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 <asm/variant/core.h>
  16 #include <asm/coprocessor.h>
  17 #include <linux/sched.h>
  18 #include <linux/mm.h>
  19 #include <linux/smp.h>
  20 #include <linux/kernel.h>
  21 #include <linux/signal.h>
  22 #include <linux/errno.h>
  23 #include <linux/wait.h>
  24 #include <linux/ptrace.h>
  25 #include <linux/unistd.h>
  26 #include <linux/stddef.h>
  27 #include <linux/personality.h>
  28 #include <asm/ucontext.h>
  29 #include <asm/uaccess.h>
  30 #include <asm/pgtable.h>
  31 #include <asm/cacheflush.h>
  32
  33 #define DEBUG_SIG  0
  34
  35 #define _BLOCKABLE (~(sigmask(SIGKILL) | sigmask(SIGSTOP)))
  36
  37 asmlinkage long sys_wait4(pid_t pid,unsigned int * stat_addr, int options,
  38                           struct rusage * ru);
  39 asmlinkage int do_signal(struct pt_regs *regs, sigset_t *oldset);
  40
  41 extern struct task_struct *coproc_owners[];
  42
  43
  44 /*
  45  * Atomically swap in the new signal mask, and wait for a signal.
  46  */
  47
  48 int xtensa_sigsuspend(struct pt_regs *regs)
  49 {
  50         old_sigset_t mask = (old_sigset_t) regs->areg[3];
  51         sigset_t saveset;
  52
  53         mask &= _BLOCKABLE;
  54         spin_lock_irq(&current->sighand->siglock);
  55         saveset = current->blocked;
  56         siginitset(&current->blocked, mask);
  57         recalc_sigpending();
  58         spin_unlock_irq(&current->sighand->siglock);
  59
  60         regs->areg[2] = -EINTR;
  61         while (1) {
  62                 current->state = TASK_INTERRUPTIBLE;
  63                 schedule();
  64                 if (do_signal(regs, &saveset))
  65                         return -EINTR;
  66         }
  67 }
  68
  69 asmlinkage int
  70 xtensa_rt_sigsuspend(struct pt_regs *regs)
  71 {
  72         sigset_t *unewset = (sigset_t *) regs->areg[4];
  73         size_t sigsetsize = (size_t) regs->areg[3];
  74         sigset_t saveset, newset;
  75         /* XXX: Don't preclude handling different sized sigset_t's.  */
  76         if (sigsetsize != sizeof(sigset_t))
  77                 return -EINVAL;
  78
  79         if (copy_from_user(&newset, unewset, sizeof(newset)))
  80                 return -EFAULT;
  81         sigdelsetmask(&newset, ~_BLOCKABLE);
  82         spin_lock_irq(&current->sighand->siglock);
  83         saveset = current->blocked;
  84         current->blocked = newset;
  85         recalc_sigpending();
  86         spin_unlock_irq(&current->sighand->siglock);
  87
  88         regs->areg[2] = -EINTR;
  89         while (1) {
  90                 current->state = TASK_INTERRUPTIBLE;
  91                 schedule();
  92                 if (do_signal(regs, &saveset))
  93                         return -EINTR;
  94         }
  95 }
  96
  97 asmlinkage int
  98 xtensa_sigaction(int sig, const struct old_sigaction *act,
  99               struct old_sigaction *oact)
 100 {
 101         struct k_sigaction new_ka, old_ka;
 102         int ret;
 103
 104         if (act) {
 105                 old_sigset_t mask;
 106                 if (!access_ok(VERIFY_READ, act, sizeof(*act)) ||
 107                     __get_user(new_ka.sa.sa_handler, &act->sa_handler) ||
 108                     __get_user(new_ka.sa.sa_restorer, &act->sa_restorer))
 109                         return -EFAULT;
 110                 __get_user(new_ka.sa.sa_flags, &act->sa_flags);
 111                 __get_user(mask, &act->sa_mask);
