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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_DLFCN_H && HAVE_CXXABI_H && __GNUG__
     31 #include <dlfcn.h>
     32 #include <cxxabi.h>
     33 #endif
     34 #if HAVE_MACH_MACH_H
     35 #include <mach/mach.h>
     36 #endif
     37 
     38 using namespace llvm;
     39 
     40 static RETSIGTYPE SignalHandler(int Sig);  // defined below.
     41 
     42 static SmartMutex<true> SignalsMutex;
     43 
     44 /// InterruptFunction - The function to call if ctrl-c is pressed.
     45 static void (*InterruptFunction)() = 0;
     46 
     47 static std::vector<std::string> FilesToRemove;
     48 static std::vector<std::pair<void(*)(void*), void*> > CallBacksToRun;
     49 
     50 // IntSigs - Signals that represent requested termination. There's no bug
     51 // or failure, or if there is, it's not our direct responsibility. For whatever
     52 // reason, our continued execution is no longer desirable.
     53 static const int IntSigs[] = {
     54   SIGHUP, SIGINT, SIGPIPE, SIGTERM, SIGUSR1, SIGUSR2
     55 };
     56 static const int *const IntSigsEnd =
     57   IntSigs + sizeof(IntSigs) / sizeof(IntSigs[0]);
     58 
     59 // KillSigs - Signals that represent that we have a bug, and our prompt
     60 // termination has been ordered.
     61 static const int KillSigs[] = {
     62   SIGILL, SIGTRAP, SIGABRT, SIGFPE, SIGBUS, SIGSEGV, SIGQUIT
     63 #ifdef SIGSYS
     64   , SIGSYS
     65 #endif
     66 #ifdef SIGXCPU
     67   , SIGXCPU
     68 #endif
     69 #ifdef SIGXFSZ
     70   , SIGXFSZ
     71 #endif
     72 #ifdef SIGEMT
     73   , SIGEMT
     74 #endif
     75 };
     76 static const int *const KillSigsEnd =
     77   KillSigs + sizeof(KillSigs) / sizeof(KillSigs[0]);
     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 
    189 void llvm::sys::RunInterruptHandlers() {
    190   SignalsMutex.acquire();
    191   RemoveFilesToRemove();
    192   SignalsMutex.release();
    193 }
    194 
    195 void llvm::sys::SetInterruptFunction(void (*IF)()) {
    196   SignalsMutex.acquire();
    197   InterruptFunction = IF;
    198   SignalsMutex.release();
    199   RegisterHandlers();
    200 }
    201 
    202 // RemoveFileOnSignal - The public API
    203 bool llvm::sys::RemoveFileOnSignal(const sys::Path &Filename,
    204                                    std::string* ErrMsg) {
    205   SignalsMutex.acquire();
    206   std::string *OldPtr = FilesToRemove.empty() ? 0 : &FilesToRemove[0];
    207   FilesToRemove.push_back(Filename.str());
    208 
    209   // We want to call 'c_str()' on every std::string in this vector so that if
    210   // the underlying implementation requires a re-allocation, it happens here
    211   // rather than inside of the signal handler. If we see the vector grow, we
    212   // have to call it on every entry. If it remains in place, we only need to
    213   // call it on the latest one.
    214   if (OldPtr == &FilesToRemove[0])
    215     FilesToRemove.back().c_str();
    216   else
    217     for (unsigned i = 0, e = FilesToRemove.size(); i != e; ++i)
    218       FilesToRemove[i].c_str();
    219 
    220   SignalsMutex.release();
    221 
    222   RegisterHandlers();
    223   return false;
    224 }
    225 
    226 // DontRemoveFileOnSignal - The public API
    227 void llvm::sys::DontRemoveFileOnSignal(const sys::Path &Filename) {
    228   SignalsMutex.acquire();
    229   std::vector<std::string>::reverse_iterator RI =
    230     std::find(FilesToRemove.rbegin(), FilesToRemove.rend(), Filename.str());
    231   std::vector<std::string>::iterator I = FilesToRemove.end();
    232   if (RI != FilesToRemove.rend())
    233     I = FilesToRemove.erase(RI.base()-1);
    234 
    235   // We need to call c_str() on every element which would have been moved by
    236   // the erase. These elements, in a C++98 implementation where c_str()
    237   // requires a reallocation on the first call may have had the call to c_str()
    238   // made on insertion become invalid by being copied down an element.
    239   for (std::vector<std::string>::iterator E = FilesToRemove.end(); I != E; ++I)
    240     I->c_str();
    241 
    242   SignalsMutex.release();
    243 }
    244 
    245 /// AddSignalHandler - Add a function to be called when a signal is delivered
    246 /// to the process.  The handler can have a cookie passed to it to identify
    247 /// what instance of the handler it is.
    248 void llvm::sys::AddSignalHandler(void (*FnPtr)(void *), void *Cookie) {
    249   CallBacksToRun.push_back(std::make_pair(FnPtr, Cookie));
    250   RegisterHandlers();
    251 }
    252 
    253 
    254 // PrintStackTrace - In the case of a program crash or fault, print out a stack
    255 // trace so that the user has an indication of why and where we died.
