigaction(int sig, const struct old_sigaction *act,
 100               struct old_sigaction *oact)
 101 {
 102         struct k_sigaction new_ka, old_ka;
 103         int ret;
 104
 105         if (act) {
 106                 old_sigset_t mask;
 107                 if (verify_area(VERIFY_READ, act, sizeof(*act)) ||
 108                     __get_user(new_ka.sa.sa_handler, &act->sa_handler) ||
 109                     __get_user(new_ka.sa.sa_restorer, &act->sa_restorer))
 110                         return -EFAULT;
 111                 __get_user(new_ka.sa.sa_flags, &act->sa_flags);
 112                 __get_user(mask, &act->sa_mask);
 113                 siginitset(&new_ka.sa.sa_mask, mask);
 114         }
 115
 116         ret = do_sigaction(sig, act ? &new_ka : NULL, oact ? &old_ka : NULL);
 117
 118         if (!ret && oact) {
 119                 if (verify_area(VERIFY_WRITE, oact, sizeof(*oact)) ||
 120                     __put_user(old_ka.sa.sa_handler, &oact->sa_handler) ||
 121                     __put_user(old_ka.sa.sa_restorer, &oact->sa_restorer))
 122                         return -EFAULT;
 123                 __put_user(old_ka.sa.sa_flags, &oact->sa_flags);
 124                 __put_user(old_ka.sa.sa_mask.sig[0], &oact->sa_mask);
 125         }
 126
 127         return ret;
 128 }
 129
 130 asmlinkage int
 131 sys_sigaltstack(struct pt_regs *regs)
 132 {
 133         const stack_t *uss = (stack_t *) regs->areg[4];
 134         stack_t *uoss = (stack_t *) regs->areg[3];
 135
 136         if (regs->depc > 64)
 137                 panic ("Double exception sys_sigreturn\n");
 138
 139
 140         return do_sigaltstack(uss, uoss, regs->areg[1]);
 141 }
 142
 143
 144 /*
 145  * Do a signal return; undo the signal stack.
 146  */
 147
 148 struct sigframe
 149 {
 150         struct sigcontext sc;
 151         struct _cpstate cpstate;
 152         unsigned long extramask[_NSIG_WORDS-1];
 153         unsigned char retcode[6];
 154         unsigned int reserved[4]; /* Reserved area for chaining */
 155         unsigned int window[4]; /* Window of 4 registers for initial context */
 156 };
 157
 158 struct rt_sigframe
 159 {
 160         struct siginfo info;
 161         struct ucontext uc;
 162         struct _cpstate cpstate;
 163         unsigned char retcode[6];
 164         unsigned int reserved[4]; /* Reserved area for chaining */
 165         unsigned int window[4]; /* Window of 4 registers for initial context */
 166 };
 167
 168 extern void release_all_cp (struct task_struct *);
 169
 170
 171 // FIXME restore_cpextra
 172 static inline int
 173 restore_cpextra (struct _cpstate *buf)
 174 {
 175 #if 0
 176         /* The signal handler may have used coprocessors in which
 177          * case they are still enabled.  We disable them to force a
 178          * reloading of the original task's CP state by the lazy
 179          * context-switching mechanisms of CP exception handling.
 180          * Also, we essentially discard any coprocessor state that the
 181          * signal handler created. */
 182
 183         struct task_struct *tsk = current;
 184         release_all_cp(tsk);
 185         return __copy_from_user(tsk->thread.cpextra, buf, XTENSA_CP_EXTRA_SIZE);
 186 #endif
 187         return 0;
 188 }
 189
 190 /* Note: We don't copy double exception 'tregs', we have to finish double exc. first before we return to signal handler! This dbl.exc.handler might cause another double exception, but I think we are fine as the situation is the same as if we had returned to the signal handerl and got an interrupt immediately...