 112                 siginitset(&new_ka.sa.sa_mask, mask);
 113         }
 114
 115         ret = do_sigaction(sig, act ? &new_ka : NULL, oact ? &old_ka : NULL);
 116
 117         if (!ret && oact) {
 118                 if (!access_ok(VERIFY_WRITE, oact, sizeof(*oact)) ||
 119                     __put_user(old_ka.sa.sa_handler, &oact->sa_handler) ||
 120                     __put_user(old_ka.sa.sa_restorer, &oact->sa_restorer))
 121                         return -EFAULT;
 122                 __put_user(old_ka.sa.sa_flags, &oact->sa_flags);
 123                 __put_user(old_ka.sa.sa_mask.sig[0], &oact->sa_mask);
 124         }
 125
 126         return ret;
 127 }
 128
 129 asmlinkage int
 130 xtensa_sigaltstack(struct pt_regs *regs)
 131 {
 132         const stack_t *uss = (stack_t *) regs->areg[4];
 133         stack_t *uoss = (stack_t *) regs->areg[3];
 134
 135         if (regs->depc > 64)
 136                 panic ("Double exception sys_sigreturn\n");
 137
 138
 139         return do_sigaltstack(uss, uoss, regs->areg[1]);
 140 }
 141
 142
 143 /*
 144  * Do a signal return; undo the signal stack.
 145  */
 146
 147 struct sigframe
 148 {
 149         struct sigcontext sc;
 150         struct _cpstate cpstate;
 151         unsigned long extramask[_NSIG_WORDS-1];
 152         unsigned char retcode[6];
 153         unsigned int reserved[4]; /* Reserved area for chaining */
 154         unsigned int window[4]; /* Window of 4 registers for initial context */
 155 };
 156
 157 struct rt_sigframe
 158 {
 159         struct siginfo info;
 160         struct ucontext uc;
 161         struct _cpstate cpstate;
 162         unsigned char retcode[6];
 163         unsigned int reserved[4]; /* Reserved area for chaining */
 164         unsigned int window[4]; /* Window of 4 registers for initial context */
 165 };
 166
 167 extern void release_all_cp (struct task_struct *);
 168
 169
 170 // FIXME restore_cpextra
 171 static inline int
 172 restore_cpextra (struct _cpstate *buf)
 173 {
 174 #if 0
 175         /* The signal handler may have used coprocessors in which
 176          * case they are still enabled.  We disable them to force a
 177          * reloading of the original task's CP state by the lazy
 178          * context-switching mechanisms of CP exception handling.
 179          * Also, we essentially discard any coprocessor state that the
 180          * signal handler created. */
 181
 182         struct task_struct *tsk = current;
 183         release_all_cp(tsk);
 184         return __copy_from_user(tsk->thread.cpextra, buf, XTENSA_CP_EXTRA_SIZE);
 185 #endif
 186         return 0;
 187 }
 188
 189 /* 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...
 190  */
 191
 192
 193 static int
 194 restore_sigcontext(struct pt_regs *regs, struct sigcontext *sc)
 195 {
 196         struct thread_struct *thread;
 197         unsigned int err = 0;
 198         unsigned long ps;
 199         struct _cpstate *buf;
 200
 201 #define COPY(x) err |= __get_user(regs->x, &sc->sc_##x)
 202         COPY(pc);
 203         COPY(depc);
 204         COPY(wmask);
 205         COPY(lbeg);
 206         COPY(lend);
 207         COPY(lcount);
 208         COPY(sar);
 209         COPY(windowbase);
 210         COPY(windowstart);
 211 #undef COPY
 212
 213         /* For PS, restore only PS.CALLINC.
 214          * Assume that all other bits are either the same as for the signal
 215          * handler, or the user mode value doesn't matter (e.g. PS.OWB).
