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      1 //===- Signals.cpp - Generic Unix Signals Implementation -----*- C++ -*-===//
      2 //
      3 //                     The LLVM Compiler Infrastructure
      4 //
      5 // This file is distributed under the University of Illinois Open Source
      6 // License. See LICENSE.TXT for details.
      7 //
      8 //===----------------------------------------------------------------------===//
      9 //
     10 // This file defines some helpful functions for dealing with the possibility of
     11 // Unix signals occurring while your program is running.
     12 //
     13 //===----------------------------------------------------------------------===//
     14 
     15 #include "Unix.h"
     16 #include "llvm/ADT/STLExtras.h"
     17 #include "llvm/Support/Mutex.h"
     18 #include <algorithm>
     19 #include <string>
     20 #include <vector>
     21 #if HAVE_EXECINFO_H
     22 # include <execinfo.h>         // For backtrace().
     23 #endif
     24 #if HAVE_SIGNAL_H
     25 #include <signal.h>
     26 #endif
     27 #if HAVE_SYS_STAT_H
     28 #include <sys/stat.h>
     29 #endif
     30 #if HAVE_CXXABI_H
     31 #include <cxxabi.h>
     32 #endif
     33 #if HAVE_DLFCN_H
     34 #include <dlfcn.h>
     35 #endif
     36 #if HAVE_MACH_MACH_H
     37 #include <mach/mach.h>
     38 #endif
     39 
     40 using namespace llvm;
     41 
     42 static RETSIGTYPE SignalHandler(int Sig);  // defined below.
     43 
     44 static SmartMutex<true> SignalsMutex;
     45 
     46 /// InterruptFunction - The function to call if ctrl-c is pressed.
     47 static void (*InterruptFunction)() = 0;
     48 
     49 static std::vector<std::string> FilesToRemove;
     50 static std::vector<std::pair<void(*)(void*), void*> > CallBacksToRun;
     51 
     52 // IntSigs - Signals that represent requested termination. There's no bug
     53 // or failure, or if there is, it's not our direct responsibility. For whatever
     54 // reason, our continued execution is no longer desirable.
     55 static const int IntSigs[] = {
     56   SIGHUP, SIGINT, SIGPIPE, SIGTERM, SIGUSR1, SIGUSR2
     57 };
     58 static const int *const IntSigsEnd = array_endof(IntSigs);
     59 
     60 // KillSigs - Signals that represent that we have a bug, and our prompt
     61 // termination has been ordered.
     62 static const int KillSigs[] = {
     63   SIGILL, SIGTRAP, SIGABRT, SIGFPE, SIGBUS, SIGSEGV, SIGQUIT
     64 #ifdef SIGSYS
     65   , SIGSYS
     66 #endif
     67 #ifdef SIGXCPU
     68   , SIGXCPU
     69 #endif
     70 #ifdef SIGXFSZ
     71   , SIGXFSZ
     72 #endif
     73 #ifdef SIGEMT
     74   , SIGEMT
     75 #endif
     76 };
     77 static const int *const KillSigsEnd = array_endof(KillSigs);
     78 
     79 static unsigned NumRegisteredSignals = 0;
     80 static struct {
     81   struct sigaction SA;
     82   int SigNo;
     83 } RegisteredSignalInfo[(sizeof(IntSigs)+sizeof(KillSigs))/sizeof(KillSigs[0])];
     84 
     85 
     86 static void RegisterHandler(int Signal) {
     87   assert(NumRegisteredSignals <
     88          sizeof(RegisteredSignalInfo)/sizeof(RegisteredSignalInfo[0]) &&
     89          "Out of space for signal handlers!");
     90 
     91   struct sigaction NewHandler;
     92 
     93   NewHandler.sa_handler = SignalHandler;
     94   NewHandler.sa_flags = SA_NODEFER|SA_RESETHAND;
     95   sigemptyset(&NewHandler.sa_mask);
     96 
     97   // Install the new handler, save the old one in RegisteredSignalInfo.