 191  */
 192
 193
 194 static int
 195 restore_sigcontext(struct pt_regs *regs, struct sigcontext *sc)
 196 {
 197         struct thread_struct *thread;
 198         unsigned int err = 0;
 199         unsigned long ps;
 200         struct _cpstate *buf;
 201
 202 #define COPY(x) err |= __get_user(regs->x, &sc->sc_##x)
 203         COPY(pc);
 204         COPY(depc);
 205         COPY(wmask);
 206         COPY(lbeg);
 207         COPY(lend);
 208         COPY(lcount);
 209         COPY(sar);
 210         COPY(windowbase);
 211         COPY(windowstart);
 212 #undef COPY
 213
 214         /* For PS, restore only PS.CALLINC.
 215          * Assume that all other bits are either the same as for the signal
 216          * handler, or the user mode value doesn't matter (e.g. PS.OWB).
 217          */
 218         err |= __get_user(ps, &sc->sc_ps);
 219         regs->ps = (regs->ps & ~XCHAL_PS_CALLINC_MASK)
 220                 | (ps & XCHAL_PS_CALLINC_MASK);
 221
 222         /* Additional corruption checks */
 223
 224         if ((regs->windowbase >= (XCHAL_NUM_AREGS/4))
 225         || ((regs->windowstart & ~((1<<(XCHAL_NUM_AREGS/4)) - 1)) != 0) )
 226                 err = 1;
 227         if ((regs->lcount > 0)
 228         && ((regs->lbeg > TASK_SIZE) || (regs->lend > TASK_SIZE)) )
 229                 err = 1;
 230
 231         /* Restore extended register state.
 232          * See struct thread_struct in processor.h.
 233          */
 234         thread = &current->thread;
 235
 236         err |= __copy_from_user (regs->areg, sc->sc_areg, XCHAL_NUM_AREGS*4);
 237         err |= __get_user(buf, &sc->sc_cpstate);
 238         if (buf) {
 239                 if (verify_area(VERIFY_READ, buf, sizeof(*buf)))
 240                         goto badframe;
 241                 err |= restore_cpextra(buf);
 242         }
 243
 244         regs->syscall = -1;             /* disable syscall checks */
 245         return err;
 246
 247 badframe:
 248         return 1;
 249 }
 250
 251 static inline void
 252 flush_my_cpstate(struct task_struct *tsk)
 253 {
 254         unsigned long flags;
 255         local_irq_save(flags);
 256
 257 #if 0   // FIXME
 258         for (i = 0; i < XCHAL_CP_NUM; i++) {
 259                 if (tsk == coproc_owners[i]) {
 260                         xthal_validate_cp(i);
 261                         xthal_save_cpregs(tsk->thread.cpregs_ptr[i], i);
 262
 263                         /* Invalidate and "disown" the cp to allow
 264                          * callers the chance to reset cp state in the
 265                          * task_struct. */
 266
 267                         xthal_invalidate_cp(i);
 268                         coproc_owners[i] = 0;
 269                 }
 270         }
 271 #endif
 272         local_irq_restore(flags);
 273 }
 274
 275 /* Return codes:
 276         0:  nothing saved
 277         1:  stuff to save, successful
 278        -1:  stuff to save, error happened
 279 */
 280 static int
 281 save_cpextra (struct _cpstate *buf)
 282 {
 283 #if (XCHAL_EXTRA_SA_SIZE == 0) && (XCHAL_CP_NUM == 0)
 284         return 0;
 285 #else
 286
 287         /* FIXME: If a task has never used a coprocessor, there is
 288          * no need to save and restore anything.  Tracking this
 289          * information would allow us to optimize this section.
 290          * Perhaps we can use current->used_math or (current->flags &
 291          * PF_USEDFPU) or define a new field in the thread
 292          * structure. */
 293
 294         /* We flush any live, task-owned cp state to the task_struct,
 295          * then copy it all to the sigframe.  Then we clear all
 296          * cp/extra state in the task_struct, effectively
 297          * clearing/resetting all cp/extra state for the signal
 298          * handler (cp-exception handling will load these new values
 299          * into the cp/extra registers.)  This step is important for
 300          * things like a floating-point cp, where the OS must reset
 301          * the FCR to the default rounding mode. */
 302
 303         int err = 0;
 304         struct task_struct *tsk = current;
 305
 306         flush_my_cpstate(tsk);
 307         /* Note that we just copy everything: 'extra' and 'cp' state together.*/
 308         err |= __copy_to_user(buf, tsk->thread.cp_save, XTENSA_CP_EXTRA_SIZE);
 309         memset(tsk->thread.cp_save, 0, XTENSA_CP_EXTRA_SIZE);
 310
 311 #if (XTENSA_CP_EXTRA_SIZE == 0)
 312 #error Sanity check on memset above, cpextra_size should not be zero.
