arch/um/os-Linux/signal.c

   1 /*
   2  * Copyright (C) 2015 Anton Ivanov (aivanov@{brocade.com,kot-begemot.co.uk})
   3  * Copyright (C) 2015 Thomas Meyer (thomas@m3y3r.de)
   4  * Copyright (C) 2004 PathScale, Inc
   5  * Copyright (C) 2004 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
   6  * Licensed under the GPL
   7  */
   8
   9 #include <stdlib.h>
  10 #include <stdarg.h>
  11 #include <errno.h>
  12 #include <signal.h>
  13 #include <strings.h>
  14 #include <as-layout.h>
  15 #include <kern_util.h>
  16 #include <os.h>
  17 #include <sysdep/mcontext.h>
  18
  19 void (*sig_info[NSIG])(int, struct siginfo *, struct uml_pt_regs *) = {
  20         [SIGTRAP]       = relay_signal,
  21         [SIGFPE]        = relay_signal,
  22         [SIGILL]        = relay_signal,
  23         [SIGWINCH]      = winch,
  24         [SIGBUS]        = bus_handler,
  25         [SIGSEGV]       = segv_handler,
  26         [SIGIO]         = sigio_handler,
  27         [SIGALRM]       = timer_handler
  28 };
  29
  30 static void sig_handler_common(int sig, struct siginfo *si, mcontext_t *mc)
  31 {
  32         struct uml_pt_regs *r;
  33         int save_errno = errno;
  34
  35         r = malloc(sizeof(struct uml_pt_regs));
  36         if (!r)
  37                 panic("out of memory");
  38
  39         r->is_user = 0;
  40         if (sig == SIGSEGV) {
  41                 /* For segfaults, we want the data from the sigcontext. */
  42                 get_regs_from_mc(r, mc);
  43                 GET_FAULTINFO_FROM_MC(r->faultinfo, mc);
  44         }
  45
  46         /* enable signals if sig isn't IRQ signal */
  47         if ((sig != SIGIO) && (sig != SIGWINCH) && (sig != SIGALRM))
  48                 unblock_signals();
  49
  50         (*sig_info[sig])(sig, si, r);
  51
  52         errno = save_errno;
  53
  54         free(r);
  55 }
  56
  57 /*
  58  * These are the asynchronous signals.  SIGPROF is excluded because we want to
  59  * be able to profile all of UML, not just the non-critical sections.  If
  60  * profiling is not thread-safe, then that is not my problem.  We can disable
  61  * profiling when SMP is enabled in that case.
  62  */
  63 #define SIGIO_BIT 0
  64 #define SIGIO_MASK (1 << SIGIO_BIT)
  65
  66 #define SIGALRM_BIT 1
  67 #define SIGALRM_MASK (1 << SIGALRM_BIT)
  68
  69 static int signals_enabled;
  70 static unsigned int signals_pending;
  71 static unsigned int signals_active = 0;
  72
  73 void sig_handler(int sig, struct siginfo *si, mcontext_t *mc)
  74 {
  75         int enabled;
  76
  77         enabled = signals_enabled;
  78         if (!enabled && (sig == SIGIO)) {
  79                 signals_pending |= SIGIO_MASK;
  80                 return;
  81         }
  82
  83         block_signals();
  84
  85         sig_handler_common(sig, si, mc);
  86
  87         set_signals(enabled);
  88 }
  89
  90 static void timer_real_alarm_handler(mcontext_t *mc)
  91 {
  92         struct uml_pt_regs *regs;
  93
  94         regs = malloc(sizeof(struct uml_pt_regs));
  95         if (!regs)
  96                 panic("out of memory");
  97
  98         if (mc != NULL)
  99                 get_regs_from_mc(regs, mc);
