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/barrier.h"
  16 #include "sysdep/mcontext.h"
  17
  18 void (*sig_info[NSIG])(int, 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, 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, &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, 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, 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, &regs);
  90 }
  91
  92 void alarm_handler(int sig, 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 = ((stack_t) { .ss_flags  = 0,
 116                                      .ss_sp     = (__ptr_t) sig_stack,
 117                                      .ss_size   = size - sizeof(void *) });
 118
 119         if (sigaltstack(&stack, NULL) != 0)
 120                 panic("enabling signal stack failed, errno = %d\n", errno);
 121 }
 122
 123 static void (*handlers[_NSIG])(int sig, mcontext_t *mc) = {
 124         [SIGSEGV] = sig_handler,
 125         [SIGBUS] = sig_handler,
 126         [SIGILL] = sig_handler,
 127         [SIGFPE] = sig_handler,
 128         [SIGTRAP] = sig_handler,
 129
 130         [SIGIO] = sig_handler,
 131         [SIGWINCH] = sig_handler,
 132         [SIGVTALRM] = alarm_handler
 133 };
 134
 135
 136 static void hard_handler(int sig, siginfo_t *info, void *p)
 137 {
 138         struct ucontext *uc = p;
 139         mcontext_t *mc = &uc->uc_mcontext;
 140         unsigned long pending = 1UL << sig;
 141
 142         do {
 143                 int nested, bail;
 144
 145                 /*
 146                  * pending comes back with one bit set for each
 147                  * interrupt that arrived while setting up the stack,
 148                  * plus a bit for this interrupt, plus the zero bit is
 149                  * set if this is a nested interrupt.
 150                  * If bail is true, then we interrupted another
 151                  * handler setting up the stack.  In this case, we
 152                  * have to return, and the upper handler will deal
 153                  * with this interrupt.
 154                  */
 155                 bail = to_irq_stack(&pending);
 156                 if (bail)
 157                         return;
 158
 159                 nested = pending & 1;
 160                 pending &= ~1;
 161
 162                 while ((sig = ffs(pending)) != 0){
 163                         sig--;
 164                         pending &= ~(1 << sig);
 165                         (*handlers[sig])(sig, mc);
 166                 }
 167
 168                 /*
 169                  * Again, pending comes back with a mask of signals
 170                  * that arrived while tearing down the stack.  If this
 171                  * is non-zero, we just go back, set up the stack
 172                  * again, and handle the new interrupts.
 173                  */
 174                 if (!nested)
 175                         pending = from_irq_stack(nested);
 176         } while (pending);
 177 }
 178
 179 void set_handler(int sig)
 180 {
 181         struct sigaction action;
 182         int flags = SA_SIGINFO | SA_ONSTACK;
 183         sigset_t sig_mask;
 184
 185         action.sa_sigaction = hard_handler;
 186
 187         /* block irq ones */
 188         sigemptyset(&action.sa_mask);
 189         sigaddset(&action.sa_mask, SIGVTALRM);
 190         sigaddset(&action.sa_mask, SIGIO);
 191         sigaddset(&action.sa_mask, SIGWINCH);
 192
 193         if (sig == SIGSEGV)
 194                 flags |= SA_NODEFER;
 195
 196         if (sigismember(&action.sa_mask, sig))
 197                 flags |= SA_RESTART; /* if it's an irq signal */
 198
 199         action.sa_flags = flags;
 200         action.sa_restorer = NULL;
 201         if (sigaction(sig, &action, NULL) < 0)
 202                 panic("sigaction failed - errno = %d\n", errno);
 203
 204         sigemptyset(&sig_mask);
 205         sigaddset(&sig_mask, sig);
 206         if (sigprocmask(SIG_UNBLOCK, &sig_mask, NULL) < 0)
 207                 panic("sigprocmask failed - errno = %d\n", errno);
 208 }
 209
 210 int change_sig(int signal, int on)
 211 {
 212         sigset_t sigset;
 213
 214         sigemptyset(&sigset);
 215         sigaddset(&sigset, signal);
 216         if (sigprocmask(on ? SIG_UNBLOCK : SIG_BLOCK, &sigset, NULL) < 0)
 217                 return -errno;
 218
 219         return 0;
 220 }
 221
 222 void block_signals(void)
 223 {
 224         signals_enabled = 0;
 225         /*
 226          * This must return with signals disabled, so this barrier
 227          * ensures that writes are flushed out before the return.
 228          * This might matter if gcc figures out how to inline this and
 229          * decides to shuffle this code into the caller.
 230          */
 231         barrier();
 232 }
 233
 234 void unblock_signals(void)
 235 {
 236         int save_pending;
 237
 238         if (signals_enabled == 1)
 239                 return;
 240
 241         /*
 242          * We loop because the IRQ handler returns with interrupts off.  So,
 243          * interrupts may have arrived and we need to re-enable them and
 244          * recheck signals_pending.
 245          */
 246         while (1) {
 247                 /*
 248                  * Save and reset save_pending after enabling signals.  This
 249                  * way, signals_pending won't be changed while we're reading it.
 250                  */
 251                 signals_enabled = 1;
 252
 253                 /*
 254                  * Setting signals_enabled and reading signals_pending must
 255                  * happen in this order.
 256                  */
 257                 barrier();
 258
 259                 save_pending = signals_pending;
 260                 if (save_pending == 0)
 261                         return;
 262
 263                 signals_pending = 0;
 264
 265                 /*
 266                  * We have pending interrupts, so disable signals, as the
 267                  * handlers expect them off when they are called.  They will
 268                  * be enabled again above.
 269                  */
 270
 271                 signals_enabled = 0;
 272
 273                 /*
 274                  * Deal with SIGIO first because the alarm handler might
 275                  * schedule, leaving the pending SIGIO stranded until we come
 276                  * back here.
 277                  */
 278                 if (save_pending & SIGIO_MASK)
 279                         sig_handler_common(SIGIO, NULL);
 280
 281                 if (save_pending & SIGVTALRM_MASK)
 282                         real_alarm_handler(NULL);
 283         }
 284 }
 285
 286 int get_signals(void)
 287 {
 288         return signals_enabled;
 289 }
 290
 291 int set_signals(int enable)
 292 {
 293         int ret;
 294         if (signals_enabled == enable)
 295                 return enable;
 296
 297         ret = signals_enabled;
 298         if (enable)
 299                 unblock_signals();
 300         else block_signals();
 301
 302         return ret;
 303 }