 216          */
 217         err |= __get_user(ps, &sc->sc_ps);
 218         regs->ps = (regs->ps & ~PS_CALLINC_MASK)
 219                 | (ps & PS_CALLINC_MASK);
 220
 221         /* Additional corruption checks */
 222
 223         if ((regs->windowbase >= (XCHAL_NUM_AREGS/4))
 224         || ((regs->windowstart & ~((1<<(XCHAL_NUM_AREGS/4)) - 1)) != 0) )
 225                 err = 1;
 226         if ((regs->lcount > 0)
 227         && ((regs->lbeg > TASK_SIZE) || (regs->lend > TASK_SIZE)) )
 228                 err = 1;
 229
 230         /* Restore extended register state.
 231          * See struct thread_struct in processor.h.
 232          */
 233         thread = &current->thread;
 234
 235         err |= __copy_from_user (regs->areg, sc->sc_areg, XCHAL_NUM_AREGS*4);
 236         err |= __get_user(buf, &sc->sc_cpstate);
 237         if (buf) {
 238                 if (!access_ok(VERIFY_READ, buf, sizeof(*buf)))
 239                         goto badframe;
 240                 err |= restore_cpextra(buf);
 241         }
 242
 243         regs->syscall = -1;             /* disable syscall checks */
 244         return err;
 245
 246 badframe:
 247         return 1;
 248 }
 249
 250 static inline void
 251 flush_my_cpstate(struct task_struct *tsk)
 252 {
 253         unsigned long flags;
 254         local_irq_save(flags);
 255
 256 #if 0   // FIXME
 257         for (i = 0; i < XCHAL_CP_NUM; i++) {
 258                 if (tsk == coproc_owners[i]) {
 259                         xthal_validate_cp(i);
 260                         xthal_save_cpregs(tsk->thread.cpregs_ptr[i], i);
 261
 262                         /* Invalidate and "disown" the cp to allow
 263                          * callers the chance to reset cp state in the
 264                          * task_struct. */
 265
 266                         xthal_invalidate_cp(i);
 267                         coproc_owners[i] = 0;
 268                 }
 269         }
 270 #endif
 271         local_irq_restore(flags);
 272 }
 273
 274 /* Return codes:
 275         0:  nothing saved
 276         1:  stuff to save, successful
 277        -1:  stuff to save, error happened
 278 */
 279 static int
 280 save_cpextra (struct _cpstate *buf)
 281 {
 282 #if XCHAL_CP_NUM == 0
 283         return 0;
 284 #else
 285
 286         /* FIXME: If a task has never used a coprocessor, there is
 287          * no need to save and restore anything.  Tracking this
 288          * information would allow us to optimize this section.
 289          * Perhaps we can use current->used_math or (current->flags &
 290          * PF_USEDFPU) or define a new field in the thread
 291          * structure. */
 292
 293         /* We flush any live, task-owned cp state to the task_struct,
 294          * then copy it all to the sigframe.  Then we clear all
 295          * cp/extra state in the task_struct, effectively
 296          * clearing/resetting all cp/extra state for the signal
 297          * handler (cp-exception handling will load these new values
 298          * into the cp/extra registers.)  This step is important for
 299          * things like a floating-point cp, where the OS must reset
 300          * the FCR to the default rounding mode. */
 301
 302         int err = 0;
 303         struct task_struct *tsk = current;
 304
 305         flush_my_cpstate(tsk);
 306         /* Note that we just copy everything: 'extra' and 'cp' state together.*/
 307         err |= __copy_to_user(buf, tsk->thread.cp_save, XTENSA_CP_EXTRA_SIZE);
 308         memset(tsk->thread.cp_save, 0, XTENSA_CP_EXTRA_SIZE);
 309
 310 #if (XTENSA_CP_EXTRA_SIZE == 0)
 311 #error Sanity check on memset above, cpextra_size should not be zero.
