arch/parisc/kernel/signal.c

   1 /*
   2  *  linux/arch/parisc/kernel/signal.c: Architecture-specific signal
   3  *  handling support.
   4  *
   5  *  Copyright (C) 2000 David Huggins-Daines <dhd@debian.org>
   6  *  Copyright (C) 2000 Linuxcare, Inc.
   7  *
   8  *  Based on the ia64, i386, and alpha versions.
   9  *
  10  *  Like the IA-64, we are a recent enough port (we are *starting*
  11  *  with glibc2.2) that we do not need to support the old non-realtime
  12  *  Linux signals.  Therefore we don't.  HP/UX signals will go in
  13  *  arch/parisc/hpux/signal.c when we figure out how to do them.
  14  */
  15
  16 #include <linux/sched.h>
  17 #include <linux/mm.h>
  18 #include <linux/smp.h>
  19 #include <linux/kernel.h>
  20 #include <linux/signal.h>
  21 #include <linux/errno.h>
  22 #include <linux/wait.h>
  23 #include <linux/ptrace.h>
  24 #include <linux/tracehook.h>
  25 #include <linux/unistd.h>
  26 #include <linux/stddef.h>
  27 #include <linux/compat.h>
  28 #include <linux/elf.h>
  29 #include <asm/ucontext.h>
  30 #include <asm/rt_sigframe.h>
  31 #include <asm/uaccess.h>
  32 #include <asm/pgalloc.h>
  33 #include <asm/cacheflush.h>
  34 #include <asm/asm-offsets.h>
  35
  36 #ifdef CONFIG_COMPAT
  37 #include "signal32.h"
  38 #endif
  39
  40 #define DEBUG_SIG 0
  41 #define DEBUG_SIG_LEVEL 2
  42
  43 #if DEBUG_SIG
  44 #define DBG(LEVEL, ...) \
  45         ((DEBUG_SIG_LEVEL >= LEVEL) \
  46         ? printk(__VA_ARGS__) : (void) 0)
  47 #else
  48 #define DBG(LEVEL, ...)
  49 #endif
  50
  51 /* gcc will complain if a pointer is cast to an integer of different
  52  * size.  If you really need to do this (and we do for an ELF32 user
  53  * application in an ELF64 kernel) then you have to do a cast to an
  54  * integer of the same size first.  The A() macro accomplishes
  55  * this. */
  56 #define A(__x)  ((unsigned long)(__x))
  57
  58 /*
  59  * Atomically swap in the new signal mask, and wait for a signal.
  60  */
  61 #ifdef CONFIG_64BIT
  62 #include "sys32.h"
  63 #endif
  64
  65 /*
  66  * Do a signal return - restore sigcontext.
  67  */
  68
  69 /* Trampoline for calling rt_sigreturn() */
  70 #define INSN_LDI_R25_0   0x34190000 /* ldi  0,%r25 (in_syscall=0) */
  71 #define INSN_LDI_R25_1   0x34190002 /* ldi  1,%r25 (in_syscall=1) */
  72 #define INSN_LDI_R20     0x3414015a /* ldi  __NR_rt_sigreturn,%r20 */
  73 #define INSN_BLE_SR2_R0  0xe4008200 /* be,l 0x100(%sr2,%r0),%sr0,%r31 */
  74 #define INSN_NOP         0x08000240 /* nop */
  75 /* For debugging */
  76 #define INSN_DIE_HORRIBLY 0x68000ccc /* stw %r0,0x666(%sr0,%r0) */
  77
  78 static long
  79 restore_sigcontext(struct sigcontext __user *sc, struct pt_regs *regs)
  80 {
  81         long err = 0;
  82
  83         err |= __copy_from_user(regs->gr, sc->sc_gr, sizeof(regs->gr));
  84         err |= __copy_from_user(regs->fr, sc->sc_fr, sizeof(regs->fr));
  85         err |= __copy_from_user(regs->iaoq, sc->sc_iaoq, sizeof(regs->iaoq));
  86         err |= __copy_from_user(regs->iasq, sc->sc_iasq, sizeof(regs->iasq));
  87         err |= __get_user(regs->sar, &sc->sc_sar);
  88         DBG(2,"restore_sigcontext: iaoq is 0x%#lx / 0x%#lx\n",
  89                         regs->iaoq[0],regs->iaoq[1]);
