arch/um/os-Linux/signal.c

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