 312 #endif
 313
 314         return err ? -1 : 1;
 315 #endif
 316 }
 317
 318 static int
 319 setup_sigcontext(struct sigcontext *sc, struct _cpstate *cpstate,
 320                  struct pt_regs *regs, unsigned long mask)
 321 {
 322         struct thread_struct *thread;
 323         int err = 0;
 324
 325 //printk("setup_sigcontext\n");
 326 #define COPY(x) err |= __put_user(regs->x, &sc->sc_##x)
 327         COPY(pc);
 328         COPY(ps);
 329         COPY(depc);
 330         COPY(wmask);
 331         COPY(lbeg);
 332         COPY(lend);
 333         COPY(lcount);
 334         COPY(sar);
 335         COPY(windowbase);
 336         COPY(windowstart);
 337 #undef COPY
 338
 339         /* Save extended register state.
 340          * See struct thread_struct in processor.h.
 341          */
 342         thread = &current->thread;
 343         err |= __copy_to_user (sc->sc_areg, regs->areg, XCHAL_NUM_AREGS * 4);
 344         err |= save_cpextra(cpstate);
 345         err |= __put_user(err ? NULL : cpstate, &sc->sc_cpstate);
 346         /* non-iBCS2 extensions.. */
 347         err |= __put_user(mask, &sc->oldmask);
 348
 349         return err;
 350 }
 351
 352 asmlinkage int xtensa_sigreturn(struct pt_regs *regs)
 353 {
 354         struct sigframe *frame = (struct sigframe *)regs->areg[1];
 355         sigset_t set;
 356         if (regs->depc > 64)
 357                 panic ("Double exception sys_sigreturn\n");
 358
 359         if (!access_ok(VERIFY_READ, frame, sizeof(*frame)))
 360                 goto badframe;
 361
 362         if (__get_user(set.sig[0], &frame->sc.oldmask)
 363             || (_NSIG_WORDS > 1
 364                 && __copy_from_user(&set.sig[1], &frame->extramask,
 365                                     sizeof(frame->extramask))))
 366                 goto badframe;
 367
 368         sigdelsetmask(&set, ~_BLOCKABLE);
 369
 370         spin_lock_irq(&current->sighand->siglock);
 371         current->blocked = set;
 372         recalc_sigpending();
 373         spin_unlock_irq(&current->sighand->siglock);
 374
 375         if (restore_sigcontext(regs, &frame->sc))
 376                 goto badframe;
 377         return regs->areg[2];
 378
 379 badframe:
 380         force_sig(SIGSEGV, current);
 381         return 0;
 382 }
 383
 384 asmlinkage int xtensa_rt_sigreturn(struct pt_regs *regs)
 385 {
 386         struct rt_sigframe *frame = (struct rt_sigframe *)regs->areg[1];
 387         sigset_t set;
 388         stack_t st;
 389         int ret;
 390         if (regs->depc > 64)
 391         {
 392                 printk("!!!!!!! DEPC !!!!!!!\n");
 393                 return 0;
 394         }
 395
 396         if (!access_ok(VERIFY_READ, frame, sizeof(*frame)))
 397                 goto badframe;
 398
 399         if (__copy_from_user(&set, &frame->uc.uc_sigmask, sizeof(set)))
 400                 goto badframe;
 401
 402         sigdelsetmask(&set, ~_BLOCKABLE);
 403         spin_lock_irq(&current->sighand->siglock);
 404         current->blocked = set;
 405         recalc_sigpending();
 406         spin_unlock_irq(&current->sighand->siglock);
 407
 408         if (restore_sigcontext(regs, &frame->uc.uc_mcontext))
 409                 goto badframe;
 410         ret = regs->areg[2];
 411
 412         if (__copy_from_user(&st, &frame->uc.uc_stack, sizeof(st)))
 413                 goto badframe;
 414         /* It is more difficult to avoid calling this function than to
 415            call it and ignore errors.  */
 416         do_sigaltstack(&st, NULL, regs->areg[1]);
 417
 418         return ret;
 419
 420 badframe:
 421         force_sig(SIGSEGV, current);
 422         return 0;
 423 }
 424
 425 /*
 426  * Set up a signal frame.