  90         DBG(2,"restore_sigcontext: r28 is %ld\n", regs->gr[28]);
  91         return err;
  92 }
  93
  94 void
  95 sys_rt_sigreturn(struct pt_regs *regs, int in_syscall)
  96 {
  97         struct rt_sigframe __user *frame;
  98         sigset_t set;
  99         unsigned long usp = (regs->gr[30] & ~(0x01UL));
 100         unsigned long sigframe_size = PARISC_RT_SIGFRAME_SIZE;
 101 #ifdef CONFIG_64BIT
 102         compat_sigset_t compat_set;
 103         struct compat_rt_sigframe __user * compat_frame;
 104
 105         if (is_compat_task())
 106                 sigframe_size = PARISC_RT_SIGFRAME_SIZE32;
 107 #endif
 108
 109         current_thread_info()->restart_block.fn = do_no_restart_syscall;
 110
 111         /* Unwind the user stack to get the rt_sigframe structure. */
 112         frame = (struct rt_sigframe __user *)
 113                 (usp - sigframe_size);
 114         DBG(2,"sys_rt_sigreturn: frame is %p\n", frame);
 115
 116         regs->orig_r28 = 1; /* no restarts for sigreturn */
 117
 118 #ifdef CONFIG_64BIT
 119         compat_frame = (struct compat_rt_sigframe __user *)frame;
 120
 121         if (is_compat_task()) {
 122                 DBG(2,"sys_rt_sigreturn: ELF32 process.\n");
 123                 if (__copy_from_user(&compat_set, &compat_frame->uc.uc_sigmask, sizeof(compat_set)))
 124                         goto give_sigsegv;
 125                 sigset_32to64(&set,&compat_set);
 126         } else
 127 #endif
 128         {
 129                 if (__copy_from_user(&set, &frame->uc.uc_sigmask, sizeof(set)))
 130                         goto give_sigsegv;
 131         }
 132
 133         set_current_blocked(&set);
 134
 135         /* Good thing we saved the old gr[30], eh? */
 136 #ifdef CONFIG_64BIT
 137         if (is_compat_task()) {
 138                 DBG(1,"sys_rt_sigreturn: compat_frame->uc.uc_mcontext 0x%p\n",
 139                                 &compat_frame->uc.uc_mcontext);
 140 // FIXME: Load upper half from register file
 141                 if (restore_sigcontext32(&compat_frame->uc.uc_mcontext,
 142                                         &compat_frame->regs, regs))
 143                         goto give_sigsegv;
 144                 DBG(1,"sys_rt_sigreturn: usp %#08lx stack 0x%p\n",
 145                                 usp, &compat_frame->uc.uc_stack);
 146                 if (compat_restore_altstack(&compat_frame->uc.uc_stack))
 147                         goto give_sigsegv;
 148         } else
 149 #endif
 150         {
 151                 DBG(1,"sys_rt_sigreturn: frame->uc.uc_mcontext 0x%p\n",
 152                                 &frame->uc.uc_mcontext);
 153                 if (restore_sigcontext(&frame->uc.uc_mcontext, regs))
 154                         goto give_sigsegv;
 155                 DBG(1,"sys_rt_sigreturn: usp %#08lx stack 0x%p\n",
 156                                 usp, &frame->uc.uc_stack);
 157                 if (restore_altstack(&frame->uc.uc_stack))
 158                         goto give_sigsegv;
 159         }
 160
 161
 162
 163         /* If we are on the syscall path IAOQ will not be restored, and
 164          * if we are on the interrupt path we must not corrupt gr31.