 100         timer_handler(SIGALRM, NULL, regs);
 101
 102         free(regs);
 103 }
 104
 105 void timer_alarm_handler(int sig, struct siginfo *unused_si, mcontext_t *mc)
 106 {
 107         int enabled;
 108
 109         enabled = signals_enabled;
 110         if (!signals_enabled) {
 111                 signals_pending |= SIGALRM_MASK;
 112                 return;
 113         }
 114
 115         block_signals();
 116
 117         signals_active |= SIGALRM_MASK;
 118
 119         timer_real_alarm_handler(mc);
 120
 121         signals_active &= ~SIGALRM_MASK;
 122
 123         set_signals(enabled);
 124 }
 125
 126 void deliver_alarm(void) {
 127     timer_alarm_handler(SIGALRM, NULL, NULL);
 128 }
 129
 130 void timer_set_signal_handler(void)
 131 {
 132         set_handler(SIGALRM);
 133 }
 134
 135 void set_sigstack(void *sig_stack, int size)
 136 {
 137         stack_t stack = {
 138                 .ss_flags = 0,
 139                 .ss_sp = sig_stack,
 140                 .ss_size = size - sizeof(void *)
 141         };
 142
 143         if (sigaltstack(&stack, NULL) != 0)
 144                 panic("enabling signal stack failed, errno = %d\n", errno);
 145 }
 146
 147 static void (*handlers[_NSIG])(int sig, struct siginfo *si, mcontext_t *mc) = {
 148         [SIGSEGV] = sig_handler,
 149         [SIGBUS] = sig_handler,
 150         [SIGILL] = sig_handler,
 151         [SIGFPE] = sig_handler,
 152         [SIGTRAP] = sig_handler,
 153
 154         [SIGIO] = sig_handler,
 155         [SIGWINCH] = sig_handler,
 156         [SIGALRM] = timer_alarm_handler
 157 };
 158
 159 static void hard_handler(int sig, siginfo_t *si, void *p)
 160 {
 161         struct ucontext *uc = p;
 162         mcontext_t *mc = &uc->uc_mcontext;
 163         unsigned long pending = 1UL << sig;
 164
 165         do {
 166                 int nested, bail;
 167
 168                 /*
 169                  * pending comes back with one bit set for each
 170                  * interrupt that arrived while setting up the stack,
 171                  * plus a bit for this interrupt, plus the zero bit is
 172                  * set if this is a nested interrupt.
 173                  * If bail is true, then we interrupted another
 174                  * handler setting up the stack.  In this case, we
 175                  * have to return, and the upper handler will deal
 176                  * with this interrupt.
 177                  */
 178                 bail = to_irq_stack(&pending);
 179                 if (bail)
 180                         return;
 181
 182                 nested = pending & 1;
 183                 pending &= ~1;
 184
 185                 while ((sig = ffs(pending)) != 0){
 186                         sig--;
 187                         pending &= ~(1 << sig);
 188                         (*handlers[sig])(sig, (struct siginfo *)si, mc);
 189                 }
 190
 191                 /*
 192                  * Again, pending comes back with a mask of signals
 193                  * that arrived while tearing down the stack.  If this
 194                  * is non-zero, we just go back, set up the stack
 195                  * again, and handle the new interrupts.