 427  */
 428
 429 /*
 430  * Determine which stack to use..
 431  */
 432 static inline void *
 433 get_sigframe(struct k_sigaction *ka, unsigned long sp, size_t frame_size)
 434 {
 435         if ((ka->sa.sa_flags & SA_ONSTACK) != 0 && ! sas_ss_flags(sp))
 436                 sp = current->sas_ss_sp + current->sas_ss_size;
 437
 438         return (void *)((sp - frame_size) & -16ul);
 439 }
 440
 441 #define USE_SIGRETURN           0
 442 #define USE_RT_SIGRETURN        1
 443
 444 static int
 445 gen_return_code(unsigned char *codemem, unsigned int use_rt_sigreturn)
 446 {
 447         unsigned int retcall;
 448         int err = 0;
 449
 450 #if 0
 451         /* Ignoring SA_RESTORER for now; it's supposed to be obsolete,
 452          * and the xtensa glibc doesn't use it.
 453          */
 454         if (ka->sa.sa_flags & SA_RESTORER) {
 455                 regs->pr = (unsigned long) ka->sa.sa_restorer;
 456         } else
 457 #endif /* 0 */
 458         {
 459
 460 #if (__NR_sigreturn > 255) || (__NR_rt_sigreturn > 255)
 461
 462 /* The 12-bit immediate is really split up within the 24-bit MOVI
 463  * instruction.  As long as the above system call numbers fit within
 464  * 8-bits, the following code works fine. See the Xtensa ISA for
 465  * details.
 466  */
 467
 468 #error Generating the MOVI instruction below breaks!
 469 #endif
 470
 471                 retcall = use_rt_sigreturn ? __NR_rt_sigreturn : __NR_sigreturn;
 472
 473 #ifdef __XTENSA_EB__   /* Big Endian version */
 474                 /* Generate instruction:  MOVI a2, retcall */
 475                 err |= __put_user(0x22, &codemem[0]);
 476                 err |= __put_user(0x0a, &codemem[1]);
 477                 err |= __put_user(retcall, &codemem[2]);
 478                 /* Generate instruction:  SYSCALL */
 479                 err |= __put_user(0x00, &codemem[3]);
 480                 err |= __put_user(0x05, &codemem[4]);
 481                 err |= __put_user(0x00, &codemem[5]);
 482
 483 #elif defined __XTENSA_EL__   /* Little Endian version */
 484                 /* Generate instruction:  MOVI a2, retcall */
 485                 err |= __put_user(0x22, &codemem[0]);
 486                 err |= __put_user(0xa0, &codemem[1]);
 487                 err |= __put_user(retcall, &codemem[2]);
 488                 /* Generate instruction:  SYSCALL */
 489                 err |= __put_user(0x00, &codemem[3]);
 490                 err |= __put_user(0x50, &codemem[4]);
 491                 err |= __put_user(0x00, &codemem[5]);
 492 #else
 493 #error Must use compiler for Xtensa processors.