 165          */
 166         if (in_syscall)
 167                 regs->gr[31] = regs->iaoq[0];
 168 #if DEBUG_SIG
 169         DBG(1,"sys_rt_sigreturn: returning to %#lx, DUMPING REGS:\n", regs->iaoq[0]);
 170         show_regs(regs);
 171 #endif
 172         return;
 173
 174 give_sigsegv:
 175         DBG(1,"sys_rt_sigreturn: Sending SIGSEGV\n");
 176         force_sig(SIGSEGV, current);
 177         return;
 178 }
 179
 180 /*
 181  * Set up a signal frame.
 182  */
 183
 184 static inline void __user *
 185 get_sigframe(struct k_sigaction *ka, unsigned long sp, size_t frame_size)
 186 {
 187         /*FIXME: ELF32 vs. ELF64 has different frame_size, but since we
 188           don't use the parameter it doesn't matter */
 189
 190         DBG(1,"get_sigframe: ka = %#lx, sp = %#lx, frame_size = %#lx\n",
 191                         (unsigned long)ka, sp, frame_size);
 192
 193         /* Align alternate stack and reserve 64 bytes for the signal
 194            handler's frame marker.  */
 195         if ((ka->sa.sa_flags & SA_ONSTACK) != 0 && ! sas_ss_flags(sp))
 196                 sp = (current->sas_ss_sp + 0x7f) & ~0x3f; /* Stacks grow up! */
 197
 198         DBG(1,"get_sigframe: Returning sp = %#lx\n", (unsigned long)sp);
 199         return (void __user *) sp; /* Stacks grow up.  Fun. */
 200 }
 201
 202 static long
 203 setup_sigcontext(struct sigcontext __user *sc, struct pt_regs *regs, int in_syscall)
 204
 205 {
 206         unsigned long flags = 0;
 207         long err = 0;
 208
 209         if (on_sig_stack((unsigned long) sc))
 210                 flags |= PARISC_SC_FLAG_ONSTACK;
 211         if (in_syscall) {
 212                 flags |= PARISC_SC_FLAG_IN_SYSCALL;
 213                 /* regs->iaoq is undefined in the syscall return path */
 214                 err |= __put_user(regs->gr[31], &sc->sc_iaoq[0]);
 215                 err |= __put_user(regs->gr[31]+4, &sc->sc_iaoq[1]);
 216                 err |= __put_user(regs->sr[3], &sc->sc_iasq[0]);
 217                 err |= __put_user(regs->sr[3], &sc->sc_iasq[1]);
 218                 DBG(1,"setup_sigcontext: iaoq %#lx / %#lx (in syscall)\n",
 219                         regs->gr[31], regs->gr[31]+4);
 220         } else {
 221                 err |= __copy_to_user(sc->sc_iaoq, regs->iaoq, sizeof(regs->iaoq));
 222                 err |= __copy_to_user(sc->sc_iasq, regs->iasq, sizeof(regs->iasq));
 223                 DBG(1,"setup_sigcontext: iaoq %#lx / %#lx (not in syscall)\n",
 224                         regs->iaoq[0], regs->iaoq[1]);
 225         }
 226
 227         err |= __put_user(flags, &sc->sc_flags);
 228         err |= __copy_to_user(sc->sc_gr, regs->gr, sizeof(regs->gr));
 229         err |= __copy_to_user(sc->sc_fr, regs->fr, sizeof(regs->fr));
 230         err |= __put_user(regs->sar, &sc->sc_sar);
 231         DBG(1,"setup_sigcontext: r28 is %ld\n", regs->gr[28]);
 232
 233         return err;
 234 }
 235
 236 static long
 237 setup_rt_frame(int sig, struct k_sigaction *ka, siginfo_t *info,
 238                sigset_t *set, struct pt_regs *regs, int in_syscall)
 239 {
 240         struct rt_sigframe __user *frame;
 241         unsigned long rp, usp;
 242         unsigned long haddr, sigframe_size;
 243         int err = 0;
 244 #ifdef CONFIG_64BIT