     98   sigaction(Signal, &NewHandler,
     99             &RegisteredSignalInfo[NumRegisteredSignals].SA);
    100   RegisteredSignalInfo[NumRegisteredSignals].SigNo = Signal;
    101   ++NumRegisteredSignals;
    102 }
    103 
    104 static void RegisterHandlers() {
    105   // If the handlers are already registered, we're done.
    106   if (NumRegisteredSignals != 0) return;
    107 
    108   std::for_each(IntSigs, IntSigsEnd, RegisterHandler);
    109   std::for_each(KillSigs, KillSigsEnd, RegisterHandler);
    110 }
    111 
    112 static void UnregisterHandlers() {
    113   // Restore all of the signal handlers to how they were before we showed up.
    114   for (unsigned i = 0, e = NumRegisteredSignals; i != e; ++i)
    115     sigaction(RegisteredSignalInfo[i].SigNo,
    116               &RegisteredSignalInfo[i].SA, 0);
    117   NumRegisteredSignals = 0;
    118 }
    119 
    120 
    121 /// RemoveFilesToRemove - Process the FilesToRemove list. This function
    122 /// should be called with the SignalsMutex lock held.
    123 /// NB: This must be an async signal safe function. It cannot allocate or free
    124 /// memory, even in debug builds.
    125 static void RemoveFilesToRemove() {
    126   // We avoid iterators in case of debug iterators that allocate or release
    127   // memory.
    128   for (unsigned i = 0, e = FilesToRemove.size(); i != e; ++i) {
    129     // We rely on a std::string implementation for which repeated calls to
    130     // 'c_str()' don't allocate memory. We pre-call 'c_str()' on all of these
    131     // strings to try to ensure this is safe.
    132     const char *path = FilesToRemove[i].c_str();
    133 
    134     // Get the status so we can determine if it's a file or directory. If we
    135     // can't stat the file, ignore it.
    136     struct stat buf;
    137     if (stat(path, &buf) != 0)
    138       continue;
    139 
    140     // If this is not a regular file, ignore it. We want to prevent removal of
    141     // special files like /dev/null, even if the compiler is being run with the
    142     // super-user permissions.
    143     if (!S_ISREG(buf.st_mode))
    144       continue;
    145   
    146     // Otherwise, remove the file. We ignore any errors here as there is nothing
    147     // else we can do.
    148     unlink(path);
    149   }
    150 }
    151 
    152 // SignalHandler - The signal handler that runs.
    153 static RETSIGTYPE SignalHandler(int Sig) {
    154   // Restore the signal behavior to default, so that the program actually
    155   // crashes when we return and the signal reissues.  This also ensures that if
    156   // we crash in our signal handler that the program will terminate immediately
    157   // instead of recursing in the signal handler.
    158   UnregisterHandlers();
    159 
    160   // Unmask all potentially blocked kill signals.
    161   sigset_t SigMask;
    162   sigfillset(&SigMask);
    163   sigprocmask(SIG_UNBLOCK, &SigMask, 0);
    164 
    165   SignalsMutex.acquire();
    166   RemoveFilesToRemove();
    167 
    168   if (std::find(IntSigs, IntSigsEnd, Sig) != IntSigsEnd) {
    169     if (InterruptFunction) {
    170       void (*IF)() = InterruptFunction;
    171       SignalsMutex.release();
    172       InterruptFunction = 0;
    173       IF();        // run the interrupt function.
    174       return;
    175     }
    176 
    177     SignalsMutex.release();
    178     raise(Sig);   // Execute the default handler.
    179     return;
    180   }
    181 
    182   SignalsMutex.release();
    183 
    184   // Otherwise if it is a fault (like SEGV) run any handler.
    185   for (unsigned i = 0, e = CallBacksToRun.size(); i != e; ++i)
    186     CallBacksToRun[i].first(CallBacksToRun[i].second);
    187 
    188 #ifdef __s390__
    189   // On S/390, certain signals are delivered with PSW Address pointing to
    190   // *after* the faulting instruction.  Simply returning from the signal
    191   // handler would continue execution after that point, instead of
    192   // re-raising the signal.  Raise the signal manually in those cases.