 494 #endif
 495         }
 496
 497         /* Flush generated code out of the data cache */
 498
 499         if (err == 0) {
 500                 __invalidate_icache_range((unsigned long)codemem, 6UL);
 501                 __flush_invalidate_dcache_range((unsigned long)codemem, 6UL);
 502         }
 503
 504         return err;
 505 }
 506
 507 static void
 508 set_thread_state(struct pt_regs *regs, void *stack, unsigned char *retaddr,
 509         void *handler, unsigned long arg1, void *arg2, void *arg3)
 510 {
 511         /* Set up registers for signal handler */
 512         start_thread(regs, (unsigned long) handler, (unsigned long) stack);
 513
 514         /* Set up a stack frame for a call4
 515          * Note: PS.CALLINC is set to one by start_thread
 516          */
 517         regs->areg[4] = (((unsigned long) retaddr) & 0x3fffffff) | 0x40000000;
 518         regs->areg[6] = arg1;
 519         regs->areg[7] = (unsigned long) arg2;
 520         regs->areg[8] = (unsigned long) arg3;
 521 }
 522
 523 static void setup_frame(int sig, struct k_sigaction *ka,
 524                         sigset_t *set, struct pt_regs *regs)
 525 {
 526         struct sigframe *frame;
 527         int err = 0;
 528         int signal;
 529
 530         frame = get_sigframe(ka, regs->areg[1], sizeof(*frame));
 531         if (regs->depc > 64)
 532         {
 533                 printk("!!!!!!! DEPC !!!!!!!\n");
 534                 return;
 535         }
 536
 537
 538         if (!access_ok(VERIFY_WRITE, frame, sizeof(*frame)))
 539                 goto give_sigsegv;
 540
 541         signal = current_thread_info()->exec_domain
 542                 && current_thread_info()->exec_domain->signal_invmap
 543                 && sig < 32
 544                 ? current_thread_info()->exec_domain->signal_invmap[sig]
 545                 : sig;
 546
 547         err |= setup_sigcontext(&frame->sc, &frame->cpstate, regs, set->sig[0]);
 548
 549         if (_NSIG_WORDS > 1) {
 550                 err |= __copy_to_user(frame->extramask, &set->sig[1],
 551                                       sizeof(frame->extramask));
 552         }
 553
 554         /* Create sys_sigreturn syscall in stack frame */
 555         err |= gen_return_code(frame->retcode, USE_SIGRETURN);
 556
 557         if (err)
 558                 goto give_sigsegv;
 559
 560         /* Create signal handler execution context.
 561          * Return context not modified until this point.
 562          */
 563         set_thread_state(regs, frame, frame->retcode,
 564                 ka->sa.sa_handler, signal, &frame->sc, NULL);
 565
 566         /* Set access mode to USER_DS.  Nomenclature is outdated, but
 567          * functionality is used in uaccess.h
 568          */
 569         set_fs(USER_DS);
 570
 571
 572 #if DEBUG_SIG
 573         printk("SIG deliver (%s:%d): signal=%d sp=%p pc=%08x\n",
 574                 current->comm, current->pid, signal, frame, regs->pc);
 575 #endif
 576
 577         return;
 578
 579 give_sigsegv:
 580         if (sig == SIGSEGV)
 581                 ka->sa.sa_handler = SIG_DFL;
 582         force_sig(SIGSEGV, current);
 583 }
 584
 585 static void setup_rt_frame(int sig, struct k_sigaction *ka, siginfo_t *info,
 586                            sigset_t *set, struct pt_regs *regs)
 587 {
 588         struct rt_sigframe *frame;
 589         int err = 0;
 590         int signal;
 591
 592         frame = get_sigframe(ka, regs->areg[1], sizeof(*frame));
 593         if (regs->depc > 64)
 594                 panic ("Double exception sys_sigreturn\n");
 595
 596         if (!access_ok(VERIFY_WRITE, frame, sizeof(*frame)))
 597                 goto give_sigsegv;
 598
 599         signal = current_thread_info()->exec_domain
 600                 && current_thread_info()->exec_domain->signal_invmap
 601                 && sig < 32
 602                 ? current_thread_info()->exec_domain->signal_invmap[sig]
 603                 : sig;
 604
 605         err |= copy_siginfo_to_user(&frame->info, info);
 606
 607         /* Create the ucontext.  */
 608         err |= __put_user(0, &frame->uc.uc_flags);
 609         err |= __put_user(0, &frame->uc.uc_link);
 610         err |= __put_user((void *)current->sas_ss_sp,
 611                           &frame->uc.uc_stack.ss_sp);
 612         err |= __put_user(sas_ss_flags(regs->areg[1]),
 613                           &frame->uc.uc_stack.ss_flags);
 614         err |= __put_user(current->sas_ss_size, &frame->uc.uc_stack.ss_size);
 615         err |= setup_sigcontext(&frame->uc.uc_mcontext, &frame->cpstate,
 616                                 regs, set->sig[0]);
 617         err |= __copy_to_user(&frame->uc.uc_sigmask, set, sizeof(*set));
 618
 619         /* Create sys_rt_sigreturn syscall in stack frame */
 620         err |= gen_return_code(frame->retcode, USE_RT_SIGRETURN);
 621
 622         if (err)
 623                 goto give_sigsegv;
 624
 625         /* Create signal handler execution context.
