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