    193   if (Sig == SIGILL || Sig == SIGFPE || Sig == SIGTRAP)
    194     raise(Sig);
    195 #endif
    196 }
    197 
    198 void llvm::sys::RunInterruptHandlers() {
    199   SignalsMutex.acquire();
    200   RemoveFilesToRemove();
    201   SignalsMutex.release();
    202 }
    203 
    204 void llvm::sys::SetInterruptFunction(void (*IF)()) {
    205   SignalsMutex.acquire();
    206   InterruptFunction = IF;
    207   SignalsMutex.release();
    208   RegisterHandlers();
    209 }
    210 
    211 // RemoveFileOnSignal - The public API
    212 bool llvm::sys::RemoveFileOnSignal(StringRef Filename,
    213                                    std::string* ErrMsg) {
    214   SignalsMutex.acquire();
    215   std::string *OldPtr = FilesToRemove.empty() ? 0 : &FilesToRemove[0];
    216   FilesToRemove.push_back(Filename);
    217 
    218   // We want to call 'c_str()' on every std::string in this vector so that if
    219   // the underlying implementation requires a re-allocation, it happens here
    220   // rather than inside of the signal handler. If we see the vector grow, we
    221   // have to call it on every entry. If it remains in place, we only need to
    222   // call it on the latest one.
    223   if (OldPtr == &FilesToRemove[0])
    224     FilesToRemove.back().c_str();
    225   else
    226     for (unsigned i = 0, e = FilesToRemove.size(); i != e; ++i)
    227       FilesToRemove[i].c_str();
    228 
    229   SignalsMutex.release();
    230 
    231   RegisterHandlers();
    232   return false;
    233 }
    234 
    235 // DontRemoveFileOnSignal - The public API
    236 void llvm::sys::DontRemoveFileOnSignal(StringRef Filename) {
    237   SignalsMutex.acquire();
    238   std::vector<std::string>::reverse_iterator RI =
    239     std::find(FilesToRemove.rbegin(), FilesToRemove.rend(), Filename);
    240   std::vector<std::string>::iterator I = FilesToRemove.end();
    241   if (RI != FilesToRemove.rend())
    242     I = FilesToRemove.erase(RI.base()-1);
    243 
    244   // We need to call c_str() on every element which would have been moved by
    245   // the erase. These elements, in a C++98 implementation where c_str()
    246   // requires a reallocation on the first call may have had the call to c_str()
    247   // made on insertion become invalid by being copied down an element.
    248   for (std::vector<std::string>::iterator E = FilesToRemove.end(); I != E; ++I)
    249     I->c_str();
    250 
    251   SignalsMutex.release();
    252 }
    253 
    254 /// AddSignalHandler - Add a function to be called when a signal is delivered
    255 /// to the process.  The handler can have a cookie passed to it to identify
    256 /// what instance of the handler it is.
    257 void llvm::sys::AddSignalHandler(void (*FnPtr)(void *), void *Cookie) {
    258   CallBacksToRun.push_back(std::make_pair(FnPtr, Cookie));
    259   RegisterHandlers();
    260 }
    261 
    262 
    263 // PrintStackTrace - In the case of a program crash or fault, print out a stack
    264 // trace so that the user has an indication of why and where we died.
    265 //
    266 // On glibc systems we have the 'backtrace' function, which works nicely, but
    267 // doesn't demangle symbols.
    268 void llvm::sys::PrintStackTrace(FILE *FD) {
    269 #if defined(HAVE_BACKTRACE) && defined(ENABLE_BACKTRACES)
    270   static void* StackTrace[256];
    271   // Use backtrace() to output a backtrace on Linux systems with glibc.