 313 #endif
 314
 315         return err ? -1 : 1;
 316 #endif
 317 }
 318
 319 static int
 320 setup_sigcontext(struct sigcontext *sc, struct _cpstate *cpstate,
 321                  struct pt_regs *regs, unsigned long mask)
 322 {
 323         struct thread_struct *thread;
 324         int err = 0;
 325
 326 //printk("setup_sigcontext\n");
 327 #define COPY(x) err |= __put_user(regs->x, &sc->sc_##x)
 328         COPY(pc);
 329         COPY(ps);
 330         COPY(depc);
 331         COPY(wmask);
 332         COPY(lbeg);
 333         COPY(lend);
 334         COPY(lcount);
 335         COPY(sar);
 336         COPY(windowbase);
 337         COPY(windowstart);
 338 #undef COPY
 339
 340         /* Save extended register state.
 341          * See struct thread_struct in processor.h.
 342          */
 343         thread = &current->thread;
 344         err |= __copy_to_user (sc->sc_areg, regs->areg, XCHAL_NUM_AREGS * 4);
 345         err |= save_cpextra(cpstate);
 346         err |= __put_user(err ? NULL : cpstate, &sc->sc_cpstate);
 347         /* non-iBCS2 extensions.. */
 348         err |= __put_user(mask, &sc->oldmask);
 349
 350         return err;
 351 }
 352
 353 asmlinkage int sys_sigreturn(struct pt_regs *regs)
 354 {
 355         struct sigframe *frame = (struct sigframe *)regs->areg[1];
 356         sigset_t set;
 357         if (regs->depc > 64)
 358                 panic ("Double exception sys_sigreturn\n");
 359
 360         if (verify_area(VERIFY_READ, frame, sizeof(*frame)))
 361                 goto badframe;
 362
 363         if (__get_user(set.sig[0], &frame->sc.oldmask)
 364             || (_NSIG_WORDS > 1
 365                 && __copy_from_user(&set.sig[1], &frame->extramask,
 366                                     sizeof(frame->extramask))))
 367                 goto badframe;
 368
 369         sigdelsetmask(&set, ~_BLOCKABLE);
 370
 371         spin_lock_irq(&current->sighand->siglock);
 372         current->blocked = set;
 373         recalc_sigpending();
 374         spin_unlock_irq(&current->sighand->siglock);
 375
 376         if (restore_sigcontext(regs, &frame->sc))
 377                 goto badframe;
 378         return regs->areg[2];
 379
 380 badframe:
 381         force_sig(SIGSEGV, current);
 382         return 0;
 383 }
 384
 385 asmlinkage int sys_rt_sigreturn(struct pt_regs *regs)
 386 {
 387         struct rt_sigframe *frame = (struct rt_sigframe *)regs->areg[1];
 388         sigset_t set;
 389         stack_t st;
 390         int ret;
 391         if (regs->depc > 64)
 392         {
 393                 printk("!!!!!!! DEPC !!!!!!!\n");
 394                 return 0;
 395         }
 396
 397         if (verify_area(VERIFY_READ, frame, sizeof(*frame)))
 398                 goto badframe;
 399
 400         if (__copy_from_user(&set, &frame->uc.uc_sigmask, sizeof(set)))
 401                 goto badframe;
 402
 403         sigdelsetmask(&set, ~_BLOCKABLE);
 404         spin_lock_irq(&current->sighand->siglock);
 405         current->blocked = set;
 406         recalc_sigpending();
 407         spin_unlock_irq(&current->sighand->siglock);
 408
 409         if (restore_sigcontext(regs, &frame->uc.uc_mcontext))
 410                 goto badframe;
 411         ret = regs->areg[2];
 412
 413         if (__copy_from_user(&st, &frame->uc.uc_stack, sizeof(st)))
 414                 goto badframe;
 415         /* It is more difficult to avoid calling this function than to
 416            call it and ignore errors.  */
 417         do_sigaltstack(&st, NULL, regs->areg[1]);
 418
 419         return ret;
 420
 421 badframe:
 422         force_sig(SIGSEGV, current);
 423         return 0;
 424 }
 425
 426 /*
 427  * Set up a signal frame.