 245         struct compat_rt_sigframe __user * compat_frame;
 246         compat_sigset_t compat_set;
 247 #endif
 248
 249         usp = (regs->gr[30] & ~(0x01UL));
 250         /*FIXME: frame_size parameter is unused, remove it. */
 251         frame = get_sigframe(ka, usp, sizeof(*frame));
 252
 253         DBG(1,"SETUP_RT_FRAME: START\n");
 254         DBG(1,"setup_rt_frame: frame %p info %p\n", frame, info);
 255
 256
 257 #ifdef CONFIG_64BIT
 258
 259         compat_frame = (struct compat_rt_sigframe __user *)frame;
 260
 261         if (is_compat_task()) {
 262                 DBG(1,"setup_rt_frame: frame->info = 0x%p\n", &compat_frame->info);
 263                 err |= copy_siginfo_to_user32(&compat_frame->info, info);
 264                 err |= __compat_save_altstack( &compat_frame->uc.uc_stack, regs->gr[30]);
 265                 DBG(1,"setup_rt_frame: frame->uc = 0x%p\n", &compat_frame->uc);
 266                 DBG(1,"setup_rt_frame: frame->uc.uc_mcontext = 0x%p\n", &compat_frame->uc.uc_mcontext);
 267                 err |= setup_sigcontext32(&compat_frame->uc.uc_mcontext,
 268                                         &compat_frame->regs, regs, in_syscall);
 269                 sigset_64to32(&compat_set,set);
 270                 err |= __copy_to_user(&compat_frame->uc.uc_sigmask, &compat_set, sizeof(compat_set));
 271         } else
 272 #endif
 273         {
 274                 DBG(1,"setup_rt_frame: frame->info = 0x%p\n", &frame->info);
 275                 err |= copy_siginfo_to_user(&frame->info, info);
 276                 err |= __save_altstack(&frame->uc.uc_stack, regs->gr[30]);
 277                 DBG(1,"setup_rt_frame: frame->uc = 0x%p\n", &frame->uc);
 278                 DBG(1,"setup_rt_frame: frame->uc.uc_mcontext = 0x%p\n", &frame->uc.uc_mcontext);
 279                 err |= setup_sigcontext(&frame->uc.uc_mcontext, regs, in_syscall);
 280                 /* FIXME: Should probably be converted as well for the compat case */
 281                 err |= __copy_to_user(&frame->uc.uc_sigmask, set, sizeof(*set));
 282         }
 283
 284         if (err)
 285                 goto give_sigsegv;
 286
 287         /* Set up to return from userspace.  If provided, use a stub
 288            already in userspace. The first words of tramp are used to
 289            save the previous sigrestartblock trampoline that might be
 290            on the stack. We start the sigreturn trampoline at
 291            SIGRESTARTBLOCK_TRAMP+X. */
 292         err |= __put_user(in_syscall ? INSN_LDI_R25_1 : INSN_LDI_R25_0,
 293                         &frame->tramp[SIGRESTARTBLOCK_TRAMP+0]);
 294         err |= __put_user(INSN_LDI_R20,
 295                         &frame->tramp[SIGRESTARTBLOCK_TRAMP+1]);
 296         err |= __put_user(INSN_BLE_SR2_R0,
 297                         &frame->tramp[SIGRESTARTBLOCK_TRAMP+2]);
 298         err |= __put_user(INSN_NOP, &frame->tramp[SIGRESTARTBLOCK_TRAMP+3]);
 299
 300 #if DEBUG_SIG
 301         /* Assert that we're flushing in the correct space... */
 302         {
 303                 unsigned long sid;
 304                 asm ("mfsp %%sr3,%0" : "=r" (sid));
 305                 DBG(1,"setup_rt_frame: Flushing 64 bytes at space %#x offset %p\n",
 306                        sid, frame->tramp);
 307         }
 308 #endif
 309