 626          * Return context not modified until this point.
 627          */
 628         set_thread_state(regs, frame, frame->retcode,
 629                 ka->sa.sa_handler, signal, &frame->info, &frame->uc);
 630
 631         /* Set access mode to USER_DS.  Nomenclature is outdated, but
 632          * functionality is used in uaccess.h
 633          */
 634         set_fs(USER_DS);
 635
 636 #if DEBUG_SIG
 637         printk("SIG rt deliver (%s:%d): signal=%d sp=%p pc=%08x\n",
 638                 current->comm, current->pid, signal, frame, regs->pc);
 639 #endif
 640
 641         return;
 642
 643 give_sigsegv:
 644         if (sig == SIGSEGV)
 645                 ka->sa.sa_handler = SIG_DFL;
 646         force_sig(SIGSEGV, current);
 647 }
 648
 649
 650
 651 /*
 652  * Note that 'init' is a special process: it doesn't get signals it doesn't
 653  * want to handle. Thus you cannot kill init even with a SIGKILL even by
 654  * mistake.
 655  *
 656  * Note that we go through the signals twice: once to check the signals that
 657  * the kernel can handle, and then we build all the user-level signal handling
 658  * stack-frames in one go after that.
 659  */
 660 int do_signal(struct pt_regs *regs, sigset_t *oldset)
 661 {
 662         siginfo_t info;
 663         int signr;
 664         struct k_sigaction ka;
 665
 666         if (!oldset)
 667                 oldset = &current->blocked;
 668
 669         signr = get_signal_to_deliver(&info, &ka, regs, NULL);
 670
 671         /* Are we from a system call? */
 672         if (regs->syscall >= 0) {
 673                 /* If so, check system call restarting.. */
 674                 switch (regs->areg[2]) {
 675                         case ERESTARTNOHAND:
 676                         case ERESTART_RESTARTBLOCK:
 677                                 regs->areg[2] = -EINTR;
 678                                 break;
 679
 680                         case ERESTARTSYS:
 681                                 if (!(ka.sa.sa_flags & SA_RESTART)) {
 682                                         regs->areg[2] = -EINTR;
 683                                         break;
 684                                 }
 685                         /* fallthrough */
 686                         case ERESTARTNOINTR:
 687                                 regs->areg[2] = regs->syscall;
 688                                 regs->pc -= 3;
 689                 }
 690         }
 691
 692         if (signr == 0)
 693                 return 0;               /* no signals delivered */
 694
 695         /* Whee!  Actually deliver the signal.  */
 696
 697         /* Set up the stack frame */
 698         if (ka.sa.sa_flags & SA_SIGINFO)
 699                 setup_rt_frame(signr, &ka, &info, oldset, regs);
 700         else
 701                 setup_frame(signr, &ka, oldset, regs);
 702
 703         if (ka.sa.sa_flags & SA_ONESHOT)
 704                 ka.sa.sa_handler = SIG_DFL;
 705
 706         spin_lock_irq(&current->sighand->siglock);
 707         sigorsets(&current->blocked, &current->blocked, &ka.sa.sa_mask);
 708         if (!(ka.sa.sa_flags & SA_NODEFER))
 709                 sigaddset(&current->blocked, signr);
 710         recalc_sigpending();
 711         spin_unlock_irq(&current->sighand->siglock);
 712         return 1;
 713 }