 428  */
 429
 430 /*
 431  * Determine which stack to use..
 432  */
 433 static inline void *
 434 get_sigframe(struct k_sigaction *ka, unsigned long sp, size_t frame_size)
 435 {
 436         if ((ka->sa.sa_flags & SA_ONSTACK) != 0 && ! on_sig_stack(sp))
 437                 sp = current->sas_ss_sp + current->sas_ss_size;
 438
 439         return (void *)((sp - frame_size) & -16ul);
 440 }
 441
 442 #define USE_SIGRETURN           0
 443 #define USE_RT_SIGRETURN        1
 444
 445 static int
 446 gen_return_code(unsigned char *codemem, unsigned int use_rt_sigreturn)
 447 {
 448         unsigned int retcall;
 449         int err = 0;
 450
 451 #if 0
 452         /* Ignoring SA_RESTORER for now; it's supposed to be obsolete,
 453          * and the xtensa glibc doesn't use it.
 454          */
 455         if (ka->sa.sa_flags & SA_RESTORER) {
 456                 regs->pr = (unsigned long) ka->sa.sa_restorer;
 457         } else
 458 #endif /* 0 */
 459         {
 460
 461 #if (__NR_sigreturn > 255) || (__NR_rt_sigreturn > 255)
 462
 463 /* The 12-bit immediate is really split up within the 24-bit MOVI
 464  * instruction.  As long as the above system call numbers fit within
 465  * 8-bits, the following code works fine. See the Xtensa ISA for
 466  * details.
 467  */
 468
 469 #error Generating the MOVI instruction below breaks!
 470 #endif
 471
 472                 retcall = use_rt_sigreturn ? __NR_rt_sigreturn : __NR_sigreturn;
 473
 474 #ifdef __XTENSA_EB__   /* Big Endian version */
 475                 /* Generate instruction:  MOVI a2, retcall */
 476                 err |= __put_user(0x22, &codemem[0]);
 477                 err |= __put_user(0x0a, &codemem[1]);
 478                 err |= __put_user(retcall, &codemem[2]);
 479                 /* Generate instruction:  SYSCALL */
 480                 err |= __put_user(0x00, &codemem[3]);
 481                 err |= __put_user(0x05, &codemem[4]);
 482                 err |= __put_user(0x00, &codemem[5]);
 483
 484 #elif defined __XTENSA_EL__   /* Little Endian version */
 485                 /* Generate instruction:  MOVI a2, retcall */
 486                 err |= __put_user(0x22, &codemem[0]);
 487                 err |= __put_user(0xa0, &codemem[1]);
 488                 err |= __put_user(retcall, &codemem[2]);
 489                 /* Generate instruction:  SYSCALL */
 490                 err |= __put_user(0x00, &codemem[3]);
 491                 err |= __put_user(0x50, &codemem[4]);
 492                 err |= __put_user(0x00, &codemem[5]);
 493 #else
 494 #error Must use compiler for Xtensa processors.