 310         flush_user_dcache_range((unsigned long) &frame->tramp[0],
 311                            (unsigned long) &frame->tramp[TRAMP_SIZE]);
 312         flush_user_icache_range((unsigned long) &frame->tramp[0],
 313                            (unsigned long) &frame->tramp[TRAMP_SIZE]);
 314
 315         /* TRAMP Words 0-4, Length 5 = SIGRESTARTBLOCK_TRAMP
 316          * TRAMP Words 5-9, Length 4 = SIGRETURN_TRAMP
 317          * So the SIGRETURN_TRAMP is at the end of SIGRESTARTBLOCK_TRAMP
 318          */
 319         rp = (unsigned long) &frame->tramp[SIGRESTARTBLOCK_TRAMP];
 320
 321         if (err)
 322                 goto give_sigsegv;
 323
 324         haddr = A(ka->sa.sa_handler);
 325         /* The sa_handler may be a pointer to a function descriptor */
 326 #ifdef CONFIG_64BIT
 327         if (is_compat_task()) {
 328 #endif
 329                 if (haddr & PA_PLABEL_FDESC) {
 330                         Elf32_Fdesc fdesc;
 331                         Elf32_Fdesc __user *ufdesc = (Elf32_Fdesc __user *)A(haddr & ~3);
 332
 333                         err = __copy_from_user(&fdesc, ufdesc, sizeof(fdesc));
 334
 335                         if (err)
 336                                 goto give_sigsegv;
 337
 338                         haddr = fdesc.addr;
 339                         regs->gr[19] = fdesc.gp;
 340                 }
 341 #ifdef CONFIG_64BIT
 342         } else {
 343                 Elf64_Fdesc fdesc;
 344                 Elf64_Fdesc __user *ufdesc = (Elf64_Fdesc __user *)A(haddr & ~3);
 345
 346                 err = __copy_from_user(&fdesc, ufdesc, sizeof(fdesc));
 347
 348                 if (err)
 349                         goto give_sigsegv;
 350
 351                 haddr = fdesc.addr;
 352                 regs->gr[19] = fdesc.gp;
 353                 DBG(1,"setup_rt_frame: 64 bit signal, exe=%#lx, r19=%#lx, in_syscall=%d\n",
 354                      haddr, regs->gr[19], in_syscall);
 355         }
 356 #endif
 357
 358         /* The syscall return path will create IAOQ values from r31.
 359          */
 360         sigframe_size = PARISC_RT_SIGFRAME_SIZE;
 361 #ifdef CONFIG_64BIT
 362         if (is_compat_task())
 363                 sigframe_size = PARISC_RT_SIGFRAME_SIZE32;
 364 #endif
 365         if (in_syscall) {
 366                 regs->gr[31] = haddr;
 367 #ifdef CONFIG_64BIT
 368                 if (!test_thread_flag(TIF_32BIT))
 369                         sigframe_size |= 1;
 370 #endif
 371         } else {
 372                 unsigned long psw = USER_PSW;
 373 #ifdef CONFIG_64BIT
 374                 if (!test_thread_flag(TIF_32BIT))
 375                         psw |= PSW_W;
 376 #endif
 377
 378                 /* If we are singlestepping, arrange a trap to be delivered
 379                    when we return to userspace. Note the semantics -- we
 380                    should trap before the first insn in the handler is
 381                    executed. Ref:
 382                         http://sources.redhat.com/ml/gdb/2004-11/msg00245.html
 383                  */
 384                 if (pa_psw(current)->r) {
 385                         pa_psw(current)->r = 0;
 386                         psw |= PSW_R;
 387                         mtctl(-1, 0);
 388                 }
 389
 390                 regs->gr[0] = psw;