    256 //
    257 // On glibc systems we have the 'backtrace' function, which works nicely, but
    258 // doesn't demangle symbols.
    259 void llvm::sys::PrintStackTrace(FILE *FD) {
    260 #if defined(HAVE_BACKTRACE) && defined(ENABLE_BACKTRACES)
    261   static void* StackTrace[256];
    262   // Use backtrace() to output a backtrace on Linux systems with glibc.
    263   int depth = backtrace(StackTrace,
    264                         static_cast<int>(array_lengthof(StackTrace)));
    265 #if HAVE_DLFCN_H && HAVE_CXXABI_H && __GNUG__
    266   int width = 0;
    267   for (int i = 0; i < depth; ++i) {
    268     Dl_info dlinfo;
    269     dladdr(StackTrace[i], &dlinfo);
    270     const char* name = strrchr(dlinfo.dli_fname, '/');
    271 
    272     int nwidth;
    273     if (name == NULL) nwidth = strlen(dlinfo.dli_fname);
    274     else              nwidth = strlen(name) - 1;
    275 
    276     if (nwidth > width) width = nwidth;
    277   }
    278 
    279   for (int i = 0; i < depth; ++i) {
    280     Dl_info dlinfo;
    281     dladdr(StackTrace[i], &dlinfo);
    282 
    283     fprintf(FD, "%-2d", i);
    284 
    285     const char* name = strrchr(dlinfo.dli_fname, '/');
    286     if (name == NULL) fprintf(FD, " %-*s", width, dlinfo.dli_fname);
    287     else              fprintf(FD, " %-*s", width, name+1);
    288 
    289     fprintf(FD, " %#0*lx",
    290             (int)(sizeof(void*) * 2) + 2, (unsigned long)StackTrace[i]);
    291 
    292     if (dlinfo.dli_sname != NULL) {
    293       int res;
    294       fputc(' ', FD);
    295       char* d = abi::__cxa_demangle(dlinfo.dli_sname, NULL, NULL, &res);
    296       if (d == NULL) fputs(dlinfo.dli_sname, FD);
    297       else           fputs(d, FD);
    298       free(d);
    299 
    300       // FIXME: When we move to C++11, use %t length modifier. It's not in
    301       // C++03 and causes gcc to issue warnings. Losing the upper 32 bits of
    302       // the stack offset for a stack dump isn't likely to cause any problems.
    303       fprintf(FD, " + %u",(unsigned)((char*)StackTrace[i]-
    304                                      (char*)dlinfo.dli_saddr));
    305     }
    306     fputc('\n', FD);
    307   }
    308 #else
    309   backtrace_symbols_fd(StackTrace, depth, STDERR_FILENO);
    310 #endif
    311 #endif
    312 }
    313 
    314 static void PrintStackTraceSignalHandler(void *) {
    315   PrintStackTrace(stderr);
    316 }
    317 
    318 /// PrintStackTraceOnErrorSignal - When an error signal (such as SIGABRT or
    319 /// SIGSEGV) is delivered to the process, print a stack trace and then exit.
    320 void llvm::sys::PrintStackTraceOnErrorSignal() {
    321   AddSignalHandler(PrintStackTraceSignalHandler, 0);
    322 
    323 #if defined(__APPLE__) && !defined(ANDROID)
    324   // Environment variable to disable any kind of crash dialog.
    325   if (getenv("LLVM_DISABLE_CRASH_REPORT")) {
    326     mach_port_t self = mach_task_self();
    327 
    328     exception_mask_t mask = EXC_MASK_CRASH;
    329 
    330     kern_return_t ret = task_set_exception_ports(self,
    331                              mask,
    332                              MACH_PORT_NULL,
    333                              EXCEPTION_STATE_IDENTITY | MACH_EXCEPTION_CODES,
    334                              THREAD_STATE_NONE);
    335     (void)ret;
    336   }
    337 #endif
    338 }
    339 
    340 
    341 /***/
    342 
    343 // On Darwin, raise sends a signal to the main thread instead of the current
    344 // thread. This has the unfortunate effect that assert() and abort() will end up
    345 // bypassing our crash recovery attempts. We work around this for anything in
    346 // the same linkage unit by just defining our own versions of the assert handler
    347 // and abort.
    348 
    349 #if defined(__APPLE__) && !defined(ANDROID)
    350 
    351 #include <signal.h>
    352 #include <pthread.h>
    353 
    354 int raise(int sig) {
    355   return pthread_kill(pthread_self(), sig);
    356 }
    357 
    358 void __assert_rtn(const char *func,
    359                   const char *file,
    360                   int line,
    361                   const char *expr) {
    362   if (func)
    363     fprintf(stderr, "Assertion failed: (%s), function %s, file %s, line %d.\n",
    364             expr, func, file, line);
    365   else
    366     fprintf(stderr, "Assertion failed: (%s), file %s, line %d.\n",
    367             expr, file, line);
    368   abort();
    369 }
    370 
    371 void abort() {
    372   raise(SIGABRT);
    373   usleep(1000);
    374   __builtin_trap();
    375 }
    376 
    377 #endif
    378