 495 #endif
 496         }
 497
 498         /* Flush generated code out of the data cache */
 499
 500         if (err == 0)
 501                 __flush_invalidate_cache_range((unsigned long)codemem, 6UL);
 502
 503         return err;
 504 }
 505
 506 static void
 507 set_thread_state(struct pt_regs *regs, void *stack, unsigned char *retaddr,
 508         void *handler, unsigned long arg1, void *arg2, void *arg3)
 509 {
 510         /* Set up registers for signal handler */
 511         start_thread(regs, (unsigned long) handler, (unsigned long) stack);
 512
 513         /* Set up a stack frame for a call4
 514          * Note: PS.CALLINC is set to one by start_thread
 515          */
 516         regs->areg[4] = (((unsigned long) retaddr) & 0x3fffffff) | 0x40000000;
 517         regs->areg[6] = arg1;
 518         regs->areg[7] = (unsigned long) arg2;
 519         regs->areg[8] = (unsigned long) arg3;
 520 }
 521
 522 static void setup_frame(int sig, struct k_sigaction *ka,
 523                         sigset_t *set, struct pt_regs *regs)
 524 {
 525         struct sigframe *frame;
 526         int err = 0;
 527         int signal;
 528
 529         frame = get_sigframe(ka, regs->areg[1], sizeof(*frame));
 530         if (regs->depc > 64)
 531         {
 532                 printk("!!!!!!! DEPC !!!!!!!\n");
 533                 return;
 534         }
 535
 536
 537         if (!access_ok(VERIFY_WRITE, frame, sizeof(*frame)))
 538                 goto give_sigsegv;
 539
 540         signal = current_thread_info()->exec_domain
 541                 && current_thread_info()->exec_domain->signal_invmap
 542                 && sig < 32
 543                 ? current_thread_info()->exec_domain->signal_invmap[sig]
 544                 : sig;
 545
 546         err |= setup_sigcontext(&frame->sc, &frame->cpstate, regs, set->sig[0]);
 547
 548         if (_NSIG_WORDS > 1) {
 549                 err |= __copy_to_user(frame->extramask, &set->sig[1],
 550                                       sizeof(frame->extramask));
 551         }
 552
 553         /* Create sys_sigreturn syscall in stack frame */
 554         err |= gen_return_code(frame->retcode, USE_SIGRETURN);
 555
 556         if (err)
 557                 goto give_sigsegv;
 558
 559         /* Create signal handler execution context.
 560          * Return context not modified until this point.
 561          */
 562         set_thread_state(regs, frame, frame->retcode,
 563                 ka->sa.sa_handler, signal, &frame->sc, NULL);
 564
 565         /* Set access mode to USER_DS.  Nomenclature is outdated, but
 566          * functionality is used in uaccess.h
 567          */
 568         set_fs(USER_DS);
 569
 570
 571 #if DEBUG_SIG
 572         printk("SIG deliver (%s:%d): signal=%d sp=%p pc=%08x\n",
 573                 current->comm, current->pid, signal, frame, regs->pc);
 574 #endif
 575
 576         return;
 577
 578 give_sigsegv:
 579         if (sig == SIGSEGV)
 580                 ka->sa.sa_handler = SIG_DFL;
 581         force_sig(SIGSEGV, current);
 582 }
 583
 584 static void setup_rt_frame(int sig, struct k_sigaction *ka, siginfo_t *info,
 585                            sigset_t *set, struct pt_regs *regs)
 586 {
 587         struct rt_sigframe *frame;
 588         int err = 0;
 589         int signal;
 590
 591         frame = get_sigframe(ka, regs->areg[1], sizeof(*frame));
 592         if (regs->depc > 64)
 593                 panic ("Double exception sys_sigreturn\n");
 594
 595         if (!access_ok(VERIFY_WRITE, frame, sizeof(*frame)))
 596                 goto give_sigsegv;
 597
 598         signal = current_thread_info()->exec_domain
 599                 && current_thread_info()->exec_domain->signal_invmap
 600                 && sig < 32
 601                 ? current_thread_info()->exec_domain->signal_invmap[sig]
 602                 : sig;
 603
 604         err |= copy_siginfo_to_user(&frame->info, info);
 605
 606         /* Create the ucontext.  */
 607         err |= __put_user(0, &frame->uc.uc_flags);
 608         err |= __put_user(0, &frame->uc.uc_link);
 609         err |= __put_user((void *)current->sas_ss_sp,
 610                           &frame->uc.uc_stack.ss_sp);
 611         err |= __put_user(sas_ss_flags(regs->areg[1]),
 612                           &frame->uc.uc_stack.ss_flags);
 613         err |= __put_user(current->sas_ss_size, &frame->uc.uc_stack.ss_size);
 614         err |= setup_sigcontext(&frame->uc.uc_mcontext, &frame->cpstate,
 615                                 regs, set->sig[0]);
 616         err |= __copy_to_user(&frame->uc.uc_sigmask, set, sizeof(*set));
 617
 618         /* Create sys_rt_sigreturn syscall in stack frame */
 619         err |= gen_return_code(frame->retcode, USE_RT_SIGRETURN);
 620
 621         if (err)
 622                 goto give_sigsegv;
 623
 624         /* Create signal handler execution context.