 196                  */
 197                 if (!nested)
 198                         pending = from_irq_stack(nested);
 199         } while (pending);
 200 }
 201
 202 void set_handler(int sig)
 203 {
 204         struct sigaction action;
 205         int flags = SA_SIGINFO | SA_ONSTACK;
 206         sigset_t sig_mask;
 207
 208         action.sa_sigaction = hard_handler;
 209
 210         /* block irq ones */
 211         sigemptyset(&action.sa_mask);
 212         sigaddset(&action.sa_mask, SIGIO);
 213         sigaddset(&action.sa_mask, SIGWINCH);
 214         sigaddset(&action.sa_mask, SIGALRM);
 215
 216         if (sig == SIGSEGV)
 217                 flags |= SA_NODEFER;
 218
 219         if (sigismember(&action.sa_mask, sig))
 220                 flags |= SA_RESTART; /* if it's an irq signal */
 221
 222         action.sa_flags = flags;
 223         action.sa_restorer = NULL;
 224         if (sigaction(sig, &action, NULL) < 0)
 225                 panic("sigaction failed - errno = %d\n", errno);
 226
 227         sigemptyset(&sig_mask);
 228         sigaddset(&sig_mask, sig);
 229         if (sigprocmask(SIG_UNBLOCK, &sig_mask, NULL) < 0)
 230                 panic("sigprocmask failed - errno = %d\n", errno);
 231 }
 232
 233 int change_sig(int signal, int on)
 234 {
 235         sigset_t sigset;
 236
 237         sigemptyset(&sigset);
 238         sigaddset(&sigset, signal);
 239         if (sigprocmask(on ? SIG_UNBLOCK : SIG_BLOCK, &sigset, NULL) < 0)
 240                 return -errno;
 241
 242         return 0;
 243 }
 244
 245 void block_signals(void)
 246 {
 247         signals_enabled = 0;
 248         /*
 249          * This must return with signals disabled, so this barrier
 250          * ensures that writes are flushed out before the return.
 251          * This might matter if gcc figures out how to inline this and
 252          * decides to shuffle this code into the caller.
 253          */
 254         barrier();
 255 }
 256
 257 void unblock_signals(void)
 258 {
 259         int save_pending;
 260
 261         if (signals_enabled == 1)
 262                 return;
 263
 264         /*
 265          * We loop because the IRQ handler returns with interrupts off.  So,
 266          * interrupts may have arrived and we need to re-enable them and
 267          * recheck signals_pending.
 268          */
 269         while (1) {
 270                 /*
 271                  * Save and reset save_pending after enabling signals.  This
 272                  * way, signals_pending won't be changed while we're reading it.
 273                  */
 274                 signals_enabled = 1;
 275
 276                 /*
 277                  * Setting signals_enabled and reading signals_pending must
 278                  * happen in this order.
 279                  */
 280                 barrier();
 281
 282                 save_pending = signals_pending;
 283                 if (save_pending == 0)
 284                         return;
 285
 286                 signals_pending = 0;
 287
 288                 /*
 289                  * We have pending interrupts, so disable signals, as the
 290                  * handlers expect them off when they are called.  They will
 291                  * be enabled again above.
 292                  */
 293
 294                 signals_enabled = 0;
 295
 296                 /*
 297                  * Deal with SIGIO first because the alarm handler might
 298                  * schedule, leaving the pending SIGIO stranded until we come
 299                  * back here.
 300                  *
 301                  * SIGIO's handler doesn't use siginfo or mcontext,
 302                  * so they can be NULL.
 303                  */
 304                 if (save_pending & SIGIO_MASK)
 305                         sig_handler_common(SIGIO, NULL, NULL);
 306
 307                 /* Do not reenter the handler */
 308
 309                 if ((save_pending & SIGALRM_MASK) && (!(signals_active & SIGALRM_MASK)))
 310                         timer_real_alarm_handler(NULL);
 311
 312                 /* Rerun the loop only if there is still pending SIGIO and not in TIMER handler */
 313
 314                 if (!(signals_pending & SIGIO_MASK) && (signals_active & SIGALRM_MASK))
 315                         return;
 316
 317         }
 318 }
 319
 320 int get_signals(void)
 321 {
 322         return signals_enabled;
 323 }
 324
 325 int set_signals(int enable)
 326 {
 327         int ret;
 328         if (signals_enabled == enable)
 329                 return enable;
 330
 331         ret = signals_enabled;
 332         if (enable)
 333                 unblock_signals();
 334         else block_signals();
 335
 336         return ret;
 337 }
 338
 339 int os_is_signal_stack(void)
 340 {
 341         stack_t ss;
 342         sigaltstack(NULL, &ss);
 343
 344         return ss.ss_flags & SS_ONSTACK;
 345 }