    272   int depth = backtrace(StackTrace,
    273                         static_cast<int>(array_lengthof(StackTrace)));
    274 #if HAVE_DLFCN_H && HAVE_CXXABI_H && __GNUG__
    275   int width = 0;
    276   for (int i = 0; i < depth; ++i) {
    277     Dl_info dlinfo;
    278     dladdr(StackTrace[i], &dlinfo);
    279     const char* name = strrchr(dlinfo.dli_fname, '/');
    280 
    281     int nwidth;
    282     if (name == NULL) nwidth = strlen(dlinfo.dli_fname);
    283     else              nwidth = strlen(name) - 1;
    284 
    285     if (nwidth > width) width = nwidth;
    286   }
    287 
    288   for (int i = 0; i < depth; ++i) {
    289     Dl_info dlinfo;
    290     dladdr(StackTrace[i], &dlinfo);
    291 
    292     fprintf(FD, "%-2d", i);
    293 
    294     const char* name = strrchr(dlinfo.dli_fname, '/');
    295     if (name == NULL) fprintf(FD, " %-*s", width, dlinfo.dli_fname);
    296     else              fprintf(FD, " %-*s", width, name+1);
    297 
    298     fprintf(FD, " %#0*lx",
    299             (int)(sizeof(void*) * 2) + 2, (unsigned long)StackTrace[i]);
    300 
    301     if (dlinfo.dli_sname != NULL) {
    302       fputc(' ', FD);
    303 #  if HAVE_CXXABI_H
    304       int res;
    305       char* d = abi::__cxa_demangle(dlinfo.dli_sname, NULL, NULL, &res);
    306 #  else
    307       char* d = NULL;
    308 #  endif
    309       if (d == NULL) fputs(dlinfo.dli_sname, FD);
    310       else           fputs(d, FD);
    311       free(d);
    312 
    313       // FIXME: When we move to C++11, use %t length modifier. It's not in
    314       // C++03 and causes gcc to issue warnings. Losing the upper 32 bits of
    315       // the stack offset for a stack dump isn't likely to cause any problems.
    316       fprintf(FD, " + %u",(unsigned)((char*)StackTrace[i]-
    317                                      (char*)dlinfo.dli_saddr));
    318     }
    319     fputc('\n', FD);
    320   }
    321 #else
    322   backtrace_symbols_fd(StackTrace, depth, STDERR_FILENO);
    323 #endif
    324 #endif
    325 }
    326 
    327 static void PrintStackTraceSignalHandler(void *) {
    328   PrintStackTrace(stderr);
    329 }
    330 
    331 /// PrintStackTraceOnErrorSignal - When an error signal (such as SIGABRT or
    332 /// SIGSEGV) is delivered to the process, print a stack trace and then exit.
    333 void llvm::sys::PrintStackTraceOnErrorSignal() {
    334   AddSignalHandler(PrintStackTraceSignalHandler, 0);
    335 
    336 #if defined(__APPLE__) && !defined(ANDROID)
    337   // Environment variable to disable any kind of crash dialog.
    338   if (getenv("LLVM_DISABLE_CRASH_REPORT")) {
    339     mach_port_t self = mach_task_self();
    340 
    341     exception_mask_t mask = EXC_MASK_CRASH;
    342 
    343     kern_return_t ret = task_set_exception_ports(self,
    344                              mask,
    345                              MACH_PORT_NULL,
    346                              EXCEPTION_STATE_IDENTITY | MACH_EXCEPTION_CODES,
    347                              THREAD_STATE_NONE);
    348     (void)ret;
    349   }
    350 #endif
    351 }
    352 
    353 
    354 /***/
    355 
    356 // On Darwin, raise sends a signal to the main thread instead of the current
    357 // thread. This has the unfortunate effect that assert() and abort() will end up
    358 // bypassing our crash recovery attempts. We work around this for anything in
    359 // the same linkage unit by just defining our own versions of the assert handler
    360 // and abort.
    361 
    362 #if defined(__APPLE__) && !defined(ANDROID)
    363 
    364 #include <signal.h>
    365 #include <pthread.h>
    366 
    367 int raise(int sig) {
    368   return pthread_kill(pthread_self(), sig);
    369 }
    370 
    371 void __assert_rtn(const char *func,
    372                   const char *file,
    373                   int line,
    374                   const char *expr) {
    375   if (func)
    376     fprintf(stderr, "Assertion failed: (%s), function %s, file %s, line %d.\n",
    377             expr, func, file, line);
    378   else
    379     fprintf(stderr, "Assertion failed: (%s), file %s, line %d.\n",
    380             expr, file, line);
    381   abort();
    382 }
    383 
    384 void abort() {
    385   raise(SIGABRT);
    386   usleep(1000);
    387   __builtin_trap();
    388 }
    389 
    390 #endif
    391