 625          * Return context not modified until this point.
 626          */
 627         set_thread_state(regs, frame, frame->retcode,
 628                 ka->sa.sa_handler, signal, &frame->info, &frame->uc);
 629
 630         /* Set access mode to USER_DS.  Nomenclature is outdated, but
 631          * functionality is used in uaccess.h
 632          */
 633         set_fs(USER_DS);
 634
 635 #if DEBUG_SIG
 636         printk("SIG rt deliver (%s:%d): signal=%d sp=%p pc=%08x\n",
 637                 current->comm, current->pid, signal, frame, regs->pc);
 638 #endif
 639
 640         return;
 641
 642 give_sigsegv:
 643         if (sig == SIGSEGV)
 644                 ka->sa.sa_handler = SIG_DFL;
 645         force_sig(SIGSEGV, current);
 646 }
 647
 648
 649
 650 /*
 651  * Note that 'init' is a special process: it doesn't get signals it doesn't
 652  * want to handle. Thus you cannot kill init even with a SIGKILL even by
 653  * mistake.
 654  *
 655  * Note that we go through the signals twice: once to check the signals that
 656  * the kernel can handle, and then we build all the user-level signal handling
 657  * stack-frames in one go after that.
 658  */
 659 int do_signal(struct pt_regs *regs, sigset_t *oldset)
 660 {
 661         siginfo_t info;
 662         int signr;
 663         struct k_sigaction ka;
 664
 665         if (!oldset)
 666                 oldset = &current->blocked;
 667
 668         signr = get_signal_to_deliver(&info, &ka, regs, NULL);
 669
 670         /* Are we from a system call? */
 671         if (regs->syscall >= 0) {
 672                 /* If so, check system call restarting.. */
 673                 switch (regs->areg[2]) {
 674                         case ERESTARTNOHAND:
 675                         case ERESTART_RESTARTBLOCK:
 676                                 regs->areg[2] = -EINTR;
 677                                 break;
 678
 679                         case ERESTARTSYS:
 680                                 if (!(ka.sa.sa_flags & SA_RESTART)) {
 681                                         regs->areg[2] = -EINTR;
 682                                         break;
 683                                 }
 684                         /* fallthrough */
 685                         case ERESTARTNOINTR:
 686                                 regs->areg[2] = regs->syscall;
 687                                 regs->pc -= 3;
 688                 }
 689         }
 690
 691         if (signr == 0)
 692                 return 0;               /* no signals delivered */
 693
 694         /* Whee!  Actually deliver the signal.  */
 695
 696         /* Set up the stack frame */
 697         if (ka.sa.sa_flags & SA_SIGINFO)
 698                 setup_rt_frame(signr, &ka, &info, oldset, regs);
 699         else
 700                 setup_frame(signr, &ka, oldset, regs);
 701
 702         if (ka.sa.sa_flags & SA_ONESHOT)
 703                 ka.sa.sa_handler = SIG_DFL;
 704
 705         spin_lock_irq(&current->sighand->siglock);
 706         sigorsets(&current->blocked, &current->blocked, &ka.sa.sa_mask);
 707         if (!(ka.sa.sa_flags & SA_NODEFER))
 708                 sigaddset(&current->blocked, signr);
 709         recalc_sigpending();
 710         spin_unlock_irq(&current->sighand->siglock);
 711         return 1;
 712 }