 391                 regs->iaoq[0] = haddr | 3;
 392                 regs->iaoq[1] = regs->iaoq[0] + 4;
 393         }
 394
 395         regs->gr[2]  = rp;                /* userland return pointer */
 396         regs->gr[26] = sig;               /* signal number */
 397
 398 #ifdef CONFIG_64BIT
 399         if (is_compat_task()) {
 400                 regs->gr[25] = A(&compat_frame->info); /* siginfo pointer */
 401                 regs->gr[24] = A(&compat_frame->uc);   /* ucontext pointer */
 402         } else
 403 #endif
 404         {
 405                 regs->gr[25] = A(&frame->info); /* siginfo pointer */
 406                 regs->gr[24] = A(&frame->uc);   /* ucontext pointer */
 407         }
 408
 409         DBG(1,"setup_rt_frame: making sigreturn frame: %#lx + %#lx = %#lx\n",
 410                regs->gr[30], sigframe_size,
 411                regs->gr[30] + sigframe_size);
 412         /* Raise the user stack pointer to make a proper call frame. */
 413         regs->gr[30] = (A(frame) + sigframe_size);
 414
 415
 416         DBG(1,"setup_rt_frame: sig deliver (%s,%d) frame=0x%p sp=%#lx iaoq=%#lx/%#lx rp=%#lx\n",
 417                current->comm, current->pid, frame, regs->gr[30],
 418                regs->iaoq[0], regs->iaoq[1], rp);
 419
 420         return 1;
 421
 422 give_sigsegv:
 423         DBG(1,"setup_rt_frame: sending SIGSEGV\n");
 424         force_sigsegv(sig, current);
 425         return 0;
 426 }
 427
 428 /*
 429  * OK, we're invoking a handler.
 430  */
 431
 432 static void
 433 handle_signal(unsigned long sig, siginfo_t *info, struct k_sigaction *ka,
 434                 struct pt_regs *regs, int in_syscall)
 435 {
 436         sigset_t *oldset = sigmask_to_save();
 437         DBG(1,"handle_signal: sig=%ld, ka=%p, info=%p, oldset=%p, regs=%p\n",
 438                sig, ka, info, oldset, regs);
 439
 440         /* Set up the stack frame */
 441         if (!setup_rt_frame(sig, ka, info, oldset, regs, in_syscall))
 442                 return;
 443
 444         signal_delivered(sig, info, ka, regs,
 445                 test_thread_flag(TIF_SINGLESTEP) ||
 446                 test_thread_flag(TIF_BLOCKSTEP));
 447
 448         DBG(1,KERN_DEBUG "do_signal: Exit (success), regs->gr[28] = %ld\n",
 449                 regs->gr[28]);
 450 }
 451
 452 static inline void
 453 syscall_restart(struct pt_regs *regs, struct k_sigaction *ka)
 454 {
 455         if (regs->orig_r28)
 456                 return;
 457         regs->orig_r28 = 1; /* no more restarts */
 458         /* Check the return code */
 459         switch (regs->gr[28]) {
 460         case -ERESTART_RESTARTBLOCK:
 461         case -ERESTARTNOHAND:
 462                 DBG(1,"ERESTARTNOHAND: returning -EINTR\n");
 463                 regs->gr[28] = -EINTR;
 464                 break;
 465
 466         case -ERESTARTSYS:
 467                 if (!(ka->sa.sa_flags & SA_RESTART)) {
 468                         DBG(1,"ERESTARTSYS: putting -EINTR\n");
 469                         regs->gr[28] = -EINTR;
 470                         break;
 471                 }
 472                 /* fallthrough */
 473         case -ERESTARTNOINTR:
 474                 /* A syscall is just a branch, so all
 475                  * we have to do is fiddle the return pointer.
 476                  */
 477                 regs->gr[31] -= 8; /* delayed branching */
 478                 break;
 479         }
 480 }
 481
 482 static inline void
 483 insert_restart_trampoline(struct pt_regs *regs)
 484 {
 485         if (regs->orig_r28)
 486                 return;
 487         regs->orig_r28 = 1; /* no more restarts */
 488         switch(regs->gr[28]) {
 489         case -ERESTART_RESTARTBLOCK: {
 490                 /* Restart the system call - no handlers present */
 491                 unsigned int *usp = (unsigned int *)regs->gr[30];
 492
 493                 /* Setup a trampoline to restart the syscall
 494                  * with __NR_restart_syscall
 495                  *
 496                  *  0: <return address (orig r31)>
 497                  *  4: <2nd half for 64-bit>
 498                  *  8: ldw 0(%sp), %r31
 499                  * 12: be 0x100(%sr2, %r0)
 500                  * 16: ldi __NR_restart_syscall, %r20
 501                  */
 502 #ifdef CONFIG_64BIT
 503                 put_user(regs->gr[31] >> 32, &usp[0]);
 504                 put_user(regs->gr[31] & 0xffffffff, &usp[1]);
 505                 put_user(0x0fc010df, &usp[2]);
 506 #else
 507                 put_user(regs->gr[31], &usp[0]);
 508                 put_user(0x0fc0109f, &usp[2]);
 509 #endif
 510                 put_user(0xe0008200, &usp[3]);
 511                 put_user(0x34140000, &usp[4]);
 512
 513                 /* Stack is 64-byte aligned, and we only need
 514                  * to flush 1 cache line.
 515                  * Flushing one cacheline is cheap.
 516                  * "sync" on bigger (> 4 way) boxes is not.
 517                  */
 518                 flush_user_dcache_range(regs->gr[30], regs->gr[30] + 4);
 519                 flush_user_icache_range(regs->gr[30], regs->gr[30] + 4);
 520
 521                 regs->gr[31] = regs->gr[30] + 8;
 522                 return;
 523         }
 524         case -ERESTARTNOHAND:
 525         case -ERESTARTSYS:
 526         case -ERESTARTNOINTR: {
 527                 /* Hooray for delayed branching.  We don't
 528                  * have to restore %r20 (the system call
 529                  * number) because it gets loaded in the delay
 530                  * slot of the branch external instruction.
 531                  */
 532                 regs->gr[31] -= 8;
 533                 return;
 534         }
 535         default:
 536                 break;
 537         }
 538 }
 539
 540 /*
 541  * Note that 'init' is a special process: it doesn't get signals it doesn't
 542  * want to handle. Thus you cannot kill init even with a SIGKILL even by
 543  * mistake.
 544  *
 545  * We need to be able to restore the syscall arguments (r21-r26) to
 546  * restart syscalls.  Thus, the syscall path should save them in the
 547  * pt_regs structure (it's okay to do so since they are caller-save
 548  * registers).  As noted below, the syscall number gets restored for
 549  * us due to the magic of delayed branching.
 550  */
 551 asmlinkage void
 552 do_signal(struct pt_regs *regs, long in_syscall)
 553 {
 554         siginfo_t info;
 555         struct k_sigaction ka;
 556         int signr;
 557
 558         DBG(1,"\ndo_signal: regs=0x%p, sr7 %#lx, in_syscall=%d\n",
 559                regs, regs->sr[7], in_syscall);
 560
 561         signr = get_signal_to_deliver(&info, &ka, regs, NULL);
 562         DBG(3,"do_signal: signr = %d, regs->gr[28] = %ld\n", signr, regs->gr[28]);
 563
 564         if (signr > 0) {
 565                 /* Restart a system call if necessary. */
 566                 if (in_syscall)
 567                         syscall_restart(regs, &ka);
 568
 569                 handle_signal(signr, &info, &ka, regs, in_syscall);
 570                 return;
 571         }
 572
 573         /* Did we come from a system call? */
 574         if (in_syscall)
 575                 insert_restart_trampoline(regs);
 576
 577         DBG(1,"do_signal: Exit (not delivered), regs->gr[28] = %ld\n",
 578                 regs->gr[28]);
 579
 580         restore_saved_sigmask();
 581 }
 582
 583 void do_notify_resume(struct pt_regs *regs, long in_syscall)
 584 {
 585         if (test_thread_flag(TIF_SIGPENDING))
 586                 do_signal(regs, in_syscall);
 587
 588         if (test_thread_flag(TIF_NOTIFY_RESUME)) {
 589                 clear_thread_flag(TIF_NOTIFY_RESUME);
 590                 tracehook_notify_resume(regs);
 591         }
 592 }